A New Lower Permian Trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma

Home , Arroyo Formation, Cacops, Diadectes, Dissorophidae, Dissorophus, Edops

Zoological Journal of the Linnean Society, 2011, 161, 789–815. With 15 ﬁgures

A new Lower Permian trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma

BRENDAN P. POLLEY and ROBERT R. REISZ*

Department of Biology, University of Toronto, Mississauga Campus, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6

Received 31 January 2010; revised 16 March 2010; accepted for publication 23 March 2010

A new trematopid amphibian, Acheloma dunni, is reported based on excellently preserved cranial and postcranial elements recovered from the Lower Permian ﬁssure ﬁll deposits of the Dolese Brothers Co. limestone quarry near Richards Spur, Oklahoma. The new taxon is characterized by lateral exposures of the palatine (l.e.p.) and ectopterygoid (l.e.e.), which are clearly visible externally and completely enclosed within the suborbital elements. This large, terrestrial carnivore may represent the top predator of the Richards Spur assemblage. A phylogenetic analysis including 12 taxa and 53 cranial characters yielded a single most parsimonious tree, placing Ach. dunni within the monophyletic Trematopidae as the sister taxon to Acheloma cumminsi. Furthermore, the analysis includes the enigmatic Ecolsonia and Actiobates within Trematopidae, forming a clade with the Upper Pennsyl- vanian Anconastes and the Lower Permian Tambachia. The study comprehensively analyses all valid and aberrant forms of Trematopidae.

ADDITIONAL KEYWORDS: Amphibia – Olsoniformes – Tetrapoda – Trematopidae.

INTRODUCTION Formation of the Clear Fork Group of Texas (Olson, 1991). This assignment has been further supported by The Dolese limestone quarry, situated near Richards biostratigraphical evidence based on the fauna recov- Spur, Oklahoma is home to the most diverse known ered from the South Grandﬁeld locality of southern assemblage of Palaeozoic terrestrial tetrapods. Oklahoma (Daly, 1973; Sullivan, Reisz & May, 2000; Regular excavation of Ordovician Arbuckle limestone Maddin, Evans & Reisz, 2006). has continually yielded fossil-rich clays and conglom- The Richards Spur assemblage represents a dra- erates (Olson, 1991). Although often disarticulated, matic departure from contemporary Early Permian fossil material is abundant and well preserved, rep- faunas. Whereas the majority of North American resenting a great variety of taxa (Reisz, 2007; localities typically yield faunal samples consistent Fröbisch & Reisz, 2008). A large proportion of this with aquatic, semi-aquatic, and terrestrial forms of fossil material (Daly, 1973; Olson, 1991) has been lowland, deltaic environments (Olson, 1956), the assigned to the small terrestrial eureptile, Captorhi- Richards Spur assemblage is comprised exclusively of nus aguti. Olson (1991) interpreted the relative abun- small and medium-sized terrestrial forms. This dance of C. aguti material as indicative of an Early unique faunal composition has led to the suggestion Permian age for the faunal assemblage. More speciﬁ- that the locality has preserved a predominantly arid, cally, he inferred that the fauna of Richards Spur upland assemblage (Sullivan et al., 2000; Anderson & was contemporaneous with the Leonardian Arroyo Reisz, 2003; Schoch, 2009). Skeletal elements of larger taxa have been reported from Richards Spur, corroborating the hypothesis that the distinct compo- *Corresponding author. E-mail: [email protected] sition of the fossil assemblage may have been the

