Morphology, Ontogeny, and Phylogenetic Relationships of the Permo-Carboniferous Tetrapod Brachydectes Newberryi from the Council Grove Group, Nebraska, USA

Home , Arroyo Formation, Batropetes, Cardiocephalus, Carrolla, Keraterpeton, Micraroter

University of Calgary PRISM: University of Calgary's Digital Repository

Graduate Studies The Vault: Electronic Theses and Dissertations

2014-10-07 Morphology, Ontogeny, and Phylogenetic Relationships of the Permo-Carboniferous tetrapod Brachydectes newberryi from the Council Grove Group, Nebraska, USA

Pardo, Jason Daniel

Pardo, J. D. (2014). Morphology, Ontogeny, and Phylogenetic Relationships of the Permo-Carboniferous tetrapod Brachydectes newberryi from the Council Grove Group, Nebraska, USA (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/27009 http://hdl.handle.net/11023/1914 master thesis

University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY

Morphology, Ontogeny, and Phylogenetic Relationships of the Permo-Carboniferous tetrapod Brachydectes newberryi from the Council Grove Group, Nebraska, USA

Jason Daniel Pardo

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF MASTER OF SCIENCES

GRADUATE PROGRAM IN BIOLOGICAL SCIENCES

UNIVERSITY OF CALGARY

CALGARY, ALBERTA

SEPTEMBER, 2014

Abstract

Lysorophia is a poorly-understood group of fossil tetrapods known from the Late

Carboniferous and Early Permian of North America. Some prior workers have noted similarities between lysorophians and modern amphibians, suggesting that lissamphibians may have evolved from lysorophian-like ancestors.

I used high resolution x-ray micro-computed tomography (HR-XCT) to study skulls of the lysorophian Brachydectes newberryi from the Early Permian of Kansas and Nebraska, USA.

I present a detailed description of the skeletal morphology of these skulls, including fine structure of the braincase. With reference to the skeletal morphology described here, I present a list of new, phylogenetically-informative characters from the braincase and incorporate these into phylogenetic analysis of early tetrapods. Lysorophians are found to be microsaurs, a diverse group of early tetrapods. The data presented here suggest that lysorophians and microsaurs may be early reptiles and thus not relevant to the discussion of lissamphibian origins.

Acknowledgments

I thank my supervisor, Jason Anderson, and my committee members, Anthony Russell,

Jessica Theodor, and H. Jamniczky, for their patient guidance through the process of researching and writing this thesis.

This research would not have been possible without access to specimens. I thank G.

Corner and J. Head (University of Nebraska State Museum), the late L. Martin and D. Miao

(University of Kansas Biodiversity Institute), L. Ivy (Denver Museum of Nature and Science), and C. Spencer & D. Wake (University of California Museum of Comparative Zoology,

University of California Berkeley) for access to these specimens. This work was also improved greatly by access to comparative CT data provided by J. Anderson.

Discussions with colleagues have been invaluable in contextualizing the fossils studied here, and in understanding the scale of the problems addressed here and elsewhere in the literature. I especially thank A. Huttenlocker, H. Maddin, J. Olori, D. Berman, A. Henrici, G.

Sobral, M. Brazeau, B. Small, H.-P. Schultze, and R. M. Joeckel for such discussions.

Table of Contents

Abstract...... i Acknowledgments………………………………………………………………………………...ii Table of Contents...... iii List of Tables...... vi List of Figures...... vii List of Abbreviations...... ix Chapter 1: Introduction...... 1 1.1 The Problem of Lissamphibian Origins...... 1 1.1.1 Evidence from early fossil lissamphibians...... 2 1.1.2 Evidence from Paleozoic tetrapods...... 4 1.1.3 Hypotheses of Lissamphibian Origins...... 7 1.2 The lysorophian Brachydectes newberryi...... 13 Chapter 2: Micro-CT Study of the Cranial Morphology of Brachydectes newberryi from the Council Grove Group (Lower Permian) of Kansas and Nebraska, USA...... 19 2.1 Introduction...... 19 2.2 Material...... 20 2.3 Methods...... 22 2.4 Description...... 23 2.4.1 Skull roof and cheek...... 23 2.4.2 Braincase...... 29 2.4.3 Palate...... 39 2.4.4 Lower jaw...... 42 2.5 Discussion...... 43 2.5.1 Homology of occipital ossifications...... 43 2.5.2 Ontogenetic changes in the skull of Brachydectes newberryi...... 45 Chapter 3: Phylogenetic Systematics of Brachydectes newberryi...... 49 3.1 Introduction...... 49

iii

3.2 Matrix Construction...... 50 3.2.1 Taxon scope and selection...... 50 3.2.2 Materials...... 51 3.2.3 Character nonindependence...... 52 3.2.4 Character sample scope...... 63 3.3 Neurocranial character diagnoses and discussion...... 65 3.4 Treatment of existing characters...... 96 3.4.1 Modified characters...... 96 3.4.2 Characters modified in topological nonindependence experiments...... 96 3.5 Methods...... 97 3.5.1 Character scoring and matrix modification...... 97 3.5.2 Phylogenetic inference using complete character matrix...... 100 3.5.3 Partition experiments...... 101 3.6 Results...... 101 3.6.1 Total dataset...... 101 3.6.2 Character partition experiments...... 109 Chapter 4: Discussion...... 119 4.1 Relationships of Brachydectes...... 119 4.1.1 Skull roof...... 119 4.1.2 Palate...... 119 4.1.3 Braincase...... 121 4.1.4 Lower Jaw...... 121 4.1.5 Postcranial...... 121 4.1.6 Revising the Brachystelechidae...... 121 4.1.7 Remarks...... 123 4.2 Relationships of lepospondyls...... 123 4.2.1 Microsauria...... 123 4.2.2 Aïstopoda...... 126 4.2.3 Adelospondyli...... 127 4.2.4 Nectridea...... 127

4.3 Relationships of the Microsauria...... 129 4.3.1 General...... 129 4.3.2 Braincase...... 131 4.3.3 Mandible...... 131 4.3.4 Ankle joint...... 132 4.3.5 Contextualizing microsaur synapomorphies...... 133 4.4 Lepospondyls and the origins of modern taxa...... 134 4.4.1 Lepospondyls and the origins of modern lissamphibians...... 134 4.4.2 Lepospondyls and the origins of amniotes...... 137 4.4.3 General considerations and macroevolutionary studies...... 139 4.5 Morphology of Brachydectes...... 140 4.5.1 Fossorial adaptations in Brachydectes...... 140 4.5.2 Neoteny and Brachydectes...... 150 4.5.3 Summary of Brachydectes morphology and ecology...... 151 4.6 Conclusions...... 153 Literature Cited...... 156 Appendix A: Character Diagnoses for Unmodified and ST/T Datasets...... 176

List of Tables Table 2.1 List of Brachydectes specimens examined...... 21 Table 2.2 Scan parameters for micro-CT scans of B. newberryi specimens...... 22

List of Figures Figure 2.1 CT volume of the skull of Brachydectes newberryi, KUVP 49541...... 25 Figure 2.2 Skull of Brachydectes newberryi, showing the posterior extent of the orbit...... 26 Figure 2.3 Braincase of Brachydectes newberryi, KUVP 49541...... 30 Figure 2.4 Posterior braincase of Brachydectes newberryi UNSM 32149...... 33 Figure 2.5 Median surface of the otic bones of UNSM 32149...... 35 Figure 2.6 Selected elements of the auditory apparatus of Brachydectes newberryi...... 37 Figure 2.7 Palatoquadrate derivatives in Brachydectes newberryi, UNSM 32149...... 40 Figure 3.1 Topological nonindependence between characters in the early tetrapod skull...... 55 Figure 3.2 Nonindependence of character states in the early tetrapod skull due to common inference of ambiguous homology...... 56 Figure 3.3 Biological nonindependence of characters due to heterochronic processes...... 58 Figure 3.4 Braincase of Acanthostega gunnari, after Clack, 1988, demonstrating characters and character states identified in this study...... 66 Figure 3.5 Braincase of Loxomma acutirhinus, after Beaumont, 1977, demonstrating characters and character states identified in this study...... 67 Figure 3.6 Neurocranium of Archeria crassidisca, after Clack & Holmes, 1988, demonstrating characters and character states identified in this study...... 68 Figure 3.7 Braincase of Greererpeton burkemorani, after Smithson, 1982, demonstrating characters and character states identified in this study...... 69 Figure 3.8 Braincase of Eryops megalocephalus, after Sawin, 1941, demonstrating characters and character states identified in this study...... 70 Figure 3.9 Braincase of Acheloma dunni, after Maddin et al., 2010, and Polly & Reisz, 2011, demonstrating characters and character states identified in this study...... 71 Figure 3.10 Braincase of Batrachosuchus watsoni, after Warren, 2000, demonstrating characters and character states identified in this study...... 73 Figure 3.11 Braincase of Seymouria baylorensis, after White, 1939, demonstrating characters and character states identified in this study...... 75 Figure 3.12 Braincase of Limnoscelis palustris, after Fracasso, 1987, demonstrating characters and character states identified in this study...... 78 Figure 3.13 Braincase of Huskerpeton englehorni, modified from Huttenlocker et al., 2013, demonstrating characters and character states identified in this study...... 81

vii

Figure 3.14 Braincase of Brachydectes newberryi, this study, demonstrating characters and character states identified in this study...... 82 Figure 3.15 Braincase of Captorhinus laticeps, after Heaton, 1979, demonstrating characters and character states identified in this study...... 84 Figure 3.16 Braincase of Ophiacodon uniformis, after Romer & Price, 1940, demonstrating characters and character states identified in this study...... 86 Figure 3.17 Cladistic analysis of full unmodified character matrix (265 characters)...... 105 Figure 3.18 Cladistic analysis of full character matrix (261 characters) correcting for topological nonindependence...... 106 Figure 3.19 Cladistic analysis of full character matrix (265 characters) reinterpreting the microsaur ‘tabular’ as a supratemporal...... 107 Figure 3.20 Cladistic analysis of full character matrix correcting for topological nonindependence and matrix reinterpreting the microsaur ‘tabular’ as a supratemporal (261 characters)...... 108 Figure 3.21 Cladistic analysis of 59 neurocranial characters...... 112 Figure 3.22 Cladistic analysis of 79 postcranial characters...... 113 Figure 3.23 Cladistic analysis of 127 dermatocranial characters, unmodified from diagnoses in Huttenlocker et al., 2013...... 114 Figure 3.24 Cladistic analysis of 123 dermatocranial characters, modified from Huttenlocker et al., 2013, to account for toplogical nonindependence...... 115 Figure 3.25 Cladistic analysis of 128 dermatocranial characters, modified from Huttenlocker et al., 2013, to interpret the microsaur ‘tabular’ as a supratemporal...... 116 Figure 3.26 Cladistic analysis of 123 dermatocranial characters, modified from Huttenlocker et al., 2013, to account for topological nonindependence and to reinterpret the microsaur ‘tabular’ as a supratemporal...... 117 Figure 4.1 Phylogenetic relationships of selected early reptiles...... 120 Figure 4.2 Comparison of cranial morphology of generalized and fossorial microteiids (Squamata: Gymnophthalmidae)...... 145 Figure 4.3 Comparison of cranial morphology of generalized and fossorial skinks (Squamata: Scincidae)...... 146 Figure 4.4 Comparison of cranial morphology of generalized and fossorial lacertoids (Squamata: Lacertoidea)...... 147 Figure 4.5 Anterior braincase ossifications in selected tetrapods...... 148

viii

List of Abbreviations Institutional: CM, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA;

DMNH, Denver Museum of Nature and Science, Denver, Colorado, USA; FMNH, Field

Museum of Natural History, Chicago, Illinois, USA; KUVP, University of Kansas Natural

History Museum, Lawrence, Kansas, USA; MVZ, Museum of Vertebrate Zoology, Berkeley,

California, USA; OMNH, Sam Noble Museum of Natural History, Norman, Oklahoma, USA;

UM, University of Michigan Museum of Natural History, Ann Arbor, Michigan, USA; UNSM,

University of Nebraska State Museum, Lincoln, Nebraska, USA.

Anatomical: aasc, ampulla of the anterior semicircular canal; ac, articular condyle of quadrate; amhsc, ampulla of the horizontal semicircular canal; ang, angular; ano, anterior novel ossification; aop, antorbital process; ap, ascending process of the supraoccipital; ape, ascending process of the epipterygoid; art, articular; asc, anterior semicircular canal; bp, basilar papilla; bptp, basipterygoid process; cbic, cerebral branch of the internal carotid; ch, choana; col, columella of stapes; cp, cultriform process; crint, crista interfenestralis; d, dentary; dff, descending flange of the frontal; dlpt, dorsal lamina of the pterygoid; dorpr, dorsal process of the stapes; en, external naris; eo, exoccipital; eoc, exoccipital cotyle; epi, epipterygoid; epx, epaxial muscle fossa; etm, ethmoid; f, frontal; fijv, foramen for the internal jugular vein; fm, foramen magnum; fotp, frontal ossification of trabecular plate; fov, foramen ovale; fsov, foramen for the supraorbital vein; fstap; foramen serving the stapedial artery; ftpl, footplate of the stapes; futr, utricular fossa; hsc, horizontal semicircular canal; hyp, hypophyseal fossa; ic, path of the internal carotid; l, lacrimal; lehsc, lateral exposure of the horizontal semicircular canal; msos, median shelf of the orbitosphenoid; mx, maxilla; n, nasal; n.I; foramen serving

olfactory nerve; n.II, foramen serving optic nerve; n.IV, trochlear nerve; n.V, foramen serving trigeminal nerve; n.XI, foramen serving hypoglossal nerve; o, orbit; op, opisthotic; os, orbitosphenoid; oslp, orbitosphenoid lamina of parietal; p, parietal; pa, pila antotica; pal, palatine; pbic, palatal branch of the internal carotid; pls, perilymphatic sac; pmx, premaxilla; po, prootic; pop, postorbital process; pp, postparietal; prf, prefrontal; prpt, palatal ramus of the pterygoid; psc, posterior semicircular canal; psn, planum septonasalis; psph, parasphenoid; pt, pterygoid; q, quadrate; rp, retroarticular process; smx, septomaxilla; sn, septum nasalis; so, supraoccipital; sov, supraorbital vein; sp, splenial; sph, sphenethmoid; spq, stapedial process of quadrate; sq, squamosal; sr, squamoral ridge; ssov; sulcus serving the supraorbital vein; st, stapes; stp, stapedial process of the quadrate; str; supratemporal ridge; stv, subtemporal vacuity; sur, surangular; t, tabular; th, trabecular horn; tp, trabecular plate; v, vomer

Chapter 1: Introduction

1.1 The Problem of Lissamphibian Origins The morphology and relationships of extinct groups of fossil organisms are often discussed in the context of the origin and evolution of modern groups. This is certainly the case for the study of the morphology and evolution of early tetrapods, which has often been investigated in terms of amniote origins (Laurin & Reisz, 1995; Paton et al., 1999) but which has recently been largely recast as a question of the origins of lissamphibians (Schoch & Carroll,

2003; Vallin & Laurin, 2004; Carroll, 2007; Anderson,2007; 2008; Anderson et al., 2008;

Marjanovic & Laurin, 2008; 2013; Maddin et al., 2012), a group that encompasses the three modern anamniote tetrapod orders (Caudata, Anura, and Gymnophiona). This approach has led workers to either approach various Paleozoic taxa as plausible ancestors of modern lissamphibians (Carroll, 2007) or to attempt to populate the lissamphibian stem with various

Paleozoic tetrapods (Ruta & Coates, 2007).

This effort has run into serious obstacles, however. Substantial gaps exist in the fossil record between the major late Paleozoic early tetrapod diversifications in the Carboniferous and

Permian and the diversification of modern lissamphibians in the Mesozoic. Additionally, these gaps are morphological as well as temporal: modern lissamphibians all look very different from late Paleozoic tetrapods in general, and suites of synapomorphies that have been found to characterize groups of Paleozoic tetrapods have been obscured or obliterated by subsequent evolution along the lissamphibian stem or among early members of the lissamphibian crown.

Although noteworthy differences exist between members of the amniote stem and modern reptiles and mammals, stem-groups for mammals (Sidor & Hopson, 1998) and reptiles (Muller &

Reisz, 2006) are more complete and provide a reasonably clear record of the stepwise loss of

early tetrapod character suites and gain of mammalian and reptilian synapomorphies. As a result, the evolution of modern reptiles and mammals from their Paleozoic ancestors is relatively well understood, and debates about the origins of these groups are generally phylogenetically constrained, although some exceptions exist (e.g. turtles).

This is not the case for lissamphibians. Early fossil lissamphibians are extremely rare, and often represented by fragmentary material. More complete material, when available, does shed light on the stepwise acquisition of synapomorphy suites that characterize frogs, salamanders, and caecilians individually, but also clearly represent animals that have lost suites of synapomorphies that characterize key Paleozoic groups.

1.1.1 Evidence from Early Fossil Lissamphibians

The fossil record of stem-anurans is the best known of all lissamphibian orders, but is still incredibly poor. The earliest unambiguous stem-anuran is Triadobatrachus massinoti, known from a single articulated specimen from the earliest Triassic (Induan) of northern Madagascar

(Rage & Roček, 1989). T. massinoti shows a number of anuran synapomorphies, including a fused frontoparietal, wide orbits merged with posterolateral vacuities, a T-shaped parasphenoid, triradiate pterygoids, a transverse palatine, anteriorly-elongate ilium, and unossified pubis (Rage

& Roček, 1989), but lacks other anuran synapomorphies, such as absence of ribs, elongate transverse processes on thoracic vertebrae, fused urostyle, and lack of fused tibiofibula and radioulna (Rage & Roček, 1989). A second Triassic taxon, Czatkobatrachus polonicus from the early Triassic of Poland, is represented by isolated postcranial elements, but exhibits a large heavily ossified humeral head, approaching the condition seen in modern frogs (Evans &

Borsuk-Bialynicka, 1998). The early Jurassic frog Prosalirus bitis from the Kayenta Formation of Arizona, USA, demonstrates the earliest urostyle, a novel fused element of the postsacral axial

skeleton, as well as the earliest occurrence of a fused tibiofibula and radioulna, indicating that P. bitis was likely employing saltatory locomotion similar to that seen in modern anurans (Shubin

& Jenkins, 1998). A few other late-surviving stem-anurans have been identified (two species of the genus Notobatrachus from the Middle Jurassic of Patagonia, [Baez & Nicoli, 2008];

Yizhoubatrachus maclientus from the Early Cretaceous of Liaoning Province, China [Gao &

Chen, 2004], and Vieraella herbsti from the Middle Jurassic of Patagonia, [Baez & Basso,

1996]).

The caudate stem is more poorly known. The earliest definitive stem-caudates appear in the Middle Jurassic (Bathonian), but are represented by relatively fragmentary material. Two species of Marmorerpeton and two other unnamed forms are known from the Middle Jurassic

Kirtlington Mammal Bed of England (Evans et al., 1988), but are represented primarily by isolated vertebrae. The stem-caudate Urupia monstrosa of the Itat Formation of Siberia, Russia, is known from a handful of vertebrae, a few fragments of dentary, and a partial femur (Skutschas

& Krasnolutskii, 2011). The only stem-caudates that are known from more than isolated fragments are the karaurids Kokartus honorarius from the Bathonian Balabansai Formation of

Kyrgyzstan and Karaurus sharovi from the Upper Jurassic (Kimmeridgian) of the Karabastau

Formation of Kazakhstan (Shishkin, 2000). Karaurids exhibit a few notable plesiomorphic characteristics, including a well-ornamented dermal component of the squamosal, vomerine tooth rows parallel to the marginal dentition, an exoccipital distinct from the opisthotic, an occiput that does not project beyond the posterior extent of the skull roof, bicapitate ribs, and separate glenoid and supraglenoid foramina in the scapulocoracoid (Skutschas & Martin, 2011).

Karaurids appear to lack bicuspid, pedicellate teeth, but this may represent a loss of the plesiomorphic condition for caudates, as bicuspid pedicellate teeth have been described for

Marmorerpeton (Evans et al., 1988). Additionally, bicuspid, pedicellate teeth are ontogenetically variable in modern caudates (Davit-Beal et al., 2006), so variation of this character among stem- caudates may have an ontogenetic or heterochronic source.

The gymnophionan stem has the worst fossil record, with only two species known. The earliest-known member of the gymnophionan stem is Eocaecilia micropodia from the Early

Jurassic Kayenta Formation. E. micropodia shows a handful of derived caecilian characteristics, including a robust articular with a strong retroarticular process, a fully-ossified sphenethmoid preserving foramina for the ventral branch of the olfactory nerve, a fully-fused os basale, caecilian jaw-opening mechanism, and a generally hyperelongate form (Jenkins et al., 2007;

Maddin et al., 2012), but lacks other key gymnophionan synapomorphies, including the reduction of the number of ossifications of the skull roof and palate, loss of limb and girdle elements, and modification of the nasolacrimal canal to accommodate the caecilian “tentacle”

(Jenkins et al., 2007; Maddin et al., 2012). The only other known stem-caecilian is Rubricaecilia monbaroni from the Lower Cretaceous (Berriasian) of Couches Rouges, Morocco (Evans &

Sigogneau-Russel, 2001), more than 40 million years younger than E. micropodia. R. monbaroni is known from vertebrae, a lower jaw, a partial palatine, and a possible femur. It shares with crown-caecilians the fusion of the lower jaw into two compound bones, the pseudodentary and pseudoangular, but exhibits other plesiomorphic conditions, such as the presence of a free palatine, an interglenoid tubercle on the atlas, and (possibly) the presence of appendicular elements (Evans & Sigogneau-Russel, 2001).

1.1.2 Evidence from Paleozoic Tetrapods An additional source of data relevant to this question lies in the morphology of Paleozoic tetrapods to seek animals that exhibit lissamphibian synapomorphies but which can still be

confidently resolved within Paleozoic tetrapod phylogeny. This approach has seen some success, and a number of archaic taxa from the late Paleozoic and early Mesozoic have been identified as possible stem-groups for either some or all modern lissamphibian orders. The Amphibamidae is a diverse group of small-bodied dissorophoid temnospondyls that have been the subject of considerable interest in recent years (Schoch & Rubidge, 2005; Huttenlocker et al., 2007;

Anderson et al., 2008a; 2008b; Frobisch & Reisz, 2008; Schoch & Frobisch, 2009; Clack &

Milner, 2010; Sigurdsen & Bolt, 2010; Bourget & Anderson, 2011; Anderson & Bolt, 2013;

Maddin et al., 2013) and have been put forth as possible stem-lissamphibians (Sigurdsen & Bolt,

2010), stem-batrachians (the clade including Anura and Caudata; Anderson et al., 2008b;

Anderson 2008; Schoch & Frobisch, 2009; Bourget & Anderson, 2011), or a combination of stem-batrachians and stem-lissamphibians (Maddin et al., 2012). Amphibamids share a number of characteristics with lissamphibians, including true metamorphosis, shortened ribs, reduced marginal bones of the palate, very large interpterygoid vacuities, and, in some taxa, pedicellate teeth with two cusps aligned labiolingually (Bolt, 1970; Clack & Milner, 2010; Sigurdsen &

Bolt, 2010). The pes of the derived amphibamid Gerobatrachus hottoni preserves a basale commune, a novel fusion of distal carpals and tarsals 1 and 2, suggesting a close affinity with batrachians (Anderson et al., 2008b). A basale commune is found otherwise only in modern caudates.

A second dissorophoid group, the Branchiosauridae, has been proposed as a candidate caudate stem (Schoch & Carroll, 2003; Carroll, 2007). Branchiosaurids, like some amphibamids, demonstrate complete metamorphosis and may have pedicellate, bicuspid teeth. In addition, branchiosaurs have been shown to exhibit early ossification of digits I and II (preaxial dominance) rather than early ossification of digit IV (postaxial dominance), a characteristic seen

only in caudates among living tetrapods (Schoch & Carroll, 2003). Branchiosaurids resolve within amphibamids in a number of recent phylogenetic treatments (Schoch & Milner, 2003;

Anderson et al., 2008b; Schoch & Frobisch, 2009), suggesting that the branchiosaurid hypothesis is not incompatible with the amphibamid hypothesis.

Microsaur lepospondyls have also been put forth as putative stem-lissamphibians or stem-gymnophionans. The microsaur Rhynchonkos stovalli has been proposed to be a possible stem-gymnophionan based on the heavily ossified nature of the skull roof, organization of the occiput, and hyperelongate axial skeleton (Carroll & Currie, 1975). Recent phylogenetic investigations have recovered a sister taxon relationship between R. stovalli and the stem- gymnophionan Eocaecilia micropodia (Anderson, 2001, 2007; Anderson et al., 2008). Restudy of the brachystelechid microsaur Carrolla craddocki, using micro-computed tomography

(Maddin et al., 2011), found that in at least some microsaurs the posterior region of the braincase was fully co-ossified into an os basale, approaching the condition seen in all known gymnophionans. Furthermore, another brachystelechid microsaur, Batropetes fritschi, has been shown to exhibit multicuspid teeth (Glienke, 2013), although the teeth of Batropetes preserve three cusps oriented proximodistally along the jaw, rather than two cusps aligned labiolingually.

Microsaurs are typically found to be stem-amniotes in most phylogenetic treatments (Ruta &

Coates, 2007; Anderson et al., 2008; Huttenlocker et al., 2013); this result would suggest that lissamphibians are actually polyphyletic.

Lysorophian lepospondyls are the final group that have received significant attention as possible stem-lissamphibians. The Lysorophia is a poorly-understood group of hyperelongate aquatic early tetrapods, typically found in seasonal estivation communities (Olson & Bolles,

1975; Hembree et al., 2004; Hembree et al., 2005; Huttenlocker et al., 2005). Lysorophians, like

lissamphibians, have a highly derived skeleton that lacks many of the character suites used to resolve Paleozoic tetrapod phylogeny, and a close relationship between lysorophians and modern lissamphibians has been proposed for over 100 years. Case (1908) recognized a number of lissamphibian-like characteristics, including a broad parasphenoid, reduced pterygoids, quadrate located anterior to the occiput, and a deep emargination in the lateral region of the skull completely separating the maxilla from the suspensorium. Williston (1908) further developed this hypothesis, suggesting that not only were lysorophians related to lissamphibians, but that they were specifically related to sirenid, proteid, and amphiumid salamanders. Moodie (1908) suggested, instead, an affinity between lysorophians and caecilians. Nussbaum (1983) noted additional similarities between the deeply emarginated skull of lysorophians and the zygokrotaphic skull of some caecilians, notably ichthyophids. A number of recent phylogenetic analyses have discovered support for the hypothesis that lysorophians represent the sister group to all living lissamphibians both in a novel phylogenetic treatment (Vallin & Laurin, 2004) as well as manipulations of other phylogenetic treatments (Marjanovic & Laurin, 2007; 2013).

Support for this result relies primarily on characters associated with common losses of bones in the posterior skull roof, cheek, and lower jaw, reduction of the appendicular skeleton, and simplification of the vertebral centra. Lysorophians are recovered within the Microsauria in some analyses (Vallin & Laurin, 2004; Marjanovic & Laurin, 2008; 2013) so the lysorophian hypothesis should not necessarily be considered incompatible with the microsaur hypothesis.

1.1.3 Hypotheses of Lissamphibian Origins

These hypothesized relationships can be summarized as a set of mutually exclusive hypotheses of lissamphibian relationships, generally referred to as the Temnspondyl Hypothesis

(TH), Lepospondyl Hypothesis (LH) and Polyphyly Hypothesis (PH) in the literature (Anderson,

2007; 2008; Anderson et al, 2008; Marjanovic & Laurin, 2008; 2013). I break from this nomenclature for three reasons. First, the TH/LH nomenclature fosters an approach of trying to place the lissamphibian crown group within identified Paleozoic clades, rather than attempting to populate the lissamphibian stem group, and in doing so persists in the use of pre-phylogenetic names that generally refer to paraphyletic grades. The use of formal names in the names of hypotheses that invalidate the clades to which these names refer is somewhat unsatisfying.

Secondly, the TH/LH nomenclature lacks taxonomic precision. Temnospondyli is an extremely populous clade, representing the majority of anamniote diversity throughout the

Carboniferous, Permian, and Triassic, and the Lepospondyli encompasses five Linnean orders and the vast majority of small-bodied tetrapod diversity in the Carboniferous and Early Permian.

The scenario of lissamphibian origins and composition of the lissamphibian crown differs significantly if, for example, we propose a close relationship between lissamphibians and stereospondyls rather than amphibamid dissorophoids (e.g. Shishkin, 1968). Similarly, the scenario of lissamphibian origins and composition of the lissamphibian crown differs significantly if we propose a close relationship between lissamphibians and diplocaulid nectrideans rather than brachystelechids and lysorophians. A more specific nomenclature underscores the fact that it is the hypothesized pattern of acquisition of lissamphibian traits that is being investigated, not the placement of the lissamphibian crown among one or another larger clade.

Third, and most importantly, the TH/LH nomenclature assumes a certain stability of early tetrapod phylogeny that may be overstated. Both the TH and LH (and to a certain extent, the

Polyphyly Hypothesis) assume a stable orthodox phylogeny of early tetrapods (Reisz & Laurin,

1998; Anderson, 2001; Ruta et al., 2003; Vallin & Laurin, 2004; Ruta & Coates, 2007; Anderson

et al., 2008a; Anderson, 2008; Marjanovic & Laurin, 2008; 2013). This phylogeny retrieves a monophyletic Amniota, with Diadectamorpha, Lepospondyli, Seymouriamorpha,

[Anthracosauria+”Embolomeri”], and [Colostei+Temnospondyli] as successive outgroups, with

“whatcheeriids” bridging the gap between Devonian and post-Devonian tetrapod diversity. This general consensus masks the presence of other more heterodox inferences of tetrapod phylogeny, which generally propose very different scenarios of character evolution and ancestral states.

Analyses emphasizing seymouriamorph diversity have consistently placed seymouriamorphs closer to the amniote crown than Lepospondyls, and periodically recover a paraphyletic

Diadectamorpha with respect to amniotes. Most concerning, a number of phylogenetic treatments of early tetrapods (Klembara et al., 2010) do not recover a monophyletic

Lepospondyli at all, and do not recover a close relationship between lepospondyls and amniotes.

Ruta et al., (2003) and Ruta and Coates (2007), for example, do not recover a monophyletic

Lepospondyli; adelospondyls are found to be closely related to colosteids and temnospondyls rather than other lepospondyls. Most problematically, McGowan (2002) has actually recovered microsaur lepospondyls within dissorophoid temnospondyls, an unlikely result in itself, but one which underscores issues of nonindependence of characters associated with miniaturization in early tetrapods. The possibility that lepospondyls may be a polyphyletic assemblage of diminutive species ranging the entirety of early tetrapod phylogeny (as has been proposed in comparative studies by Smithson, 1985, and Panchen, 1991, for example) threatens the longevity of nomenclature that assumes and requires monophyly or, at the very least, paraphyly of the group.

The first hypothesis, typically referred to as the Temnospondyl Hypothesis (Anderson,

2007) but herein referred to as the Amphibamid Hypothesis (AH), states that lissamphibians

form a clade within a paraphyletic Amphibamidae, closely related to the amphibamids

Platyrhinops lyelli, Amphibamus grandiceps, Doleserpeton annectens, Tersomius texensis,

Tersomius dolesensis, and Gerobatrachus hottoni, and (possibly) branchiosaurids, typically with

Gerobatrachus hottoni representing a stem-batrachian and thus the earliest crown-lissamphibian.

This hypothesis implies that the ancestral lissamphibian had pedicellate bicuspid teeth, a tympanic ear, and a relatively lightly built skull. It also implies that the ancestral lissamphibian underwent metamorphosis (Schoch, 2014) and had amphibious or terrestrial adults. Furthermore, this implies that very tetrapodomorphs with digits fall outside of the tetrapod crown, suggesting that the characteristics governing evolutionary success of modern tetrapod groups arose extremely early in the history of the group.

A second hypothesis, typically referred to as the polyphyly hypothesis but here referred to as the Caecilian-Recumbirostran Hypothesis (CRH), states that batrachians evolved from amphibamid temnospondyls as in the AH, but that caecilians evolved from lepospondyls, particularly the recumbirostran microsaur Rhynchonkos stovalli, indicating that caecilians are more closely related to amniotes than to batrachians and that lissamphibians are polyphyletic

(Carroll & Curry, 1975; Carroll, 2007; Anderson, 2008; Anderson et al., 2008). Many of the conclusions of the AH remain applicable to batrachian origins, with some key differences. The

CRH suggests that pedicellate bicuspid teeth either evolved multiple times or that bicuspidity and pedicelly are ontogenetically variable characteristics that appear similarly in caecilians and batrachians due to parallel paedomorphosis in each lineage. The tympanic middle ear is restricted to batrachians and some temnospondyls, whereas it is inferred that caecilians evolved from taxa lacking a tympanic middle ear. Batrachians are interpreted as evolving from animals with a relatively lightly-built skull, but caecilians are reconstructed as having evolved from microsaurs

with heavily-built stegokrotaphic skulls. Finally, whereas metamorphosis and an amphibious lifestyle is found to be ancestral for batrachians, caecilians are found to have evolved from a fossorial direct-developing ancestor, suggesting a persistent fossorial lifestyle in the caecilian stem for over 320 million years. Under the CRH, the earliest crown-tetrapods were physiologically lissamphibian-like, with evolution of the amniote condition proceeding more or less directly from the lissamphibian condition.