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 789 790 B. P. POLLEY and R. R. REISZ product of palaeoecological factors, rather than tapho- atops thomasi; however, the family remained largely nomic biases (Sullivan et al., 2000). These large unexamined until Olson’s (1941) comprehensive remains include isolated elements assignable to a study. In his review, he erected several new species of varanopid (Maddin et al., 2006), the sphenacodontid Acheloma and Trematops: Acheloma pricei, Acheloma Thrausmosaurus (Evans, Maddin & Reisz, 2009), the whitei, and Trematops willistoni. He later expanded dissorophid Cacops (Sullivan et al., 2000; Reisz, the family by describing Trematopsis seltini (Olson, Schoch & Anderson, 2009), a large trematopid sug- 1956) and Trematops stonei (Olson, 1970). The type gested to be Acheloma (Bolt, 1974a; Schultze & specimen of Trematopsis was later found to be a Chorn, 1983; Sullivan et al., 2000), Seymouria (Sulli- junior synonym of Cacops (Milner, 1985b). Moreover, van & Reisz, 1999), and an unidentified eryopid, Olson was first to recognize the close affinities possibly Eryops (Olson, 1991). between trematopids and the diverse group of terres- Similar to the typical smaller taxa, the large forms trially adapted amphibians of the family Disso- recovered from Richards Spur appear to represent rophidae. Dissorophids span a greater temporal and taxa that were primarily terrestrial. As early geographical range than trematopids and are distin- amniotes, there is little doubt that the varanopid and guished from trematopids by the possession of sphenacodontid were well suited for life on land. armoured dermal plates associated with the neural Dissorophids and trematopids, collectively forming spines and the absence of an elongated external naris the clade Olsoniformes (Anderson et al., 2008), are (Olson, 1941; Carroll, 1964a; DeMar, 1966b; DeMar, considered the most terrestrial representatives of late 1968). Palaeozoic temnospondyl amphibians (Bolt, 1969; Subsequent authors also recognized the close rela- Berman, Reisz & Eberth, 1987; Sumida, Berman & tionship of trematopids and dissorophids (Vaughn, Martens, 1998; Dilkes & Brown, 2007; Markey & 1969; Berman, Reisz & Eberth, 1985, 1987; Dilkes, Marshall, 2007; Schoch, 2009). Likewise, authors 1990; Daly, 1994; Sumida et al., 1998; Anderson et al., agree that Seymouria was principally terrestrial, 2008). However, because ingroup relationships of both dependent on an aquatic habitat only during repro- families remained largely unresolved, several taxo- duction and very early growth stages (Sullivan & nomic problems arose when forms seemingly possess- Reisz, 1999; Berman, 2000; Klembara et al., 2007; ing a combination of trematopid and dissorophid Schoch, 2009). Although it may be argued that ery- characters were discovered and described. Mordex opids may have been aquatic or semi-aquatic, the calliprepes and Parioxys ferricolus were both origi- identification of the skull fragment as Eryops is nally described as trematopids (Romer, 1947). Mordex doubtful, and the fragment is not diagnostic. In fact, was later synonymized with Amphibamus (Carroll, we propose that it is more appropriate to designate 1964a) only to be resurrected as a dissorophid with a the skull fragment as Temnospondyli incertae sedis. trematopid-like elongated external naris (Milner, Described here is a new large trematopid skull 1986). Presently, Mordex is in the process of once (OMNH 73281) collected from Richards Spur in 2006. again being reclassified as a basal trematopid (Milner, Although trematopids were previously known from 2007). Parioxys is still considered closely related to Richards Spur on the basis of isolated, fragmentary dissorophids, but has been removed from Trematopi- elements, the newly recovered skull is nearly com- dae and placed within its own family, Parioxyidae plete, showing little distortion. This material repre- (Mustafa, 1955; Carroll, 1964b). sents the largest recorded taxon of the Richards Spur Longiscitula houghae (DeMar, 1966a) was origi- assemblage, rivalling the varanopid described by nally described as possessing both a trematopid-like Maddin et al. (2006) in size. Trematopids form a external naris and the distinctive dermal armour of monophyletic clade of poorly understood temno- dissorophids. Re-examination of the type specimen spondyl amphibians known from the Late Pennsylva- revealed the apparent elongated external naris was nian and Early Permian of North America and central an artefact of preservation (Bolt, 1974c). Milner Germany (Berman et al., 1987; Dilkes, 1990; Sumida (2003) eventually synonymized L. houghae with Dis- et al., 1998). The taxonomic history of Trematopidae sorophus multicinctus. The enigmatic Ecolsonia cut- is long and complex. Whereas the monophyly of the lerensis was described as sharing affinities with clade has remained largely unquestioned, the group dissorophids but was tentatively assigned to Trem- as a whole has yet to be subjected to rigorous phylo- atopidae by Vaughn (1969) based on its elongated genetic analysis. external naris and lack of exostoses and armour. Trematopidae as erected by Williston (1910) Berman et al. (1985) argued the skull proportions and included only two taxa known from Lower Permian structure of the otic notch of Ecolsonia were in fact type specimens: Acheloma cumminsi (Cope, 1882) and indicative of dissorophid affinities, and that its elon- Trematops milleri (Williston, 1909). Mehl (1926) gated external naris evolved convergently. Daly described an additional species of Trematops, Trem- (1994) incorporated Ecolsonia into her study of disso-

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 NEW LOWER PERMIAN TREMATOPID 791 rophoid relationships but was unable to resolve its premaxilla and maxilla obscured by matrix and a assignment (Sumida et al., 1998). Eaton (1973) tightly associated captorhinid lower jaw. Only the described the Late Pennsylvanian Actiobates pea- most anterior portions of the lower jaws are present bodyi as a dissorophid; however, he stipulated that but remain disarticulated. The atlas-axis complex is the distinction between trematopids and dissorophids present along with disarticulated elements compris- was non-existent and all taxa assigned to both fami- ing the third and fourth cervical vertebrae. lies should fall under Dissorophidae. Later authors The referred specimens consist of well-preserved that recognized both families agree Actiobates is a large postcranial elements, jaw joint, and two small trematopid possibly exhibiting an early stage of devel- partial skulls. The pelvic girdle OMNH 73514 is opment (Berman et al., 1985; Milner, 1985a; Daly, nearly complete and associated with a femur, tibia, 1994). Partly for these reasons, both Ecolsonia and fibula, and disarticulated elements of the pes. OMNH Actiobates have been excluded from most cladistic 52365 consists of partial elements comprising the jaw analyses of trematopid relationships (Berman et al., articulation. OMNH 52545 is a complete right 1987; Dilkes, 1990; Sumida et al., 1998). humerus. BMRP2007.3.4 is a small partial skull mea- Currently, Trematopidae consists of five known suring 56 mm along its dorsal midline. It appears to genera. Actiobates peabodyi is at least provisionally have been extensively acid prepared, leaving the still a valid trematopid (Berman et al., 1987; Milner, dermal sculpturing severely eroded but all sutures 1985a; Dilkes, 1990; Daly, 1994; Sumida et al., 1998). clearly visible. The anterior-most half of the skull is Anconastes vesperus (Berman et al., 1987) represents absent along with the braincase, palate, and most of a Late Pennsylvanian trematopid from Texas. Dilkes the lower jaw. BMRP2007.3.1 is a partial skull con- & Reisz (1987) found Trematops milleri to be a junior sisting only of the antorbital bar and its associated synonym of Acheloma cumminsi, and retained the cheek region. name Acheloma for the genus. Dilkes (1990) synony- The holotype of Acheloma cumminsi (AMNH 4205) mized the small Early Permian trematopid taxa was examined for anatomical comparison. The mate- erected by Olson (1941) into a new genus, Phonerpe- rial consists of a nearly complete but substantially ton pricei. Finally, the Early Permian Tambachia crushed skull, a string of 22 articulated presacral trogallas (Sumida et al., 1998) recovered from central vertebrae, both scapulocoracoids, and both humeri. Germany represents the most recent addition to the Also examined was the type specimen of Acheloma family. Here we describe a new species of trematopid stonei (CMNH 10969), represented by a distorted and comprehensively re-evaluate the interrelation- partial skull. The specimen was observed for com- ships of trematopids using a phylogenetic analysis. parative purposes but left out of the analysis because Furthermore, this study is the first to include the of its lack of informative characters. A cast of the only aberrant Ecolsonia and Actiobates in an analysis specimen of Acheloma thomasi (MU 501) was also of trematopid ingroup relationships in an attempt made available for study. to resolve their taxonomic positions and define Specimens of almost all other trematopid taxa were Trematopidae. also available for study, including the holotype (CM 41711) and paratype (CM 28590) of Anconastes vesperus; the holotype (UCLA VP 1734) and paratypes MATERIAL (CM 38017; CM 41703) of Ecolsonia cutlerensis; and The holotype, OMNH 73281, consists of an exception- the holotype (MNG 7722) of Tambachia trogallas. ally preserved skull measuring 164 mm along its Observations of Phonerpeton pricei were based on a midline. The skull has experienced no crushing but complete skull with partial postcranial skeleton has been slightly sheared to the right. All other (AMNH 7150) and published reconstructions (Dilkes, damage appears to have occurred as a result of the 1990). blasting and transport operations of the quarry from Specimens of Actiobates peabodyi were not exam- which it was recovered. The antorbital region of the ined. Comparisons and character coding was accom- left side of the skull is substantially damaged and plished using published illustrations and descriptions remains unprepared. The rest of the skull has been (Eaton, 1973; Milner, 1985a). prepared and shows little sign of damage with the following exceptions: the posterior portion of the quadratojugals and tabulars are broken, whereas the ABBREVIATIONS quadrates are missing entirely. Also, a break is present along the roof of the skull between the frontal INSTITUTIONAL ABBREVIATIONS and nasal, extending onto a portion of the prefrontal. AMNH, American Museum of Natural History, New The palate has been extensively prepared; leaving York, NY; BMRP, Burpee Museum of Natural History, only a small area along the medial edges of the right Rockford, IL; CM, Carnegie Museum of Natural