A third persistent hypothesis, generally called the Lepospondyl Hypothesis, but here referred to as the Brachystelechid-Lysorophian Hypothesis (BLH), states that lissamphibians are monophyletic within a clade of lepospondyls including the brachystelechids Carrolla craddocki and Batropetes fritschi and the lysorophian Brachydectes (Vallin & Laurin, 2004; Marjanovic &

Laurin, 2007; Marjanovic & Laurin, 2013), in some analyses also including the Nectridea and

Aïstopoda in a clade called Holospondyli (Marjanovic & Laurin, 2013). This result, while not recovered by the majority of analyses on the subject, appears as a sub-optimal parsimony island in many analyses (Marjanovic & Laurin, 2013) which becomes a viable phylogenetic result in its own right in some matrix manipulations. The BLH suggests that pedicellate teeth evolved numerous times throughout digited tetrapodomorphs, and that multicuspid teeth evolved multiple times among anamniote tetrapodomorphs. Additionally, the BLH infers greater significance of postcranial characters, particularly characters associated with the evolution of holospondyly, than of cranial characters. Furthermore, in the BLH the bones of the cheek spanning from the posterior edge of the maxilla to the suspensorium (the jugal, quadratojugal, and postorbital) are interpreted as having been lost early among stem-lissamphibians. More generally, the BLH reconstructs the ancestor of modern lissamphibians as a fossorial direct-developing animal with a heavily-built skull and elongate to hyperelongate trunk. The BLH places a significant portion of

Paleozoic tetrapod diversity outside of the vertebrate crown, a finding that would limit phylogenetic constraints on inference of soft tissue anatomy and physiology of most early tetrapod diversity. Phylogenetic analyses recovering the BLH (e.g. Vallin & Laurin, 2004) also typically recover a close relationship between caudates and caecilians (a Procera clade) among modern lissamphibians rather than the typical Batrachia.

Although a number of phylogenetic studies of Paleozoic tetrapods have been performed in recent years with the goal of testing the relationships between various Paleozoic taxa and modern lissamphibians (Paton et al., 1999; McGowan, 2002; Vallin & Laurin, 2004; Ruta &

Coates, 2007; Anderson et al., 2008b; Marjanovic & Laurin, 2008; 2013), these analyses are often little better than equivocal given current knowledge of Paleozoic tetrapod morphology and diversity (Ruta & Coates, 2007; Marjanovic & Laurin, 2013). The solution to this problem is necessarily revision of the morphology of fossils relevant to these debates, but effort in this direction has been sorely imbalanced. A great deal of recent effort has been directed towards understanding the morphology and development of amphibamid temnospondyls, including the description of a number of new species (Huttenlocker et al., 2007; Anderson et al., 2008a;

2008b; Frobisch & Reisz, 2008; Bourget & Anderson, 2011; Anderson & Bolt, 2013), revision of the morphology of previously-described taxa (Schoch & Rubidge, 2005; Sigurdsen, 2008;

Sigurdsen & Bolt, 2010; Clack & Milner, 2010; Maddin et al., 2013), and characterization of ontogeny of various taxa (Schoch & Carroll, 2002; Schoch & Milner, 2003). Less effort has been directed towards relevant lepospondyl taxa, however. A few new lepospondyl species have been described in recent years (Anderson, 2002b; Anderson et al., 2009; Henrici et al., 2011; Clack,

2011; Glienke, 2012; Huttenlocker et al., 2013), but none belong to taxa considered relevant to lissamphibian origins. Knowledge of the morphology of several species has been revised as well

(Anderson, 2002; Anderson et al., 2003; Vallin & Laurin, 2004; Bolt and Rieppel, 2009; Milner

& Ruta, 2009; Maddin et al., 2010; Huttenlocker et al., 2013; Glienke, 2013), but of those, only two taxa, Carrolla craddocki (Maddin et al., 2013) and Batropetes fritschi (Glienke, 2013) have been closely associated with lissamphibian origins. The ontogeny of two lepospondyl taxa has recently been studied in detail (Olori, 2013) and aspects of the ontogeny of the aïstopod

Phlegethontia have been noted by Anderson et al. (2003), but both taxa are only distantly related to the lepospondyl groups implicated in lissamphibian origins. A number of taxa more closely associated with the BLH and CRH have not been redescribed to date, including the putative stem-caecilian, Rhynchonkos stovalli, of focal interest to the CRH, the brachystelechid

Quasicaecilia texana, and the lysorophian Brachydectes, of focal interest to the BLH. Moreover, no description of the ontogeny of these taxa has been published, making it difficult to compare ontogeny of these taxa to other early tetrapods as well as extant lissamphibians and amniotes.

1.2 The Lysorophian Brachydectes newberryi The purpose of this thesis is not to provide a decisive assessment of these hypotheses, nor to investigate early tetrapod phylogeny and character evolution more broadly, although these subjects are addressed briefly in later chapters, but instead to shed some light on one key taxon according to the Brachystelechid-Lysorophian Hypothesis, the lysorophian Brachydectes newberryi. Other relevant taxa (Rhynchonkos stovalli and Quasicaecilia texana) are also currently under revision, but will not be addressed directly in this thesis.

Brachydectes newberryi was first described by Cope (1868) on the basis of pair of partial lower jaws from the Upper Freeport Coal of Linton Diamond Mine, Jefferson County, Ohio.

Subsequent material was reported as Molgophis macrurus (Cope, 1868), and Cocytinus gyrinoides (Cope, 1871). Early descriptions of the skull of Brachydectes focused on fossils from

the Permian redbeds of Texas and Oklahoma (Case, 1908; Williston, 1908; Broom, 1918; Sollas,

1920) under the name Lysorophus tricarinatus. Later work by Bolt & Wassersug (1975) revised some aspects of the morphology of Brachydectes based on the Texas-Oklahoma material, and, most recently, Wellstead (1991) conducted an extensive revision of the Lysorophia primarily using flattened specimens from the Pennsylvanian cannel coal at Linton, Ohio, with a significant revision of the morphology as well.

Given this extensive history of work on the group, it seems almost superfluous to revise the morphology of this animal yet again. There are, however, a number of reasons why such a restudy is necessary. First, interpretations of skull bone homologies differ between morphological descriptions of Brachydectes and these different interpretations have distinct implications for both interpretation of the relationships of Brachydectes among early tetrapods as well as possible relationships with lissamphibians (e.g. Marjanovic & Laurin, 2008; Marjanovic

& Laurin, 2013). Second, prior descriptions have focused largely on the morphology of the dermal skull, with limited treatment of the braincase. This is largely due to the nature of the lysorophian fossil record; the majority of specimens known are preserved either as impressions of crushed specimens in cannel coals (e.g. Linton Diamond Mine, Hook & Baird, 1986; Five

Points Cannel Coal, Hook & Baird, 1993) or specimens from nodular and difficult to prepare redbeds deposits (Case, 1908; Williston, 1908; Broom, 1918; Olson & Bolles, 1975; Wellstead,

1991). Prior treatments of the braincase and internal morphology of the skull have provided only a poor glimpse of internal morphology based on serial grinding (Sollas, 1920) or thin sectioning

(Bolt & Wassersug, 1975), and have taken a back seat to descriptions of superficial cranial anatomy, even within these descriptive works. The external morphology of Brachydectes and other lysorophians has been notoriously difficult to compare to other Paleozoic tetrapods (see

Marjanovic & Laurin, 2008, for an example), suggesting that internal morphology, especially braincase morphology, may be the only anatomical region of the skeleton of Brachydectes that is more broadly comparable with other Paleozoic tetrapods. Finally, a number of recent descriptions utilizing micro-computed tomography (micro-CT) methods have greatly elucidated new aspects of lepospondyl anatomy previously unknown, primarily within the braincase

(Anderson et al., 2009; Maddin et al., 2011; Huttenlocker et al., 2013). A broader survey of the distribution of such anatomical features within lepospondyls, including lysorophians, is necessary to understand the homology and phylogenetic importance of this morphology.

Due to the limits of the lysorophian fossil record, restudy of cannel coal or redbeds specimens using traditional techniques is likely to have only a limited impact on our understanding of these taxa, and poor radio contrast of redbeds specimens makes micro-CT study of these specimens difficult. However, abundant new material has recently been reported from the earliest Permian Eskridge Shale of Nebraska (Huttenlocker et al., 2005) and Speiser Shale of

Kansas (Hembree et al., 2004; 2005) within the Council Grove Group (CGG), a larger sequence of terrigenous and nearshore marine sediments. The CGG spans the latest Carboniferous

(Gzhelian) through the earliest Permian, representing the entirety of the Asselian in Kansas and

Nebraska, and possibly extending into the Sakmarian (Swin et al., 2008). These sediments record a series of fifth-order transgression-regression sequences bounded by well-developed fossil soils representing low-stand deposits. These fossil soils, which are typically grey-green, but sometimes also reddish-brown or mottled, are classifiable as vertisols or aridisols (Joeckel,

1991) and represent periodically waterlogged muds with limited organic content and high groundwater influence. Traces of roots (Joeckel, 1991) and vertebrate burrows (McAllister,

1990; Hembree et al., 2004; 2005; Huttenlocker et al., 2005) have been reported from these fossil

soil horizons. Fossil vertebrates are abundant in these horizons, including gnathorhizid lungfishes (McAllister, 1991; Huttenlocker et al., 2005; Pardo et al., in press), dvinosaur temnospondyls (Hotton, 1959; Coldiron, 1978; Huttenlocker et al., 2005; Englehorn et al., 2008), amphibamid temnospondyls (Huttenlocker et al., 2005; 2007), recumbirostran microsaurs

(Foreman & Schultz, 1984; Huttenlocker et al., 2005; 2013), diplocaulid nectrideans (Foreman &

Martin, 1988), and rare diadectids and synapsids (Foreman & Martin, 1988; Huttenlocker et al.,

2005), as well as numerous specimens of the lysorophian Brachydectes newberryi. These vertebrate-bearing localities have been interpreted as seasonal wetland systems (Hembree et al.,

2004; Huttenlocker et al., 2005), similar to either vernal pools or playa lakes. Vertebrate bone from these deposits typically shows little diagenetic alteration, and the surrounding matrix generally exhibits little to no diagenetic precipitation of iron (unlike redbeds fossils), a fact which has made possible micro-CT studies of CGG fossils (Huttenlocker et al., 2013; Pardo et al., in press). The vertebrate assemblage at these localities appears to be largely autochthonous, although some taxa (such as the synapsids, diadectids, and microsaurs) may have been only occasional users of the wetland system and are represented primarily by rare isolated fragments

(but not always, see Huttenlocker et al., 2013), in comparison with abundant obligate aquatic species (such as lungfishes), which are typically found articulated in burrow structures likely associated with aestivation (McAllister, 1991; Huttenlocker et al., 2005). The lysorophians in the

CGG paleosols appear to fall into the latter category; lysorophians are the most common tetrapods in vertebrate-bearing horizons in CGG paleosols and are generally found partially or completely articulated, typically within flask-shaped burrow structures (Hembree et al., 2003;

2004; Huttenlocker et al., 2005). This means that partial to complete skulls are abundant in major collections of the Council Grove Group made by the University of Nebraska State Museum

(UNSM), the University of Kansas (KUVP), and the Denver Museum of Nature and Science

(DMNH). A total of 13 skulls were available for study. The smallest of these has a length of

10.5 mm, and the largest, while incomplete, would have exceeded 30 mm in length. Although small and large specimens from the Eskridge Shale have been attributed to separate species in the past (Brachydectes newberryi and B. elongatus, respectively, Huttenlocker et al., 2005) and the specimens from the Speiser Shale have been attributed to B. elongatus exclusively (Hembree et al., 2004; 2005), restudy of these collections confirms that these skulls represent a growth series belonging to a single morphotype, which falls within morphological variation described by

Wellstead (1991) for Brachydectes newberryi and, intriguingly, Pleuroptyx clavatus, but outside of the range of morphological variation described for B. elongatus (=Lysorophus tricarinatus).

Micro-CT scanning of these materials has yielded significant new data on the skull of B. newberryi, including the first complete look at the braincase of a lysorophian.

In this thesis, I report the results of this micro-CT study of the skull of Brachydectes newberryi from the Eskridge Shale and Speiser Shale. First, I redescribe the skull of

Brachydectes newberryi, significantly clarifying the morphology of the braincase and clarifying the identity and morphology of the bones of the palate, skull roof, cheek, and lower jaw, and describing ontogenetic changes in shape and ossification level in the skull of Brachyectes. I then define a number of new cranial characters, with an emphasis on neurocranial characters, to help infer the position of Brachydectes within lepospondyl phylogeny, and implement these characters in a phylogenetic analysis of lepospondyls in order to explore the relationships of

Brachydectes and the broader phylogenetic context of the highly-derived morphology of lysorophians more generally. Finally, I discuss the implications of new morphological, ontogenetic, and phylogenetic data for the evolution of Brachydectes specifically, and

lepospondyls more broadly, as well as their functional implications for the ecology and behavior of Brachydectes.

Chapter 2: Micro-CT Study of the Cranial Morphology of Brachydectes newberryi from the

Council Grove Group (Lower Permian) of Kansas and Nebraska, USA

2.1 Introduction

Despite the apparent importance of lysorophians in relation to studies of lissamphibian origins, little consensus exists on the structure and homology of the cranial skeleton of this group. Cranial anatomy of lysorophians was initially studied by Williston (1908) on the basis of external anatomy of complete skulls from the Permian of Texas, but the first comprehensive description of the cranial anatomy of this group was accomplished by Sollas

(1920) using a serial grinding technique. This study provided the first description of the braincase of a lysorophian, but with poor resolution of the morphology of fine structure, such as foramina serving cranial nerves and blood vessels. Bolt and Wassersug (1975) further refined the description of the lysorophian snout using a serial sectioning technique, confirming that lysorophians lacked a kinetic maxilla, but once again did not significantly address the anatomy of the braincase. Wellstead (1991) produced an extensive description of lysorophian fossils as part of a revision of the order. His descriptions were based primarily on latex peels of specimens from the Carboniferous-aged Upper Freeport Coal of Linton, Ohio, but incorporated skulls from the Permian-aged Arroyo Formation of Texas. Whereas the descriptions of Wellstead (1991) are extensive and highly-detailed in regard to external (typically skull roof) anatomy, the anatomy of the braincase was incompletely described, either because the specimens examined were substantially crushed; were derived from redbeds and exhibit substantial surficial weathering; or because dermal elements obscured the anatomy of internal structures.

Additionally, each descriptive effort has drawn significantly different conclusions about the homology of elements of the skull roof, cheek, and braincase. Most recently, Marjanovic &

Laurin (2008) suggested a novel arrangement of the cheek and occiput based on comparison between the illustrations of Wellstead (1991) and published descriptions of Batropetes fritschi

(Carroll & Gaskill, 1978; Glienke, 2013). In this interpretation of the skull, the orbit encompasses the entire fenestrate region between the prefrontal and the suspensorium, but no description of lysorophian anatomy has explicitly investigated these interpretations. The homology of much of the lysorophian skull, and how these homologies affect our interpretation of soft tissues within the lysorophian head, remain uncertain.

I present here a new description of exceptionally well-preserved skulls of the lysorophian

Brachydectes newberryi from the earliest Permian (Asselian) of the Eskridge and Speiser Shale

(Council Grove Group) of Nebraska and Kansas respectively. This study has several aims: (1) to provide a description of the skull of B. newberryi in well-preserved specimens by employing high-resolution 3-D imaging techniques; (2) to sample a wide range of sizes, including very large adults, to ensure that putative paedomorphic and juvenile morphologies are adequately distinguished in the description of this species; (3) to describe, in detail, the anatomy of the ossified braincase of B. newberryi in order to facilitate phylogenetic and functional comparison with other early tetrapods; (4) to resolve the homology of the cranial ossifications of B. newberryi with reference to specific robust anatomical characteristics.

2.2 Material

To describe the anatomy of Brachydectes newberryi, I studied thirteen specimens from the Council Grove Group of Kansas and Nebraska. Of these, five were collected from exposures

of the Speiser Shale west of Eskridge, Kansas, and eight were collected from exposures of the

Eskridge Formation east of Humboldt, Nebraska. Specimen numbers and locality data can are presented in Table 2.1.

Specimen Number Formation Locality

DMNH 7854 Eskridge Mayer Farm

DMNH 43224 Eskridge Mayer Farm

DMNH 49902 Eskridge Mayer Farm

DMNH 51121 Eskridge Mayer Farm

DMNH 51122 Eskridge Mayer Farm

DMNH 52081 Eskridge Mayer Farm

UNSM 32100 Eskridge Shot in the Dark

UNSM 32149 Eskridge Shot in the Dark

KUVP 49537 Speiser Eskridge

KUVP 49538 Speiser Eskridge

KUVP 49539 Speiser Eskridge

KUVP 49540 Speiser Eskridge

KUVP 49541 Speiser Eskridge

Table 2.1. List of Brachydectes newberryi specimens examined.

For comparison with Brachydectes newberryi, I also scanned fossil skulls of the microsaurs Rhynchonkos stovalli (FMNH UR 1039) and Proxilodon bonneri (KUVP 8967), as well as skulls of the salamanders Amphiuma tridactylum (MVZ 241480), Proteus anguinus

(MVZ 47277), Siren intermedia (MVZ 196215) and Hynobius amjiensus (MVZ 231110). Scan parameters and voxel size were adjusted for each specimen and tomographic slice stacks were reconstructed in nrecon version 1.6.6.0 (Skyscan, 2011). HRXCT stacks of the microsaur

Huskerpeton englehorni (UNSM 32144) generated by Huttenlocker et al. (2013) and surface models of Carrolla craddocki generated by Maddin et al. (2011) were also analyzed with permission (JSA).

Specimen Number Formation Locality Voxel Size Voltage Current Filter Resolution UNSM 32100 Eskridge Fm Shot in the Dark, NE 29.1 100 kV 60 uA Aluminum Md UNSM 32149 Eskridge Fm Shot in the Dark, NE 17 130 kV 61 uA Brass Sm KUVP 49541 Speiser Shale Eskridge, KS 38.9 100 kV 60 uA Aluminum Md KUVP 49537 Speiser Shale Eskridge, KS 19.4 130 kV 61 uA Brass Sm KUVP 49540 Speiser Shale Eskridge, KS 21.2 80 kV 60 uA None Md KUVP 49538 Speiser Shale Eskridge, KS 38.9 100 kV 60 uA Aluminum Md KUVP 49539 Speiser Shale Eskridge, KS 25.2 100 kV 60 uA Aluminum Sm DMNH 52108 Eskridge Fm Mayer Farm, NE 9.5 130 kV 61 uA Aluminum Sm DMNH 47854 Eskridge Fm Mayer Farm, NE 22 65 kV 80 uA None Md

Table 2.2. Scan parameters for micro-CT scans of Brachydectes newberryi specimens examined in this study.

2.3 Methods

In order to study internal anatomy, I employed high resolution x-ray micro-computed tomography (HRXCT). HRXCT has been shown to be a highly effective tool for visualizing fine details of anatomy in both fossil and extant samples (Anderson et al., 2003; Maddin et al., 2011;

Maddin 2012), and HRXCT has recently been employed in the study of other lepospondyl taxa

(Anderson et al, 2009; Maddin et al., 2011; Huttenlocker et al, 2013), including skulls from lysorophian-bearing deposits within the Council Grove Group (Huttenlocker et al., 2013; Pardo et al., in press). All skulls included in this study were scanned using a Skyscan 1173 machine with scan parameters and voxel size adjusted for each specimen (Table 2.2). Tomographic slice stacks were reconstructed in nrecon version 1.6.6.0 (Skyscan, 2011) and voxels were attributed to individual bones manually and visualized as 3D models in Amira 5.4.0 (Visage Imaging, Inc.) using the LabelField, Resample, and SurfaceGen modules.

2.4 Description

2.4.1 Skull Roof and Cheek

The skull of Brachydectes newberryi is extremely specialized in comparison with that of other early tetrapods (including other lepospondyls) and exhibits significant reduction of dermal skull elements, especially along the orbit and cheek (Figure 2.1C). Most strikingly, the lateral region of the cheek lacks dermal ossification between the orbit and the squamosal, resulting in a deep lateral emargination of the ventral cheek that is continuous with the orbit and extends dorsally to the parietals (Figure 2.1C, Figure 2.2). Previous workers have disagreed on the extent of the orbit within this region, and most recently Marjanovic and Laurin (2008) suggested that the orbit encompasses the entire lateral unossified region (although this was amended by

Marjanovic & Laurin, 2013). In the Council Grove skulls, a low postorbital process of the parietal is present near the prefrontal-parietal suture, confirming that the orbit is restricted to the very anterior extent of this unossified region (Figure 2.1A,C; Figure 2.2). The remainder appears to be a greatly enlarged lateral cheek emargination, similar to that seen in the hapsidopareiontids

Hapsidopareion and Llistrofus (Daly, 1973; Carroll & Gaskill, 1978; Bolt & Rieppel, 2009), the

ostodolepids Tambaroter and Pelodosotis (Henrici et al., 2011; Daly, 1973; Carroll & Gaskill,

1978), and juveniles of the gymnarthrid Cardiocephalus (Anderson & Reisz, in prep.), although significantly deeper than seen in these taxa. This emargination may have accommodated enlarged adductor mandibularis externalis musculature (Figure 2.2B), in which case the morphology seen in B. newberryi may indicate further increase in the size of this muscle in

Brachydectes in comparison with other lepospondyls.

The skull roof of B. newberryi was well-described by previous authors (Sollas, 1920;

Wellstead, 1991). The median skull roof consists of paired nasals, frontals, parietals, and postparietals, as in the majority of early tetrapods. The nasals, frontals, parietals, and postparietals are all subequal in length. The prefrontal is well integrated into the anterior skull roof, forming a bridge between the frontals and maxillae, whereas posteriorly the tabular is reduced and integrated into the dermatocranial support for the suspensorium.

Figure 2.1. CT volume of the skull of Brachydectes newberryi, KUVP 49541. A, dorsal view; B, ventral view, with lower jaws removed; C, lateral view; and D, occipital view. Scale = 1 cm.

Figure 2.2. Skull of Brachydectes newberryi, showing the posterior extent of the orbit. A, photograph of DMNH 43224 in right dorsolateral view; B, interpretive drawing of DMNH 43224 in right dorsolateral view, showing extent of the orbit and m. adductor mandibulae externalis.

Scale equals 5 mm.

Anteriorly the nasals contact the premaxillae along a low, broad suture. Lateral to this is a broad, laterally-flaring emargination associated with the dorsal margin of the external naris.

Posteriorly, the nasals overlap the frontals in a deep interdigitating suture. The median suture between the nasal pair is straight, without significant interdigitation.

The frontal is roughly rectangular, and is flanked laterally by the prefrontal, which excludes it from both the orbit and the temporal emargination. The median suture between the frontal pair is straight, but shows shelf-like interdigitation in transverse section in larger specimens. Posteriorly, the frontal is sutured to the parietal via a series of deep lappets that

incise posteriorly into the parietal. Some variation exists in the general shape of the frontal pair.

In some specimens, the frontal pair is roughly rectangular, whereas in others the frontal pair is trapezoidal and tapers anteriorly. In a few specimens, the frontal pair expands anteriorly.

Frontal shape is one of the characters used by Wellstead (1991) to differentiate Brachydectes newberryi from B. elongatus, but the range of shapes preserved in the Council Grove lysorophian suggests that the morphologies described by Wellstead (1991) can exist as end-members of a continuum of morphologies within a single species. This may indicate that only one species of lysorophian, Brachydectes newberryi, can be identified with certainty, but it is also possible that the redbeds specimens from Texas and Oklahoma previously attributed to Lysorophus tricarinatus will demonstrate diagnostic morphology distinct from that seen in B. newberryi.

The parietal pair is also broadly rectangular, and together the two parietals are as wide as the prefrontals and frontals combined. No pineal foramen is present and no pineal fossa is present on the ventral surface of the parietals. The median suture between parietals is essentially straight, with minimal interdigitation. Posteriorly, the parietal interdigitates with deep incisures in the postparietal pair.

The postparietals lie directly posterior to, and are equal in width to, the parietals. The postparietals contribute to the sloping dorsal portion of the occiput, with a deep fossa on the occipital surface of each postparietal accommodating the epaxial musculature. No fenestra is present in the occiput between the postparietals, the occipital arch, and the otic bones. The ventral surface of the postparietals contains impressions of the semicircular canals and may represent investment of the dorsal otic capsule by the postparietals.

The temporal region consists of three bones: the squamosal, the tabular, and the quadrate

(Figure 2.1C). The squamosal makes up the majority of this region. It is a slender bone that

descends from the occiput anteriorly towards the jaw articulation, intersecting the coronal plane at the level of the palate at an angle of approximately 40 degrees. The ventral end of the squamosal wraps around the lateral surface of the quadrate. A strong ridge is present on the occipital surface of the squamosal, and likely served as the point of origin of the depressor mandibulae.

The tabular is a small triangular bone that overlaps the dorsal portion of the squamosal and the lateral surface of the postparietal. (Figure 2.1A-C) The lateral surface of the bone is marked by a large fossa that appears to be an extension of the lateral emargination of the cheek.

Posteriorly, the tabular projects beyond the occipital surface. This structure is not equivalent to the “tabular horns” seen in some nectrideans or the tabular prongs seen in adelospondyls, and forms the margin of a fossa for the epaxial musculature rather than constituting an actual projection from the posterior skull roof.

The premaxilla is small with a reduced pars dorsalis (Figure 2.1C,D). No vomerine shelf of the premaxilla is present. The premaxillary dentition is reduced, with only 3-4 large, conical teeth. The pars dorsalis is aligned along the midline without an internarial fontanelle. The external nares are large, and face anteriorly, and restrict the contact between the premaxilla and nasal to a small suture along the midline.

The maxilla is also reduced (Figure 2.1C,D). No palatal shelf of the maxilla is present, but a tight suture does exist between the maxilla and palatine. The maxillary dentition is relatively reduced, with 5-8 large conical teeth. The maxilla makes up the ventral margin of the orbit, but does not extend posterior to the postorbital process of the skull roof. The pars dorsalis is relatively limited, but is tightly sutured to the lacrimal in the antorbital region. Anteriorly, the maxilla participates in the margin of the external naris and choana.

2.4.2 Braincase

The braincase of B. newberryi is well-ossified and robust (Figure 2.3, 2.4). Ossifications are present within the sphenethmoid region, within the pila antotica and basisphenoid, the otic capsule, and the occipital arch.

Ossifications within the ethmoid and anterior sphenoid region consist of an anterior median bone and paired sphenethmoids.

The anterior median bone (Figure 2.3E,F) is a lozenge-shaped element at the base of the anterior region of the braincase, and does not contribute to the lateral walls of the braincase. It is closely associated with the cultriform process of the parasphenoid, and these two elements may, in fact, be co-ossified, as no separate median ossification has been identified by previous workers

(Sollas, 1920; Bolt & Wassersug, 1975). Dorsally, the median anterior bone invades the columella ethmoidalis (Figure 2.3E). This ossification within the columella ethmoidalis is complete in the largest specimen studied (UNSM 32149) but is incomplete in smaller specimens

(e.g. KUVP 49541) and absent entirely in the smallest specimens. An anterior median bone has previously been described in Carrolla craddocki as the sphenethmoid (Maddin et al., 2011) and appears to be present in a variety of other microsaurs as well (Szostakiwskij et al., in prep.).

Figure 2.3. Braincase of Brachydectes newberryi, KUVP 49541. A, dorsal view; B, right lateral view; C, ventral view; D, left lateral view; E, left anteroventral oblique view, with skull roofing bones present; F, left anterior oblique view, with skull roofing bones present; G, occipital view, with skull roofing bones present. Scale equals 1 cm.

Paired sphenethmoids make up the lateral wall of the anterior sphenoid region, extending from the anterior median bone posteriorly to the optic foramen (Figure 2.3A,B,D). The sphenethmoid in B. newberryi is a long, low, robust vertical wall similar in morphology to that of

Carrolla craddocki (Maddin et al., 2011) rather than the thin, bulging structure seen in more conservative ‘microsaurs’ such as Huskerpeton englehorni (Huttenlocker et al., 2013). A deep notch is present at the posteroventral corner of the bone for accommodation of the optic nerve

(Figure 2.3B,D). Contra the condition seen in H. englehorni and Nannaroter mckinziei

(Huttenlocker et al., 2013), no descending flange of the frontal articulates with the orbitosphenoid. Anteriorly, the surface of the sphenethmoid is smooth and lacking in facets for articulation with the trabecular plate dorsally and the antorbital cartilage ventrally, contra the condition seen in lissamphibians. It appears likely that no lateral connection between the orbitosphenoid and the nasal capsule was present in Brachydectes. Similar morphology in

Carrolla craddocki (Maddin et al., 2011), Huskerpeton englehorni (Huttenlocker et al., 2013), and Nannaroter mckinziei (Huttenlocker et al., 2013) suggests that this may represent a more general ‘microsaur’ condition. The pila metoptica is unossified, unlike the condition seen in

Rhychonkos and ostodolepids (Carroll & Gaskill, 1978, Anderson et al., 2009) but consistent with the morphology found in Carrolla craddocki (Maddin et al., 2011) and Huskerpeton englehorni (Huttenlocker et al., 2013).

The pila antotica is fully ossified, and is narrow, teardrop-shaped in cross section, and firmly sutured to the ventral surface of the parietal (Figure 2.3A,C; Figure 2.4B). Between the pila antotica, the hypophyseal fossa is broad and weakly posteriorly-directed (Figure 2.4B). The dorsum sellae delineate a shallow hypophyseal fossa at the midline, but ascend laterally into

broad ridges along the medial surface of the pila antotica, and reach the anterior contact between the pila antotica and the parietals.

Posterior to the pila antotica, there is a large antotic fenestra (Figure 2.3E,F, 2.4B, which in larger specimens is partially to completely bisected by a bony bridge into a dorsal and ventral foramen. The ventral portion of this fenestra appears to have served the postganglionic trigeminal nerve. Anteriorly, the dorsal foramen opens into a sulcus on the ventral surface of the parietals (Figure 2.4C), and posteriorly passes dorsally and medially to the semicircular canals of the inner ear (Figure 2.6E-G, sov). Similar anatomy of the antotic fenestra has been described by Maddin et al. (2011) in the brachystelechid Carrolla craddocki, although in C. craddocki the prootic fenestra is completely subdivided into the trigeminal foramen and a dorsal foramen.

Maddin et al. (2011) suggested that the dorsal foramen may serve a homologue of the dorsal vein of lissamphibians. In lissamphibians, the dorsal vein drains a venuous plexus along the posterior wall of the orbit into a lateral sinus within the braincase (Francis, 1934), and is closely associated with the trigeminal nerve. The morphology of the foramen and associated sulcus and canal in

Brachydectes newberryi is generally inconsistent with such soft tissue morphology, and instead a single lateral cranial vein (perhaps homologous to the supraorbital vein of some reptiles) passed from the dorsal orbit through the prootic fissure, finally entering the lateral cranial sinus medial to the otic capsules. The precise homology of this foramen remains uncertain, however.

Figure 2.4. Posterior braincase of Brachydectes newberryi UNSM 32149. A, left lateral view; B, left anterior oblique view, with squamosal and quadrate present; C, left anteroventral oblique view, with squamosal and quadrate present; D, left posterior oblique view, with squamosal and quadrate present. Scale bar = 5 mm.

The otic capsules consist of distinct prootic and opisthotic elements (Figure 2.3, 2.4). In smaller specimens, the prootic and opisthotic are small and relatively distinct, but in the largest specimen (UNSM 32149) these elements are more completely ossified, and approach each other ventral to the horizontal semicircular canal (Figure 2.4A). The prootic is roughly triangular, with the apex sutured to the parasphenoid at the level of the basipterygoid processes. The opisthotic is tall and pillar-like, with a strong vertical crista along the medial surface, here interpreted as a crista interfenestralis (Figure 2.5). The prootic and opisthotic co-ossified with the squamosal and parietal dorsally and with the parasphenoid ventrally (Figure 2.4D. The fenestra vestibularis is roughly oval in shape and fits the stapes closely both anteriorly and posteriorly, seemingly without space for an opercular cartilage. Laterally, the crista parotica exists as a strong horizontal ridge on the prootic, bracing against the squamosal. This ridge may be homologous to the paroccipital process (Heaton, 1979), although the latter involves more significant contributions from the opisthotic.

The medial surface of the otic capsule preserves osteological correlates of the structure of the inner ear, permitting creation of a virtual endocast of the inner ear and description of the gross morphology of this structure (Figure 2.6). Traces of the courses of the semicircular canals and saccular region are preserved as sulci along the medial surface of the otic bones. The semicircular canals are restricted to the upper portion of the otic capsule and directly abut the utriculus, with no intervening bone. Ampullae are preserved as weak swellings in the fossae for the semicircular canals, but lack distinct morphology. The horizontal semicircular canal is laterally exposed just ventral to the crista parotica. A large saccular region is present ventral to the utriculus, and is expanded greatly below the semicircular canals. A medial projection of the saccular region is preserved as a pit in the basioccipital bone, and may have housed the basilar

papilla (Figure 2.6F). The median wall of the otic capsule is incompletely ossified, preventing detailed characterization of the paths of the facial, vestibulocochlear, and abducens nerves.

Figure 2.5. Medial surface of the otic bones of UNSM 32149. Scale equals 5 mm.

The stapes has a round to oval footplate and well-developed columella, and is well- ossified in larger specimens (Figure 2.4D, Figure 2.6H-K). A shallow groove is present along the perimeter of the footplate. The columella flares distally, forming a broad articulation with the dorsal portion of the quadrate. A small foramen halfway along the length of the columella likely transmitted the stapedial artery (Figure 2.6J). A robust dorsal process is present in the largest specimen (UNSM 32149), but not in smaller specimens (e.g. KUVP 49541), which extends proximally from the midpoint of the columella towards the paroccipital process (Figure

2.4D), although it does not directly articulate with the otic capsule. The deep notch between the dorsal process of the stapes and the base of the columella would likely have encased the vena capita lateralis. In some specimens, the columella is weakly mineralized between the footplate and the distal tip, and in some cases the distal tip of the columella appears to be a separate but distinct ossification. It is possible that this element may be a distinct extracolumella (as is seen in some reptiles and amphibians), or that it represents a second ossification centre in an element that co-ossifies in fully adult specimens.