History, Pittsburgh, PA; CMNH, Cleveland Museum Referred specimens: BMRP2007.3.4, small trematopid of Natural History, Cleveland, OH; MCZ, Museum skull; BMRP2007.3.1, trematopid snout; OMNH of Comparative Zoology, Harvard University, Cam- 52365, jaw articulation; OMNH 73514, pelvic girdle; bridge, MA; MNG, Museum der Natur, Gotha, OMNH 52545, right humerus. Germany; MU, University of Missouri, Columbia, MO; OMNH, Sam Noble Oklahoma Museum of Occurrence: Dolese Brothers Co. limestone quarry, Natural History, University of Oklahoma, Norman, near Richards Spur, Comanche County, Oklahoma; OK; UCLA VP, University of California, Los Angeles, fissure fill deposits in Ordovician Arbuckle limestone CA. probably equivalent to Leonardian Arroyo Formation of Clear Fork Group, Lower Permian. ANATOMICAL ABBREVIATIONS a, angular; art, articular; at, atlas; axi, axial inter- Etymology: The specific name honours Brent Dunn, centrum; axn, axial neural spine; bo, basioccipital; c, who has graciously collected and donated several centrale; c3, third cervical vertebra; c4, fourth cervi- specimens from the Dolese Brothers Co. limestone cal vertebra; cr, cervical rib; ct, cultriform process; d, quarry for study. dentary; ect, ectopterygoid; eo, exoccipital; f, frontal; fe, femur; fi, fibula; i, intermedium; il, ilium; in.f, internarial fenestra; is, ischium; j, jugal; l, lacrimal; DESCRIPTION l.e.e., lateral exposure of the ectopterygoid; l.e.p., GENERAL DESCRIPTION lateral exposure of the palatine; m, maxilla; n, nasal; As observed in all other trematopids (Berman et al., obt, obturator foramen; op, opisthotic; p, parietal; paf, 1987; Dilkes, 1990; Sumida et al., 1998), the skull of para-articular foramen; pal, palatine; pc, pleuro- Acheloma dunni is tall, box-like, and roughly trian- centrum; pco, precoronoid; pf, postfrontal; pm, gular in shape (Figs 1, 2). The surface of the skull roof premaxilla; po, postorbital; pp, postparietal; pra, is covered in deep, rounded dermal pitting. Overall, prearticular; prf, prefrontal; ps, parasphenoid; pt, the skull most closely resembles Acheloma cumminsi pterygoid; ptf, post temporal fenestra; pu, pubis; q, in its large size, the presence of an enlarged, elongate quadrate; qj, quadratojugal; s, stapes; sa, surangular; key-hole shaped, external narial opening, and slit-like se, sphenethmoid; sm, septomaxilla; so, supraoccipi- otic notch with broad, overhanging shelf (Dilkes & tal; sp, splenial; sq, squamosal; st, supratemporal; t, Reisz, 1987). However, whereas the skull roof of tabular; ti, tibia; tib, tibiale; v, vomer. OMNH 73281 is slightly larger in both overall length and width than the holotype of Ach. cumminsi SYSTEMATIC PALAEONTOLOGY (AMNH 4205), the snout of Ach. dunni is narrower TEMNOSPONDYLI ZITTEL, 1887–1890 and considerably less robust. Descriptions are based EUSKELIA YATES &WARREN, 2000 primarily on OMNH 73281 and other specimens as cited. DISSOROPHOIDEA BOLT, 1969 OLSONIFORMES ANDERSON ET AL., 2008 SKULL ROOF TREMATOPIDAE WILLISTON, 1910 The premaxilla of Ach. dunni has a well-developed Revised diagnosis: The clade consisting of Acheloma posterodorsal alary process, overlapping the antero- cumminsi and all other taxa that share a more recent lateral area of the nasal. An internarial fenestra common ancestor with Ach. cumminsi than with measuring 3 mm in diameter is situated along the Dissorophus. midline suture between the premaxillae. The same structure is present in the type specimen of Ach. ACHELOMA COPE, 1882 cumminsi but is proportionately larger, measuring Revised generic diagnosis: Large trematopid temno- 7 mm in diameter. A proportionately large internarial spondyl characterized by the following autapomor- fenestra is also present in Phonerpeton (Dilkes, 1990), phies: toothed, raised crest running anteroposteriorly whereas the structure appears to be completely along the vomer, mesial to the choana; otic notch with absent in all other trematopids (Berman et al., 1985, a nearly horizontal ventral margin. 1987; Dilkes, 1990; Sumida et al., 1998). The presence of an internarial fenestra is not exclusive to trem- ACHELOMA DUNNI SP. NOV. atopids as it has been identified in a variety of other (FIGS 1–14) dissorophoids (Carroll, 1964a; Bolt, 1977a; Reisz Type specimen: OMNH 73281, nearly complete skull et al., 2009). Mehl (1926) described the partial snout with associated atlas–axis complex and partial lower of the Lower Permian trematopid Acheloma thomasi jaw. (as Trematops thomasi) from Snyder, Oklahoma that

Figure 1. Reconstruction of skull of Acheloma dunni in A, dorsal view; B, ventral view; C, right lateral view. Abbreviations: ct, cultriform process; ect, ectopterygoid; f, frontal; in.f, internarial fenestra; j, jugal; l, lacrimal; l.e.e., lateral exposure of the ectopterygoid; l.e.p., lateral exposure of the palatine; m, maxilla; n, nasal; op, opisthotic; p, parietal; pal, palatine; pf, postfrontal; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; ps, parasphenoid; pt, pterygoid; q, quadrate; qj, quadratojugal; s, stapes; se, sphenethmoid; sm, septomaxilla; sq, squamosal; st, supratemporal; t, tabular; v, vomer. Scale bar = 50 mm. possessed a reduced or perhaps absent internarial the assertion was made only under the condition that fenestra. Authors have generally accepted Olson’s the internarial fenestra was in fact present. Mehl did (1941) suggestion that Ach. thomasi is a junior not list a specimen number in his description and it synonym of Ach. cumminsi (as T. milleri), although appears the only record of Ach. thomasi material is of