Figure 2.6. Selected elements of the auditory apparatus of Brachydectes newberryi. A, Position of the otic endocast in KUVP 49541, right lateral view; B, position of the otic endocast in KUVP

49541, dorsal view; C, right otic endocast of KUVP 49541, lateral view; D, right otic endocast of

KUVP 49541, medial view; E, left otic endocast of UNSM 32149, lateral view; F, left otic endocast of UNSM 32149, medial view; G, left otic endocast of UNSM 32149, dorsal view; H-

K, stapes (right) in medial (H), dorsal (I), lateral (J), and ventral (K) view. Scale equals 1 cm

(A,B), 5 mm (C-K).

The occipital arch consists of a well-ossified basioccipital, paired exoccipitals, and a single median supraoccipital (Figure 2.3A,B,D,G). Surfaces on the basicoccipital and exoccipitals contribute to the occipital cotyle, which is unpaired and crescentic. The occipital cotyle is weakly concave, and accepts the odontoid process of the atlas. The bases of the exoccipitals are swollen anteriorly along the suture with the parasphenoid. The metotic foramen passes through the suture between the exoccipital and opisthotic, and served as the passage for the vagus nerve and jugular vein. A second foramen, which pierces the exoccipital just lateral to the occipital cotyle, serves the hypoglossal nerve (Figure 2.3D). The synotic tectum is occupied by a single broad supraoccipital bone, as in other ‘microsaurs’ (Maddin et al., 2011;

Huttenlocker et al., 2013). A pointed ascending process of this ossification extends anteriorly beneath the postparietals and is exposed medially up to the posterior margin of the parietals. No

supraoccipital sinus is present. A posterior shelf of the supraoccipital roofs the foramen magnum; the dorsolateral surfaces of this shelf serve as an articular surface for the proatlas. The supraoccipital is present as a single ossification across all ontogenetic stages studied here.

2.4.3 Palate

The parasphenoid of Brachydectes newberryi is a broadly triangular element in ventral view, and represents the majority of the ossified palate. The cultriform process is laterally expanded to the extent that it is nearly as broad as the basipterygoid processes, and extends to the anterior end of the sphenethmoid ossification, where it tapers rapidly to a point. The basal plate of the parasphenoid is roughly rectangular, without the broad triangular posterior expansion seen in some ‘microsaurs’ (Huttenlocker et al., 2013). The basipterygoid processes lie directly ventral to the pleurosphenoids, and are narrower than the widest extent of the basal plate of the parasphenoid. Posteriorly, the parasphenoid is deeply notched, exposing the basioccipital. The parasphenoid is firmly sutured to the ventral surface of both the anterior and posterior regions of the braincase.

Figure 2.7. Palatoquadrate derivatives in Brachydectes newberryi, UNSM 32149. A, lateral view; B, Anterior view; C, Posterior view. Scale equals 5 mm.

The branches of the internal carotid artery leave clear grooves and canals on and through the ventral and lateral surface of the parasphenoid (Figure 2.3C), recording the pattern of some of the cranial circulation in Brachydectes. The route of the internal carotid artery coursed along a sulcus on the ventral surface of the parasphenoid, just medial to the basipterygoid processes. At the level of the latter, this sulcus gives rise to another deep groove medially that terminates at a foramen that pierces the basal plate of the parasphenoid and emerges from the medial surface of the pleurosphenoid within the hypophyseal fossa (Figure 2.3C). This canal would have enclosed the cerebral branch of the internal carotid artery. The main sulcus continues laterally, anterior to the basipterygoid process, and follows a shallow groove on the lateral surface of the cultriform process. This groove would have housed the palatal branch of the internal carotid artery. In contrast to the condition seen in temnospondyls (Yates & Warren, 2000, Fig 5) and

lissamphibians (Francis, 1934) where the internal carotid divides into cerebral and palatal branches either within the parasphenoid itself or within the hypophyseal fossa, the internal carotid artery of Brachydectes appears to have been divided into cerebral and palatal branches prior to entering the braincase, consistent with the morphology seen in stem and crown amniotes

(Muller et al., 2011). A similar morphology has been figured for Nannaroter mckinzei (Anderson et al. 2009) and Quasicaecilia texana (Carroll, 1990) but has not been remarked upon, the implication of this being that this morphology of the cranial circulation may be consistent throughout recumbirostrans.

The vomers are narrow, rod-like bones and contact each other anteriorly at the midline of the palate, anterior to the cultriform process of the parasphenoid. A short premaxillary process extends along the midline of the anterior palate to meet the premaxilla, but neither premaxillary shelf nor a maxillary process or shelf is present. Posteriorly, the palatine process of the vomer is narrow and extends just lateral to the cultriform process. A series of 6-8 large, robust teeth extends along the midline of each vomer.

The palatine is a short, strutlike element that connects the maxilla to the palatine ramus of the pterygoid. The palatine and maxilla are typically found together in specimens even when disarticulated from the remainder of the skull, suggesting that these elements may be more tightly sutured than the remainder of the palate. Neither teeth nor denticles are present on the palatines.

The pterygoids are greatly reduced in comparison with those of other early tetrapods

(Figure 2.1D, Figure 2.7). The palatine ramus is foreshortened, with only a short posterior sutural contact with the posterior end of the palatine and no contact with the vomers. The body of the pterygoid extends adjacent to the posterior portion of the cultriform process of the parasphenoid,

eliminating any interpterygoid vacuity. The quadrate process is anteriorly displaced and descends obliquely along the medial surface of the quadrate. The medial surface of the pterygoid is reflected dorsally to form a low dorsal process lateral to the pleurosphenoid. The basal process is reduced to a shallow facet at the anterior extremity of the dorsal process. No transverse process extends into the subtemporal vacuity. Teeth and denticles are absent from the body of the pterygoid.

An epipterygoid is present and ossified only in the largest specimen scanned, UNSM

32149 (Figure 2.7). The epipterygoid is a simple element, with a broad, roughly-horizontal ventral facet for articulation with the pterygoid, and a simple, slender dorsal stalk, comparable to the condition seen in amniotes. The epipterygoid does not articulate with the skull roof and appears to serve a reduced role in support of the palate in comparison with the microsaurs

Pantylus cordatus (Romer, 1963) and Huskerpeton englehorni (Huttenlocker at el., 2013). The epipterygoid contributes substantially to the conus recessus.

The quadrate is relatively simple in morphology (Figure 2.7). The condyle is trochlear in morphology and is somewhat mediolaterally compressed. The anterior surface of the quadrate is weakly concave, with a weak transverse ridge running from the lateral trochlea of the condylar surface to the medial surface. Posteriorly the quadrate tapers to a sharp ridge, which extends to a tubercle-like stapedial process in the largest specimen. A shallow sulcus present on the medial surface may be equivalent to the sulcus assigned to the so-called “chorda tympani nerve.”

2.4.4 Lower Jaw

The lower jaw of Brachydectes newberryi has been adequately described by Sollas (1920) and

Wellstead (1991) and little difference exists between the described morphology and that

observed in the Council Grove skulls. The number of ossifications is greatly reduced; only a dentary, angular, surangular, prearticular, splenial, coronoid, and articular are present. The dentary is relatively short with a deep coronoid expansion that is continued posteriorly by the surangular. As previously described, Brachydectes newberryi has a relatively low tooth count, with approximately 5-6 teeth in total. The dentary appears to be the only bone contributing to the symphysis. A large oval fenestra is present in the lateral jaw, between the dentary, angular and surangular. The coronoid is simple and does not intervene between the dentary and prearticular, and is instead limited to the anterior margin of the adductor fossa. A short retroarticular process is present extending posteriorly from the angular. The articular is narrow but deep, fitting closely into the trochlea of the quadrate. The prearticular makes up the majority of the medial surface of the jaw. A single, small Meckelian foramen is present. No denticle field is present on the medial surface of the jaw.

2.5.1 Homology of Occipital Ossifications

The occipital arch of Brachydectes newberryi, as for “microsaurs,” contains a broad ossification within the synotic tectum. Recent authors have argued against homology between this ossification and the supraoccipital bone of amniotes, in part because some lepospondyls

(primarily nectrideans, but also microbrachomorph microsaurs) and all seymouriamorphs lack such an ossification (Berman, 2000; Huttenlocker et al., 2013). Thus, a single median ossification within the syntotic tectum has been added to a long list of hypothesized convergences between microsaurs and amniotes. Ultimately, the test of this homology is phylogenetic (Chapter 3, and discussed in Chapter 4), but a survey of the morphology here is worthy of discussion.

Some variation exists in the presence and composition of ossifications within the synotic tectum in early vertebrates. In early stem-tetrapods, the synotic tectum is separated from the occipital arch by the otoccipital fissure, and is massively co-ossified with the otic capsules, as has been described in Acanthostega (Clack, 1998). Distinct supraoccipital ossifications arise in embolomere-grade tetrapods such as Archeria (Clack & Holmes, 1988) and baphetids such as

Kyrinion (Clack, 2003), but remain separated from the occipital arch by the otoccipital fissure.

The otoccipital fissure is not retained in adults within the tetrapod crown group, but ossifications of the synotic tectum are not ubiquitously preserved, and are absent from many temnospondyls

(Berman, 2000), colosteids (Smithson, 1982), and seymouriamorphs (White, 1939).

Within temnospondyls, the synotic tectum is generally invaded by processes from the exoccipital, and no separate supraoccipital, paired or unpaired, exists. This appears to be the case in modern lissamphibians as well (Lebedkina, 2004; Rose, 2003), where ossification of the synotic tectum occurs via extension of the exoccipital bones, and no separate supraoccipital ossification is present. However, in some dissorophid temnospondyls, the synotic tectum appears to be massively co-ossified, similar to the condition seen in stem-tetrapods (Schoch, 1999).

Within diadectamorphs, a single, massive supraoccipital bone is present in adults, but is paired in juveniles (Berman, 2000), with a conspicuous suture between left and right supraoccipital bones. A similar fusion of a paired supraoccipital is seen in various mammals as well (Strong, 1925). In reptiles, a single median supraoccipital bone is present throughout ontogeny (de Beer, 1937). The cosmopolitan distribution of this ossification among crown and late stem amniotes, and the pattern of ossification of the occiput suggests that the dorsal ossification of the occiput in recumbirostran lepospondyls, including Brachydectes newberryi, is likely a true supraoccipital. The absence of this ossification in nectrideans, Microbrachis, and

seymouriamorphs may be a result of either paedomorphosis in these taxa, misleading phylogenetic topologies, or a combination of the two.

2.6.2 Ontogenetic changes in the skull of Brachydectes newberryi

Reconstruction of a partial growth sequence is made possible by the substantial range of sizes in the sample of specimens examined here, with the smallest skull studied exhibiting a total skull length of 10.5 mm and the largest skull representing an animal with a skull length over 30 mm in length. Most skulls are approximately 10 mm or 20 mm in length; intervening sizes are not widely represented in this sample.

Ossification of all dermal bones has already been completed by the smallest studied specimen. In some other lepospondyls (Anderson, 2002; Olori, 2013), a number of dermal bones ossify relatively late in development, but this is not the case in Brachydectes.

Ossification of some endochondral elements progresses through the ontogenetic sequence sampled here. In smaller specimens (e.g. DMNH 52081) the columella ethmoidalis is completely unossified. Ossification of this cartilage is partial in larger specimens (e.g. KUVP

49541), where it forms the medial surface of the foramen housing the olfactory nerve.

Completion of ossification of the columella ethmoidalis is seen in the largest specimen (UNSM

32149) in which the entire space between the olfactory foramina is completely invaded by the median anterior bone. Complete ossification of the otic capsule is also ontogenetically delayed; the prootic and opisthotic are small floating elements in the smallest specimens, but ossify more completely at larger sizes, suturing to the parasphenoid, squamosal, and parietal in KUVP 49541, with many of the sutures completely obliterated in the largest specimen, UNSM 32149. In

UNSM 32149, there is also a distinct crista parotica extending from the lateral wall of the prootic

and opisthotic to brace against the squamosal; this structure is only weakly developed in KUVP

49541 and completely absent from smaller specimens.

Two specific structures initiate ossification late in ontogeny, and are observed only in

UNSM 32149. The epipterygoid is fully ossified in UNSM 32149, but is unossified in all other specimens of Brachydectes studied here. In addition, the distal portion of the columella, including its dorsal process, is only seen in UNSM 32149. In smaller specimens, the columella is a short, weakly-developed process extending from the footplate, and in the smallest specimens, the columella is essentially absent.

These observations presents several implications. The first is that all but one of the

Brachydectes specimens surveyed here likely represent immature specimens, with smaller specimens likely representing extremely immature animals. It is important to note that the majority of specimens of Brachydectes studied by previous authors (Sollas, 1920; Bolt &

Wassersug, 1975; Wellstead, 1991) are much smaller than UNSM 32149, and in some cases even smaller than the smallest specimens studied here. For characteristics that develop relatively late in ontogeny (dorsal process of the columella, epipterygoid, crista parotica), descriptions focusing on juvenile material (and phylogenetic analyses relying on those descriptions) may miss important anatomical structures that were present in adult Brachydectes.

A second implication is that some of the taxonomic diversity previously identified among lysorophians may instead represent ontogenetic variation. Wellstead (1991) reviewed lyrosophian diversity and concluded that only three taxa could be consistently identified:

Brachydectes newberryi, which primarily included small specimens with a skull length of less than one centimeter, Brachydectes elongatus (=Lysorophus tricarinatus) which primarily included specimens with a skull length between one and two centimeters, and Pleuroptyx

clavatus, which consisted of a few very large specimens with a skull length likely exceeding three centimeters. Wellstead (1991) diagnosed Brachydectes as distinct from Pleuroptyx on the basis of a broader pair of parietals, a more robust pectoral girdle, and well-developed alae on the ribs in the latter taxon. Parietal pair width appears to be variable, even within Wellstead’s sample. The remaining characteristics appear to refer to development and/or ossification of endochondral elements, which appear to develop late in ontogeny in B. newberryi. Within

Brachydectes, Wellstead (1991) identified two species: B. newberryi and B. elongatus. B. newberryi is distinguished from B. elongatus on the basis of the size of the lateral mandibular fenestra, the relative width of the parietal pair, the number of presacral vertebrae, and the presence of an unforked second epibranchial in the latter taxon. The lateral mandibular fenestra does appear to close during ontogeny (compare Figure 2.1C with Figure 2.2B), and relative width of the parietal pair is highly variable, with substantial overlap within the material surveyed by Wellstead (1991) as well as the material studied here. The substantial variation in presacral vertebra counts suggests some degree of interspecific variation, but it is difficult to align this with variation in cranial morphology, as few skulls described by Wellstead (1991) and no skulls studied here are articulated with a complete set of presacral vertebrae, limiting the use of vertebral counts in species identification. The morphology of the second epibranchial does appear to differ between B. newberryi and B. elongatus, but it is unclear whether this represents taphonomic, ontogenetic, or intraspecific variation. If Pleuroptyx clavatus and Brachydectes elongatus are to be retained as valid taxa, rather than relegated as junior synonyms of

Brachydectes newberryi, then these taxa will need to be revised and consistent morphological differences between them will have to be identified.

The limited ontogenetic timing data provides for some comparison with other early tetrapods. Anderson (2002) has suggested that miniaturization in Phlegethontia may have been accomplished via early ossification of endochondral elements, which would have restricted later ossification of the dermal skeleton. The ossification sequence data reported here suggests that ossification in Brachydectes followed a different trajectory, with ossification of all dermal bones occurring early in ontogeny, with delays in ossification of some endochondral elements

(specifically the otic capsule, columella, and epipterygoid) until late in skeletal maturity.

Whether this represents an alternate mode of miniaturization from that reported by Anderson

(2002) is questionable, as adult Brachydectes appear to be comparatively large, and well within the size range of microsaurs, and of early tetrapods in general, and substantially larger than typical “miniaturized” taxa.

Chapter 3: Phylogenetic Systematics of Brachydectes newberryi

3.1 Introduction

The relationships of Brachydectes newberryi among Paleozoic tetrapods, and with modern tetrapod groups, have been somewhat contentious since its discovery. Early workers looked to modern lissamphibians (Williston, 1908) and modern squamates (Broili, 1908) for answers to the relationships of Brachydectes, and its relationships with the broader diversity of

Paleozoic tetrapods were considered largely intractable. Early workers finally settled on the conclusion that Brachydectes was an early lissamphibian, likely related to modern salamanders

(Sollas, 1920), but that the ancestry of modern amphibians would remain uncertain until the discovery of additional material. Later workers suggested that Brachydectes may be related to a variety of other small early tetrapods with spool-shaped vertebrae (Carroll & Gaskill, 1978;

Wellstead, 1991). This group, termed Lepospondyli, has been the subject of ongoing interest in the question of lissamphibian origins (McGowan, 2002; Vallin & Laurin, 2004; Marjanovic &

Laurin, 2007; 2008; 2013), although a more general consensus has arisen that lissamphibians, or at least batrachians, fall within the Temnospondyli (McGowan, 2002; Ruta & Coates, 2007;

Carroll, 2007; Anderson, 2007; Anderson et al., 2008; Sigurdsen & Bolt, 2010; Sigurdsen &

Green, 2011; Maddin & Anderson, 2012).

In this chapter, I incorporate the new data from Chapter 2 into an existing phylogenetic analysis of lepospondyl relationships. This includes revision of character codings for the lysorophian Brachydectes, implementation of a substantial sample of new characters of the neurocranium, inclusion of new early tetrapod operational taxon units (OTUs), and modification of a small number of characters to assess possible effects of character nonindependence.

3.2 Matrix Construction

3.2.1 Taxon Scope and Selection

The tendency of recent studies of lepospondyl relationships, and of the relationships of early tetrapods more broadly, has been to intensively sample lepospondyl taxa, resulting in matrices with a very large number of operational taxonomic units (OTUs) and comparatively few characters. The most extensive phylogenetic effort with respect to lepospondyl relationships was begun by Anderson (2001), who sampled 183 characters for 49 taxa, the majority of which were lepospondyls. This analysis was subsequently expanded by Anderson (2007) to 197 characters and 62 taxa, including primarily additional temnospondyl taxa in order to test questions of lissamphibian origins and lissamphibian monophyly, and thus covers two major clades of

Paleozoic anamniotes (lepospondyls and temnospondyls) albeit with significantly less extensive sampling of temnospondyls and only cursory sampling of other anamniote lineages, such as

‘anthracosaurs’ and seymouriamorphs. In later iterations of this matrix, highly fragmentary or poorly-known taxa such as Quasicaecilia were removed, and newly-described species, such as the stem-batrachian Gerobatrachus hottoni, were added (Anderson et al., 2008, Anderson et al.,

2009, Henrici et al., 2011, Huttenlocker et al., 2013). The most recent published iteration of this matrix is that of Huttenlocker et al. (2013), which incorporates 60 taxa (35 of which are lepospondyls) and 227 characters. Ruta et al. (2003) and Ruta and Coates (2007) have engaged in similar broad-scale taxon selection. Ruta et al., (2003), for example, sampled 319 characters for 90 taxa (33 of which were lepospondyls), a matrix expanded by Ruta and Coates (2007) to sample 339 characters for 102 taxa with an equivalent sampling of lepospondyl taxa.

An additional matrix initially produced by Laurin & Reisz (1997) has been subsequently expanded by Laurin & Reisz (1999) and Vallin & Laurin (2004) to assess lepospondyl

phylogeny, but with relatively reduced sampling. Vallin & Laurin (2004) sample 161 characters for 49 taxa, of which only ten are lepospondyls, and of which five (Adelospondyli, Aistopoda,

Nectridea, Lysorophia, and Brachystelechidae) are composite taxa.

The goal of this study is to assess specifically the relationships of Brachydectes newberryi among lepospondyls, and thus I have chosen to sample lepospondyls as broadly as possible. A secondary goal of this study is to assess the place of Brachydectes newberryi within larger patterns of skull evolution in early tetrapods, so I have also sampled a smaller number of well-preserved and completely-described early tetrapods as well.

3.2.2 Materials

The following material was consulted directly during recoding of characters and coding of new characters:

Aïstopods—Coloraderpeton brilli (CM 47687), specimen and CT scans; Lethiscus stocki

(MCZ 2185), CT scans (Anderson et al., 2003)

Nectrideans—Ductilodon pruitti (KUVP 129734, KUVP 28359, KUVP 81079), specimens and CT scans; Diploceraspis burkei (CM 25207, CM 23516), specimens; Crossotelos annulatus (KUVP 350), specimen and CT scans

Microsaurs—Huskerpeton englehorni (UNSM 32144), specimen and CT scan;

Micraroter erythrogeios (FMNH UR 2311), specimen and CT scan; cf. Micraroter erythrogeios

(BPI 3539), specimen; Pelodosotis elongatus (UM 11156), specimen and CT scan; Rhynchonkos stovalli (FMNH UR 1039), specimen and CT scan; Proxilodon bonneri (KUVP 47367), specimen and CT scan; Nannaroter mckinzei (OMNH 73107), CT scan; Quasicaecilia texana

(USNM 22079), specimen and CT scan.

Lysorophians—Brachydectes newberryi (Eskridge Formation: DMNH 7854, DMNH

43224, DMNH 49902, DMNH 51121, DMNH 51122, DMNH 52081, UNSM 32100, UNSM

32149; Speiser Shale: KUVP 49537, KUVP 49538, KUVP 49539, KUVP 49540, KUVP 49541)

Temnospondyls—Eoscopus lockardi (KUVP 80408, KUVP 80409, DMNH 8167), specimens and CT scans; Plemmyradytes shintoni (DMNH 45809), specimen and CT scan;

Tersomius dolesensis (OMNH 3709), specimen and CT scan; Acroplous vorax (DMNH 44396), specimen and CT scan.

Reptilia—Petrolacosaurus kansensis (KUVP 33606, KUVP 33607, KUVP 33608)

3.2.3 Character Nonindependence

Much debate has taken place about the importance of character formulation in early tetrapod phylogeny, and for questions of lepospondyl phylogeny and lissamphibian origins more specifically (Anderson, 2007; Marjanovic & Laurin, 2008; 2013; Frobisch & Schoch, 2009).

Much of this discussion has focused on whether significant portions of the matrix are comprised of ontogenetically variable characters (Anderson 2007; Marjanovic & Laurin, 2008; Frobisch &

Schoch, 2009) or whether critical character support comes from shared character states involving loss of elements (Schoch & Milner, 2003; Anderson, 2007), but other widespread issues have received somewhat less attention, despite potentially having a much greater impact on phylogeny. These problems include logical nonindependence of characters, topological nonindependence of characters, nonindependence of characters due to dependence on resolution of uncertain homology, and biological nonindependence of characters, often a result of ontogenetic and size-related variation.

All phylogenetic methods make the explicit assumption that variation in each character is completely independent of variation in every other character. In maximum parsimony methods, this permits simple summation of tree length for each character for all characters in the matrix.

In parametric methods (maximum likelihood and Bayesian methods), this permits direct multiplication of the joint likelihood of each character for all characters in the matrix without reference to conditional probabilities where change in one character biases change in another.

Because independence is an explicit assumption of the methods as they have been implemented to date (Brazeau, 2011), violations of this assumption of independence will mean that presence of certain character states may be counted multiple times while calculating tree length or tree likelihood, with the effect that these character states will be implicitly weighted (Brazeau, 2011).

As such, violations of the assumption of independence represent a substantial concern during matrix construction.

Logical nonindependence between characters occurs when coding a character as a specific state for any taxon will necessarily mean that a second character will be restricted in possible states. For example, imagine two characters: process A absent (yes/no) and process A present (yes/no). It is logically not possible for process A to both be present and absent. These two characters describe the same structure in two separate ways. The problem of logical nonindependence has been discussed in detail by Maddison (1993), primarily with regard to matrices which include characters which describe the presence or absence of a structure as well as characters that describe a condition of that structure. Maddison (1993) specifically focuses on a theoretical example where one character describes the presence or absence of a tail, and a second character describes the color of the tail. This combination of characters permits one to describe the color of a nonexistent tail, which is a logical impossibility. Maddison (1993)

suggests several possible solutions to this problem, including implementation of step-matrices and fusion of multiple characters into a single multi-state character. Other authors (Lee &

Bryant, 1999; Brazeau, 2011) have argued against one or more of these possible solutions on the basis that these either assume knowledge of character transformation (Lee & Bryant, 1999) or may inadvertently obscure phylogenetic information by eliminating statements of underlying homology (Lee & Bryan, 1999; Brazeau, 2011). It is clear that logical nonindependence is a major issue in early tetrapod phylogeny, especially given trends in limb reduction and loss, dermatocranial simplification, and vertebral simplification, but the best way to address these pervasive problems in early tetrapod phylogeny is unclear, in part because there is no consensus on how to handle logical nonindependence in general. Due to the scope of the problem in early tetrapod morphology in general, and in the phylogenetic matrices discussed here, logical nonindependence will not be dealt with directly in this chapter.

Topological nonindependence between characters occurs when two characters are logically independent a priori but where the topological relationship of the structures used as the basis of these characters will necessarily mean that the state of one character will restrict the possible states of a second. For example, consider two characters: parietal-postorbital contact

(present/absent) and tabular-postfrontal contact (present/absent) (Figure 3.1). Due to the arrangement of bones of the skull, a contact between the parietal and postorbital will necessarily exclude a contact between the tabular and postfrontal. Thus, these two characters actually describe two aspects of the same morphological condition. An improved combined character diagnosis could be stated as: relationship of parietal, postparietal, supratemporal, and tabular bones (suture between postfrontal and tabular/suture between parietal and postorbital).

Figure 3.1. Topological nonindependence between characters in the early tetrapod skull. Cranial morphology based on Huskerpeton englehorni, after Huttenlocker et al. (2013). Character numbers and states refer to the character list of Anderson (2007). A, with tabular-postfrontal contact present; B, with parietal-postfrontal contact precluding tabular-postfrontal contact.

Figure 3.2. Nonindependence of character states in the early tetrapod skull due to common inference of ambiguous homology. Skull based on Huskerpeton englehorni, after Huttenlocker et al. (2013). Characters and character states refer to Anderson (2007). A, with large temporal bone interpreted as a tabular; B, with large temporal bone interpreted as supratemporal.

Nonindependence of characters due to dependence on resolution of uncertain homology applies specifically to characters where states of multiple characters involve presence or absence of certain structures on a specific bone, but where the identity of that bone is uncertain in some or all OTUs. An example of this would include characters associated with the identity of the temporal bones in early tetrapods. In plesiomorphic early tetrapods, the skull roof lateral to the parietals and postparietals is comprised of three bones, the intertemporal, supratemporal, and tabular bones. In many early tetrapods, the temporal arcade is reduced to one or two bones. In taxa where two bones are present, these two bones are generally interpreted as the supratemporal and tabular, with loss of the intertemporal. In taxa where only a single bone is present, however, the remaining bone is identified alternately as a supratemporal or tabular depending on the taxon, with some manner of uncertainty in some boundary cases, such as most microsaurs and diplocaulid nectrideans. Depending on the identification of this element, characters associated with the presence or absence of the tabular and supratemporal, characters associated with the anterior extent of the tabular, characters associated with the occipital extent of the supratemporal, and characters associated with occipital structures of the tabular are all strongly nonindependent

(Figure 3.2).

Figure 3.3. Biological nonindependence of characters due to heterochronic processes. Characters and character states refer to Anderson (2007). A, Seymouria sanjuanensis, juvenile, after

Klembara et al., 2006; B, Seymouria sanjuanensis, adult, after Klembara et al., 2006; C,

Discosauriscus austriacus, adult, after Klembara et al., 2006.

Finally, multiple characters can exhibit nonindependence due to common biological cause, a phenomenon broadly describable as correlated character evolution (O’Keefe & Wagner,

2001). Biological nonindependence of characters can result from a variety of biological phenomena. Developmental constraint can restrict the number of possible phenotypes, with suites of anatomically specific characteristics co-varying with more general gross morphology

(Goswami & Polly, 2010; Gold et al., 2014). Heterochrony can also serve as a source of character co-variation, especially in clades, such as salamanders, where multiple lineages have employed neoteny in parallel (Wiens et al., 2005). Constraints on function, especially in specialized niches, may also produce correlated evolution of multiple characters, including characteristics involving the origin and insertion of muscles or muscle groups, characteristics associated with functionally integrated locomotory structures, and suites of characteristics associated with feeding mechanics (Metzger & Herrel, 2005; Pierce et al., 2010) or fossoriality

(Kearney & Stuart, 2004; Kleinteich et al., 2012). Finally, morphology is itself the product of developmental processes governed by genes. Gene products are often employed in multiple signalling pathways (Valenta et al., 2012), and signalling pathways may be conserved between multiple morphogenetic processes (Protas et al., 2008; Chang et al., 2009), with the result that multiple discrete character suites may demonstrate correlated effect as a result of a common

genetic cause, a phenomenon known as pleiotropy. Inference of biological nonindependence is, unlike forms of logical nonindependence, a nontrivial matter, as biological nonindependence is a biological hypothesis rather than a logical or topological statement. Biological nonindependence, thus, cannot be assumed; it must be demonstrated with data and methods appropriate to the specific hypothesis. Developmental constraint may be testable via statistical study of morphological covariation and laboratory manipulations of developmental processes.

Functional constraint may be investigated via biomechanical modeling of theoretical functional performance across morphospace (Pierce et al., 2010; Kleinteich et al., 2012). Effects of heterochrony can be identified via life history surveys in well-understood groups (Wiens et al.,

2005). Pleiotropy can be identified via gain-of-function and loss-of-function experiments (e.g.

Chang et al., 2009) or strongly implicated by quantitative genetic methods (e.g. QTL; Protas et al., 2008), but is difficult to identify in raw morphological data alone. At a minimum, biological nonindependence can be identified by testing for covariation within phylogenetic datasets either with or without a reference tree (e.g. O’Keefe & Wagner, 2001; Pagel, 1994). Although this form of character nonindependence has received the most attention within early tetrapod phylogenetic datasets (Anderson, 2007; Marjanovic & Laurin, 2008; 2013; Frobisch & Schoch, 2009), most of these treatments of biological nonindependence have excluded characters from phylogenetic matrices a priori without directly testing for nonindependence (e.g. Marjanovic & Laurin, 2008,

2013; Sigurdsen & Green, 2011). While it is certainly the case that many characters incorporated into current phylogenetic matrices are nonindependently variable, especially with respect to heterochronic processes (Figure 3.3), more extensive study of ontogenetic trajectories, functional morphology, and intraspecific variation in early tetrapods is necessary to identify these.

Furthermore, ontogenetic characters may still retain phylogenetic information (Maddin et al.,

2012), making their a priori exclusion circumspect.

I have revised the matrix of Anderson (2001, 2007) and Huttenlocker et al., (2013) to account for logical and topological nonindependence as well as nonindependence of characters due to differing interpretation of bone homologies. This has resulted in four operational matrices:

(1) the unmodified matrix, (2) a matrix modified to account for logical and topological nonindependence but maintaining the assumptions of temporal bone homology in the original matrix, (3) an unmodified matrix reinterpreting the temporal bone in “microsaurs” as a supratemporal rather than a tabular, and (4) a matrix modified to account for logical and topological nonindependence, and reinterpreting the temporal bone of “microsaurs” as a supratemporal. I have not modified the matrix to account for biological nonindependence, as determination of biological nonindependence of characters is a nontrivial inferential step and outside of the scope of this study.

I have also assembled a braincase-only character matrix which, while including character data from prior datasets, has been significantly revised. Characters, when possible, refer to relationships between distinct tissue types or between distinct cartilaginous precursors. This includes, but is not limited to, inferences of the relationship between cartilaginous precursors within the braincase (e.g. presence or absence of median fusion of the trabeculi cranii) on the basis of braincase ossifications, the extent of ossification of braincase structures (e.g. presence or absence of ossification within the pila metoptica), the relationship between braincase structures and inferred soft tissue structures such as cranial nerves and blood vessels (e.g. the path of the profundus nerve), or the relationship between the neurocranium and dermatocranial elements of the palate and skull roof (e.g. the presence of posterior processes of the vomers along the

cultriform process and sphenethmoid region of the anterior braincase). The rationale behind this is threefold. First, this avoids entirely simple topological nonindependence as discussed above, as well as other forms of topological nonindependence associated with changes in general skull morphology. Secondly, such characters permit clear diagnoses with definitive boundary conditions, eliminating boundary cases entirely for at least part of the dataset. Finally, and most importantly, these character diagnoses imply explicit changes in the relationships between tissues and as such serve as not only hypotheses of homology of structures, but also hypotheses about the processes which shape those structures.

All mutually exclusive morphologies pertaining to a structure have been included as states of the same character. This means that some characters are multistate by necessity.

Brazeau (2011) has recently reviewed approaches to character coding, and has advised against the use of multistate characters in situations where (1) multiple states reflect several independent but contingent characters or (2) where an “absent” state may reflect absence of multiple non- equivalent structures. I have taken care to ensure that character diagnoses proposed herein do not violate these two guidelines. Where multistate characters do appear, these states generally refer to positional relationships between overlapping structures (e.g. character 20, posterior extent of the basal plate of the parasphenoid with respect to neurocranial structures) or multiple ossification patterns of a single cartilaginous precursor (e.g. character 32, nature of

“supraoccipital” centres of ossification within the synotic tectum).

No multistate characters are treated here as ordered, as character ordering makes implicit assumptions about transformational series. All characters have been compared to ensure that no logical or topological nonindependence exists between characters. Where possible, I have specified relationships between cartilaginous precursors (trabeculae, pilae, tecta) rather than

named bony elements (‘pleurosphenoid’, ‘sphenethmoid’, ‘orbitosphenoid’, ‘supraoccipital’) to avoid the effects of different interpretation of ossification homologies and naming conventions between taxa. Character states for each character have been illustrated to establish visual diagnoses to supplement written diagnoses and to provide a visual record of these characters to aid future efforts to code boundary cases.

3.2.4 Character Sample Scope

As the primary purpose of this study is to test the phylogenetic relationships of

Brachydectes newberryi specifically, new characters proposed here include only those that can be coded for B. newberryi. Because the dermal skull of B. newberryi is highly reduced, new characters are predominantly associated with the structure of the braincase, identified via comparison with the published literature and recently described CT scans of the microsaurs

Nannaroter mckinzei (Anderson et al., 2009), Carrolla craddocki (Maddin et al., 2011), and

Huskerpeton englehorni (Huttenlocker et al., 2013). In a few cases, character data were interpreted from CT scans of the aïstopods Lethiscus stocki (Anderson et al., 2003, Anderson et al., in prep.) and Coloraderpeton brilli (Anderson et al., in prep) in order to scrutinize the lysorophian-aïstopod relationship recovered by Anderson (2001, 2007), Anderson et al. (2008), and Huttenlocker et al., (2013).

I have decided to emphasize neurocranial characters for several reasons. First and foremost, neurocranial characters are largely overlooked in current phylogenetic studies relevant to the question of lepospondyl relationships generally and of the relationships of Brachydectes more specifically. For example, the current iteration of the Anderson (2001) lepospondyl matrix as reported by Huttenlocker et al. (2013) contains only 20 neurocranial characters (8.8% of total character coverage). An additional braincase character (an amphibian-type ear) has also been

proposed by Maddin and Anderson (2012), although this is a compound character, as it incorporates information on the presence of an amphibian sensory papilla, the pathway of the re- entrant fluid circuit, and the orientation of the periotic canal. The early tetrapod supermatrix of

Ruta and Coates (2007) contains only 16 braincase characters (4.7% of total character coverage).

The matrix of Vallin and Laurin (2004) identifies 15 braincase characters (96% of total character coverage). Morphology of the braincase, then, appears to be a largely untapped source of data with potential to greatly inform inference of early tetrapod phylogeny. Furthermore, a number of recent studies have demonstrated that the neurocranium is substantially more conservative than other skeletal modules (Goswami & Polly, 2006) and has the potential to resolve otherwise intractable phylogenetic problems (Friedman, 2007; Maddin, 2012; Maddin & Anderson, 2012;

Maddin et al., 2012a; 2012b;). Neurocranial data have largely not been implemented in phylogenetic analyses of early tetrapods thus far because internal structures of the skull are largely inaccessible to study. The recent availability of CT data for a number of lepospondyl taxa

(Anderson et al., 2003; Anderson et al., 2009; Maddin et al., 2011; Huttenlocker et al., 2013) has made study of internal cranial structure, including morphology of the neurocranium, much easier and has eliminated the need to destructively sample unique specimens in order to glean this important information.

Focusing on braincase characters has additional benefits. One consistent phylogenetic result of various phylogenetic analyses is a close relationship between aïstopods and lysorophians (Anderson, 2001; Anderson, 2007; Anderson et al., 2008; Ruta et al., 2003; Ruta &

Coates, 2007; Huttenlocker et al., 2013; Marjanovic & Laurin, 2013), a relationship that is in part supported by similar reductions of the dermal skull as well as limb reduction and axial elongation, despite the presence of a number of characters that suggest a more basal position of

aïstopods within the tetrapod tree (Carroll, 1998). In addition, it has been suggested by Anderson

(2007) and Marjanovic and Laurin (2008) that common losses of bones or ontogenetic adulthood in different lineages may be biasing one or more of these phylogenetic analyses. Although the potential exists for ontogeny and common loss to bias evolution of braincase characters as well as characters of the postcranium and dermal skull, the vast majority of the braincase characters identified here are not simple presence/absence formulations. In many cases, these characters represent substantial differences in the structure of the braincase, cranial circulation, cranial nerves, sensory structures, and brain.

3.3 Neurocranial character diagnoses and discussion

I report the full list of neurocranial (N) characters here with full diagnoses and discussion of morphology. Previously reported characters are renumbered here by region of the neurocranium.

For reference, I provide illustrations of early tetrapod braincases in standardized orientations. To identify characters associated with the acquisition of the crown tetrapod neurocranium, I have illustrated three putative stem tetrapods: Acanthostega gunnari (Figure

3.4), the baphetid Loxomma acutirhinus (Figure 3.5) and the embolomere Archeria crassidisca

(Figure 3.6). To identify characters associated with the acquisition of derived temnospondyl morphology, I have illustrated the colosteid Greererpeton burkemorani (Figure 3.7), the eryopid

Eryops megalocephalus (Figure 3.8), the trematopid Acheloma dunni (Figure 3.9), and the brachyopid Batrachosuchus watsoni (Figure 3.10). To identify characters associated with the acquisition of amniote morphology, I have illustrated the seymouriid Seymouria baylorensis

(Figure 3.11), the diadectamorph Limnoscelis palustris (Figure 3.12), the recumbirostran

Huskerpeton englehorni (Figure 3.13), the cocytinid Brachydectes newberryi (Figure 3.14), the

eureptile Captorhinus laticeps (Figure 3.15), and the synapsid Ophiacodon uniformis (Figure

3.16).

Figure 3.4. Braincase of Acanthostega gunnari, after Clack, 1988, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view; B, neurocranium, ventral view, dermal elements of the right palate removed; C, neurocranium, occipital view, bones of the cheek and suspensorium removed.

Figure 3.5. Braincase of Loxomma acutirhinus, after Beaumont, 1977, demonstrating characters and character states identified in this study. Left lateral view.

N01. Trabecula cranii: (0) without significant median fusion posterior to solum nasi (platytrabic);

(1) fused medially posterior to solum nasi to form elongate trabecula communis (tropitrabic)

(Figure 3.13B). Plesiomorphically, sarcopterygians have widely-spaced trabeculae separate along the majority of their length, resulting in an open hypophyseal fenestra that runs the majority of the length of the sphenoid region of the skull and which is floored only by the cultriform process of the parasphenoid. Median fusion of the trabeculae to form a trabecula communis occurs in some amniotes, and appears to be associated with the presence of an interorbital septum (de Beer, 1937).

The trabeculae are often not fully ossified in adult early tetrapods, but sockets of unfinished bone are present in the anterior sphenethmoid region to accommodate these structures, which may be widely-spaced (State 0) or fused at the midline (State 1) depending on the taxon.

Figure 3.6. Neurocranium of Archeria crassidisca, after Clack & Holmes, 1988, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view; B, neurocranium, occipital view.

N02. Dorsal trabeculae: (0) dorsal trabeculae provide dorsolateral bridge between sphenoid region and nasal capsule; (1) dorsal trabeculae absent or incomplete, no dorsolateral bridge between

sphenoid region and nasal capsule. The plesiomorphic condition in osteichthyans is that the trabecular horn, upon reaching the sphenoseptal commissure, curves posterodorsally until it reaches the interorbital cartilage. In early tetrapods, this dorsal trabecula runs widely parallel to the anterior-posterior axis of the skull, and meets the orbital cartilage. In amniotes and possibly some microsaurs, the dorsal trabecula is thin or absent.

Figure 3.7. Braincase of Greererpeton burkemorani, after Smithson, 1982, demonstrating characters and character states identified in this study. A, neurocranium, ventral view, dermal elements of the right palate removed; B, occipital view, left stapes removed.

Figure 3.8. Braincase of Eryops megalocephalus, after Sawin, 1941, demonstrating characters and character states identified in this study. Left lateral view.

N03. Ossification between optic foramen and pila antotica: (0) Ossification complete between optic foramen and pila antotica; (1) pila metoptica and associated cartilaginous taeniae unossified

(Figure 3.14A). In some early tetrapods, a wide fenestra is present in the median orbital wall in the

region of the foramina for the optic, oculomotor, and trochlear nerves (e.g. Carrolla craddocki,

Maddin et al., 2011; but also Greererpeton burkemorani, Smithson, 1982).

Figure 3.9. Braincase of Acheloma dunni, after Maddin et al., 2010, and Polly & Reisz, 2011, demonstrating characters and character states identified in this study. Occipital view, left stapes removed.

N04. Ossification within the columella ethmoidalis: (0) absent; (1) novel median ossification forming the median margin of the foramen serving the olfactory nerve (Figure 3.14B). A novel ossification in the median portion of the ethmoid region is present in Carrolla craddocki (Maddin et al., 2011) and Brachydectes newberryi (this study, Ch. 2), and may be present in Quasicaecilia texana (Carroll, 1990; pers. obs.). Median ossifications of the columella ethmoidalis are present in some specimens attributed to Rhynchonkos stovalli, although these are absent from the type specimen (M. Szostakiwskyj, pers. comm., 2013; Szostakiwskyj et al., in prep.). The columella

ethmoidalis is partly ossified in some caudates, but this is a derived condition that is accomplished in different ways in different caudate lineages (pers. obs.).

N05. Path of profundus branch of trigeminal nerve: (0) enclosed in lateral wall of sphenoid region of braincase and exits laterally via a series of small foramina (Figure 3.4A); (1) extramural. In plesiomorphic tetrapods and other sarcopterygians, the profundus nerve arises from a separate ganglion and separates from the main branch of the trigeminal prior to exiting the braincase. In this condition, the profundus branch runs anteriorly within the lateral wall of the braincase, sending a series of branches through the nasal capsule to innervate mechanosensory and electrosensory organs in the skin of the dorsal region of the snout (Bemis & Northcutt, 1992; Clack, 1998). These branches are identifiable as a series of small foramina piercing the lateral wall of the sphenethmoid in the vicinity of the ethmoid region. In the derived condition, the profundus arises from the trigeminal ganglion, and exits the antotic fissure alongside other branches of the trigeminal nerve, and runs anteriorly within the orbit, and no foramina are present in the lateral wall of the sphenethmoid.

N06. Foramina for optic nerve and trigeminal nerve: (0) confluent (Figure 3.4A); (1) widely separate (Figure 3.8). In some stem tetrapods, a single large fissure serves the optic and trigeminal nerves (Clack, 1998). In most early tetrapods, however, these nerves exit the skull separately, with the optic nerve exiting far anterior to the trigeminal.

N07. Lateral head vein: (0) vein exits braincase via foramen for trigeminal nerve (Figure 3.5);

(1) vein exits braincase far dorsal to foramen for trigeminal nerve. In most tetrapods, a plexus of veins drains the meninges via a small vein that meets the lateral head vein within the temporal region (Francis, 1934). This vein is referred to by a variety of names, including the dorsal vein

(Maddin, 2011; Maddin et al., 2011), the prootic cranial vein (Francis, 1934), as well as other

names. In some early tetrapods and lissamphibians, this vein seems to exit the cranial cavity via the antotic fissure, along with the trigeminal nerve, around which it sometimes anastomoses

(Francis, 1934). In at least some microsaurs, a large foramen apparently serves this vein, which exits the braincase far dorsally (Maddin et al., 2011; this study, Ch. 2), sometimes following a groove in the ventral surface of the skull roof.

Figure 3.10. Braincase of Batrachosuchus watsoni, after Warren, 2000, demonstrating characters and character states identified in this study. A, neurocranium, ventral view, dermal elements of the right palate removed; B, neurocranium, occipital view, left stapes removed.

N08. Anterior extent of cultriform process: (0) cultriform process extends to anterior margin of sphenethmoid; (1) cultriform process extends far anterior to sphenethmoid; (2) cultriform process does not reach anterior margin of sphenethmoid.

N09. Olfactory bulbs: (0) narrow; (1) endocasts swollen, leaving considerable impressions in lateral and ventral wall of sphenoid region and in ventral surface of frontal (Figure 3.13B). In most early tetrapods, the olfactory bulb is comparatively small and does not leave an impression on the internal surface of the sphenethmoid region. In some microsaurs, however, the olfactory bulb is extremely large and leaves significant paired impressions in the surrounding bones. This can be seen clearly in the digital endocast or even in transverse section (tomographic or in hand sample). This character may be a function of miniaturization to some degree, but the absence of swollen olfactory bulbs in the small-bodied species Carrolla craddocki, Quasicaecilia texana,

Brachydectes newberryi, Lethiscus stocki, and Coloraderpeton brillii, and presence of swollen olfactory bulbs in the larger Micraroter erythrogaios, suggests that this character is not solely size-dependent.

Figure 3.11. Braincase of Seymouria baylorensis, after White, 1939, demonstrating characters and character states identified in this study. Left lateral view.

N10. Ventral flange from skull roof articulating with sphenethmoid: (0) absent; (1) present on frontal and parietal; (2) present on frontal only (Figure 3.13A). Huttenlocker et al., (2013) recognized that the sphenethmoid articulates with a flange from the skull roof, but recognized a flange from the frontal only in Huskerpeton englehorni and Nannaroter mckinzei. A descending flange is present on the frontal and parietal in several microsaur taxa as well as captorhinids and some other early tetrapods. The distinction between the frontal-only flange and a more extensive flange that ranges along the frontal and parietal allows for a more complete description of the range of conditions for this character.

N11. Descending lamina of the parietal invades the medial orbital wall between the

‘pleurosphenoid’ and ‘sphenethmoid’ elements: (0) no; (1) yes. In Lethiscus stocki and

Coloraderpeton brilli, a deep flange is present on the ventral surface of the parietal and separates the anterior and posterior ossifications of the sphenoid region. This differs significantly from the flange described in character N10 in that it does not provide a lateral brace to an ossified sphenoid bone, but rather serves as the primary ossification of the medial orbital wall. This appears to be restricted to aïstopods.

N12. Foramen for oculomotor nerve: (0) exits skull dorsal to foramen for optic nerve (Figure

3.4A), (1) exits braincase at or below foramen for optic nerve. The location of the foramen serving the optic nerve is constrained by the optic chiasma to the ventral portion of the sphenoid region, but such constraint does not apply to the oculomotor nerve. In many early tetrapods, the oculomotor nerve exists the braincase far dorsal to the optic nerve. This is not universally the case, and the oculomotor nerve exists the median orbital wall at approximately the same level as the optic nerve in some early tetrapods, as well as lissamphibians and amniotes.

N13. Intermaxillary fossa: (0) present; (1) absent (Figure 3.13B). This character is roughly equivalent to character 95 of Anderson (2001, 2007). In salamanders, a deep ventral fossa between the nasal capsules houses the maxillary glands. Similar fossae can be observed in a wide variety of early tetrapods, but some early tetrapods appear to lose this structure entirely. In those cases, the nasal capsules meet at the midline to form an internasal septum.

N14. Intermaxillary fossa: (0) paired (Figure 3.4B); (1) unpaired. In many early tetrapods, the intermaxillary fossa is divided sagittally by a median ridge or septum, generally involving contribution from the vomer. In most salamanders and some temnospondyls, this median ridge is absent, resulting in an unpaired fossa.

N15. Sphenethmoid forms interorbital septum: (0) no (Figure 3.13A); (1) yes (Figure 3.12A). In some seymouriamorphs, diadectamorphs, and amniotes, the olfactory tracts within the sphenethmoid region are vaulted above the cultriform process of the parasphenoid by a deep median keel, termed the interorbital septum.

N16. Anterior extent of cultriform process of parasphenoid: (0) cultriform process extends anteriorly to level of posterior margin of choana; (1) cultriform process short, barely reaching the level of the posterior margin of the orbit. In seymouriamorphs, keraterpetid nectrideans, and diadectamorphs, and some amniotes, the cultriform process of the parasphenoid is greatly shortened, appearing as a short, broad triangle. In these cases, it appears that the shortening of the cultriform process reflects a more general process of withdrawing the braincase posteriorly rather than a simple replacement of the parasphenoid anteriorly by other dermal elements.

Figure 3.12. Braincase of Limnoscelis palustris, after Fracasso, 1987, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view; B, neurocranium, ventral view, dermal elements of the right palate removed; C, neurocranium, occipital view.

N17. Sutural contact between cultriform process of parasphenoid and vomer: (0) no; (1) yes, with posterior processes of vomer along cultriform process and anterior sphenoid region (Figure

3.10A). Modification of character 107 of Anderson (2001, 2007). In most early tetrapods, contact between the vomers and cultriform process is loose and incidental, if it occurs at all, and the vomers are only broadly sutured to the lateral palatal elements. In some temnospondyls and in diplocaulid nectrideans, posterior processes of the vomers extend along the cultriform process of the parasphenoid, sometimes with a dorsal lamina bracing laterally against the anterior sphenethmoid region of the braincase. These posterior processes are broadly sutured (or sometimes fused) to the cultriform process.

N18. Lateral wall of the nasal capsule underplated by lateral processes of the vomer and palatine:

(0) no; (1) yes (Figure 3.10A). In most early tetrapods, the lateral wall of the nasal capsule is thinly underplated by the maxilla and premaxilla, and sometimes reinforced by the septomaxilla.

In diplocaulid nectrideans and in some stereospondyl temnospondyls, the lateral processes of the vomer and palatine reinforce this region substantially, excluding the maxilla and premaxilla from the choanal margin.

N19. Cultriform process of parasphenoid vaulted high above palatal surface: (0) no (Figure 3.8);

(1) yes (Figure 3.16).

N20. Posterior extent of parasphenoid beneath braincase: (0) floors sphenoid region only (Figure

3.4B); (1) floors sphenoid and otoccipital regions. Within some stem-tetrapods, the parasphenoid is relatively anteriorly restricted, extending posteriorly only as far as the basipterygoid processes, leaving the floor of the occiput and otic capsules ventrally exposed. This condition is seen also in early sarcopterygians, including early stem-tetrapods, where the anterior restriction of the parasphenoid permits ventral exposure of the intracranial joint (Ahlberg, 1991), but is retained in some limbed stem-tetrapods (e.g. Acanthostega gunnari), even after closure of the intracranial

joint (Clack, 1988). The derived state, where an expanded basal plate of the parasphenoid floors the majority of the otoccipital region, is seen in most Paleozoic tetrapods, however.

N21. Basal tubera: (0) present, with significant endochondral contribution (Figure 3.11); (1) present, with contribution of parasphenoid only (Figure 3.9); (2) absent. A number of early tetrapods have large ventral expansions along the ventral surface of the otoccipital region, which presumably serve as the attachment site for basicranial musculature. Where present, these structures typically have a parasphenoid contribution anteriorly. In some early tetrapods, this anterior contribution of the parasphenoid floors a ventral swelling of the basisphenoid. In other early tetrapods, the basal tubera are derivatives of the parasphenoid only, and roof paired fossae in the ventral surface of the neurocranium (Maddin et al., 2010). A number of early tetrapod taxa, including various temnospondyls (Englehorn et al., 2008), microsaurs (Carroll & Gaskill, 1978), nectrideans, and amniotes (Heaton, 1979) have lost these structures entirely.

N22. Path of common internal carotid artery: (0) enters basisphenoid directly posterior to basal tubera; (1) follows vidian sulcus along posterior surface of basal plate of parasphenoid, enters parasphenoid via vidian canal in basal plate of parasphenoid, divides into cerebral and palatal branches after entering parasphenoid (Figure 3.10A); (2) follows vidian sulcus along posterior surface of basal plate of parasphenoid or lateral wall of braincase, divides into cerebral and palatal branches prior to entering the skull (Figure 3.14B). This character is similar to character 62 of

Yates and Warren (2000), which describes several derived conditions of the path of the internal carotid and its branches within temnopondyls. The states defined by Yates and Warren (2000) primarily focus on the paths of the cerebral and palatal branches of the internal carotid artery after dividing within or dorsal to the parasphenoid, and thus do not encompass conditions seen outside

of Temnospondyli. State 1 of the current implementation corresponds roughly to States 0 and 1 of

Yates & Warren (2000).

Figure 3.13. Braincase of Huskerpeton englehorni, modified from Huttenlocker et al., 2013, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view, based on CT scans of holotype; B, neurocranium, ventral view, dermal elements of the right palate removed.

Figure 3.14. Braincase of Brachydectes newberryi, this study, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view; B, neurocranium, ventral view, right stapes and dermal elements of the right palate removed; C, occipital view, left stapes removed.

N23. Buccohypophyseal foramen in parasphenoid: (0) open; (1) absent. A persistent buccohypophyseal canal that pierces the parasphenoid is plesiomorphic for sarcopterygians

(Friedman, 2007). A number of digited stem-tetrapods retain a foramen through the parasphenoid

(Clack, 1988; 1998). In most early tetrapods, however, this foramen is completely closed.

N24. Morphology of pila antotica: (0) thin, broad sheet (Figure 3.13A); (1) robust dorsoventral pillar bracing the skull roof against the palate (Figure 3.14A). State 1 is seen in Carrolla craddocki (Maddin et al., 2011), Quasicaecilia texana (pers. obs.), and Brachydectes newberryi

(this study, Ch. 2).

N25. Basicranial fissure: (0) present (Figure 3.4A); (1) absent (Figure 3.7A). A fissure between the basisphenoid and otoccipital region is plesiomorphic for osteichthyans (Ahlberg, 1991). In sarcopterygians, this fissure is expanded into a flexible joint between the sphenoid and otoccipital regions of the skull (Ahlberg, 1991; Dutel et al., 2013), but this joint is quickly reduced into an immobile fissure in early tetrapods and some elpistostegalids (Downs et al.,

2008). In lissamphibians, amniotes, and various early tetrapods, this fissure closes at an embryonic stage, much like the otoccipital fissure, but some early tetrapods retain the fissure into adulthood.

N26. Location of the vidian sulcus: (0) along ventral surface of braincase (Figure 3.14B); (1) along lateral surface of braincase (Figure 3.13A, 3.15B). The internal carotid, prior to branching or entering the ventral neurocranium, typically follows a groove along either the ventral or lateral surface of the parabasisphenoid complex.

Figure 3.15. Braincase of Captorhinus laticeps, after Heaton, 1979, demonstrating characters and character states identified in this study. A, neurocranium, left lateral view; B, neurocranium, ventral view, right stapes and dermal elements of the right palate removed; C, occipital view, left stapes removed.

N27. Basipterygoid joint: (0) epipterygoid comprises entire conus recessus; (1) substantial contribution to conus recessus by pterygoid; (2) conus recessus comprised entirely of pterygoid without epipterygoid participation; (3) pterygoid and parasphenoid broadly sutured without development of a conus recessus (Figure 3.10A). This character represents an expansion of character 107 of Anderson (2001, 2007) to include the variety of character states observed in early tetrapods. The articulation between the palate and the parabasisphenoid complex varyingly involves contributions from the epipterygoid, pterygoid, or a combination of the two. In a highly derived condition, seemingly restricted to diplocaulid nectrideans and stereospondyl temnospondyls, this articulation is heavily sutured, eliminating the features of the synovial joint used to discern between states 0-2. Rather than treat these as separate characters, I have elected to treat the sutured condition as a fourth state in order to avoid overweighting issues.

N28. Hypophyseal fossa: (0) single unpaired sulcus; (1) paired sulci divided medially by ridge originating on dorsum sellae.

N29. Bone flanking the dorsum sellae: (0) concurrent with fully ossified lateral skull roof (Figure

3.5); (1) subparallel with sagittal plane (‘pleurosphenoid’); (1) strongly oblique to or perpendicular to sagittal plane possibly incorporating epipterygoid (‘laterosphenoid’) (Figure 3.10A); (2) restricted to dorsum sellae only (Figure 3.16).

N30. Parasphenoid basal plate: (0) roughly quadrangular, basipterygoid articulations narrowly spaced; (1) rectangular laterally, anteroposteriorly narrow, basipterygoid articulations distant.

Unchanged from character 105 of Anderson (2007).

Figure 3.16. Braincase of Ophiacodon uniformis, after Romer & Price, 1940, demonstrating characters and character states identified in this study. Left lateral view.

N31. Sphenethmoid: (0) ossified; (1) unossified. Unchanged from character 114 of Anderson

(2007).

N32. Ossification within the synotic tectum: (0) synotic tectum massively co-ossified with otic capsules (Figure 3.4C); (1) supraoccipital paired at some point in ontogeny (Figure 3.12C); (2) supraoccipital unpaired throughout ontogeny; (3) no supraoccipital bone; synotic tectum invaded by dorsal processes of exoccipitals (Figure 3.9). The composition of the dorsal portion of the occiput of early tetrapods has been the subject of some debate in recent years. The plesiomorphic condition preserves a close relationship between ossification of the synotic tectum and the otic

capsules, with little integration between the otic unit and the occipital arch, such as the condition seen in Acanthostega gunnari (Clack, 1988). Most tetrapods, however, more closely integrate the synotic tectum with the occipital arch. A paired supraoccipital (state 1) is seen in a number of early tetrapods, including a variety of “anthracosaurs” and “embolomeres” and, apparently, juvenile diadectamorphs (Berman, 2000). The supraoccipital of mammals initiates from paired ossification centres as well (de Beer, 1937). The supraoccipital of reptiles, and apparently microsaurs, forms from a single median ossification center. A derived condition, observed in some temnospondyls

(Maddin et al., 2010) and in modern lissamphibians, involves postnatal growth of the exoccipitals into the synotic tectum, where they form either a median suture or otherwise fuse completely.

N33. Median ascending process of the supraoccipital: (0) absent; (1) present (Figure 3.15A). In some reptiles (Heaton, 1979; Reisz, 1981) and microsaurs a median process extends antero- dorsally along the ventral median suture between the postparietals, sometimes as far anterior as the parietals.

N34. Lateral ascending process of the supraoccipital: (0) absent; (1) present (Figure 3.15A). In some reptiles (Heaton, 1979; Reisz, 1981), two winglike processes extend anterolaterally from the supraoccipital. The ventral surface of these processes typically preserves a lamina that contributes to the medial wall of the otic capsule. Lateral ascending processes are also present in some microsaurs (Huttenlocker et al., 2013), but the full distribution of this character within Microsauria is uncertain.

N35. Margin of fenestra vestibularis: (0) parasphenoid excluded by neurocranial elements, basisphenoid and basioccipital (Figure 3.4A); (1) parasphenoid contributes to anterioventral margin of fenestra vestibularis (Figure 3.8); (2) parasphenoid floors entire fenestra vestibularis

(Figure 3.14A); (3) ossification of otic capsules completely surrounds fenestra vestibularis (Figure

3.11). This character is discussed in some detail by Clack (1998) with respect to the morphology of Acanthostega gunnari. State 1 is seen in a number of digited stem tetrapods and some early crown tetrapods along both the amniote and lissamphibian stem. In amniotes, microsaurs, and derived temnospondyls, the occipital arch is excluded entirely from the ventral margin of the fenestra vestibulae.

N36. Crista intervestibularis: (0) crista intervestibularis absent; (1) crista intervestibularis present.

A vertically oriented crista is present on the medial surface of the opisthotic in some early tetrapods, specifically some reptiles (Heaton, 1979) and some microsaurs. This crista forms a complete wall between the lagena and the ampulla of the posterior semicircular canal in some derived diapsids, but is generally less well-developed in early tetrapods, and where present it seems to be expressed as a low ridge. In Brachydectes and some other taxa, this ridge comprises the primary body of the opisthotic, as the flat exterior surface of the otic capsule remains unossified.

N37. Morphology of the crista parotica: (0) crista parotica meets exoccipitals only, forming lateral wall of posttemporal fossa but not bracing against dermal skull (Figure 3.4C), (1) crista parotica drawn out dorsolaterally into paroccipital process that contacts the tabular, (2) crista parotica drawn out laterally into paroccipital process that contacts the cheek and/or suspensorium

(Figure 3.15C). Robust struts bracing the otoccipital region of the braincase against the skull roof or cheek are present in a variety of early tetrapods. These struts have all been termed

“paroccipital processes” despite substantially different construction and uncertain homology.

This formulation of the character attempts to avoid some of the issues associated with less specific statements of this character seen previously. The plesiomorphic condition is equivalent to that seen in Acanthostega gunnari (Clack, 1998) as well as digitless stem tetrapods such as

Eusthenopteron, in which the otoccipital region is suspended beneath the skull roof by a series of

dorsal processes of the otic capsule and occipital arch that contact the ventral surface of the parietals and postparietals. A dorsolateral process of the crista parotica that braces against a ventral flange of the tabular is seen in a variety of early tetrapods, including temnospondyls, nectrideans, and colosteids, and serves a secondary function as either the posteromedial wall of the spiracular recess or as the posteromedial wall of the stapedial canal, depending on the taxon.

In some amniotes and some microsaurs, the crista parotica projects laterally towards the squamosal and/or quadrate, where it braces against the cheek.

N38. Dorsal process of stapes: (0) absent; (1) present, articulating with or approaching crista parotica (Figure 3.15C). A stout dorsal process of the columella is present in some amniotes

(Heaton, 1979) as well as Brachydectes newberryi (this study, Ch. 2). The plesiomorphic condition appears to be present in most early tetrapods, but the distribution of this character in microsaurs is uncertain, as the stapes of these taxa are generally poorly preserved.

N39. Facets on dorsal surface of supraoccipital: (0) absent; (1) present. The supraoccipital of some microsaurs and some amniotes preserves paired shallow facets on either side of a sagittal ridge that accept the postparietals and, in some cases, the parietals. In Brachydectes, the postparietals are withdrawn laterally into these fossae and expose the median ridge of the supraoccipital dorsally.

N40. Otoccipital fissure: (0) present (Figure 3.4A); (1) absent (Figure 3.8). The presence of a significant fissure between the otic capsules (including the synotic tectum) and occipital arch is plesiomorphic for sarcopterygians (Friedman, 2007; Ahlberg, 1991) and very probably for teleostomes (Maisey, 2002; Brazeau, 2009). In early tetrapods, this fissure is preserved between supraoccipital ossifications within the synotic tectum and exoccipital ossifications of the occipital arch (Clack, 1988). The embryonic closure of the otoccipital fissure is observable in both modern

lissamphibians and modern amniotes (de Beer, 1937), and is evidenced by a closer relationship between the supraoccipital and exoccipital, or with invasion of the synotic tectum by dorsal processes of the exoccipitals (Maddin et al., 2010).

N41. Crista parotica: (0) Descends posteriorly; (1) horizontal along the extent of its length.

N42. Position of quadrate with respect to otic capsules: (0) quadrates ventral and lateral to otic capsules; (1) quadrates mostly lateral to and greater than or equal to twice the width of the otic capsules; (2) quadrates mostly ventral to otic capsules; (3) quadrates approaching or abutting lateral wall of otic capsules. This character is a replacement for character 82 of Anderson (2001,

2007). Character 82 of Anderson (2001, 2007) attempts to describe the general shape of the skull from the occipital surface. Anderson (2001, 2007) recognizes three states: low and wide, high and wide, and high and narrow. These very general descriptions specify neither the structures that contribute to these shapes nor variation within each of these general shape classes. This restatement of the character attempts to alleviate this problem. Much of the variation in skull shape in occipital view is a function of the relative position of the quadrates with respect to the braincase. Low and wide occiputs sensu Anderson (2001, 2007) are seen in taxa where the quadrates are widely spaced, far lateral to the braincase, with little to no ventral displacement. High and narrow occiputs typically are seen in taxa where the quadrates are substantially ventrally displaced, with little to no lateral spacing. High and wide occiputs are accomplished in one of two ways; either the quadrates are both widely spaced and significantly ventrally displaced (as in seymouriids, diadectids, and some early amniotes), or the otoccipital region dominates the occipital surface of the skull, with the suspensorium closely integrated with the otoccipital region (as in microsaurs and aïstopods).

States 0, 1, and 2 of this coding scheme include information about length of the adductor mandibulae and palatal surface area, two variables associated with feeding mode in modern

tetrapods (Metzger & Herrel, 2005; Heiss et al., 2013). State 3 seen in a number of modern fossorial and miniaturized groups (Carroll, 1991). This character, as with other general skull shape characters, is likely highly constrained by function and ecology, and possibly even ontogeny.

Although it is tempting to atomize this character into a number of separate characters associated with the width of the quadrates, ventral displacement of the suspensorium, and verticality of the suspensorium, this variation stereotypically varies with feeding mode, ontogenetic stage, and adult body size in modern taxa in ways that suggest more finely parsing this character may overweight convergences. Ultimately this character was included for sake of consistency with prior analyses, but future workers should give serious consideration to whether this character brings novel information to the phylogenetic analysis.

N43. Size of otic capsules: (0) otic capsules comprise less than 2/3 total width of otoccipital region;

(1) otic capsules comprise greater than 2/3 total width of otoccipital region. This character essentialy compares the relative width of the pons and inner ear. In most early tetrapods, the inner ear is a relatively small structure. In a few taxa, however, the inner ear is greatly enlarged, and makes up the vast majority of the posterior braincase. This may be a function of auditory acuity, miniaturization (Carroll, 1991) or both. The width of the otic capsule is measured from the widest point of the horizontal semicircular canal to the apex of the supraoccipital lamina of the median otic wall (when present) or the medialmost impression of the saccular region on the ventral surface of the skull roof. Width of the braincase is measured from the widest point of the horizontal semicircular canal to the midline of the skull. Because this character is intended to compare the width of the inner ear and pons, structures of the crista parotica (e.g. various “paroccipital processes”, character N37) are systematically excluded from this diagnosis. The threshold value

between state 0 and state 1 is arbitrary and could stand to be honed via a study of sensory organ size in early tetrapods.

N44. Otic trough: (0) absent; (1) present (Figure 3.12B). Modified from character 58 of Reisz and

Laurin (1995) and character 6 of Berman (2000). In diadectamorphs and synapsids, a trough extends posteriorly from the fenestra vestibularis, termed the otic trough. The function of this structure is not clear (Fracasso, 1979; Berman, 2000) but it appears to be distributed more or less universally among diadectamorphs and synapsids, but is not found in reptiles or stem-amniotes.

This structure is apparently unrelated to the basal tubera (N21).

N45. Articulation between the epipterygoid and prootic: (0) none; (1) elongate facet on anterior surface of prootic for articulation of the epipterygoid.

N46. Opisthotic obscures occipital in lateral view: (0) no; (1) yes (Figure 3.12B).

N47. Fenestra vestibularis at end of broad, winglike lateral extension of the otic capsule: (0) no

(Figure 3.13A); (1) yes (Figure 3.12B).

N48. Cristae in occipital region: (0) comprised primarily of ascending flanges from braincase

(Figure 3.6A); (1) comprised primarily of descending flanges from the skull roof (Figure 3.16).

In most early tetrapods, the otoccipital region is suspended beneath the skull roof by cristae, producing deep posttemporal fossae for the insertion of the epaxial musculature and creating the posteromedial wall of the spiracular fossa or stapedial canal. These cristae are comprised primarily of contributions from the lateral wall of the braincase, including the crista parotica and a dorsolateral crista, but in some taxa (e.g. Seymouria baylorensis, Limnoscelis palustris, and

Ophiacodon) these cristae are comprised primarily of descending flanges from the squamosal, tabular, and postparietal.