Figure 2. Skull of Acheloma dunni, holotype (OMNH 73281) in dorsal view. Abbreviations: f, frontal; in.f, internarial fenestra; j, jugal; l, lacrimal; l.e.e., lateral exposure of the ectopterygoid; l.e.p., lateral exposure of the palatine; m, maxilla; n, nasal; pf, postfrontal; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; qj, quadratojugal; sq, squamosal; st, supratemporal; t, tabular. Scale bar = 50 mm. a cast of the type specimen (MU 501) in the Univer- majority of the ventral border of the external naris sity of Missouri at Columbia collections (Katz, 2008). where the maxilla also has a well-developed medial The cast is in poor condition; however, it is informa- shelf that forms the floor of the external naris. tive enough to indicate that the internarial fenestra is The conspicuous elongated external narial opening, absent. often cited as the defining character of trematopids Seven teeth are preserved on each premaxilla, (Olson, 1941, 1970; Vaughn, 1969; Eaton, 1973; Daly, along with another six empty alveoli. Initially, there 1994), is bordered by the premaxilla, maxilla, nasal, is a steady increase in size of teeth posteriorly, with prefrontal, and lacrimal. The increase in the height of the largest being in the ninth or tenth tooth position. the maxilla in conjunction with a lateral expansion of The last three teeth in the premaxillary series the nasal along the margin of the external naris, decrease in size posteriorly. The preserved teeth on partitions the external naris into distinct anterior and the maxilla exhibit a similar pattern, at first increas- posterior sections. This gives the narial opening an ing in size posteriorly and reaching their maximum overall keyhole shape (Fig. 3). The dorsal expansion size at about the seventh or eighth tooth position, of the maxilla occurs just posterior to the area where beneath the posterior margin of the external naris. the septomaxilla is located in the opening in all other The remaining teeth gradually decrease in size pos- trematopids (Sumida et al., 1998), including Ecolso- teriorly. There are 18 preserved teeth on the right nia, delineating the posterior extent of the functional maxilla with spaces for at least ten more. The maxilla external naris (Bolt, 1974c; Berman et al., 1987; is a long and slender element, stretching posteriorly Dilkes, 1993). Although the septomaxilla is not pre- past the level of the anterior border of the otic notch. served in Ach. dunni, it probably was in a similar The maxilla has the greatest dorsal expansion at the position. A laterally concave, smooth lamina known as level of the largest teeth, beneath the enlarged exter- the narial flange (Dilkes, 1990, 1993) descends from nal narial opening. Its dorsal edge makes up the the ventral surface of the skull roof and lies in close

Figure 3. Skull of Acheloma dunni, holotype (OMNH 73281) in right lateral view. Abbreviations: ct, cultriform process; f, frontal; j, jugal; l, lacrimal; l.e.e., lateral exposure of the ectopterygoid; l.e.p., lateral exposure of the palatine; m, maxilla; n, nasal; pf, postfrontal; pm, premaxilla; po, postorbital; prf, prefrontal; pt, pterygoid; qj, quadratojugal; se, sphenethmoid; sq, squamosal; st, supratemporal; t, tabular; v, vomer. Scale bar = 50 mm. association with the external naris. Comprised of (Dilkes, 1990), and was also revealed in Anconastes contributions of the nasal, prefrontal, and lacrimal, and Tambachia (Sumida et al., 1998). Examination of the narial flange makes broad contact with the antor- the holotype of Ecolsonia (UCLA VP 1734) indicates a bital bar. This condition is common amongst other median vomerine septum is present. Contact between trematopid taxa (Eaton, 1973; Berman et al., 1987; the skull roof and the median vomerine septum can Dilkes & Reisz, 1987; Dilkes, 1990; Sumida et al., be confirmed in only Ach. cumminsi (Dilkes & Reisz, 1998). A narial flange has been found in other disso- 1987); however, the same structure approaches the rophoids including Doleserpeton (Carroll, 1964a; Bolt, skull roof but does not contact it in Phonerpeton 1974c; Reisz et al. 2009); however, the structure does (Dilkes, 1990), and in Ecolsonia. The dorsal extent of not appear to contact the antorbital bar in any of the median vomerine septum is unknown in either these taxa. A narial flange is visible in the holotype of specimen of Anconastes (CM 41711; CM 28590) or Ecolsonia in cross section; however, the configuration Tambachia (MNG 7722). If the median vomerine of the narial flange cannot be confirmed because the septum made even cartilaginous contact with the area surrounding the antorbital bar remains absent skull roof, the strut-like structure may be an adapta- or unprepared in all specimens. tion to withstand compressive and shearing forces The nasal capsule of Ach. dunni is floored by the acting on the rostrum and vomers, respectively, vomer and palatine. The choana lies well anterior to during feeding. Anteriorly, the vomerine walls bifur- the posterior margin of the external naris as in Ach. cate, contacting the ventrolateral surfaces of the cumminsi (Dilkes & Reisz, 1987). The posterior premaxillae. border of the choana is in line with the posterior The lacrimal makes up the ventral half of the margin of the external naris in all other trematopids antorbital bar, contributing to both the posteroventral (Eaton, 1973; Berman et al., 1985, 1987; Dilkes, 1993; margin of the external narial opening and the Sumida et al., 1998). A partially prepared sheet of anteroventral margin of the orbit. Anteriorly, the bone bone is exposed medial to the narial flange. It appears has a relatively short subnarial process, suturing to be the dorsally directed laminar process running bluntly with the dorsally expanded portion of the along the midline of the rostrum, referred to as the maxilla (Fig. 3). A short subnarial process is also median vomerine septum by Dilkes (1990). This present in Tambachia and Actiobates (Sumida et al., structure is present in Ach. cumminsi, Phonerpeton 1998). In other trematopids, the lacrimal extends