N49. Opisthotic excluded from the occipital surface by tabular process of the exoccipital: (0) no

(Figure 3.6B, Figure 3.7B, Figure 3.9); (1) yes (Figure 3.10B). In some temnospondyls and in diplocaulid nectrideans, a dorsolateral process of the exoccipital is present and sutures broadly to a medioventral process of the tabular, excluding the opisthotic from the occipital surface and precluding any opisthotic contribution to the paroccipital process.

N50. Insertion of the epaxial musculature on occiput: (0) deep within post-temporal fossae; (1) in broad, shallow fossae along occipital surface of postparietals (Figure 3.14B). In sarcopterygians more broadly, and in many early tetrapods, the epaxial muscles insert within a pair of narrow, deep pits between the skull roof and braincase. These deep pits are laterally flanked by the crista parotica, which connects the braincase to the temporal region. Some early tetrapods, primarily microsaurs, deviate from this condition, with the epaxial muscles instead growing out over the posterior skull roof, allowing for a closer connection between the otoccipital region and the skull roof. In these cases, broad, shallow fossae are present on broad occipital lappets of the postparietals and posterior temporal bones, and the post-temporal fossae are absent.

N51. Foramen for internal jugular vein: (0) between supraoccipital and exoccipital (Figure

3.6A); (1) between opisthotic and exoccipital (Figure 3.13A); (2) through exoccipital (Figure

3.10B); (3) through posterior notch in fenestra vestibularis (Figure 3.5). A large foramen in the otoccipital region serves the internal jugular vein and vagus nerve. In some forms, this foramen is relatively dorsal in position and exits the braincase between the synotic tectum and exoccipitals, generally within the otoccipital fissure when the latter structure is present. In many derived forms, this foramen exits in a more lateral location, between the exoccipitals and the opisthotic or opisthotic region of the otic capsule when the otic is coossified. This character replaces, in part, character 86 of Anderson (2007). Anderson (2001, 2007) recognized a possible

state in which the internal jugular vein foramen is completely enclosed by the exoccipital, a state exemplified by Rhynchonkos stovalli according to the description of Carroll and Gaskill (1978).

Recent restudy of this material suggests an alternate interpretation of this region (M.

Szostakiwskyj, pers. comm., 2013; Szostakiwskyj et al., in prep.), but this character does appear in some nectrideans, temnospondyls, and lissamphibians.

N52. Hypoglossal nerve foramina: (0) multiple (Figure 3.8); (1) single; (2) absent. Nerve XII exits the occipital arch through the exoccipital. In some early tetrapods, the nerve divides into dorsal and ventral branches within the metotic fossa, exiting via two separate foramina, but in many early tetrapods, the nerve does not branch and thus exits the occiput through a single canal.

Lissamphibians have lost this nerve entirely (Duellman & Trueb, 1994), and thus do not preserve a foramen to carry it.

N53. Occipital articulation: (0) round (Figure 3.6B); (1) U-shaped; (2) paired (Figure 3.9). This character is modified from character A85 of Anderson (2001, 2007). The occipital condyle of most early tetrapods is a single round structure, but some variations do exist. In some early tetrapods, the occipital condyle wraps partway around the foramen magnum, creating a U-shape, with a ventral condyle on the basioccipital and paired cotylar surfaces on the exoccipitals, lateral to the foramen magnum. In diplocaulid nectrideans, several lineages of temnospondyl, and modern lissamphibians, the basioccipital is reduced or entirely lost, and the exoccipital cotyles are the only remaining surface of articulation between the occipital arch and the atlas. These cotyles are generally ventral and lateral to the foramen magnum and do not meet at the midline, resulting in an occipitoatlantal joint with significant dorsoventral mobility but almost no lateral mobility.

N54. Ventral process of exoccipital reaches basipterygoid joint along palatal surface: (0) absent;

(1) present (Figure 3.10A). This is essentially a restatement of character 117 of Anderson (2001,

2007) in order to eliminate some ambiguity present in the original character diagnosis. In diplocaulid nectrideans and some stereospondyl temnospondyls, a broad process of the ventral portion of the exoccipital flanks the posterior portion of the basal plate of the parasphenoid, participating in the basipterygoid joint and excluding the parasphenoid from the ventral margin of the foramen ovale. In both diplocaulids and stereospondyls, the basipterygoid joint is modified into a broad, immobile sutured contact, but whether this correlation is due to functional constraint or phylogenetic signal is unclear. Exoccipital participation in a mobile basipterygoid joint is not logically inconceivable, but is simply not observed in any known early vertebrate.

This character may represent ventral invasion of the otic capsule by the exoccipital rather than a distinct process of the exoccipital.

N55. Atlantoccipital joint concavity: (0) occipital condyle concave (Figure 3.7B); (1) occipital condyle convex (Figure 3.15A). Unchanged from character 84 of Anderson (2007).

N56. Stapes: (0) perforated stem (Figure 3.7B); (1) imperforate stem. Character 108 of Anderson

(2007), with removal of state 2.

N57. Stapes orientation: (0) lateral towards quadrate (Figure 3.7B); (1) dorsal towards squamosal embayment. Minor modification of character 109 of Anderson (2007)

N58. Footplate of stapes: (0) oval; (1) round; (2) palmate. Unchanged from character 110 of

Anderson (2007).

N59. Dorsal sinus between ossified synotic tectum (supraoccipital) and parietals: (0) absent; (1) present. Unchanged from character 222 of Huttenlocker et al. (2013).

3.4 Treatment of Existing Characters

I incorporated these 59 braincase characters into a more comprehensive sampling of characters based on the matrix of Anderson (2001) as modified by Anderson (2007), Anderson et al., (2008) and Huttenlocker et al. (2013). Several modifications were made to this matrix. The following diagnoses refer to the character and states used in Huttenlocker et al (2013) as

HPSA2013.

3.4.1 Modified Characters

HPSA2013 Character 134, new diagnosis. Dermal armor associated with neural spines:

(0) absent, (1) present. Character 134 of the original dataset refers to a derived state observed in some nectrideans, where the neural spine is fused to a median ossification of dermal origin.

Such osteoderms are known in other early tetrapods, including chroniosuchians, the stereospondyls Sclerothorax hypselonotus (Schoch, 2007), Peltobatrachus pustulatus (Panchen,

1959), and the Plagiosauroidea, dissorophid temnospondyls, and some extant salamandrid caudates and leptodactylid anurans. The morphology and histology of nectridean armor has not been sufficiently characterised to permit comparison of individual osteoderm characters, so this character has not been further atomized, but it should be revisited at some point in the future.

3.4.2 Characters Modified in Topological Nonindependence Experiments

HPSA2013 Character 4, Character 7, Character 51: combined. New diagnosis:

Intertemporal: (0) present, (1) absent, replaced by lateral expansion of parietal, (2) absent,

replaced by anterior expansion of supratemporal/tabular. Character 51 recognizes the presence or absence of a sutural contact between the parietal and squamosal. The morphology described by this character is topologically nonindependent from the morphology described by character 7, which identifies the presence or absence of a contact between the tabular and postorbital. A number of characters in the matrix of Anderson (2001, 2007) consist of descriptions of the sutural pattern of the temporal region atomized into a series of presence/absence statements concerning contacts between dermal skull elements. In some cases, two or more of these statements may inadvertently describe the same sutural pattern in some or all OTUs. This is the case for characters 7 and 51 (Figure 3.1). Contact between the parietal and squamosal (51:1) precludes contact between the tabular and postorbital (7:1), and vice versa. In actuality, characters 7 and 51 are meant to differentiate conditions in which the bones of the anterior temporal row (primarily the intertemporal, character 4) have been lost (Character 4, State 1) and replaced by expansions of either the parietal or the posterior temporal bones, specifically the tabular (J. Anderson, pers. comm.). The modified character treats these three characters as separate states of the same character and avoids this issue of topological nonindependence.

HPSA2013 Characters 99, 100, 101: combined. New diagnosis: anterior extent of palatine ramus of pterygoid: (0) well-developed, meeting in midline, (1) contacts vomer but does not meet at midline, (2) does not reach vomer, contact with palatine and ectopterygoid only, (3) contact with posteriormost extent of marginal palate only. Characters 99, 100, and 101 are all topologically nonindependent and pertain to the extent of the palatine ramus of the pterygoid.

3.5 Methods

3.5.1 Character scoring and matrix modification

Modifications to the matrix of Anderson (2001, 2007) as modified by Huttenlocker et al.

(2013) have been discussed above but are summarized in their complete form here for reference.

Fifty-nine neurocranial characters have been added. The diagnoses for these characters are discussed below. Partial or complete conflict between these characters and characters diagnosed by Anderson (2001), Anderson (2007), and Huttenlocker et al. (2013) necessitates deletion of several characters from the source matrix.

The matrix of Anderson (2001, 2007) is taxonomically insufficient to investigate some questions of lepospondyl relationships. Taxonomic sampling is dense for the Lepospondyli and for dissorophoid temnospondyls, but is extremely sparse elsewhere. Sparse sampling outside of these two taxa makes it difficult to assess the monophyly of lepospondyls, the plesiomorphic condition of major lepospondyl groups and of lepospondyls more generally, and character evolution more broadly along the amniote stem. Evolution of characters along the amniote stem is particularly difficult to address with this dataset, as no indisputable amniote is present in the matrix. Instead, the seymouriamorph Seymouria baylorensis and the diadectomorph Limnoscelis paludis serve as stand-ins for Amniota. Neither diadectomorphs nor seymouriamorphs are considered to be amniotes in contemporary analyses (Ruta et a., 2003), and seymouriamorphs are considered to fall stem-ward of both diadectamorphs and lepospondyls with respect to amniotes in some analyses (Laurin & Reisz, 1995, Ruta et al., 2003). Exclusion of true amniotes from the analysis makes it difficult to assess this result, to assess polarity of characters along the amniote stem more generally, and to determine the lepospondyl root.

Seventeen taxa have been added to the source matrix to more completely sample the diversity of skull roof, braincase, and postcranial morphology among Paleozoic tetrapods, and to more fully contextualize the derived morphology exhibited by Brachydectes newberryi. Added

taxa are: two baphetids (Kyrinion martilli and Loxomma acutirhinus) and an embolomere

(Archeria crassidisca) in order to better contextualize evolution along the tetrapod stem. Two aïstopods (Lethiscus stocki and Coloraderpeton brilli) were added to contextualize the incomplete data available for the aïstopods Phlegethontia and Oestocephalus and to test the robustness of the aïstopod-lysorophian relationship recovered previously by Anderson (2001,

2007), Huttenlocker et al. (2013), and Marjanovic & Laurin (2013). The short-horned diplocaulid nectridean Ductilodon pruitti was included to contextualize the highly derived morphology of the diplocaulid nectrideans Diplocaulus magnicornus and Diploceraspis burkei. The brachystelechid microsaur Quasicaecilia texana was added in order to more completely sample the range of morphologies of this family. Two eureptiles (the captorhinid Captorhinus laticeps and the araeoscelid Petrolacosaurus kansensis) and a synapsid (Ophiacodon uniformis) were added to differentiate between the amniote stem and amniote crown, and to investigate the relative placements of seymouriamorphs, diadectomorphs, and lepospondyls along the amniote stem.

One seymouriamorph (Kotlassia prima) was added in order to more completely sample the diversity of seymouriamorph morphology. A broad sampling of temnospondyls was added in order to address deficiencies in the sampling of the lissamphibian stem. These are an edopoid

(Edops craigi), two dvinosaurs (Trimerorhachis insignis and Acroplous vorax), and three stereospondyls (Lydekkerina huxleyi, Gerrothorax pulcherrimus, and Batrachosuchus watsoni).

These taxa were primarily coded from published descriptions, although I have made personal observations of fossils or CT scans of some taxa. Source of character codings is reported in

Table 3.1.

All added braincase characters were coded from the literature, and from personal observation of specimens and/or CT scans. Source data are reported in Table 3.2.

Four alternate datasets were produced. The first dataset is unmodified from that reported by Huttenlocker et al. (2013) with the exception of the addition of the braincase characters described above. The second dataset has been modified to account for logical and topological nonindependence of characters in the original dataset. This includes merging of several topologically or logically nonindependent characters in several cases and amended diagnoses for merged characters. The third dataset has been modified to account for an alternate interpretation of the homology of the single large temporal bone of ‘microsaurs.’ No character definitions have been altered, but the coding of seven characters has been modified for a number of taxa, summarized in Table 4. The fourth dataset incorporates the modified character diagnoses from the nonindependence dataset and the alternate codings from the supratemporal dataset.

Three character bins were established based on anatomical region: neurocranial, dermatocranial, and postcranial. Characters were assigned to bins using the matrix editing program MESQUITE v.2.75 (Maddison & Maddison, 2011).

3.5.2 Phylogenetic Inference Using Complete Character Matrix

All four complete matrix variations were analyzed in order to assess the phylogenetic position of Brachydectes and the larger phylogenetic context of microsaurs and other lepospondyls.

Maximum parsimony analyses were conducted in the phylogenetic inference software

PAUP*4.0b (Swofford, 2002). Trees were rooted using the Devonian stem-tetrapod

Acanthostega gunnari as an outgroup. Due to the large number of taxa, the full heuristic method

100

was used to search for most parsimonious trees (MPTs) in each analysis. The set of MPTs for each analysis was then summarized as strict and majority rule consensus trees using PAUP*4.0b.

3.5.3 Partition Experiments

Phylogenetic analyses were conducted on individual character partitions to investigate differences in phylogenetic signal between anatomical regions and the potential for mosaic evolution within early tetrapod evolution. Three anatomical partitions were investigated for differences in phylogenetic signal. The first partition consists solely of the neurocranial character set proposed in this chapter. The second partition consists of all dermatocranial characters within the matrix of Huttenlocker et al. (2013). The third consists of all postcranial characters within the matrix of Huttenlocker et al. (2013). Partitions were analyzed for each matrix treatment (unmodified, topology, supratemporal, and topology + supratemporal). Taxa with minimal character coverage for a partition have been excluded based on an arbitrary 50% completeness criterion. Exclusion of taxa from analysis is necessary as braincase and postcranium are poorly represented or poorly-described for many taxa, and may be completely unknown for some OTUs. Phylogenetic analyses were conducted in PAUP*4.0b using the full heuristic method to assess trees according to the maximum parsimony objective criterion.

3.6 Results

3.6.1 Total Dataset

101

All four versions of the total dataset recover topologies that differ from previously reported results in critical ways. First and foremost, Brachydectes newberryi forms a clade with the brachystelechids Carrolla craddocki, Batropetes fritschi, and Quasicaecilia texana in all versions of the total dataset, in accordance with previous results of Vallin & Laurin (2004) and

Marjanovic & Laurin (2013), suggesting a close relationship between lysorophians and brachystelechid ‘microsaurs’ not previously found in analyses built around the Anderson (2001) lepospondyl matrix. In addition, the monophyly of lepospondyls is not supported in any of the matrix modifications, but the degree to which lepospondyls are found to be polyphyletic differs depending on treatment. All treatments place the diplocaulid nectrideans Diplocaulus,

Diploceraspis, and Ductilodon within the Temnospondyli in a clade including the brachyopid stereospondyl Batrachosuchus watsoni, the plagiosauroid stereospondyl Gerrothorax pulcherriumus, the lydekkerinid stereospondyl Lydekkerina huxleyi, and the eobrachyopid dvinosaur Acroplous vorax, distant from the keraterpetontids Keraterpeton, Diceratosaurus, and

Batrachiderpeton, and all other nectrideans.

Parsimony analysis of the unmodified dataset (Figure 3.17) recovers a monophyletic

Lepospondyli (diplocaulids excepted) as the sister group of crown Amniota, with the diadectamorph Limnoscelis paludis and the seymouriamorphs Kotlassia prima and Seymouria baylorensis forming successive outgroups. Within Lepospondyli, the microbrachomorph- recumbirostran dichotomy is recovered, with the exception of Utaherpeton, which is recovered as the sister taxon of microbrachomorphs+tuditanomorphs. Within Recumbirostra, two main clades exist: a clade consisting of brachystelechids, Brachydectes, Rhynchonkos, and pantylids, and a clade consisting of ostodolepids and gymnarthrids. Hapsidopareiontids and Tuditanus are recovered as stem-recumbirostrans. Aïstopods are recovered within urocordylids.

102

Parsimony analysis of the dataset corrected for topological nonindependence (Figure

3.18) recovers a nonmonophyletic Lepospondyli. Recumbirostrans are recovered as the sister group to Amniota, with tuditanids+hapsidopareiontids, microbrachomorphs, and a monophyletic

Seymouriamorpha forming successive outgroups. The diadectamorph Limnoscelis palustris is recovered as a crown amniote within the synapsid stem. Recumbirostra is divided into two major clades, one consisting of pantylids, ostodolepids, and gymnarthrids, and a second consisting of

Rhynchonkos, Brachydectes, and brachystelechids. Tambaroter, Proxilodon, and Huskerpeton are found to be basal recombirostrans. Aïstopods form a clade with Scincosaurus apart from the

Urocordylidae.

Parsimony analysis of the original dataset recoded to interpret the large bone of the

‘microsaur’ temporal series as a supratemporal rather than a tabular (Figure 3.19) recovers a monophyletic Recumbirostra as the sister taxon of Reptilia within the Amniota. Within

Recumbirostra, two major clades are found: one consisting of pantylids, gymnarthrids, and ostodolepids, and one consisting of brachystelechids, Brachydectes, Rhynchonkos, and a clade including Tambaroter, Huskerpeton, and Proxilodon. Hapsidopareiontids and tuditanids are recovered as stem-recumbirostrans. The diadectamorph Limnoscelis palustris, the seymouriamorphs Seymouria baylorensis and Kotlassia prima, and the Microbrachomorpha form successive outgroups to Amniota. Aïstopods fall within Microbrachomorpha as the sister taxon to Utaherpeton, with no specific relationship to nectrideans.

Parsimony analysis of the dataset corrected for topological nonindependence and to interpret the large bone of the ‘microsaur’ temporal series as a supratemporal (Figure 3.20) recovers the majority of lepospondyls as the monophyletic sister taxon of reptiles within crown

Amniota. Recumbirostra and Microbrachomorpha appear as major divisions within

103

Lepospondyli. Within Recumbirostra, Brachystelechidae, Pantylidae, Ostodolepidae, and

Gymnarthridae are all recovered as monophyletic, but no resolution above the family level exists. Within Microbrachomorpha, aïstopods fall out as the sister taxon to Scincosaurus but show no close relationship with other nectrideans. Tuditanids and hapsidopareiontids are recovered along the microbrachomorph stem.

104

Figure 3.17. Cladistic analysis of full unmodified character matrix (265 characters). Strict consensus of 123 trees. Tree length = 1773, CI = 0.2104, RCI = 0.1243.

105

Figure 3.18. Cladistic analysis of full character matrix (261 characters) correcting for topological nonindependence. Strict consensus of 63 trees. Tree length = 1762, CI = 0.2111, RCI

= 0.1243

106

Figure 3.19. Cladistic analysis of full character matrix (265 characters) reinterpreting the microsaur ‘tabular’ as a supratemporal. Strict consensus of 109 trees. Tree length = 1772, CI =

0.2105, RCI = 0.1237

107

Figure 3.20. Cladistic analysis of full character matrix correcting for topological nonindependence and matrix reinterpreting the microsaur ‘tabular’ as a supratemporal (261 characters). Strict consensus of 105 trees. Tree lenth = 1764, CI = 0.2109, RCI = 0.1238.

108

In all of the unpartitioned datasets, Eocaecilia is recovered within the Recumbirostra, a result which supports the Caecilian-Recumbirostran Hypothesis of Carroll and Currie (1975),

Carroll (2007), Anderson (2007, 2008), and Anderson et al. (2008). It is worth noting, however, that in two of the four modified matrices reported here, Amniota is found to be polyphyletic as well.

3.6.2 Character Partition Experiments

Phylogenetic analyses of individual character partitions recover substantially different phylogenies. This may indicate that some character partitions contain greater phylogenetic information, or that morphological evolution of early tetrapods may have exhibited some degree of mosaicism.

The neurocranium submatrix (Figure 3.21) recovers a vastly polyphyletic Lepospondyli.

Recumbirostra is found to be the sister taxon of Reptilia. Brachydectes newberryi is recovered within the Brachystelechidae as the sister taxon to Carrolla craddocki. Nannaroter mckinzei is the sister taxon of the Brachystelechidae, and together these form a polytomy with Huskerpeton englehorni, Pantylus cordatus, and the scincosaurid nectridean Scincosaurus crassus.

Rhynchonkos stovalli and the ostodolepids Micraroter erythrogeios and Pelodosotis elongatus form a basal polytomy with the remainder of the Recumbirostra. The diadectamorph Limnoscelis palustris and the seymouriamorphs Seymouria baylorensis and Kotlassia prima are recovered as successive outgroups to pelycosaur-grade synapsids within the amniote crown. The nectridean

Diceratosaurus brevirostris is recovered within this ‘seymouriamorph’ grade as well.

109

Diplocaulids are found within trematosaur stereospondyls as the sister taxon of the brachyopoid

Batrachosuchus watsoni. The aïstopods Coloraderpeton brilli and Lethiscus stocki are found to be stem-tetrapods, stemward of the baphetids Loxomma acutirhinus and Kyrinion martilli.

The postcranium submatrix (Figure 3.22) recovers a polyphyletic Lepospondyli as well.

A monophyletic Microsauria is resolved as the sister taxon of Eureptiles within Amniota. Within

Microsauria two major clades are present; a clade consisting of Tuditanus, Rhynchonkos,

Batropetes, Brachydectes, and Microbrachis, and a clade consisting of pantylids, gymnarthrids, and ostodolepids. The diadectamorph Limnoscelis palustris and the seymouriamorph Seymouria baylorensis form successive outgroups to crown Amniota. The remainder of Lepospondyli

(Aïstopoda+Adelospondyli+Nectridea) are resolved as the sister taxon of Micromelerpetontidae within dissorophoid temnospondyls.

The dermatocranial submatrix was assessed in all four matrix manipulations. Different treatments of the dermatocranial submatrix produced substantially different topologies, possibly reflecting a generally weak signal within the dermatocranial dataset.

The unmodified dermatocranial submatrix (Figure 3.23) does not recover a monophyletic

Lepospondyli, and recovers very little topological resolution in the tree more generally.

Hapsidopareiontids and tuditanids form the sister taxon to Amniota+Diadectamorpha, but the

Recumbirostra falls out separate from this clade, and forms an extensive polytomy with keraterpetontid nectrideans, urocordylid nectrideans, stereospondyls plus diplocaulid nectrideans,

Scincosaurus, Adelogyrinus, Greererpeton, Phlegethontia, Oestocephalus, Seymouriamorpha, and most species level diversity among the Temnospondyli. Within Recumbirostra, pantylids, gymnarthrids, and ostodolepids form a clade, although no support exists for a monophyletic

110

Gymnarthridae, with Tambaroter+Huskerpeton+Proxilodon, Rhynchonkos, and Brachydectes forming successive outgroups.

The tree recovered from analysis of the dermatocranial submatrix corrected for topological nonindependence (Figure 3.24) preserves several features of the uncorrected analysis, namely the sister taxon relationship between hapsidopareiontids+tuditanids and amniotes+diadectamorphs. The majority of lepospondyls form the sister taxon to this clade, with the Recumbirostra nested within nectrideans, and with aïstopods nesting either within recumbirostrans as the sister taxon of Brachydectes or basal to the nectridean+Recumbirostra clade at the base of Lepospondyli (note that in this analysis, aïstopods are found to be polyphyletic). Temnospondyls are monophyletic and are found here to include the Diplocaulidae within a well-resolved Stereospondyli.

The dermatocranial submatrix corrected to interpret the large bone of the ‘microsaur’ temporal region as a supratemporal rather than a tabular (Figure 3.25) recovers ‘microsaurs’ as a paraphyletic assemblage of stem-amniotes, with Tuditanus, hapsidopareiontids,

Recumbirostrans, and Asaphestera+Microbrachis forming successive outgroups to Amniota.

Within Recumbirostra, two major clades are found: one consisting of brachystelechids,

Brachydectes, Rhynchonkos, and pantylids, and a second consisting of ostodolepids, gymnarthrids, Tambaroter, Huskerpeton, and Proxilodon. Outside of this Microsaur+Amniote clade, keraterpetontids, adelospondyls, and urocordylids form a series of successive outgroups.

A clade consisting of seymouriamorphs and embolomeres is the sister taxon to Temnospondyli.

Diplocaulid nectrideans once again are found within a well-resolved Stereospondyli. Aïstopods are not found to be monophyletic; some taxa form a clade with Brachydectes within the

Recumbirostra, whereas others are found at the base of the Amniote stem.

111

Figure 3.21. Cladistic analysis of 59 neurocranial characters. Strict consensus of 158 trees. Tree length = 238, CI = 0.3782, RCI = 0.2644.

112

Figure 3.22. Cladistic analysis of 79 postcranial characters. Strict consensus of 55 trees. Tree length = 397, CI = 0.2720, RCI = 0.1596.

113

Figure 3.23. Cladistic analysis of 127 dermatocranial characters, unmodified from diagnoses in

Huttenlocker et al., 2013. Strict consensus of 1120 trees. Tree length = 919, CI = 0.1904, RCI =

0.1184.

114

Figure 3.24. Cladistic analysis of 123 dermatocranial characters, modified from Huttenlocker et al., 2013, to account for toplogical nonindependence. Strict consensus of 125 trees. Treelength =

905, CI = 0.1923, RCI = 0.1193.

115

Figure 3.25. Cladistic analysis of 128 dermatocranial characters, modified from Huttenlocker et al., 2013, to interpret the microsaur ‘tabular’ as a supratemporal. Strict consensus of 90 trees.

Tree length = 938, CI = 0.1876, RCI = 0.1149.

116

Figure 3.26. Cladistic analysis of 123 dermatocranial characters, modified from Huttenlocker et al., 2013, to account for topological nonindependence and to reinterpret the microsaur ‘tabular’ as a supratemporal. Strict consensus of 142 trees. Tree length = 910, CI = 0.1912, RCI = 0.1177.

117

The dermatocranial submatrix corrected both for topological nonindependence and to interpret the large bone of the ‘microsaur’ temporal region as a supratemporal rather than a tabular (Figure 3.26) recovers a monophyletic Lepospondyli (sans Diplocaulidae) as the sister clade of Amniota+Diadectamorpha. Within Lepospondyli, Recumbirostra is recovered, but includes some aïstopods. Ostodolepids and pantylids are nested within gymnarthrids, and the clade brachystelechids+Brachydectes occupies a basal position within Recumbirostra. An aïstopod, nectrideans (minus diplocaulids), hapsidopareiontids+Asaphestera+Microbrachis, and

Tuditanus+Utaherpeton form successive outgroups to Recumbirostra. Seymouriamorpha is found within a large polytomy at the base of crown Tetrapoda, as are the aïstopods

Coloraderpeton and Lethiscus.

118

Chapter 4: Discussion

4.1 Relationships of Brachydectes

The phylogenetic analyses presented here support the identification of Brachydectes as the sister taxon of the Brachystelechidae, Quasicaecilia + Batropetes + Carrolla, within broader

Recumbirostra (Figure 4.1). Such a relationship has previously been advocated by Vallin &

Laurin (2004) and Marjanovic & Laurin (2013) on the basis of a less extensive dataset, but support for this relationship has not been identified in the lepospondyl matrix of Anderson (2001,

2007) to date. The results presented here suggest that the Anderson (2001, 2007) matrix likely does contain some support for a Brachydectes + brachystelechid clade, but the present result is largely driven by the neurocranial characters identified here. Support for this relationship also comes from characters throughout the skeleton. A summary of synapomorphies by anatomical region is as follows:

4.1.1. Skull Roof

Brachystelechids and Brachydectes lack a quadratojugal. The prefrontal participates in the naris. The lacrimal lacks a dorsal process.

4.1.2 Palate

The ectopterygoid is absent or highly reduced. The palatine process of pterygoid is reduced.

The quadrate process of the pterygoid is absent. The quadrate anteriorly displaced, approximately at level of basipterygoid processes of the parasphenoid or braincase.

119

Figure 4.1. Phylogenetic relationships of selected early reptiles. A, the captorhinid Captorhinus laticeps, after Heaton, 1979, in dorsal, right lateral, and palatal aspect; B, the ostodolepid

Huskerpeton englehorni, after Huttenlocker et al., 2013, in dorsal, right lateral, and palatal aspect; C, the brachystelechid Batropetes fritschi, after Glienke, 2013, in dorsal, right lateral, and palatal aspect; D, the brachystelechid Carrolla craddocki, after Maddin et al., 2011, in dorsal, right lateral, and palatal aspect; E, the cocytinid Brachydectes newberryi, this study, in dorsal, right lateral, and palatal aspect. Skulls not drawn to scale.

120

4.1.3 Braincase

Brachystelechids and Brachydectes share a robust, pillar-like pila antotica that braces against the skull roof; a thickened, robust sphenethmoid; and an ossified columella ethmoidalis that braces dorsally against the nasals.

4.1.4 Lower Jaw

The coronoid series is reduced to a single toothless element that contributes solely to the medial coronoid process; there is extended contact between prearticular and dentary medial to the tooth row; the splenial is reduced with no lateral exposure; lateral fenestration is present between dentary, surangular and angular; the dentary has fewer than ten large teeth.

4.1.5 Postcranial

Intercentra absent.

4.1.6 Revising the Brachystelechidae

Brachystelechidae was established by Carroll & Gaskill (1978) to accommodate the species

Batropetes fritschi, and the diagnosis of the family was considered equivalent to the diagnosis of the species B. fritschi. Studies of the additional brachystelechids Carrolla and Quasicaecilia have avoided revising the diagnosis of this higher taxon (Langston & Olson, 1986; Carroll, 1991a;

Maddin et al., 2011), as have studies revising Batropetes and its junior synonym Brachystelechus

(Carroll, 1991b; Glienke, 2013). Thus, a new diagnosis of the Brachystelechidae is necessary to distinguish them from the Cocytinidae.

121

Brachystelechidae, Revised Diagnosis—Recumbirostran microsaurs with the following synapomorphies: parietals wider than frontals with anterior waisting; frontals participate in orbital margin; parietal-squamosal contact; supratemporal/tabular absent; postparietals absent; interpterygoid vacuities broad; otoccipital region massively co-ossified into a single os basale; teeth multicuspid.

Brachystelechidae, Phylogenetic Diagnosis—Recumbirostran reptiles more closely related to Batropetes fritschi than to Brachydectes newberryi.

Cocytinidae, Revised Diagnosis—Recumbirostran microsaurs with the following synapomorphies: parietals with parallel lateral margins; pineal foramen absent without epiphyseal fossa on ventral surface of skull roof; no frontal participation in orbital margin; prefrontal-parietal contact; jugal absent; postfrontal absent; postorbital absent; supratemporal/tabular falciform; supraoccipital exposed dorsally between postparietals; temporal region with extensive emargination; postorbital bar absent.

Cocytinidae, Phylogenetic Diagnosis—Recumbirostran reptiles more closely related to

Brachydectes newberryi than to Batropetes fritschi.

Cocytinoidea Cope 1875

Type genus—Brachydectes

Morphological diagnosis—Series of pits along dorsal margin or orbit; anteriorly-canted suspensorium; intercentra absent; marginal teeth few, large, and laterally compressed; robust ossification within columella ethmoidalis; pila antotica robust and pillar-like; sphenethmoid thick and robust without fossae for olfactory bulbs and cerebrum; pila metoptica unossified.

122

Phylogenetic diagnosis—All descendants of the last common ancestor of Brachydectes newberryi and Batropetes fritschi.

4.1.7 Remarks

A close relationship between cocytinids (“lysorophians”) and brachystelechids has been recognized by a number of workers (Vallin & Laurin, 2004; Marjanovic & Laurin, 2008; 2013; this study) but this clade has not been formally named. The repeated occurrence of this topology in multiple independent phylogenetic analyses and the presence of many unambiguous synapomorphies of this clade makes establishment of a name for it necessary. The ICZN requires that family level taxa (superfamilies, families, and subfamilies) adhere to the principle of coordination (ICZN Article 36.1). The family Cocytinidae COPE 1875 holds priority over the

Brachystelechidae CARROLL and GASKILL 1978 as the name-bearer, and thus Brachydectes

(=Cocytinus) becomes the name-bearing type of the superfamily Cocytinoidea.

4.2 Relationships of Lepospondyls

4.2.1 Microsauria

The order Microsauria was originally erected to contain a variety of small-bodied early tetrapods from coal measures localities at Joggins (Dawson, 1863). Since that time, a number of

‘microsaur’ taxa have been recognized as early reptiles (Hylonomus, Steen, 1934;

Cephalerpeton, Gregory, 1948) and vice versa (Batropetes, Carroll, 1991; Archerpeton, Reisz &

Modesto, 1996), but the taxon has otherwise remained more or less intact. Two major groups have been recognized: the Tuditanomorpha, a group of relatively reptile-like microsaurs with various terrestrial and fossorial adaptations, and the Microbrachomorpha, a poorly understood group consisting largely of aquatic perennibranchiate forms with similarity between taxa largely

123

limited to symplesiomorphies of the Lepospondyli specifically, or even of crown tetrapods more generally. A clade of derived tuditanomorphs with explicit fossorial adaptations has been repeatedly recovered in phylogenetic analyses of the group (Anderson, 2007; Anderson et al.,

2008; Huttenlocker et al., 2013) and has been termed Recumbirostra in reference to the recumbent premaxilla and premaxillary dentition.

The presence of gills in some microbrachomorphs (Schoch & Witzmann, 2011) has led to the expectation of larval gills in tuditanomorphs, and to the suggestion that Brachydectes may represent a neotenic tuditanomorph retaining larval gills. To date, no gills have been found in any tuditanomorph, including extremely small and likely juvenile species (e.g. Llistrofus, Bolt &

Rieppel, 2009)

In this analysis, Tuditanomorpha is consistently recovered within Reptilia as the sister taxon of Eureptilia, as represented by Captorhinus+Petrolacosaurus, a phylogenetic position that may preclude branchiate larvae in Tuditanomorpha. Although the analyses presented in this thesis suggest that microbrachomorph microsaurs (such as Microbrachis pelikani and

Utaherpeton franklini) are distributed throughout the Tuditanomorpha, such support is inconsistent and these taxa lack synapomorphies of the Tuditanomorpha. Revision of the morphology of these animals is likely necessary, and the possibility exists that the similarities between these taxa and tuditanomorphs may result from shared “loss” characters associated with small size, such as loss of bones of the temporal arcade and apparent loss of late-ossifying structures of the stapes, epipterygoid, braincase, and postcranium, as well as characters that directly characterize small size (e.g. skull length, character 1 of Anderson, 2001). A number of authors have voiced skepticism of character suites associated with miniaturization and neoteny

(Anderson, 2007; Frobisch & Schoch, 2009; Marjanovic & Laurin, 2008; 2013), but

124

implementation of these criticisms has been largely lacking in phylogenetic studies of lepospondylous early tetrapods (including this one). Rigorous reassessment of the independence of these characters should take into account conserved aspects of ontogeny and patterns of miniaturization in early tetrapods, but is outside of the scope of this thesis.

Interestingly, much of the debate on the relationships of microsaurs has focused on the possibility that microsaurs may represent the stem group of reptiles (Vaughn, 1962; Gregory,

1965; Carroll & Baird, 1968) or of amniotes more generally (Laurin & Reisz, 1995; Anderson,

2001), but a number of characters have been identified which would seemingly preclude a microsaurian origin of reptiles. These include the unique microsaurian condyle-cotyle arrangement of the occiput, the lack of an otic emargination, and absence of a transverse descending toothed flange on the pterygoid. Instead, it appears the inverse may be true: microsaurs may represent highly-derived reptiles. If so, microsaurian characters previously identified as evidence of a relatively basal position of microsaurs within tetrapods may instead represent synapomorphies of the Microsauria, and may reflect adaptation of microsaurs to a fossorial habitat. This is discussed below.

The placement of microsaurs within Amniota also precludes a number of other possible phylogenetic placements of microsaurs. One persistent hypothesis states that microsaurs may be the sister taxon of some or all temnospondyls (Milner, 1993; McGowan, 2002). My results do not preclude the possibility that some putative microsaurs (e.g. Microbrachis or Hyloplesion) may be closely related to Temnospondyli, but they would exclude the majority of microsaurs, and the broader microsaur “concept” that has been established over the past 130 years and described in detail by Carroll & Gaskill (1978), from such a hypothesis. Phylogenetic analysis of character partitions explains this result to some degree; postcranial characters in particular support a close

125

relationship between some microsaurs and Temnospondyls (Chapter 3) likely due to the plesiomorphic nature of the pectoral girdle of both groups and reduction of bony processes on the appendicular skeleton of these taxa due to the aquatic lifestyle inferred for both groups.

4.2.2 Aïstopoda

The relationships of the order Aïstopoda have been poorly understood since the original descriptions of the order. Carroll (1998) identified a number of characters he considered evidence that aistopods may be very early stem-tetrapods, possibly at the grade of the Devonian tetrapod Acanthostega, but phylogenetic analyses have not borne that result out. Instead, aistopods have been largely found within a monophyletic Lepospondyli, closely related to orwithin urocordylid nectrideans (Anderson, 2001; 2007; Anderson et al., 2008; Huttenlocker et al. 2013). This result has even appeared in phylogenetic analyses that fail to recover a monophyletic Lepospondyli (Klembara et al., 2010).

A revision of the morphology and phylogenetic relationships of the Aïstopoda among early tetrapods will appear elsewhere, and will thus be discussed only briefly here. Although the monophyly of aïstopods is of little doubt (Anderson, 2001; Anderson et al., 2003), aïstopods are generally not recovered as a monophyletic group in the analyses reported here. This may be the result of inconsistent coding of dermatocranial morphology, or it may suggest that the disparity between ophiderpetontid and phlegethontiid aïstopods has resulted in homoplastic similarity with different taxa. The position of aistopods within the Nectridea is not well represented and may be as spurious as the results that place them within Recumbirostra. The braincase-only matrix analyzed here (Chapter 3) recovers a monophyletic Aïstopoda within the tetrapod stem, a position that is apparently more broadly supported by characters of the lower jaw, dermatocranium, and braincase (Anderson et al., pers. comm.)

126

4.2.3 Adelospondyli

The phylogenetic relationships of adelospondyls have not been assessed in depth in this analysis, as no adelospondyl fossils have been directly studied, and only one taxon has been coded into this phylogeny. The phylogenetic manipulations presented here suggest that adelospondyls are closely related to the Nectridea, but this result may be spurious, as members of this clade appears throughout the tree. The phylogenetic analysis of Ruta et al. (2003) recovered adelospondyls as the sister taxon of colosteids, whereas Holmes (1989) observed similarities between the teeth of Adelogyrinus and the embolomere Archeria. Contra the results presented here, it seems likely that adelospondyls are far removed from the base of crown Amniota, either as derived stem-tetrapods, or early members of the lissamphibian or amniote stem.

4.2.4 Nectridea

The Nectridea is a morphologically disparate group, but its monophyly has not generally been questioned. Previous analyses have recovered nectrideans within a monophyletic

Lepospondyli on the amniote stem (Anderson, 2001; Ruta et al., 2003; Vallin & Laurin, 2004) or as the sister taxon to Temnospondyli (Clack & Finney, 2005).

The monophyly of Nectridea is rejected by the analyses presented here. The scincosaurid

Scincosaurus is found to be a tuditanomorph microsaur rather than a nectridean. This result is less surprising than it appears. Scincosaurus differs significantly from other nectrideans in a number of ways: its humerus retains an entepicondylar foramen and well-developed deltopectoral crest, not seen in any other nectridean; it has parapophyses shared between vertebrae (as in reptiles) rather than lying within the midline of the centrum (as in other nectrideans); it has a numerically-reduced dentary dentition of very large teeth (as in

127

brachystelechid microsaurs, and in contrast to the teeth of other nectrideans); it lacks dorsal dermal armor (unlike other nectrideans); lacks multiple coronoids (as in other nectrideans); and retains five digits on the manus (unlike other nectrideans).

In addition, no support exists for a monophyletic Keraterpetontidae that includes the diplocaulids Diplocaulus, Diploceraspis, Ductilodon, and presumably Peronedon (not included here). Instead, diplocaulids are found to be phylogenetically distant from all other nectrideans within stereospondyl temnospondyls, a placement supported by braincase and dermatocranial characters as well as the comprehensive dataset. These characters include characters of the occiput (the presence of a tabular process of the exoccipital that excludes the opisthotic from the occipital surface, loss of any supraoccipital ossification, paired exoccipital condyles), the palate

(the presence of a ventral process of the exoccipital that forms a sutural contact with the pterygoid and parasphenoid, the presence of a broad sutural contact between the pterygoid and parasphenoid, the presence of posterior processes of the vomer that extend along the ventrolateral surface of the sphenethmoid, the presence of lateral processes of the vomer and palatine that underplate the lateral wall of the nasal capsule and exclude the marginal tooth- bearing bones from the choanal margin), and the braincase (the presence of a laterally-flaring

“laterosphenoid” structure in the sphenoid region, temnospondyl-like division of the canals housing the internal carotids within the braincase). A more thorough description of diplocaulid morphology and phylogenetics will appear elsewhere.

The remainder of Nectridea (Keraterpetontidae+Urocordylidae) is generally recovered in the analyses presented here, but demonstrates little stability in phylogenetic placement, jumping from various crown amniote positions to Temnospondyli to various other positions within crown

Tetrapoda. This suggests three things. First, keraterpetontid and urocordylid morphology likely

128

requires revision with reference to early tetrapod morphology more broadly, with the intention of testing nectridean monophyly. Secondly, it is possible that these groups also do not form a monophyletic group. Thirdly, and more broadly, the character sample used in these analyses may not be adequate to assess nectidean relationships and monophyly. It is worth noting that keraterpetontids demonstrate some morphology generally considered characteristic of seymouriamorphs, such as the paddle-shaped transverse process of the pterygoid, the presence of pterygoid denticles on raised radiating ridges, the very short, triangular cultriform process of the parasphenoid, the flaring lateral processes of the basal plate of the parasphenoid, and the broad median contact between the palatine rami of the left and right pterygoids. None of these characteristics are found in urocordylids. In addition, the broad dermal armor of keraterpetontids is reminiscent of the dermal armor of chroniosuchan seymouriamorphs (Buchwitz et al., 2010) but shares little similarity with the dermal armor of both urocordylids and diplocaulids.

4.3 Relationships of the Microsauria

4.3.1 General

One of the novel results of the phylogenetic analyses presented in this thesis is the placement of the majority of microsaurs within Amniota, specifically within the reptile stem. Although the

Microsauria was initially conceived of as a group of small early reptiles (Dawson, 1863; Cope,

1875), attention quickly shifted to addressing the possibility of whether the Microsauria represented a viable stock from which reptiles or amniotes could have evolved (Gregory, 1965;

Vaughn, 1962; Carroll & Baird, 1968) as a unique diversification of stem-amniotes, or as some unique tetrapod lineage with little significant relationship to any modern group. A number of authors, including Gregory (1965), Vaughn (1962), and Carroll & Baird (1968), have numerous characteristics unique to microsaurs that would preclude a microsaurian origin of reptiles or even

129

amniotes. Carroll & Baird (1968) condensed this list down to five characters: (1) a single large bone in the temporal region, (2) absence of a transverse flange (alary process) on the pterygoid,

(3) the arrangement of the occiput and atlas/axis, (4) absence of trunk intercentra, and (5) scale structure. Contra the assertions of Carroll & Baird (1968), none of these characters necessarily preclude a close relationship between reptiles and microsaurs. A large bone in the temporal region is not observed in all microsaurs (primarily brachystelechids and cocytinids, but also

Llistrofus, see Rieppel & Bolt, 2009) and could potentially be derived from the reptilian condition, where a single small temporal bone is present (Heaton, 1979). A transverse flange of the pterygoid is present in some microsaurs (Rieppel & Bolt, 2009; Anderson et al., 2009;

Huttenlocker et al., 2013), as are trunk intercentra (Carroll & Gaskill, 1978). Microsaur scale structure is not directly comparable with scales in any other early tetrapod and thus are not interpretable in relation to other early tetrapod taxa. This leaves the unique condyle-cotyle occipital structure of microsaurs, which appears to represent a true synapomorphy of microsaurs, but does not itself suggest any specific relationship. So, while the condyle-cotyle occipital structure would suggest a monophyletic Microsauria, the character list offered by Carroll &

Baird (1968) does not appear to support any particular relationship between microsaurs and other early tetrapod lineages.

However, a number of characters suggest that microsaurs represent a clade of early reptile. Some of these have been identified in this study (Chapter 3) whereas others have been noted previously by other workers (Gregory, 1965; Vaughn, 1962; Carroll & Baird, 1968), although generally these characters have been interpreted as convergences between microsaurs and reptiles rather than synapomorphies of reptiles including microsaurs. These include

130

morphology of the braincase, lower jaw, pectoral girdle, and ankle joint. These will each be discussed in detail below.

4.3.2 Braincase

Braincase support for a reptilian origin of microsaurs is extensive and widely-distributed.

Reptiles and microsaurs share a single median supraoccipital bone that develops from an unpaired ossification centre (Chapter 3). This differs distinctly from stem-amniotes like

Proterogyrinus which exhibit a paired supraoccipital, or diadectamorphs and synapsids which have a single supraoccipital bone that develops from paired ossification centres that either co- ossify or fuse in late embryonic or postnatal development (Berman, 2000; Strong, 1925).

Moreover, the supraoccipitals of microsaurs and of reptiles share a number of features, including: broad winglike lateral ascending processes, a median ascending process that braces against the skull roof (or protrudes through it, in Brachydectes), and ventral laminae representing a partial ossification of the median wall of the otic capsule along the ventral surface of the lateral ascending processes.

Additional character support for a microsaur-reptile relationship can be found in the anatomy of the inner ear. A distinct crista (the crista interfenestralis) is present on the medial surface of the opisthotic in both early reptiles (Heaton, 1979; Gardner et al., 2010) and microsaurs (Chapter 2) that delineates the lagenar recess from the metotic recess.

4.3.3 Mandible

Several characters of the lower jaw suggest a close relationship between microsaurs and reptiles as well. As in other amniotes, but contra the condition observed in other “lepospondyls”

131

and in most stem-amniotes, most microsaurs have only a single edentulous coronoid that contributes to the median surface of the coronoid process of the dentary. In some microsaurs, the coronoid is restricted to the posterior portion of the jaw, and a substantial sutural contact is present between the dentary and splenial medial to the tooth row. In others, the coronoid expands anteriorly and may exhibit a partial tooth row or denticle field. The plesiomorphic condition is likely the condition exhibited by other early amniotes, with posterior restriction of the coronoid or coronoids to the anterior margin of the adductor fossa.

4.3.4 Ankle Joint

The morphology of the ankle joint of early amniotes has recently been reviewed by

Meyer & Anderson (2013) but will be discussed briefly here in context of microsaur origins.

The early amniote ankle involves two proximal tarsal elements: an astragalus (formed from the fusion of the tibiale, intermedium, and third centrale) and the calcaneum. In the early reptile

Hylonomus, in the early eureptile Captorhinus, and in diadectamorphs, the astragalus is fully fused but retains traces of sutures between the astragalar precursor elements. An identical condition is observed in the microsaur Tuditanus (Carroll & Baird, 1968), complete with sutures between the tibiale, intermedium, and third centrale, and a single separate distal fourth centrale.

Carroll & Baird (1968) note a similar arrangement of the ankle in Pantylus cordatus as well as

Ricnodon, a putative hapsidopareiontid. Sutures are not observed in the astragalus of early synapsids (Meyer & Anderson, 2013) but are observed in some diadectamorphs (Berman &

Henrici, 2003). Given the phylogenetic results presented in Chapter 3, it appears that microsaurs simply retained a typical reptile ankle, with two proximal tarsal elements. More generally, this would suggest that tarsal fusion in early amniotes was actually rather conservative, and that the

132

majority of tarsal fusion associated with amniote origins occurred prior to the origin of the amniote crown.

4.3.5 Contextualizing Microsaur Synapomorphies

Microsaurs exhibit a number of characteristics that distinguish them from other reptiles, and these differences have been used to place microsaurs outside of the amniote crown, either along the amniote or lissamphibian stem. Traditionally, the numerous observed resemblances between microsaurs and early reptiles have been disregarded as convergences prior to the adoption of phylogenetic systematics (Vaughn, 1962; Baird, 1964; Gregory, 1965; Carroll & Baird, 1968).

These resemblances occur in disparate anatomical complexes and do not reflect convergent functional or size constraints between microsaurs and early reptiles. Some workers (e.g. Baird,

1964) have gone so far as to appeal to the early tetrapod research community to not revisit the microsaur-reptile question as the similarities (inferred as convergences) had been so extensively documented. Revisiting microsaur morphology, especially within the braincase, suggests the opposite; pre-phylogenetic hypotheses of microsaur and reptile origins may have placed undue importance on single character evolution scenarios, and that the extensive “convergences” expounded upon by earlier authors may be reptile plesiomorphies, and that features identified as contradicting an amniote origin of microsaurs may instead represent apparent reversals associated with fossoriality. This underscores the importance of assessing the monophyly and relationships of major Paleozoic groups with appropriate skepticism of contentious historical groups.

133

4.4 Lepospondyls and the Origins of Modern Tetrapod Taxa

4.4.1 Lepospondyls and the Origins of Modern Lissamphibians

The description of the morphology of Brachydectes and the phylogenetic treatment presented here rejects the Lepospondyl Hypothesis in general and the Brachystelechid-

Lysorophian Hypothesis more specifically. Not only does Brachydectes lack lissamphibian synapomorphies found within Temnospondyli, such as pedicellate teeth, but it is now also clear that Brachydectes shares numerous amniote synapomorphies not seen in lissamphibians, temnospondyls, or more basal stem-amniotes and stem-tetrapods.

Although the structure of the dermal skull of Brachydectes is generally ambiguous, the braincase demonstrates numerous features consistent with amniote rather than lissamphibian affinities. Despite the presence of a wide cultriform process, the presence of a broad median bone between the lateral ossifications of the sphenethmoid region suggests persistent median fusion of the ethmoid trabeculae posterior to the ethmoid region (tropitraby), as in amniotes, rather than the widely-spaced parallel trabeculae (platytraby) seen in lissamphibians. Cranial circulation as inferred by distribution of foramina and virtual endocasts of internal canals within the region of the sella turcica is consistent with an amniote affinity as well, with division of the internal carotid outside of the skull and the cerebral branch of the internal carotid entering the braincase within the hypophyseal fossa. As in other microsaurs, and in stem and crown reptiles, a single median supraoccipital ossifies within the synotic tectum from a single ossification centre.

This differs from basal tetrapods, in which the supraoccipital is paired, from synapsids, diadectamorphs, and mammals, in which the supraoccipital is unpaired but develops from paired centres of ossification, and from temnospondyls and lissamphibians, in which no supraoccipital bone develops at all and the synotic tectum is invaded by dorsomedial processes of the

134

exoccipitals (although a median ossification of the synotic tectum appears to be present in the dissorophids Cacops and Kamacops (Schoch, 1999). Rather than exhibiting the typical paired occipital condyle of lissamphibians and temnospondyls, the occipital condyle of Brachydectes is dominated by a contribution from the basioccipital, as in early tetrapods, but with the condyle- cotyle arrangement typical of microsaurs. The otic capsule preserves evidence of a well- developed saccular region, as in reptiles and the microsaur Carrolla, but in contrast to the condition observed in lissamphibians and temnospondyls, in which the saccular region is only weakly developed. The median surface of the opisthotic preserves a weakly-developed crista interfenestralis, a structure seen in modern reptiles, in the neodiapsid Youngina (Gardner et al.,

2010), and in the captorhinid Captorhinus (Heaton, 1979), that divides the vestibular and occipital recesses.

The placement of Brachydectes within microsaurs, which has here been retrieved within

Amniota on the reptile stem, further renders the interpretation of Brachydectes as a perennibranchiate neotene with homology to neotenic salamanders (e.g. Siren, Necturus, etc) dubious. Although monophyly of lissamphibians has been the subject of some skepticism in recent years (Carroll, 2007; Anderson et al., 2008), the monophyly of extant Amniota is well- supported by osteological, physiological, and molecular data. Furthermore, although the branchial skeleton of Brachydectes is well-ossified, it lacks grooves or channels for the branchial arteries of early tetrapods (Schoch & Witzmann, 2011), suggesting that it likely did not play a role in gas exchange. Various reptiles exhibit well-ossified hyoid skeletons to assist in air- gulping (Brainerd & Overkowicz, 2006), suction capture of aquatic prey (Lemell et al., 2002), or attachment of lingual musculature (Smith, 1984), so the presence of an ossified hyobranchial skeleton in Brachydectes does not preclude a primary reliance on pulmonary respiration in

135

Brachydectes, even if Brachydectes was primarily aquatic or subaquatic. The absence of evidence for gills in any stage in the ontogeny of Brachydectes does not provide support for hypotheses of similarity of ontogeny between Brachydectes and lissamphibians, nor for hypotheses of similarity of physiology.

In contrast, the relationship between dissorophoid temnospondyls and modern lissamphibians is well-supported by neurocranial anatomy, general morphology, ontogeny, and physiology. Dissorophoids and lissamphibians both exhibit widely separate trabecular cartilages in the sphenethmoid region (platytraby) and invasion of the synotic tectum by the exoccipitals.

Although greater integration of the occipital arch with the otic region is a characteristic of crown tetrapods more generally (following closure of the otoccipital and basicranial fissures early in crown tetrapod development), the integration between the occipital arch and the otic region in temnospondyls more generally exceeds that seen in other tetrapod groups. Not only do the ossifications of the occipital arch invade the synotic tectum, but the foramen serving the internal jugular vein and vagus nerve pierces the exoccipital in several temnospondyl taxa as well as some lissamphibians, possibly suggesting invasion of the posterior otic capsule by the exoccipital as well. This may also explain the ventral process of the exoccipital in trematosaur stereospondyls and diplocaulids, which may represent an invasion of the ventral otic capsule by the occipital ossification in those taxa, and the tabular process of the exoccipital in these same taxa, which may represent invasion of the crista parotica by the exoccipital.

Temnospondyls also exhibit ontogenetic features similar to those seen in modern lissamphibians. Temnospondyls have branchiate larvae (Schoch & Witzmann, 2011), exhibit lissamphibian-like metamorphosis (Schoch & Carroll, 2002; Schoch & Milner, 2003; Schoch,

2014), and follow lisamphibian-like polyphenism, with neotenic and metamorphic adults in some

136

lineages (Schoch & Frobisch, 2006) and microphagous and macrophagous “cannibal” morphs in others (Schoch, 2014). In addition, some temnospondyls demonstrate salamander-like preaxial dominance in digit ossification (Frobisch & Schoch, 2006).

4.4.2 Lepospondyls and the Origins of Amniotes

The origin of amniotes is periodically revisited, with new observations and data brought to bear on the timing and evolutionary context of the origin of the amniote crown. Current phylogenetic hypotheses generally recover diadectamorphs, lepospondyls, seymouriamorphs, and sometimes anthracosaurs as successive outgroups to Amniota. In this framework, each of these clades is relatively well-populated and exhibits extensive diversification and subsequent extinction.

However, several problems exist. First, the early evolution of both stem-reptiles and stem-mammals is marked by huge morphological gaps. Within reptiles, only one lineage of reptile outside of the Eureptilia has been identified, the Parareptilia, and the parareptiles that occupy the most basal position within that lineage are the highly derived mesosaurs, a Middle

Permian lineage of secondarily aquatic reptiles. Other features of parareptile evolution are equally perplexing, such as the reacquisition of an otic notch in Lanthanosuchus and

“nycteroleters” and the presence of enamel and dentine folding similar to the plesimorphic

“labyrinthodont” condition among derived members of the taxon. Early synapsid evolution is equally problematic. It is marked by massive morphological gaps, both between synapsid families and between synapsids and known reptiles and stem amniotes. Despite the generally large size of synapsids, abundant synapsid fossils, and high worker interest, these gaps remain

137

unfilled and many aspects of early synapsid evolution remain uncertain. Numerous convergences have been observed between diadectamorphs and early synapsids in intricate morphology of the inner and middle ear, particularly the presence of an otic trough and a lateral elongation of the otic capsule. The suggestion that these features may be homologous between diadectamorphs and synapsids has been rejected on the basis that these features are absent in varanopids and caseasaurs, which have been interpreted as basal synapsids by some workers. However, recent analyses have suggested that varanopids and caseasaurs may actually represent a clade apart from edaphosaurids, ophiacodontids, and sphenacodontids (Benson, 2013), in which case the absence of these features from varanopids and caseasaurs may be apomorphic. The results presented here suggest that diadectamorphs may be synapsids in a broad sense, a hypothesis which should be reassessed.

The disappearance of “Lepospondyli” more broadly, and the placement of microsaurs particularly within crown Amniota as stem-reptiles, presents an additional problem for the current framework of amniote origins. The braincase characters and partition experiments presented here suggest that Lepospondyli has largely been held together by “loss characters” shared due to common constraint of miniaturization, and that there is little underlying similarity between major lepospondyl groups. This has two major impacts on questions of amniote origins.

First, this further depopulates the amniote stem, leaving only seymouriamorphs and possibly some embolomeres. Secondly, the removal of microsaurs from the amniote stem makes the amniote stem considerably less amniote-like, or more specifically, less eureptile-like. A number of amniote characteristics appear to have been polarized by the presence of microsaurs on the amniote stem, including the number of supraoccipitals, the presence/absence of an otic notch, the presence of “labyrinthine” or “plicidentine” infolding of dental tissues, and the presence of teeth

138

on the transverse flange of the pterygoid. These characteristics all directly relate to both our understanding of the morphology of basal amniotes as well as the morphology, physiology, and ecology of stem-amniotes.

4.4.3 General Considerations and Macroevolutionary Studies

One of the major goals of early tetrapod phylogenetics is to provide a phylogenetic framework on which to test macroevolutionary hypotheses. Early tetrapod evolution is of particular interest in phylogenetic studies because it offers a unique glimpse at initial diversification of vertebrates in the terrestrial realm, and because it provides a sense of the evolutionary trends that produced modern tetrapod clades. A number of recent studies have investigated trends in size evolution (Laurin, 2004), palatal evolution (Kimmel et al., 2009), evolution of trophic function (Anderson et al., 2013), and evolutionary rate (Ruta et al. 2006;

Wagner et al., 2006), but these studies rely heavily on a phylogenetic consensus published by

Ruta et al. (2003) and Ruta & Coates (2007). The phylogenetic relationships supported by my study conflict strongly with the phylogenetic consensus of Ruta et al. (2003) and Ruta & Coates

(2007) in several key ways that may potentially impact macroevolutionary studies of early tetrapod diversification. Elimination of the clade Lepospondyli suggests that amniote characteristics may have arisen much earlier within the amniote stem than previously thought, in which case the presence of amniote-like characteristics in Caerorhachis and Casineria may reflect the presence of amniote-like morphology in late stem-tetrapods rather than near-amniotes.

Secondly, this places the morphologically diverse recumbirostrans within amniotes, suggesting that amniotes were much more morphologically diverse in the Carboniferous and Permian than previously thought. Thirdly, the recognition that some or all nectrideans may be temnospondyls further reduces morphological disparity of stem-amniotes. Nectrideans generally occupy

139

morphospace already recognized in temnospondyls (Yates & Warren, 2000), suggesting that, rather than representing unique morphospace exploration, nectrideans may instead represent early members of temnospondyl groups that occupied this morphospace until the Jurassic

(Warren & Hutchinson, 1982). Finally, it appears that size may have been more labile among early tetrapods than previously thought (Laurin, 2004), with small size originating among various lineages of stem tetrapods, stem amniotes, crown amniotes, and stem-lissamphibians.

Specific tests of macroevolutionary processes in early tetrapod evolution is beyond the scope of this study, but the possibility that prior macroevolutionary studies may have been biased by convergence in the original phylogenetic datasets should be given consideration, and these macroevolutionary patterns should be reassessed once early tetrapod phylogeny stabilizes.

4.5 Morphology of Brachydectes

4.5.1 Fossorial adaptations of Brachydectes

Bolt and Wassersug (1975) and Wellstead (1991) have commented on possible fossorial adaptations of Brachydectes, but resolution of the phylogenetic relationships of Brachydectes in this study (Chapter 3) permits a more precise discussion of how and why the morphology of

Brachydectes differs from other early tetrapods, and thus a better understanding of its ecology.

That Brachydectes inhabited burrows at least part of the year is supported by direct evidence; skeletons of Brachydectes are readily found within burrow structures (Olson & Bolles,

1975; Hembree et al., 2004; Hembree et al., 2005; Huttenlocker et al., 2005). These burrows have generally been interpreted as estivation burrows (Hembree et al., 2004, 2005; Huttenlocker et al., 2005) excavated in soft subaqueous sediment, partly due to the sedimentology of these

140

localities (Hembree et al., 204, 2005; Huttenlocker et al., 2005) and partly due to the common interpretation of Brachydectes as an aquatic gill-breathing early tetrapod.

However, the skeletal evidence for fossoriality in Brachydectes has remained somewhat equivocal. Bolt and Wassersug (1975) argued for a greater role of fossoriality in the ecology of

Brachydectes, based on comparisons with modern amphisbaenid squamates, and specifying multiple lines of anatomical evidence. They identified two general lines of anatomical evidence; the skull and palate were heavily reinforced to withstand compression and torsion stresses, and the jaw and suspensorium were modified to allow the mouth to open within enclosed spaces.

Morphology identified in support of the former includes a dramatically thickened skull roof, deep sinuous sutures between skull roofing elements, and robust connections between the braincase, skull roof, and palate, whereas the latter is supported by the ventrally-recessed glenoid fossa and anteriorly-canted suspensorium. Bolt and Wassersug (1975) also make note of the roughly wedge-shaped skull of Brachydectes, and a close relationship between the stapes and jaw articulation. Bolt & Wassersug (1975) concluded that Brachydectes likely burrowed within soft sediment in freshwater environments.

Wellstead (1991) rejected much of this argument, and argued that the morphology identified by Bolt & Wassersug (1975) could be better explained by buccopharyngeal pumping

(incorrectly identified by Wellstead as aquatic inertial feeding) rather than facultative or obligate fossoriality. Foremost among these characteristics is the anteriorly-canted suspensorium and ventrally recessed glenoid fossa, which Wellstead regarded as adaptations for increasing speed of jaw depression and gape size, respectively. Structural adaptations involved in the reinforcement of the braincase were reinterpreted by Wellstead as adaptations associated with small size rather than fossoriality.

141

Resolution of Brachydectes within the Cocytinoidea permits more specific and constrained comparison of lysorophian morphology with the skulls of more conservative relatives, primarily the brachystelechid Carrolla, for which the skull has recently been described in detail (Maddin et al., 2011), as well as the recently described non-cocytinoid microsaurs

Nannaroter mckinzei (Anderson et al., 2009) and Huskerpeton englehorni (Huttenlocker et al.,

2013).

Cocytinoids, including Brachydectes and Carrolla, are characterized by a number of neurocranial and dermatocranial characteristics consistent with fossorial adaptations seen in other taxa. Most notably, the sphenethmoid and pleurosphenoid are thickened into robust supports between the parasphenoid and skull roof. Additionally, a novel ossification is seen in the columella ethmoidalis, forming an additional bony support between the cultriform process of the parasphenoid and the anterior portion of the frontals. Together, these structures suggest resistance to strong dorsoventral compressive forces on the frontals and parietals. This contrasts somewhat with the condition observed in ostodolepids, where the contact between the premaxilla and nasal is upturned into a shovel-like structure braced by laminae from the premaxilla and vomer, in which force is likely concentrated at the apex of the snout.

Brachydectes differs from brachystelechids and other microsaurs in a few key regards.

Most conspicuously, the cheek is completely open from the orbit to the suspensorium, accommodating an enlarged m. adductor mandibularis externalis (mame). An emarginated cheek is observed in various microsaurs, including hapsidopareiontids (Daly, 1973; Carroll & Gaskill

1978; Rieppel & Bolt, 2009), ostodolepids (Daly, 1973; Carroll & Gaskill, 1978, Anderson et al.,

2009), Tambaroter carrolli (Henrici et al., 2011), and Huskerpeton englehorni (Huttenlocker et al., 2013), but the condition seen in Brachydectes newberryi (Wellstead, 1991; this study) and

142

other cocytinids (Sollas, 1920; Bolt & Wassersug, 1975; Wellstead, 1991) is exaggerated in comparison with other microsaurs, and reaches dorsally to the parietals. This is partially accomplished via the loss of the quadratojugal, jugal, postorbital, and postfrontal in cocytinids, and partially accomplished via the modification of the squamosal into a thin strap restricted to the lateral surface of the quadrate. Additionally, Brachydectes and other cocytinids have secondarily lost the recumbent premaxilla of other recumbirostrans, and the external nares face anteriorly. The cultriform process of Brachydectes and other cocytinids is also laterally expanded in comparison with other microsaurs, including brachystelechids, making the sphenethmoids and pleurosphenoids vertical rather than angled dorsolaterally.

Additional features of the otic region can be observed in cocytinids specifically. In most microsaurs, the crista parotica forms a weak paroccipital process bracing against the squamosal or suspensorium. In cocytinids, the crista parotica is restricted to a weak ridge on the prootic which braces against the squamosal. Within the otic capsule itself, the fossae for the semicircular canals are compressed directly against the utricular fossa without ossification between these spaces. Laterally, the horizontal canal is exposed between the prootic and opisthotic.

Morphology of the braincase in cocytinids, and in cocytinoids more generally, suggests greater resistance to dorsoventral forces on the skull centered on the frontals and parietals and a reduction of the role of a rostral scoop in excavation, suggesting a different mode of burrowing from shovel-snouted microsaurs such as Pelodosotis (Carroll & Gaskill, 1978) or Nannaroter

(Anderson et al., 2009). Adaptation for headfirst burrowing are found in a variety of modern reptiles, including gymnophthalmids (Figure 4.2), scincids (Figure 4.3), and amphisbaenids

(Figure 4.4). Fossorial reptiles show relatively predictable convergence in cranial morphology, including expansion of the cultriform process, expansion of the lower temporal fenestra,

143

reduction of the orbit, fusion of the otic and occipital elements into a single os basale, reduction in tooth count, and bracing of the sphenoid region of the braincase by ventral laminae of the skull roof. Rostral morphology tends to be correlated with burrowing mode in amphisbaenids

(Kearney, 2003; Kearney & Stuart, 2004) and gymnophthalmids (Barros et al., 2011). In gymnophthalmids and amphisbaenids, a steeply-inclined shovel-like skull is typically associated with burrowing in sandy substrate, whereas a rounder skull is associated with burrowing in denser soil (Barros et al., 2011). It is possible that similar morphological differences between ostodolepids and cocytinoids, respectively, may reflect similar substrate preferences.

Burrowing in consolidated sediment may also explain ossification of the columella ethmoidalis in cocytinoids (Figure 4.5E,F) in comparison with other microsaurs. Such ossifications are rare within ‘microsaurs’, and are absent in Huskerpeton englehorni (Figure

4.5A,B), Nannaroter mckinzei (Huttenlocker et al., 2013), and the type specimen of

Rhynchonkos stovalli (M. Szostikjwskj, pers. comm.), but a completely ossified columella ethmoidalis has been described for the brachystelechids Carrolla craddocki (Figure 4.5C,D,

Maddin et al., 2011) and Quasicaecilia texana (Carroll 1990). Ossifications of the columella ethmoidalis are rare in extant reptiles, but do appear in caecilians (Maddin et al., 2012) as well as a small number of caudates that engage in headfirst burrowing. In the sirenid Siren intermedia

(Figure 4.5I,J), ossification of the orbitosphenoid persists anteriorly into the ethmoid region, ossifying within the lateral portions of the columella ethmoidalis, but not ossifying to the midline

(Reilly & Altig, 1996). Siren intermedia engages in headfirst burrowing during the excavation of estivation burrows (Reilly & Altig, 1996). In the amphiumid Amphiuma tridactylum (Figure

4.5K,L), ossifications of the columella ethmoidalis are paired and fused to the medial surface of the frontals, but represent a separate ossification from the orbitosphenoid. Amphiuma tridactylum

144

constructs networks of burrows in wetlands, typically at or around the level of groundwater

(Knepton, 1954). A separate medial ossification of the ethmoid region is present in the proteid

Proteus anguinus (Figure 4.5M,N). Such ossifications are absent in other caudates (Figure

4.5G,H), including hyperossified salamandrids.