Figure 4. Acheloma dunni, referred specimen (BMRP2007.3.4) in left lateral view. Abbreviations: f, frontal; j, jugal; l, lacrimal; l.e.e., lateral exposure of the ectopterygoid; l.e.p., lateral exposure of the palatine; m, maxilla; n, nasal; pf, postfrontal; po, postorbital; prf, prefrontal; sq, squamosal; st, supratemporal; t, tabular. Scale bar = 10 mm. anteriorly to a point about level with the subdivision The most intriguing feature of Ach. dunni is the of the external narial opening. presence of several distinct exposures of sculptured The prefrontal is a triangular bone that makes up bone visible on the lateral surface of the cheek the dorsal half of the antorbital bar. Anteriorly, it region. The roughly oval-shaped elements lie adja- contributes to the posterodorsal margin of the exter- cent to one another, bordered ventrally by the nal narial opening. The posterior process of the premaxilla and dorsally by the lacrimal and jugal. frontal forms the anterodorsal margin of the orbit and Three separate elements can be seen in OMNH makes contact with the frontal. The prefrontal does 73281 and BMRP2007.3.4 (Fig. 4). The most ante- not contact the postfrontal; instead, the frontal sepa- rior element appears to be a l.e.p. It is comprised of rates the two elements and contributes to the dorsal a sculptured lateral expansion of a portion of the border of the orbit. palatine lying just posterior to the palatal fang and The jugal is tall and broad, spanning most of the replacement pit. Posterior to the l.e.p. is a small length of the cheek region. Dorsally, it contributes to l.e.e., consisting of only the most anterior portion of the circumorbital series by forming the ventral the ectopterygoid. The third and largest exposure is margin of the orbit. It extends ventrally to meet the formed by a secondary lateral expansion of the maxilla near the posterior limit of the latter. The ectopterygoid associated with the lateral margin of posterior-most portions of the jugal form a tall and the socket housing the ectopterygoid fang and slightly curved wedge, contacting the squamosal dor- replacement pit. A similar pattern is observed in sally, and the quadratojugal posteroventrally. BMRP2007.3.1 although it would appear that the

Figure 5. Acheloma dunni, referred specimen (BMRP2007.3.1) in right lateral view. Abbreviations: j, jugal; l, lacrimal; l.e.e., lateral exposure of the ectopterygoid; l.e.p., lateral exposure of the palatine; m, maxilla; n, Figure 6. Acheloma dunni, referred specimen (OMNH nasal; prf, prefrontal. Scale bar = 10 mm. 52365). Partial right upper jaw articulation in dorsal view. Abbreviations: pt, pterygoid; q, quadrate; qj, quadratoju- lateral exposures of the ectopterygoid are fused gal; st, supratemporal. Scale bar = 10 mm. (Fig. 5). Occurrences of an l.e.p. contributing the ventral margin of the orbit have been reported in several taxa possess relatively large orbits and narrow sub- dissorophoids (Bolt, 1974b) and the basal dvinosau- orbital bars, it is the maxilla and not the palatine or roids Acroplous and Isodectes (Sequeira, 1998; Engle- ectopterygoid that contributes to the ventral margin horn, Small & Huttenlocker, 2008). An l.e.p. and l.e.e. of the orbit. Examination of the holotype of Ach. have been recognized in the trematopid Phonerpeton, cumminsi conﬁrms previous accounts that neither an although the relationship between the two exposures l.e.p. nor l.e.e. are present (Bolt, 1974b; Dilkes & varies between specimens (Dilkes, 1990). Neither an Reisz, 1987). l.e.p. nor l.e.e. are present in Actiobates, Anconastes, Posteriorly, the orbit is bordered by the postfrontal Ecolsonia,orTambachia (Eaton, 1973; Berman et al., and postorbital (Fig. 3). Both bones are roughly tri- 1985, 1987; Sumida et al., 1998). Although all four angular in shape. The postfrontal contacts both the

Figure 7. Skull of Acheloma dunni, holotype (OMNH 73281) in ventral view. Abbreviations: bo, basioccipital; cf, cultriform process; ect, ectopterygoid; in.f, internarial fenestra; m, maxilla; op, opisthotic; pal, palatine; pm, premaxilla; ps, parasphenoid; pt, pterygoid; s, stapes; sm, septomaxilla; v, vomer. Scale bar = 50 mm.

Figure 8. Skull of Acheloma dunni, holotype (OMNH 73281) in occipital view. Abbreviations: bo, basioccipital; eo, exoccipital; op, opisthotic; pp, postparietal; ps, parasphenoid; pt, pterygoid; s, stapes; so, supraoccipital; sq, squamosal; t, tabular. Scale bar = 50 mm.

frontal and parietal medially, and the supratemporal The squamosal is a large element, forming a sub- posteriorly. The postorbital is a narrow element stantial portion of the otic notch. The sculptured forming a broad, interdigitated suture with the squa- lateral margin of the embayment of the squamosal mosal. Only the dorsal and ventral-most points of appears horizontal in outline in its most anterior the postorbital make constricted contact with the portion. Medially, the squamosal has an internally supratemporal and jugal, respectively. Together, the directed flange that makes up the ventral surface of postfrontal, postorbital, and squamosal form a narrow the otic notch. The flange is deflected ventrally at an area of bone separating the orbit and the otic notch. acute angle, and contacts the quadratojugal posteri-

Figure 9. Partial left lower jaw of Acheloma dunni, holotype (OMNH 73281) in A, lateral view; B, medial view; C, dorsal view; D, ventral view. Abbreviations: d, dentary; pco, precoronoid; sp, splenial. Scale bar = 10 mm.

orly. Together, the squamosal, supratemporal, and otic notch is unpreserved and undescribed in Ancon- tabular contribute to the dorsal margin of the otic astes and Actiobates, respectively. notch. The bones form a deep posterolaterally Dorsally, the squamosal forms the majority of the directed supratympanic shelf overhanging a well- anteroposteriorly directed supratympanic flange. The defined, unsculptured supratympanic flange. Pres- slope of the squamosal constricts the otic notch dor- ence of a supratympanic shelf has been confirmed in soventrally; however the bone lacks the distinct semi- Ach. cumminsi and Phonerpeton; however, the lunar curvature observed in other dissorophoids. supratympanic shelf appears to be replaced by sculp- Amongst trematopids, a semilunar curvature of the turing covering the lateral area above the otic notch squamosal has been recorded in Ecolsonia, Phonerpe- in both Ecolsonia and Tambachia. The area above the ton, and Tambachia (Berman et al., 1985; Dilkes,

Figure 10. Partial right lower jaw of Acheloma dunni, holotype (OMNH 73281) in A, lateral view; B, medial view; C, dorsal view; D, ventral view. Abbreviations: d, dentary; pco, precoronoid; sp, splenial. Scale bar = 10 mm.

1990; Sumida et al., 1998). A semilunar curvature of the tabulars is unknown in all specimens of Ach. the squamosal is absent in Ach. cumminsi, whereas dunni. the area is unpreserved in Anconastes (Berman et al., OMNH 52365 preserves the posterior-most portion 1987). Posteriorly, the squamosal contacts the of the otic notch (Fig. 6). The posteroventral margin of tabular, excluding the semilunar ﬂange of the the squamosal slopes ventrally, overlapping the supratemporal (Bolt, 1974a) from the ventral margin quadratojugal. The quadratojugal forms the posterior of the supratympanic ﬂange. The posterior extent of end of the otic notch before curving sharply dorsally

Figure 11. Acheloma dunni, referred specimen (OMNH 52365). Partial right lower jaw articulation in A, lateral view; B, posterior view. Abbreviations: a, angular; art; articular; pra, prearticular; sa, surangular. Scale bar = 10 mm. and contributing to the lateral surface of a robust, terior to the larger fangs. A distinct toothed, raised rounded jaw articulation. A medially projecting crest runs anteroposteriorly along the medial border process of the quadratojugal contacts the quadrate. of the choana. The same crest has been observed in The quadrate is a narrow, unsculptured bone forming some primitive temnospondyls (Ruta & Bolt, 2006). the posterolateral corner of the skull. The dorsal The crest continues onto a posterolateral process of surface of OMNH 52365is slightly damaged and what the vomer that ﬂanks the medial edge of the palatine would appear to be the dorsal process of the quadrate and contacts the pterygoid. has broken off. The ventral surface of the palatine is mainly occu- pied by a massive fang and a large replacement pit. As mentioned above, the palatine forms the posterior PALATE border of the choana. Medially, the palatine is excluded The vomers are densely covered with small, recurved from the interpterygoid vacuity by contact between the teeth. Anteriorly, the vomers are smooth, deﬂected vomer and the palatal ramus of the pterygoid. Reten- laterally and contact the premaxillae. The dorsal tion of the vomer-pterygoid contact and a rather extent of the bones contacts the nasals, forming a narrow interpterygoid vacuity is common amongst deep internarial pit (Fig. 7). The ventral area of the trematopids but considered primitive (Berman et al., internarial fenestra is visible in this vicinity and 1985, 1987; Dilkes & Reisz, 1987; Dilkes, 1990; Sumida appears laterally expanded with respect to its dorsal et al., 1998). In most dissorophoids, contact between compliment. A prominent shelf housing a large fang the vomer and pterygoid is lost and the palatine and/or with a replacement pit on each vomer overhangs the ectopterygoid contribute to the lateral margins of an posterior margin of the internarial pit and is level expanded interpterygoid vacuity. Posteromedially, the with the anterior margin of the choana. An additional palatine has a small, toothed, ridge-like swelling that set of accessory fang pairs are situated directly pos- contacts the pterygoid.

Figure 12. Atlas-axis complex and associated cervical vertebrae of Acheloma dunni, holotype (OMNH 73281) in A, right lateral view; B, left lateral view; C, anterior view. Abbreviations: at, atlas; axi, axial intercentrum; axn, axial neural spine; c3, third cervical vertebra; c4, fourth cervical vertebra; cr, cervical rib; pc, pleurocentrum. Scale bar = 10 mm.

Figure 13. Acheloma dunni, referred specimen (OMNH 52545). Right humerus in A, posterior view; B, extensor view; C, anterior view; D, ﬂexor view; E, proximal view; F, distal view. Scale bar = 50 mm.