Figure 4.2. Comparison of cranial morphology of generalized and fossorial microteiids

(Squamata: Gymnophthalmidae). Left, the generalized microteiid Vanzosaura rubricauda, after

Guerra and Montero, 2009, in A, dorsal, C, right lateral, and E, palatal aspect; right, the fossorial microteiid Calyptotommatus nicterus, after Roscito and Rodriguez, 2012, in B, dorsal, D, right lateral, and F, palatal aspect. 1, enlarged semicircular canals; 2, reduced orbit; 3, flange of

145

parietal reinforcing sphenoid region; 4, os basale; 5, enlarged cultriform process of parasphenoid;

6, reduced palatal fenestra. Skulls not drawn to scale.

Figure 4.3. Comparison of cranial morphology of generalized and fossorial skinks (Squamata:

Scincidae). Left, the generalized skink Amphiglossus splendidus, after Gauthier et al., 2012, in A, dorsal, C, left lateral, and E, palatal aspect; right, the fossorial skink Acontias meleagris, after

Rieppel, 1981, in B, dorsal, D, left lateral, and F, palatal aspect. 1, recumbent premaxilla with pars dorsalis forming an anterior keel; 2, expanded emargination in cheek; 3, wedge-shaped snout; 4, descending flange of parietal reinforcing sphenoid region of braincase; 5, enlarged teeth with reduced tooth count. Skulls not drawn to scale.

146

Figure 4.4. Comparison of cranial morphology of generalized and fossorial lacertoids

(Squamata: Lacertoidea). Left, the lacertid Parvilacerta parva, after Muller (2002), in A, dorsal,

C, right lateral, and E, palatal aspect; right, the fossorial amphisbaenian Trogonophis weigmanni, after Gans, 1960, in B, dorsal, D, right lateral, and F, palatal aspect. 1, closure of pineal foramen;

2, loss of temporal bones; 3, deeply interdigitating sutures in anterior skull; 4, reduced orbit; 5, descending flange of parietal reinforcing sphenoid region of braincase; 6, loss of postorbital bar;

7, downturned premaxilla; 8, os basale; 9, enlarged teeth and reduced tooth count; 10, enlarged cultriform process. Skulls not drawn to scale.

147

148

Figure 5. Anterior braincase ossifications in selected tetrapods. A, left lateral, and; B, left oblique view of the anterior braincase ossifications of the generalized recumbirostran

Huskerpeton englehorni, UNSM 32144, demonstrating an unfinished bone surface at the articulation between the ossified sphenethmoid and the cartilaginous ethmoid; C, left lateral, and;

D, left oblique view of the anterior braincase ossifications of the brachystelechid Carrolla craddocki, modified from Maddin et al., 2011, demonstrating a fully-ossified median ethmoid septum; E, left lateral, and; F, left oblique view of the anterior braincase ossifications of

Brachydectes newberryi, KUVP 49541, demonstrating median ossifications of the ethmoid septum along the medial surfaces of the olfactory fenestrae; G, left lateral, and; H, left oblique view of the anterior braincase ossifications of the hynobiid Hynobius amjiensus, MVZ 231110, demonstrating ossifications of the sphenethmoid but without ossifications within the ethmoid cartilage; I, left lateral, and; J, left oblique view of the anterior braincase ossifications of the sirenid Siren intermedia, MVZ 196215, demonstrating invasion of the ethmoid and surrounding the olfactory fenestrae by the orbitosphenoid; K, left lateral, and; L, left oblique view of the anterior braincase ossifications of the amphiumid Amphiuma tridactylum, MVZ 241480, demonstrating invasion of the columella ethmoidalis by the frontals; M, left lateral, and; N, left oblique view of the anterior braincase ossifications of the proteid Proteus anguiformis, MVZ

47277, demonstrating a novel ossification within the columella ethmoidalis. Scale = 5 mm.

149

The implications of the distinct morphology of cocytinids, and of Brachydectes specifically, are less clear. The emarginated cheek of cocytinids would have housed a massive mame in comparison with all other microsaurs, suggesting an increase in bite. A tradeoff between bite force and cross-sectional area has been shown in modern fossorial reptiles

(Vanhooydonck et al., 2011), so it is possible that the increased mame size anteroposteriorly is compensation for reduced width of the mame. Much of the remainder of cocytinid morphology suggests that cocytinids were under high selection for minimal cross-sectional area, likely due to the constraints of burrowing in consolidated substrate. Similar constraints on cranial cross- sectional area are seen in fossorial amphisbaenids (Gans, 1960), scincids (Rieppel, 1982), snakes

(Olori & Bell, 2012), and other lizards, as well as some fossorial salamanders (Erdman &

Cundall, 1984). The otic capsules contribute substantially to width of the skull, with the cheek flattened directly against the otic capsule and the bony septa between the semicircular canals and utriculus lost, minimizing the size of the otic capsule while retaining a large utricular and saccular region. This is especially evident in the lateral exposure of the horizontal semicircular canal, which is generally enclosed solidly within the bone forming the base of the crista parotica in other microsaurs (Maddin et al., 2011) and early reptiles (Heaton, 1979). Carroll (1991) has suggested that the size of the nasal capsule, eye, and otic capsule are limiting factors in miniaturization in early tetrapods, and similar adaptations have been observed in miniaturized and fossorial snakes (Olori, 2010). The adaptations observed in the otic capsule of Brachydectes appear to corroborate this hypothesis.

4.5.2 Neoteny and Brachydectes

150

Brachydectes and other cocytinids exhibit a suite of characteristics interpreted by some authors as evidence of neoteny in this lineage. Specifically, the well-ossified hyobranchial skeleton, the emarginated cheek, and the presence of median sutures between neural arches have been noted as possible evidence that cocytinids are morphologically comparable with larval

(premetamorphic) anamniotes (Wellstead, 1991; Marjanovic & Laurin, 2008). The morphological study presented here shows that this is likely not the case.

Although Brachydectes does have a fully ossified hyobranchial skeleton, no grooves are present on the surface of the hyobranchial elements. Grooves on the hyobranchial skeleton have been interpreted to be an osteological proxy for the branchial arteries by Schoch & Witzmann

(2011), and thus as evidence of internal gills. The absence, then, of these grooves on the hyobranchial skeleton of Brachydectes suggests an absence of branchial arteries and of internal gills in this taxon. This is not surprising in an amniote, but is not consistent with larval anamniotes, which generally do preserve the branchial arteries (Schoch & Witzmann, 2011), at least among stem-tetrapods and stem-lissamphibians. Whereas this does not preclude the existence of external gills, the presence of an ossified hyobranchium is not itself substantive evidence in favor of gills, internal or external.

Lack of ossification in the cheek is also not direct evidence of neoteny. As discussed above, the deeply emarginated cheek of Brachydectes appears to be a function of the size of the mame rather than a strict ontogenetic feature, and other osteological proxies of mame size

(coronoid process size and trigeminal nerve foramina size) also support enlargement of this muscle. Increased size of the mame may have permitted greater bite forces, or it may represent compensation for lost mechanical advantage resulting from the anteriorly-canted suspensorium.

Either way, neoteny does not stand as a primary explanation for this morphology.

151

Lack of fusion between right and left neural arches likely is a juvenile character, but this does not necessarily support neoteny. In at least one larger specimen of Brachydectes newberryi studied here (UNSM 32149), the anterior cervical vertebrae do show partial to complete fusion of the neural arches. It is possible that the smaller lysorophian fossils currently known, including the material studied here, represent immature specimens. Alternately, this could reflect true paedomorphosis of this specific characteristic, but this does not support the hypothesis that

Brachydectes morphology is indicative of true neoteny.

4.5.3 Summary of Brachydectes Morphology and Ecology

Contra previous workers (e.g. Wellstead, 1991), Brachydectes appears to have been primarily fossorial, as evidenced by the highly reinforced braincase. Skull shape and robustness of the braincase is consistent with morphology seen in extant squamates and caudates that engage primarily in headfirst burrowing in moist, consolidated sediments. The morphology of the sphenoid and ethmoid regions of Brachydectes may specifically represent adaptations to resist downward force on the skull roof in the region of the frontal and parietal bones. This is consistent with similar anatomy in “round-headed” amphisbaenids (Gans, 1960; Kearney, 2003) and head adpression marks on the surface of burrow structures containing Brachydectes skeletons (Hembree et al., 2004, 2005). It is unclear whether Brachydectes was aquatic or semiaquatic, but fossorial and semiaquatic lifestyles are observed in some squamates (Semlitsch et al., 1988) as well as some caudates (Reilly & Altig, 1996). Brachydectes, however, lacked internal gills and probably lacked external gills as well. The presence of skeletons of

Brachydectes in burrow structures may represent seasonal aestivation or may represent dwelling chambers in established burrow systems. Seasonal aestivation is not limited to water-dependent fish and amphibians, and is also seen in some modern reptiles, including turtles (Peterson &

152

Stone, 2000), snakes (Winne et al., 2006), and even crocodilians (Christian et al., 1996); if

Brachydectes burrows are determined to be solely aestivation structures, this does not necessarily indicate retention of a physiology dependent on standing water for reproduction or respiration.

The fact that burrows of Brachydectes differ from lungfish burrows in terms of both distribution and taphonomy within single localities (Hembree et al., 2004) may further support the inference that cocytinid physiology differed from lungfish physiology in key ways.

Brachydectes is substantially larger than most other microsaurs, with the exception of

Euryodus, Pantylus, Micraroter, and Pelodosotis, and is the largest species within the

Cocytinoidea. The skull of Brachydectes is elongated and laterally-compressed in comparison with other microsaurs, with reduction of dermal elements to accommodate musculature and reduction of endochondral bone to accommodate size-constrained sensory structures, most notably the otic capsules. Lower cross-sectional area of the skull and body would have facilitated headfirst burrowing in consolidated sediments, in a similar manner to the situation evident in modern fossorial squamates (Gans, 1960) and caudates (Reilly & Altig, 1996). The reduced limbs and elongate trunk region are consistent with such adaptation.

4.6 Conclusions

Micro-CT assisted study of the braincase of the lepospondyl Brachydectes has clarified the morphology and relationships of this previously enigmatic Permo-Carboniferous tetrapod. A phylogenetic analysis of 59 braincase characters is employed and supports microsaur affinity of

Brachydectes and a reptile affinity of microsaurs both in isolation and when combined into a comprehensive character matrix of early tetrapods. The morphology of Brachydectes does not support the Lepospondyl Hypothesis of lissamphibian origins, or even lepospondyl monophyly.

Characters supporting a microsaur-reptile relationship include a supraoccipital that develops

153

from a single median ossification center, a crista interfenestralis along the median surface of the opisthotic, and a single coronoid in the lower jaw that contributes substantially to the coronoid process. Within microsaurs, Brachydectes is closely related to the Brachystelechidae, a relationship supported by the presence of an ossified columella ethmoidalis, and a robust, pillar- like pila antotica braced against the skull roof. Differences between microsaurs and other early reptiles are primarily associated with fossoriality, including modification of the rostrum for excavating burrows in soil, extensive ossification of the skull roof to withstand compressive forces from headfirst burrowing, elongation of the axial skeleton, and reduction of the limbs.

Abundant squamate and occasional caudate analogues exist for this entire suite of characters, suggesting repeated convergence of fossorial tetrapod morphology and conservation of the fossorial tetrapod niche for over 320 million years.

The morphology of Brachydectes is extreme compared with that of other microsaurs, but lies well within the range of morphologies seen in modern fossorial squamates. Brachydectes differs from other microsaurs in having a greatly emarginated temporal region to accommodate jaw adductor musculature and a laterally compressed skull to reduce cross-sectional area of soil displaced during burrowing. The loss of the characteristic recumbent rostrum of other microsaurs in Brachydectes is coupled with commensurate changes in the reinforcement of the skull roof, suggesting that Brachydectes burrowed employing dorsal adpression of the skull, a mode of burrowing novel for microsaurs but common in various fossorial squamates. The variation in microsaur skull shapes may reflect differences in burrowing substrate preference, with

Brachydectes occupying consolidated soils on the periphery of seasonal wetlands, ostodolepids occupying unconsolidated sandy soils, and other microsaurs occupying intermediate habitats. If so, not only do individual microsaurs demonstrate extreme convergence with various groups of

154

fossorial squamates, but it is also possible that the entire microsaur diversification exploited fossorial reptile niche space in a manner parallel to numerous modern fossorial reptile clades, including amphisbaenids, scincids, gymnophthalmids, gerrhonotids, and snakes.

In this thesis, I introduced Brachydectes in the context of current debates on the origin of modern lissamphibians among Paleozoic tetrapod diversity, as a candidate stem-lissamphibian.

Restudy of Brachydectes using modern techniques tells a very different story. Morphology of the skull, and particularly the morphology of the braincase, of Brachydectes, and microsaurs in general, suggests that the story of Brachydectes is not the story of amphibian origins at all, but rather the story of how reptiles exploited a characteristic niche for the first time.

155

Literature Cited

Ahlberg, P. E. (1991). A re‐examination of sarcopterygian interrelationships, with special

reference to the Porolepiformes.Zoological Journal of the Linnean Society, 103(3), 241-

287.

Anderson, J. S. (2001). The phylogenetic trunk: maximal inclusion of taxa with missing data in

an analysis of the Lepospondyli (Vertebrata, Tetrapoda). Systematic Biology 50(2), 170-

193.

Anderson, J. S. (2002). Revision of the aïstopod genus Phlegethontia (Tetrapoda: Lepospondyli).

Journal of Paleontology, 76(6), 1029-1046.

Anderson, J.S., 2007. Incorporating ontogeny into the matrix: a phylogenetic evaluation of

developmental evidence for the origin of modern amphibians. In Anderson, J.S., and H.-

D. Sues (Eds.) Major Transitions in Vertebrate Evolution (pp. 182-227). Bloomington,

Indiana: Indiana University Press.

Anderson, J. S. (2008). Focal review: the origin (s) of modern amphibians. Evolutionary Biology,

35(4), 231-247.

Anderson, J. S., & Bolt, J. R. (2013). New information on amphibamids (Tetrapoda,

Temnospondyli) from Richards Spur (Fort Sill), Oklahoma. Journal of Vertebrate

Paleontology, 33(3), 553-567.

Anderson, J. S., Carroll, R. L., & Rowe, T. B. (2003). New information on Lethiscus stocki

(Tetrapoda: Lepospondyli: Aistopoda) from high-resolution computed tomography and a

156

phylogenetic analysis of Aistopoda. Canadian Journal of Earth Sciences, 40(8), 1071-

1083.

Anderson, J. S., Reisz, R. R., Scott, D., Fröbisch, N. B., & Sumida, S. S. (2008). A stem

batrachian from the Early Permian of Texas and the origin of frogs and salamanders.

Nature 453(7194), 515-518.

Anderson, J. S., Scott, D., & Reisz, R. R. (2009). Nannaroter mckinziei, a new ostodolepid

‘microsaur’(Tetrapoda, Lepospondyli, Recumbirostra) from the Early Permian of

Richards Spur (Ft. Sill), Oklahoma. Journal of Vertebrate Paleontology, 29(2), 379-388.

Báez, A. M., & Basso, N. G. (1996). The earliest known frogs of the Jurassic of South America:

review and cladistic appraisal of their relationships. Münchner Geowissenschaftliche

Abhandlungen. Reihe A. Geologie und Paläontologie, 30, 131-158.

Báez, A. M., & Nicoli, L. (2008). A New Species of Notobatrachus (Amphibia, Salientia) from

the Middle Jurassic of Northwestern Patagonia. Journal of Paleontology, 82(2), 372-376.

Baird, D. (1965). Paleozoic lepospondyl amphibians. American Zoologist, 5(2), 287-294.

Barros, F. C., Herrel, A., & Kohlsdorf, T. (2011). Head shape evolution in Gymnophthalmidae:

does habitat use constrain the evolution of cranial design in fossorial lizards? Journal of

Evolutionary Biology 24(11): 2423-2433.

Beaumont, E. H. (1977). Cranial morphology of the Loxommatidae (Amphibia:

Labyrinthodontia). Philosophical Transactions of the Royal Society of London. Series B,

Biological Sciences, 29-101.

157

Bemis, W. E., & Northcutt, R. G. (1992). Skin and blood vessels of the snout of the Australian

lungfish, Neoceratodus forsteri, and their significance for interpreting the cosmine of

Devonian lungfishes. Acta Zoologica, 73(2), 115-139.

Berman, D. S. (2000). Origin and early evolution of the amniote occiput. Journal of

Paleontology 74(5):938-956.

Berman, D. S., & Henrici, A. C. (2003). Homology of the astragalus and structure and function

of the tarsus of Diadectidae. Journal of Paleontology, 77(1), 172-188.

Bolt, J. R. (1969). Lissamphibian origins: possible protolissamphibian from the Lower Permian

of Oklahoma. Science, 166(3907), 888-891.

Bolt, J. R., & Rieppel, O. (2009). The holotype skull of Llistrofus pricei Carroll and Gaskill,

1978 (Microsauria: Hapsidopareiontidae). Journal of Paleontology, 83(3), 471-483.

Bolt, J. R., & Wassersug, R. J. (1975). Functional morphology of the skull in Lysorophus; a

snake-like Paleozoic amphibian (Lepospondyli). Paleobiology, 1(3), 320-332.

Bourget, H., & Anderson, J. S. (2011). A new amphibamid (Temnospondyli: Dissorophoidea)

from the Early Permian of Texas. Journal of Vertebrate Paleontology, 31(1), 32-49.

Brainerd, E. L., & Owerkowicz, T. (2006). Functional morphology and evolution of aspiration

breathing in tetrapods. Respiratory Physiology & Neurobiology, 154(1), 73-88.

Brazeau, M. D. (2009). The braincase and jaws of a Devonian ‘acanthodian’and modern

gnathostome origins. Nature, 457(7227), 305-308.

Brazeau, M. D. (2011). Problematic character coding methods in morphology and their

effects. Biological Journal of the Linnean Society,104(3), 489-498.

158

Broom, R., 1918. Observations on the genus Lysorophus Cope. Annals and Magazine of Natural

History 2:232-240.

Buchwitz, M., & Voigt, S. (2010). Peculiar carapace structure of a Triassic chroniosuchian

implies evolutionary shift in trunk flexibility. Journal of Vertebrate Paleontology, 30(6),

1697-1708.

Carroll, R. (1966). Microsaurs from the Westphalian B of Joggins, Nova Scotia. Proceedings of

the Linnean Society of London 177(1):63-97.

Carroll, R. L. (1990). A tiny microsaur from the Lower Permian of Texas: size constraints in

Palaeozoic tetrapods. Palaeontology, 33(4), 893-909.

Carroll, R. L. (1991). Batropetes from the Lower Permian of Europe—a microsaur, not a reptile.

Journal of Vertebrate Paleontology, 11(2), 229-242.

Carroll, R. L. (1998). Cranial anatomy of ophiderpetontid aïstopods: Palaeozoic limbless

amphibians. Zoological Journal of the Linnean Society, 122(1‐2), 143-166.

Carroll, R. L. (2007). The Palaeozoic ancestry of salamanders, frogs and caecilians. Zoological

Journal of the Linnean Society 150(s1):1-140.

Carroll, R. L., & Baird, D. (1968). The Carboniferous amphibian Tuditanus (Eosauravus) and

the distinction between microsaurs and reptiles. American Museum Novitates: 2337.

Carroll, R. L., & Currie, P. J. (1975). Microsaurs as possible apodan ancestors. Zoological

Journal of the Linnean Society, 57(3), 229-247.

Carroll, R. L., & Gaskill, P. (1978). The Order Microsauria (Vol. 126). Memoirs of the American

Philosophical Society (126): 1-208.

159

Case, E.C., 1908. Notes on the skull of Lysorophus tricarinatus. Bulletin of the American

Museum of Natural History 24:531-533.

Chang, S. H., Jobling, S., Brennan, K., & Headon, D. J. (2009). Enhanced Edar signalling has

pleiotropic effects on craniofacial and cutaneous glands. PLoS One, 4(10), e7591.

Christian, K., Green, B., & Kennett, R. (1996). Some physiological consequences of estivation

by freshwater crocodiles, Crocodylus johnstoni. Journal of Herpetology 30(1):1-9.

Clack, J. A. (1998). The neurocranium of Acanthostega gunnari Jarvik and the evolution of the

otic region in tetrapods. Zoological journal of the Linnean Society, 122(1‐2), 61-97.

Clack, J. A. (2003). A new baphetid (stem tetrapod) from the Upper Carboniferous of Tyne and

Wear, UK, and the evolution of the tetrapod occiput. Canadian Journal of Earth Sciences

40(4):483-498.

Clack, J. A., & Finney, S. M. (2005). Pederpes finneyae, an articulated tetrapod from the

Tournaisian of western Scotland. Journal of Systematic Palaeontology, 2(4), 311-346.

Clack, J. A., & Holmes, R. (1988). The braincase of the anthracosaur Archeria crassidisca with

comments on the interrelationships of primitive tetrapods. Palaeontology, 31(1), 85-107.

Clack, J. A., & Milner, A. R. (2009). Morphology and systematics of the Pennsylvanian

amphibian Platyrhinops lyelli (Amphibia: Temnospondyli). Transactions of the Royal

Society of Edinburgh: Earth and Environmental Science, 100(03), 275-295.

Coldiron, R. W. (1978). Acroplous vorax Hotton (Amphibia, Saurerpetontidae) restudied in light

of new material. American Museum novitates; no. 2662.

Cope, E. D. (1868). Synopsis of the extinct Batrachia of North America. Proceedings of the

Academy of Natural Sciences, Philadelphia 1868:208-221.

160

Cope, E. D. (1871). Observations on the extinct batrachian fauna of the Carboniferous of Linton,

Ohio. Proceedings of the American Philosophical Society 12:77.

Cope, E.D. (1875) Check list of North American Batrachia and Reptilia with a systematic list of

the higher groups, and an essay on geographical distribution based on the specimens

contained in the U.S. National Museum. Washington: U.S. Government Printing Office,

104 pp.

Daly, E. (1973). A lower Permian vertebrate fauna from southern Oklahoma. Journal of

Paleontology, 47(3), 562-589.

Dawson, J. W. (1863). Air-breathers of the Coal Period: descriptive account of the remains of

land animals found in the Coal Formation of Nova Scotia. Montreal: Dawson Brothers,

81 pp.

De Beer, S. G. (1937). The Development of the Vertebrate Skull (Vol. 24, pp. +-552). Oxford:

Clarendon Press.

Duellman, W. E., & Trueb, L (1994). Biology of amphibians. Baltimore: Johns Hopkins

University Press.

Englehorn, J., Small, B. J., & Huttenlocker, A. (2008). A redescription of Acroplous vorax

(Temnospondyli: Dvinosauria) based on new specimens from the Early Permian of

Nebraska and Kansas, USA. Journal of Vertebrate Paleontology, 28(2), 291-305.

Erdman, S., & Cundall, D. (1984). The feeding apparatus of the salamander Amphiuma

tridactylum: morphology and behavior. Journal of Morphology, 181(2), 175-204.

161

Evans, S. E., & Borsuk-Bialynicka, M. (1998). A stem-group frog from the Early Triassic of

Poland. Acta Palaeontol Pol, 43(4), 573-580.

Evans, S. E., & Sigogneau‐Russell, D. (2001). A stem‐group caecilian (Lissamphibia:

Gymnophiona) from the Lower Cretaceous of North Africa. Palaeontology, 44(2), 259-

273.

Evans, S. E., Milner, A. R., & Mussett, F. (1988). The earliest known salamanders (Amphibia,

Caudata): a record from the Middle Jurassic of England. Geobios, 21(5), 539-552.

Foreman, B. C., & Martin, L. D. (1988). A review of Paleozoic tetrapod localities of Kansas and

Nebraska. Kansas Geological Survey Guidebook, series, 6, 133-145.

Francis, E.T.B., 1934. The Anatomy of the Salamander. Ithaca, New York: Society for the Study

of Amphibians and Reptiles.

Fröbisch, N. B., Carroll, R. L., & Schoch, R. R. (2007). Limb ossification in the Paleozoic

branchiosaurid Apateon (Temnospondyli) and the early evolution of preaxial dominance

in tetrapod limb development. Evolution & Development 9(1):69-75.

Fröbisch, N. B., & Reisz, R. R. (2008). A new Lower Permian amphibamid (Dissorophoidea,

Temnospondyli) from the fissure fill deposits near Richards Spur, Oklahoma. Journal of

Vertebrate Paleontology, 28(4), 1015-1030.

Fröbisch, N. B., & Schoch, R. R. (2009). Testing the impact of miniaturization on phylogeny:

Paleozoic dissorophoid amphibians.Systematic Biology, 58(3), 312-327.

162

Gans, C. (1960). Studies on amphisbaenids (Amphisbaenia, Reptilia). 1, A taxonomic revision of

the Trogonophinae, and a functional interpretation of the amphisbaenid adaptive pattern.

Bulletin of the AMNH 119(3):129-204.

Gao, K. Q., & Chen, S. (2004). A new frog (Amphibia: Anura) from the Lower Cretaceous of

western Liaoning, China. Cretaceous Research, 25(5), 761-769.

Gardner, N. M., Holliday, C. M., & O’Keefe, F. R. (2010). The braincase of Youngina capensis

(Reptilia, Diapsida): new insights from high-resolution CT scanning of the holotype.

Palaeontologia Electronica, 13(2), 19.

Glienke, S. (2012). A new “microsaur”(Amphibia; Lepospondyli) from the Rotliegend of the

Saar–Palatinate region (Carboniferous/Permian transition; West Germany).

Paläontologische Zeitschrift, 86(3), 297-311.

Glienke, S. (2013). A taxonomic revision of Batropetes (Amphibia, Microsauria) from the

Rotliegend (basal Permian) of Germany. Neues Jahrbuch für Geologie und

Paläontologie-Abhandlungen, 269(1), 73-96.

Gold M.E.L, Brochu C.A, Norell M.A (2014) An Expanded Combined Evidence Approach to

the Gavialis Problem Using Geometric Morphometric Data from Crocodylian Braincases

and Eustachian Systems. PLoS ONE 9(9): e105793

Goswami, A., & Polly, P. D. (2010). The Influence of Modularity on Cranial Morphological

Disparity in Carnivora and Primates (Mammalia). PLoS ONE 5(3): e9517.

Gregory, J. T. (1948). The structure of Cephalerpeton and affinities of the Microsauria.

American Journal of Science, 246(9), 550-568.

163

Gregory, J. T. (1965). Microsaurs and the origin of captorhinomorph reptiles. American

Zoologist, 5(2), 277-286.

Guerra, C., & Montero, R. (2009). The skull of Vanzosaura rubricauda (Squamata:

Gymnophthalmidae). Acta Zoologica, 90(4), 359-371.

Heaton, M.J. (1979). Cranial anatomy of primitive captorhinid reptiles from the late

Pennsylvanian and early Permian Oklahoma and Texas. Oklahoma Geological Survey

Bulletin 127:1-80.

Hembree, D. I., Martin, L. D., & Hasiotis, S. T. (2004). Amphibian burrows and ephemeral

ponds of the Lower Permian Speiser Shale, Kansas: evidence for seasonality in the

midcontinent. Palaeogeography, Palaeoclimatology, Palaeoecology, 203(1), 127-152.

Hembree, D. I., Hasiotis, S. T., & Martin, L. D. (2005). Torridorefugium eskridgensis (new

ichnogenus and ichnospecies): amphibian aestivation burrows from the Lower Permian

Speiser Shale of Kansas. Journal of Paleontology, 79(3), 583-593.

Henrici, A. C., Martens, T., Berman, D. S., & Sumida, S. S. (2011). An ostodolepid

‘microsaur’(Lepospondyli) from the Lower Permian Tambach Formation of central

Germany. Journal of Vertebrate Paleontology, 31(5), 997-1004.

Holmes, R. (1989). The skull and axial skeleton of the Lower Permian anthracosauroid

amphibian Archeria crassidisca Cope. Palaeontographica Abteilung A, 161-206.

Hook, R. W., & Baird, D. (1986). The diamond coal mine of Linton, Ohio, and its

Pennsylvanian-age vertebrates. Journal of Vertebrate Paleontology, 6(2), 174-190.

164

Hook, R. W., & Baird, D. (1993). A new fish and tetrapod assemblage from the Allegheny

Group (late Westphalian, Upper Carboniferous) of eastern Ohio, USA. New research on

Permo-Carboniferous faunas. Compiled by U. Heidtke. Pollichia-Buch, 29, 143-154.

Hotton, N. (1959). Acroplous vorax, a new and unusual labyrinthodont amphibian from the

Kansas Permian. Journal of Paleontology, 33(1), 161-178.

Huttenlocker, A. K., Pardo, J. D., & Small, B. J. 2005. An earliest Permian nonmarine vertebrate

locality from the Eskridge Formation, Nebraska, p. 133-143. In The Nonmarine Permian.

Lucas, S.G., and K.E. Zeigler (Eds.), New Mexico Museum of Natural History and

Science Bulletin 30.

Huttenlocker, A. K., Pardo, J. D., & Small, B. J. (2007). Plemmyradytes shintoni, gen. et sp.

nov., an Early Permian amphibamid (Temnospondyli: Dissorophoidea) from the Eskridge

Formation, Nebraska. Journal of Vertebrate Paleontology, 27(2), 316-328.

Huttenlocker, A. K., Pardo, J. D., Small, B. J., & Anderson, J. S. (2013). Cranial morphology of

recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early

morphological evolution inferred by micro-computed tomography. Journal of Vertebrate

Paleontology, 33(3), 540-552.

Jenkins Jr, F. A., Walsh, D. M., & Carroll, R. L. (2007). Anatomy of Eocaecilia micropodia, a

limbed caecilian of the Early Jurassic. Bulletin of the Museum of Comparative Zoology

158(6):285-365.

Joeckel, R. M. (1991). Paleosol stratigraphy of the Eskridge Formation; Early Permian

pedogenesis and climate in southeastern Nebraska. Journal of Sedimentary Research

61(2):234-255.

165

Kearney, M. (2003). Systematics of the Amphisbaenia (Lepidosauria: Squamata) based on

morphological evidence from recent and fossil forms. Herpetological Monographs,

17(1), 1-74.

Kearney, M., & Stuart, B. L. (2004). Repeated evolution of limblessness and digging heads in

worm lizards revealed by DNA from old bones. Proceedings of the Royal Society of

London. Biological Sciences 271(1549):1677-1683.

Kleinteich, T., Maddin, H. C., Herzen, J., Beckmann, F., & Summers, A. P. (2012). Is solid

always best? Cranial performance in solid and fenestrated caecilian skulls. Journal of

Experimental Biology, 215(5), 833-844.

Klembara, J., Berman, D. S., Henrici, A. C., Ĉerňanský, A., & Werneburg, R. (2006).

Comparison of cranial anatomy and proportions of similarly sized Seymouria

sanjuanensis and Discosauriscus austriacus. Annals of Carnegie Museum, 75(1), 37-49.

Knepton, J. C. (1954). A note on the burrowing habits of the salamander Amphiuma means

means. Copeia 1954(1):68.

Kobayu, D., H. Endo, C. Mitgutsch, G. Suwa, K.C. Catania, C.P.E. Zollikofer, S. Oda, K.

Koyasu, M. Ando, and M.R. Sánchez-Villagra, 2011. Heterochrony and developmental

modularity of cranial osteogenesis in lipotyphlan mammals. EvoDevo 2:21.

Langston, W., & Olson, E. C. (1986). Carrolla craddocki, a new genus and species of microsaur

from the Lower Permian of Texas, Vol. 43. Austin: Pearce-Sellards Series, Texas

Memorial Museum, University of Texas at Austin. pp.1-20.

Laurin, M., & Reisz, R. R. (1995). A reevaluation of early amniote phylogeny. Zoological

Journal of the Linnean Society, 113(2), 165-223.

166

Laurin, M., & Reisz, R. R. (1999). A new study of Solenodonsaurus janenschi, and a

reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of

Earth Sciences, 36(8), 1239-1255.

Lee, D. C., & Bryant, H. N. (1999). A reconsideration of the coding of inapplicable characters:

assumptions and problems. Cladistics, 15(4), 373-378.

Lemell, P., Lemell, C., Snelderwaard, P., Gumpenberger, M., Wochesländer, R., & Weisgram, J.

(2002). Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae). Journal of

Experimental Biology, 205(10), 1495-1506.

Maddin, H. C., Olori, J. C., & Anderson, J. S. (2011). A redescription of Carrolla craddocki

(Lepospondyli: Brachystelechidae) based on high‐resolution CT, and the impacts of

miniaturization and fossoriality on morphology. Journal of Morphology, 272(6), 722-

743.

Maddin, H. C., & Anderson, J. S. (2012). Evolution of the amphibian ear with implications for

lissamphibian phylogeny: insight gained from the caecilian inner ear. Fieldiana Life and

Earth Sciences, 59-76.

Maddin, H. C., Fröbisch, N. B., Evans, D. C., & Milner, A. R. (2013). Reappraisal of the Early

Permian amphibamid Tersomius texensis and some referred material. Comptes Rendus

Palevol, 12(7), 447-461.

Maddin, H. C., Jenkins Jr, F. A., & Anderson, J. S. (2012). The braincase of Eocaecilia

micropodia (Lissamphibia, Gymnophiona) and the origin of caecilians. PloS One, 7(12),

e50743.

167

Maddin, H. C., Russell, A. P., & Anderson, J. S. (2012). Phylogenetic implications of the

morphology of the braincase of caecilian amphibians (Gymnophiona). Zoological

Journal of the Linnean Society, 166(1), 160-201.

Maddison, W. P. (1993). Missing data versus missing characters in phylogenetic analysis.

Systematic Biology, 42(2), 576-581.

Marjanović, D., & Laurin, M. (2007). Fossils, molecules, divergence times, and the origin of

lissamphibians. Systematic Biology, 56(3), 369-388.

Marjanović, D., & Laurin, M. (2008). A reevaluation of the evidence supporting an unorthodox

hypothesis on the origin of extant amphibians. Contributions to Zoology, 77(3).

Marjanovic, D., & Laurin, M. (2013). The origin (s) of extant amphibians: a review with

emphasis on the “lepospondyl hypothesis”. Geodiversitas, 35(1), 207-272.

McAllister, J. A. (1991). The lungfish Gnathorhiza and its burrows from the Permian of Kansas

(Doctoral dissertation, University of Kansas, Systematics and Ecology).

McGowan, G. J. (2002). Albanerpetontid amphibians from the Lower Cretaceous of Spain and

Italy: a description and reconsideration of their systematics. Zoological Journal of the

Linnean Society, 135(1), 1-32.

Metzger, K. A., & Herrel, A. (2005). Correlations between lizard cranial shape and diet: a

quantitative, phylogenetically informed analysis.Biological Journal of the Linnean

Society, 86(4), 433-466.

168

Meyer, T. E., & Anderson, J. S. (2013). Tarsal fusion and the formation of the astragalus in

Hylonomus lyelli, the earliest amniote, and other early tetrapods. Journal of Vertebrate

Paleontology, 33(2), 488-492.

Moodie, R.L., 1909. The Lysorophidae. American Naturalist 43:116-119.

Müller, J., & Reisz, R. R. (2006). The phylogeny of early eureptiles: comparing parsimony and

Bayesian approaches in the investigation of a basal fossil clade. Systematic Biology,

55(3), 503-511.

Müller, J., J. Sterli, and J. Anquentin, 2011. Carotid circulation in amniotes and its implications

for turtle relationships. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen

261:289-297.

Nussbaum, R.A., 1983. The evolution of a unique dual jaw-closing mechanism in caecilians

(Amphibia: Gymnophiona) and its bearing on caecilian ancestry. Zoological Journal of

London 199:545-554.

O'Keefe, F. R., & Wagner, P. J. (2001). Inferring and testing hypotheses of cladistic character

dependence by using character compatibility. Systematic Biology 50(5), 657-675.

Olori, J. C. (2010). Digital endocasts of the cranial cavity and osseous labyrinth of the burrowing

snake Uropeltis woodmasoni (Alethinophidia: Uropeltidae). Copeia, 2010(1), 14-26.

Olori, J. C. (2013). Ontogenetic sequence reconstruction and sequence polymorphism in extinct

taxa: an example using early tetrapods (Tetrapoda: Lepospondyli). Paleobiology, 39(3),

400-428.

169

Olori, J. C. (2013). Morphometric analysis of skeletal growth in the lepospondyls Microbrachis

pelikani and Hyloplesion longicostatum (Tetrapoda, Lepospondyli). Journal of

Vertebrate Paleontology, 33(6), 1300-1320.

Olori, J. C., & Bell, C. J. (2012). Comparative skull morphology of uropeltid snakes

(Alethinophidia: Uropeltidae) with special reference to disarticulated elements and

variation. PloS One, 7(3), e32450.

Olson, E.C., and K. Bolles, 1975. Permo-Carboniferous fresh water burrows. Fieldiana Geology

33:271-290.

Paton, R. L., Smithson, T. R., & Clack, J. A. (1999). An amniote-like skeleton from the early

Carboniferous of Scotland. Nature 398(6727):508-513.

Peterson, C. C., & Stone, P. A. (2000). Physiological Capacity for Estivation of the Sonoran

Mud Turtle, Kinosternon sonoriense. Copeia, 2000(3), 684-700.

Pierce, S. E., Angielczyk, K. D., & Rayfield, E. J. (2008). Patterns of morphospace occupation

and mechanical performance in extant crocodilian skulls: a combined geometric

morphometric and finite element modeling approach. Journal of Morphology, 269(7),

840.

Polley, B. P., & Reisz, R. R. (2011). A new Lower Permian trematopid (Temnospondyli:

Dissorophoidea) from Richards Spur, Oklahoma. Zoological Journal of the Linnean

Society, 161(4), 789-815.

Protas, M., Tabansky, I., Conrad, M., Gross, J. B., Vidal, O., Tabin, C. J., & Borowsky, R.

(2008). Multi‐trait evolution in a cave fish, Astyanax mexicanus. Evolution &

Development, 10(2), 196-209.

170

Rage, J. C., & Rocek, Z. (1989). Redescription of Triadobatrachus massinoti (Piveteau, 1936) an

anuran amphibian from the early Triassic. Palaeontographica A, 206, 1-16.

Reilly, S. M., & Altig, R. (1996). Cranial ontogeny in Siren intermedia (Caudata: Sirenidae):

paedomorphic, metamorphic, and novel patterns of heterochrony. Copeia 1996(1):29-41.

Reisz, R. R., & Modesto, S. P. (1996). Archerpeton anthracos from the Joggins Formation of

Nova Scotia: a microsaur, not a reptile. Canadian Journal of Earth Sciences, 33(5), 703-

709.

Rieppel, O. (1981). The skull and the jaw adductor musculature in some burrowing scincomorph

lizards of the genera Acontias, Typhlosaurus and Feylinia. Journal of Zoology, 195(4),

493-528.

Rieppel, O., 1993. Studies on skeleton formation in reptiles. V. Patterns of ossification in the

skeleton of Alligator mississippiensis Daudin (Reptilia, Crocodylia). Zoological Journal

of the Linnean Society 109:301-325.

Romer, A.S., 1969. The cranial anatomy of the Permian amphibian Pantylus. Breviora: Museum

of Comparative Zoology 314:1-37.

Roscito, J. G., & Rodrigues, M. T. (2012). Skeletal development in the fossorial

gymnophthalmids Calyptommatus sinebrachiatus and Nothobachia ablephara. Zoology,

115(5), 289-301.

Rose, C.S. 2003. The developmental morphology of salamander skulls. In: Amphibian Biology,

Vol. 5. Osteology, H. Heatwole and M Davies, ed., Australia: Surrey Beatty and Sons

Pty. Ltd., pp. 1686-1783.

171

Ruta, M., & Coates, M. I. (2007). Dates, nodes and character conflict: addressing the

lissamphibian origin problem. Journal of Systematic Palaeontology, 5(1), 69-122.

Ruta, M., Jeffery, J. E., & Coates, M. I. (2003). A supertree of early tetrapods. Proceedings of

the Royal Society of London. Series B: Biological Sciences, 270(1532), 2507-2516.

Sawin, R. S., Franseen, E. K., West, R. R., Ludvigson, G. A., & Watney, W. L. (2008).

Clarification and changes in Permian stratigraphic nomenclature in Kansas. Kansas

Geological Survey.

Schoch, R. R. (2014). Life cycles, plasticity and palaeoecology in temnospondyl amphibians.

Palaeontology, 57(3), 517-529.

Schoch, R. R., & Carroll, R. L. (2003). Ontogenetic evidence for the Paleozoic ancestry of

salamanders. Evolution & Development 5(3):314-324.

Schoch, R. R., & Rubidge, B. S. (2005). The amphibamid Micropholis from the Lystrosaurus

assemblage zone of South Africa. Journal of Vertebrate Paleontology, 25(3), 502-522.

Schoch, R. R., & Fröbisch, N. (2006). Metamorphosis and neoteny: alternative pathways in an

extinct amphibian clade. Evolution, 60(7), 1467-1475.

Schoch, R. R., & Witzmann, F. (2011). Bystrow’s Paradox–gills, fossils, and the fish‐to‐tetrapod

transition. Acta Zoologica, 92(3), 251-265.

Semlitsch, R. D., Pechmann, J. H., & Gibbons, J. W. (1988). Annual emergence of juvenile mud

snakes (Farancia abacura) at aquatic habitats. Copeia 1988:243-245.

Shishkin, M. A. (1968). On the cranial arterial system of the labyrinthodonts. Acta Zoologica,

49(1‐2), 1-22.

172

Shishkin, M. A. (2000). Mesozoic amphibians from Mongolia and the Central Asiatic republics.

In: M. J. Benton, M. A. Shishkin, D. M. Unwin and E. N. Kurochkin (Eds.). The age of

dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge: 297-308.

Shubin, N. H., & Jenkins, F. A. (1995). An early Jurassic jumping frog. Nature, 377(6544), 49-

52.

Sigurdsen, T. (2008). The otic region of Doleserpeton (Temnospondyli) and its implications for

the evolutionary origin of frogs. Zoological Journal of the Linnean Society, 154(4), 738-

751.

Sigurdsen, T., & Bolt, J. R. (2010). The Lower Permian amphibamid Doleserpeton

(Temnospondyli: Dissorophoidea), the interrelationships of amphibamids, and the origin

of modern amphibians. Journal of Vertebrate Paleontology, 30(5), 1360-1377.

Sigurdsen, T., & Green, D. M. (2011). The origin of modern amphibians: a re‐

evaluation. Zoological Journal of the Linnean Society, 162(2), 457-469.

Skutschas, P. P., & Krasnolutskii, S. A. (2011). A new genus and species of basal salamanders

from the Middle Jurassic of Western Siberia, Russia. Proc Zool Inst RAS (Vol. 315, pp.

167-175).

Skutschas, P., & Martin, T. (2011). Cranial anatomy of the stem salamander Kokartus

honorarius (Amphibia: Caudata) from the Middle Jurassic of Kyrgyzstan. Zoological

Journal of the Linnean Society, 161(4), 816-838.

Smithson, T. R. (1982). The cranial morphology of Greererpeton burkemorani Romer

(Amphibia: Temnospondyli). Zoological Journal of the Linnean Society, 76(1), 29-90.

173

Smith, K. K. (1984). The use of the tongue and hyoid apparatus during feeding in lizards

(Ctenosaura similis and Tupinambis nigropunctatus). Journal of Zoology, 202(1), 115-

143.

Smithson, T. R. 1982. The cranial morphology of Greererpeton burkemorani Romer (Amphibia:

Temnospondyli). Zoological Journal of the Linnean Society 76(1):29-90.

Sollas, W. J. (1920). On the Structure of Lysorophus, as Exposed by Serial Sections.

Philosophical Transactions of the Royal Society of London. Series B, Containing Papers

of a Biological Character, 209(360-371), 481-527.

Steen, M. C. (1934). The amphibian fauna from the South Joggins. Nova Scotia. Proceedings of

the Zoological Society of London 104(3):465-504.

Strong, R. M. (1925). The order, time, and rate of ossification of the albino rat (Mus norvegicus

albinus) skeleton. American Journal of Anatomy, 36(2), 313-355.

Valenta, T., Hausmann, G., & Basler, K. (2012). The many faces and functions of β‐catenin. The

EMBO Journal, 31(12), 2714-2736.

Vallin, G., & Laurin, M. (2004). Cranial morphology and affinities of Microbrachis, and a

reappraisal of the phylogeny and lifestyle of the first amphibians. Journal of Vertebrate

Paleontology, 24(1), 56-72.

Vanhooydonck, B., Boistel, R., Fernandez, V., & Herrel, A. (2011). Push and bite: trade‐offs

between burrowing and biting in a burrowing skink (Acontias percivali). Biological

Journal of the Linnean Society, 102(1), 91-99.

174

Vaughn, P. P. (1962). The Paleozoic microsaurs as close relatives of reptiles, again. American

Midland Naturalist, 79-84.

Warren, A. A., & Hutchinson, M. N. (1983). The last labyrinthodont? A new brachyopoid

(Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of

Queensland, Australia. Philosophical Transactions of the Royal Society of London. B,

Biological Sciences, 303(1113), 1-62.

Wellstead, C.F., 1982. A Lower Carboniferous aïstopod amphibian from Scotland.

Palaeontology 25:193-208.

Wellstead, C. F. (1991). Taxonomic revision of the Lysorophia, Permo-Carboniferous

lepospondyl amphibians. Bulletin of the AMNH 209:1-90.

White, T. E. 1939. Osteology of Seymouria baylorensis Broili. Bulletin of the Museum of

Comparative Zoology, Harvard University, 85:325-409.

Williston, S.W., 1908. Lysorophus, a Permian urodele. Biological Bulletin 15(5):229-240.

Winne, C. T., Willson, J. D., & Gibbons, J. W. (2006). Income breeding allows an aquatic snake

Seminatrix pygaea to reproduce normally following prolonged drought‐induced

aestivation. Journal of Animal Ecology, 75(6), 1352-1360.

Yates, A.M., and A.A. Warren, 2000. The phylogeny of ‘higher’ temnospondyls (Vertebrata:

Choanata) and its implications for the monophyly and origins of the Stereospondyli.

Zoological Journal of the Linnean Society 128:77-121.

175

Appendix A: Character Diagnoses for Unmodified and ST/T Datasets

1. Basal Skull Length

0 >70mm

1 70mm

2 50-70mm

3 50 70mm

4 30-50mm

5 30 50mm

6 <30mm

7 30mm

2. Skull trunk

0 0.45

1 0.30 0.45

2 0.20 0.29

3 0.20

3. Skull proportions

0 longer than wide

1 wider than long

176

4. Intertemporal

0 present

1 absent

5. Supratemporal

0 present

1 absent

6. ST exposure on occiput

0 absent

1 present

7. Tabular postorbital

0 absent

1 Present

8. T PF

0 absent

1 present

9. Postfrontal shape

0 broadly quadrangular

1 falciform

177

10. Squamosal Tabular

0 absent

1 present

2 fused

11. Squamosal Temporal area

0 weakly overlapping

1 sutural

12. Lacrimal prefrontal suture

0 simple butt joint

1 interdigitating

2 prefrontal broadly underplates lacrimal

13. Lacrimal

0 present

1 absent

14. L to naris

0 present

1 absent

15. L to orbit

178

0 absent

1 present

16. lacrimal orbital processes

0 only ventral present

1 dorsal and ventral present

2 neither present

17. lacrimal jugal contact

0 present

1 absent

18. Quadratojugal

0 present

1 absent

19. Quadratojugal Jugal contact

0 present

1 absent

20. Quadratojugal Maxillary contact

0 present

1 absent

179

21. Frontals

0 paired

1 fused

22. Frontal into orbit

0 no

1 yes

23. Anterior laterally flaring frontals

0 absent

1 present

24. Nasals

0 present

1 absent

25. Narial flange

0 absent

1 present

26. alary processes of premax

0 absent

1 present

180

27. Internarial fontanelle

0 absent

1 present

28. Septomaxilla

0 ossified

1 unossified

29. Prefrontal into external naris

0 distant from

1 near

2 present

30. external naris in dorsal view

0 exposed

1 not exposed

31. External naris shape

0 circular

1 posteriorly extended, along L-PF suture

2 posteriorly extended excavation of L only

32. dorsal exposure of premax

181

0 broad

1 narrow

2 none

33. dorsal shape of skull

0 triangular

1 diamond

2 rounded

34. Posterior skull margin

0 concave

1 straight

2 convex

3 undulating.

35. snout shape

0 blunt

1 pointed

36. snout length

0 short

1 long

182

37. Q internal flange of Sq

0 absent

1 present

38. otic notch presence

0 present

1 absent

39. Large otic notch approaching orbit

0 absent

1 intermediate

2 close

40. otic notch structure

0 open posteriorly

1 closed posteriorly

41. semilunar flange of supratempor

0 absent

1 present

42. supratympanic flange

0 absent

183

1 present "trematopid"

2 present “dissorophid”

43. supratympanic shelf

0 absent

1 present

44. raised orbital rim

0 absent

1 present

45. Postorbital

0 present

1 absent

46. J PO interfingered processes

0 absent

1 present

47. PO in orbital margin

0 present

1 absent

48. shape of postorbital

184

0 irregular trapezoid

1 triangular, apex caudal

49. Palpebral ossifications

0 absent

1 mosaic of bone plates present in orbit

50. Parietal postorbital contact

0 absent

1 present

51. parietal squamosal contact

0 absent

1 present

52. parietal tabular contact

0 absent

1 present

53. postparietal fusion

0 paired

1 fused

2 absent

185

54. parietal foramen

0 present

1 absent

55. postparietal size

0 moderate

1 large

56. postparietal squamosal contact

0 absent

1 present

57. postparietal length

0 large, quadrangular

1 abbreviated anteroposteriorly, elongate lateral rectangle

58. squamosal jugal contact

0 present

1 absent

59. Tabular

0 present

1 absent

186

60. Posterolateral projection from lateral margin of tabular above squamosal embayment

0 absent

1 present

61. Tabular horns

0 absent

1 present

62. Tabular horns shape

0 parallel or slightly divergent

1 widely divergent

63. Sq forms base of tabular horn

0 absent

1 present

64. Lateral line canal grooves

0 present

1 absent

65. Dermal sculpturing

0 circular pits

1 shallow ridges and grooves

187

2 little to none

66. premaxilla anterior margin

0 vertical

1 overturned

67. Maxilla into orbit

0 no

1 yes

68. Maxilla into external naris

0 present

1 absent

69. Maxilla entire ventral naris

0 absent

1 present

70. maxilla

0 longer than palatine

1 shorter than palatine

71. marginal teeth orientation

0 vertical

188

1 turned medially

72. marginal teeth largest anterior

0 absent

1 present

73. marginal teeth shape

0 pointed pegs

1 blunt pegs

2 large cones

74. Number of premax teeth

0 >=10

1 5-9

2 <5

75. Number of max teeth

0 >=30

1 20-29

2 15-19

3 <15

76. teeth laterally compressed

189

0 no

1 yes

77. Enlarged teeth mid toothrow

0 absent

1 present

78. teeth

0 simple points

1 multiple cusps

79. Multiple Cusp Orientation

0 Labio-lingual

1 antero-posterior

80. Enamel fluting

0 absent

1 present

81. labyrinthine in folding

0 present

1 absent

82. jaw articulation

190

0 posterior to occiput

1 even with occiput

2 anterior to occiput

3 far anterior (>20% BSL)

83. Internal nares

0 widely separated

1 narrowly separated

84. Palatal teeth presence

0 present

1 absent

85. Palatine teeth

0 single pit pairs

1 multiple in rows

2 multiple random

86. LEP

0 absent

1 present

87. Anterior palatine

191

0 short anteromedial process articulating with vomer at choana

1 long anteromedial process more medial than lateral

2 palatine absent

88. vomerine teeth

0 present

1 absent

89. Vomer teeth

0 single pit pairs

1 Multiple in rows

2 Multiple random

90. denticles on pterygoid

0 present

1 absent

91. teeth on pterygoid

0 absent

1 present

92. tooth pedicely

0 absent

192

1 present

93. denticles on vomers

0 present

1 absent

94. denticles on palatines

0 present

1 absent

95. denticles on parasphenoid

0 present

1 absent

96. Palatal teeth size

0 larger than marginals

1 equal to marginals

2 smaller than marginals

97. parasphenoid

0 medial of stapes

1 under footplate of stapes

98. interpterygoid vaccuities

193

0 narrow closed

1 wide

2 fused at midline

99. pterygoids contact anteriorly

0 present

1 absent

100. Pterygoid palatine suture

0 present

1 absent

101. Pterygoid vomer contact

0 present

1 absent

102. lat process of pt into posttemp

0 absent

1 present

103. ectopterygoid

0 present lacking fang pit pair

1 present with fang pit pair

194

104. Ectopterygoid palatine width

0 wider than maxilla

1 narrower than maxilla

105. pharangeobranchial pouches

0 absent

1 present

106. dentary

0 long

1 short

107. dentary forms coronoid process

0 absent

1 present

108. surangular

0 normal

1 reduced

2 absent

109. angular

0 narrow

195

1 deep

110. number of splenals

0 2

1 1

2 0

111. splenal exposed laterally

0 present

1 absent

112. meckelian fossae

0 2 or more

1 1

2 0

113. Ventral border of Meckel s foss

0 splenal

1 angular

114. retroarticular process presence

0 absent

1 present

196

115. retroarticular process shape

0 straight

1 hooked

116. articulation to tooth row

0 above

1 equal

2 below

117. angular extends to lat view

0 posterior tooth row

1 middle of tooth row

118. number of coronoids

0 3

1 2

2 1

3 0

119. coronoid teeth or denticle presence

0 present

1 absent

197

120. coronoid teeth size

0 larger than marginals

1 equal to marginals

2 smaller than marginals

121. symphysis

0 dentary and splenal

1 dentary alone

122. jaw sculpture

0 present

1 absent

123. ossified hyoids

0 present

1 absent

124. Gill Osteoderms

0 absent

1 present noninterdigitating

2 toothed interdigitating rakers

125. parahyoid

198

0 absent

1 present

126. number of accessory articulation

0 0

1 1

2 2 or more

127. number of presacrals

0 25 35

1 20 24

2 35

3 20

128. vertebral development

0 arches then centra

1 centra and arches simultaneously

129. caudal processes btw depression

0 absent

1 present

130. trunk intercentra

199

0 present

1 absent

131. trunk neural arch to centrum

0 loosely articulated

1 sutured

2 fused

132. base of neural spine

0 equal to or wider than haemal

1 smaller than haemal spine

133. height of neural spines

0 even

1 alternating

134. Dermal armor associated with neural arches

0 Absent

1 Present

135. neural spine shape lat

0 ant post sides parallel rect

1 non parallel triangular

200

136. Neural spine lateral suface

0 smooth

1 crenulated

137. Pleurocentra

0 paired rhachitomous

1 closely approaching ventrally

2 fused dominant weight bearing element

138. haemal arch presence

0 present

1 absent

139. haemal arch fusion

0 loosely articulated intercentr

1 fused to mid length of centrum

140. haemal arch length

0 longer than or equal to neurals

1 shorter than neurals

141. haemal accessory articulations

0 none

201

1 one

2 two

142. haemal arch shape

0 non parallel triangular

1 parallel rectangular

143. tail termination

0 tapers

1 deep with sudden end

144. Tail length

0 elongate equal to or exceeding trunk and skull length

1 forshortened markedly shorter than trunk

145. trunk arches

0 paired

1 fused

146. spinal nerve foramina

0 absent

1 present

147. extended transverse processes

202

0 absent

1 present

148. transverse process

0 on arch pedicle

1 on centrum

149. atlas axis intercentra

0 present

1 absent

150. Atlas Anterior centrum

0 same size as posterior

1 laterally expanded

151. atlas centrum

0 multipartite

1 single notochordal

2 single odontoid

152. atlas neural arch centrum fusion

0 loosely articulated

1 sutured to centrum

203

2 fused to centrum

153. atlas parapophyses

0 on centrum

1 on transverse process

2 absent

154. atlas neural arch midline fusion

0 paired

1 sutured at midline

2 fused at midline

155. atlas acessory articulation

0 absent

1 zygosphene

2 zygantra

156. Proatlantes

0 present

1 absent

157. second cervical arch

0 expanded to more posterior

204

1 equal to more posterior

2 shorter than more posterior

158. atlas ribs

0 one pair

1 two pairs

2 absent

159. cervical rib distal shape

0 spatulate

1 pointed

160. ribs anterior to sacrum

0 short

1 long

161. Ribs

0 elongated and sometimes curved

1 straight

2 short simple rod

162. Costal Process at rib head

0 absent

205

1 present

163. number of sacrals

0 1

1 2

2 3

164. sacral parapophysis

0 on centrum

1 on transverse process

165. number pairs of caudal ribs

0 5 or more

1 4

2 3

3 2 or fewer

166. interclavicle posterior stem length

0 no or short

1 long

167. interclavicle posterior stem breadth

0 wide

206

1 narrow

168. interclavicle shape

0 diamond shaped

1 t shaped

169. interclavicle anterior plate

0 broad

1 narrow

170. interclavicle shape diamond

0 broad diamond

1 narrow diamond

171. interclavicle anterior fimbrati

0 present

1 absent

172. interclavicle sculpture

0 present

1 absent

173. Cleithrum head dorsal extent

0 aligned along anterior rim of scapula

207

1 posterodorsally enlarged head wrapping around dorsal scapula

174. Cleithrum head size and shape

0 dorsally greatly expanded much wider than shaft

1 simple rod without or slight dorsal expansion

175. Cleithrum ossification

0 ossified

1 unossified

176. cleithrum overall shape

0 rounded or pointed dorsally

1 t or y shaped

177. proximal clavicle blades

0 widely separate

1 articulate medially

2 interdigitate

178. supraglenoid foramen

0 present

1 absent

179. number coracoid foramina

208

0 none

1 1

2 2

180. scapulocoracoid occification

0 both

1 scapula only

2 absent

181. entepicondylar foramen

0 present

1 absent

182. torsion in humerus

0 absent

1 less than 80 degrees

2 more than 80 degrees

183. deltapectoral crest

0 weak

1 intermediate

2 prominent

209

184. Supinator process

0 absent

1 present

185. humerus length

0 long 4 trunk centra

1 short

186. radius humerus

0 0.7

1 0.5 0.7

2 0.5

187. olecranon process

0 unossified

1 ossified

188. carpals

0 fully or partially ossified

1 unossified

189. basale commune

0 absent

210

1 present

190. number digits manus

0 5 or more

1 4

2 3

191. pelvis

0 fused

1 sutured

2 poorly ossified

192. Anteriorly inclined ilium

0 absent

1 present

193. illiac blade

0 2 dorsal processes

1 narrowly bifurcate

2 single blade

194. internal trochanter articulatio

0 disctinct

211

1 continuous

195. femoral shaft

0 robust

1 slender

196. femur

0 long

1 short

197. tarsals

0 ossified

1 unossified

198. elongate tibiale and fibulare

0 absent

1 present

199. number of distal tarsals

0 6

1 5 or fewer

200. astragalus

0 absent

212

1 present

201. number of digits pes

0 5 or more

1 4 or less

202. dorsal margin of splenial only contacts first coronoid

0 absent

1 present

203. postparietal lappet

0 mostly exposed posteriorly

1 equal posteriorly and dorsally

2 mostly exposed dorsally

204. cheek emargination

0 absent

1 present

205. Parietal anterior waisting

0 absent

1 present

206. Parietal width relative to frontal

213

0 greater

1 equal or less

207. Trabecula cranii

0 Without significant median fusion posterior to solum nasi (platytrabic)

1 fused medially posterior to solum nasi to form elongate trabecula communis

(tropitrabic)

208. Dorsal trabeculae

0 dorsal trabeculae provide dorsolateral bridge between sphenoid region and nasal

capsule

1 dorsal trabeculae absent or incomplete, no dosolateal bridge between sphenoid region

and nasal capsule

209. Ossification between optic foramen and pila antotica

0 ossification complete between optic foramen and pila antotica

1 pila metoptica and associated cartilaginous taeniae unossified

210. Ossification within columella ethmoidalis

0 absent

1 present

211. Path of profundus branch of trigeminal nerve

214

0 enclosed in lateral wall of sphenoid region of braincase and exits laterally via series of

small foramina

1 extramural

212. Foramina for optic nerve and trigeminal nerve

0 confluent

1 widely separate

213. Lateral head vein

0 No distinct foramen for lateral head vein

1 Distinct foramen within the antotic fissure serving the lateral head vein

214. Anterior extent of cultriform process of parasphenoid

0 cultriform process extends to anterior margin of sphenethmoid

1 cultriform process extends far anterior to sphenethmoid

2 cultriform process does not reach anterior margin of sphenethmoid

215. Olfactory bulbs

0 narrow

1 endocasts swollen, leaving considerable impressions in lateral and ventral wall of

sphenoid region and in ventral surface of frontal

216. Flange from skull roof articulating with sphenethmoid

0 absent

215

1 present on frontal and parietal

2 present on frontal only

217. Descending lamina of parietal invades medial orbital wall between 'pleurosphenoid' and

'sphenethmoid' elements

0 no

1 yes

218. Foramen for oculomotor nerve

0 exits braincase far dorsal to foramen for optic nerve

1 exits braincase at or below optic nerve

219. Intermaxillary fossa

0 present

1 absent

220. Intermaxillary fossa

0 paired

1 unpaired

221. Sphenethmoid forms interorbital septum

0 no

1 yes

222. Anterior extent of cultriform process along palate

216

0 cultriform process extends anteriorly to level of posterior margin of choana

1 cultriform process dramatically shortened, barely reaching the level of the posterior

margin of the orbit

223. Sutural contact between cultriform process of parasphenoid and vomer

0 no

1 yes

224. Lateral wall of the nasal capsule underplated by lateral processes of the vomer and palatine

0 no

1 yes

225. Cultriform process vaulted high above palatal surface

0 no

1 yes

226. Posterior extent of parasphenoid beneath braincase

0 floors sphenoid region only

1 floors sphenoid and otic region

2 floors sphenoid, otic, and occipital regions

227. Basal tubera

0 present, with significant endochondral contribution

1 present, with contribution of parasphenoid only

217

2 absent

228. Path of common internal carotid artery

0 enters basisphenoid directly posterior to basal tubera

1 follows vidian sulcus along posterior surface of basal plate of parasphenoid, enters

parasphenoid via vidian canal in basal plate of parasphenoid, divides into cerebral and

palatal branches after entering parasphenoid

2 follows vidian sulcus along posterior surface of basal plate of parasphenoid or lateral

wall of braincase, divides into cerebral and palatal branches prior to entering the skull

229. Bucohypophyseal foramen in parasphenoid

0 open

1 absent

230. Morphology of pila antotica

0 pila antotica is a thin, broad sheet

1 pila antotica is a robust dorsoventral pillar bracing the skull roof against the palate

231. Basicranial fissure

0 present

1 absent

232. Location of vidian sulcus

0 along ventral surface of braincase

218

1 along lateral surface of braincase

233. Basipterygoid joint

0 epipterygoid comprises entire conus recessus

1 substantial contribution to conus recessus by pterygoid

2 conus recessus comprised entirely of pterygoid without epipterygoid participation

3 pterygoid and parasphenoid broadly sutured without development of a conus recessus

234. Hypophyseal fossa

0 single unpaired sulcus

1 pairedsulci divided medially by ridge originating on dorsum sellae

235. Bone flanking the dorsum sellae

0 concurrent with fully ossified lateral skull roof

1 subparallel with sagittal plane ('pleurosphenoid')

2 strongly oblique to or perpendicular to sagittal plane ('laterosphenoid')

3 restricted to dorsum sellae only

236. Basal plate of parasphenoid

0 roughly quadrangular, basipterygoid articulations narrowly spaced

1 rectangular laterally, anteroposteriorly narrow, basipterygoid articulations distant

237. Sphenethmoid

219

0 ossified

1 unossified

238. Ossification within the synotic tectum

0 synotic tectum massively coossified with otic capsules

1 supraoccipital paired at some point in ontogeny

2 supraoccipital unpaired throughout ontogeny

3 no supraoccipital bone; synotic tectum invaded by dorsal processes of exoccipitals

239. Median ascending process of supraoccipital

0 absent

1 present

240. Lateral ascending processses of the supraoccipital

0 absent

1 present

241. Margin of fenestra vestibuli

0 parasphenoid excluded by neurocranial elements (basisphenoid and basioccipital)

1 parasphenoid contributes to anteroventral margin of fenestra vestibuli

2 parasphenoid floors entire fenestra vestibuli

3 Ossification of otic capsule surrounds entire fenestra vestibuli

220

242. Crista interfenestralis

0 crista interfenestralis absent

1 crista interfenestralis present

243. Morphology of crista parotica

0 crista parotica meets exoccipitals only, forming lateral wall of posttemporal fossa but

not bracing against dermal skull

1 crista parotica drawn out dorsolaterally into paroccipital process that contacts the

tabular

2 crista parotica drawn out laterally into paroccipital process that contacts the cheek

and/or suspensorium

244. Dorsal process of stapes

0 absent

1 present

245. Facets on dorsal surface of supraoccipital

0 absent

1 present

246. Otoccipital fissure

0 present

1 absent

221

247. Crista parotica

0 Descends posteriorly

1 Horizontal along the extent of its length

248. Position of quadrate with respect to otic capsules

0 quadrates ventral and lateral to otic capsules

1 quadrates mostly lateral to and greater or equal to twice the width of the otic capsules

2 quadrates mostly ventral to otic capsules

3 quadrates approaching or abutting lateral wall of otic capsules

249. Size of otic capsuiles

0 otic capsules comprise less than 2/3 the width of otoccipital region

1 otic capsules comprise greater than 2/3 total width of otoccipital region

250. Otic trough

0 absent

1 present

251. Articulation between the epipterygoid and prootic

0 none

1 elongate facet on anterior surface of prootic for articulation of epipterygoid

252. Opisthotic obscures occipital in lateral view

222

0 no

1 yes

253. Fenestra vestibularis at end of broad, winglike lateral extension of the otic capsule

0 no

1 yes

254. Cristae in otoccipital region

0 comprised primarily of ascending flanges from braincase

1 comprisd primarily of descending flanges from skull roof

255. Opisthotic excluded from the occipital surface by tabular process of the exoccipital

0 no

1 yes

256. Insertion of epaxial musculature on occiput

0 deep within temporal fossae

1 in broad, shallow fossae along occipital surface of postparietals

257. Foramen for internal jugular vein

0 between supraoccipital and exoccipital

1 between opisthotic and exoccipital

2 through exoccipital

223

3 Posterior notch of fenestra vestibuli

258. Foramina for hypoglossal nerve

0 multiple

1 single

2 none

259. Occipital condyle shape

0 round

1 U-shaped

2 paired

260. Ventral process of exoccipital reaches basipterygoid joint along palatal surface

0 absent

1 present

261. Occipital condyle shape

0 Concave

1 Convex

262. Columella of stapes

0 perforate

1 imperforate

224

263. Orientation of stapes

0 Dorsal, towards tabular or otic notch

1 anteroventral, towards quadrate

264. Stapedial footplate shape

0 oval

1 round

2 palmate

265. Dorsal sinus between synotic tectum and skull roof

0 absent

1 present

225

226