The ectopterygoid is a smaller palatal element than basipterygoid region makes broad contact with the either the palatine or the pterygoid, but still houses a basipterygoid process of the parasphenoid. The basi- large fang and replacement pit. The overall size of the cranial joint is firmly sutured and immobile. Exami- ectopterygoid teeth does not exceed that of the mar- nation of AMNH 4205 reveals that the basicranial ginal teeth in Ach. cumminsi (Dilkes & Reisz, 1987). joint of Ach. cumminsi is also sutured, and not indis- Although the tips of the fangs are broken in OMNH tinguishably fused as described by Dilkes & Reisz 73281, the teeth of Ach. dunni are clearly larger than (1987). The basicranial joint is mobile in Anconastes any of the preserved marginal teeth. Posteriorly, the and Tambachia (Sumida et al., 1998). ectopterygoid forms the rounded anterior border of the adductor fossa. Similar to the palatine, a raised toothed ridge runs posterolaterally along the ectop- BRAINCASE terygoid onto the pterygoid. The parasphenoid is complete and visible in ventral The right pterygoid of OMNH 73281 is nearly com- view of the skull (Fig. 8). The long, narrow cultriform plete, missing only the posterior-most portion of the process arches along the midline of the skull, reach- quadrate ramus. The entire palatal ramus and basip- ing its maximum height at a point about level with terygoid region of the pterygoid are covered in a dense the centre of the orbit. Although the tapered anterior shagreen of small teeth, whereas the quadrate ramus end of the cultriform process undoubtedly reached the appears smooth. Although slightly damaged, a curved vomers, the area remains damaged and details of transverse flange runs along the posterior margin attachment between the elements are unknown. of the palatal ramus into the adductor fossa. The Dorsally, the cultriform process articulates with an dorsomedially directed internal process of the ossified sphenethmoid. The sphenethmoid contacts

Figure 14. Acheloma dunni, referred specimen (OMNH 73514). Partial pelvic girdle and hindlimb. Abbreviations: c, centrale; fe, femur; fi, fibula; i, intermedium; il, ilium; is, ischium; obt, obturator foramen; pu, pubis; ti, tibia; tib, tibiale. Scale bar = 5 mm. Illustration by Heidi Richter. tightly the ventral surface of the frontal and postfron- forming the majority of the dorsal margin of the tal. The body of the parasphenoid is rectangular, foramen magnum. In the only specimen of Ach. stonei extending thin laterally expanding wings posteriorly. (CMNH 10969) and Phonerpeton, this area consists of A deep anteroposterior depression runs medially a gap, partially separating the exoccipitals and post- along the ventral surface. A distinct triangular patch parietals. The same gap is present in the aberrant of tiny teeth sits on a transverse, tall ridge medial to temnospondyl Platyhystrix and is interpreted as evi- the basipterygoid processes. The denticles extend only dence of a cartilaginous supraoccipital (Berman, onto the posterior tip of the cultriform process. The 2000). absence of parasphenoidal dentition was used to unite It is possible that the robust dorsal expansion of the Acheloma and Phonerpeton (Dilkes, 1990); however, exoccipitals of Ach. dunni represents an ossified re-examination of AMNH 4205 indicates that small supraoccipital fused to the exoccipitals. Within tem- teeth are in fact present on the parasphenoid of Ach. nospondyls, similar ossifications thought to be cumminsi but only the most proximal borders of the homologous to the supraoccipital have been recorded dentition have been preserved. Amongst dissoro- in Eryops and Edops (Berman, 2000). Originally, Car- phoids in which the area is known, only Broiliellus roll’s (1964a) description of Dissorophus angustus and Dissorophus lack parasphenoidal dentition included an account of a supraoccipital similar to that (Sumida et al., 1998). of Ach. dunni; however, according to the character The basioccipital is tightly associated with the coding of Laurin & Reisz (1997), the supraoccipital is parasphenoid and only enough of the bone has been absent. The only other recorded instance of an ossified prepared to confirm its presence. The basioccipital supraoccipital within Temnospondyli is in Schoch’s joins the exoccipitals to form the paired occipital (1999) description of the braincase of Kamacops acer- condyles; however, the suture between the two ele- valis. However, the structure of the supraoccipital of ments is not visible. The exoccipitals are narrow K. acervalis differs greatly from that of Ach. dunni ventrally and form the lateral borders of the foramen and other temnospondyls. Whereas the supraoccipital magnum. Each exoccipital makes contact with the appears fused to the exoccipitals in Ach. dunni,in posterolateral edge of the occipital flange of the post- K. acervalis the bone fuses with the opisthotics, sepa- parietals. Interestingly, dorsal to this contact, the rating the exoccipitals from the postparietals in a exoccipitals appear robust, and medially expanded, manner similar to its homologue in microsaurs,

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 NEW LOWER PERMIAN TREMATOPID 805 lysorophids, amniotes, and diadectomorphs (Schoch, clockwise. The atlas-axis complex is a massive struc- 1999; Berman, 2000). ture exhibiting an interesting configuration. The Both stapes are complete and preserved in place atlantal neural arches are present but only the right (Figs 1, 8). The thin, anteroposteriorly compressed half appears to be complete. Both elements are ori- shaft is curved with its distal end fitting into an open entated dorsally and are greatly separated from their posteroventral notch along the supratympanic flange. counterpart medially by a single robust anterior A distinct stapedial foramen is visible on the posterior expansion of the axial neural spine. Williston (1909) surface of the footplate (Figs 7, 8). The foramen is described a similar orientation of the neural arches in considered primitive in temnospondyls (Daly, 1994), Ach. cumminsi (as Trematops milleri). The prezyga- but is retained in all trematopids. The footplate is pophyses are orientated almost vertically, probably roughly tetrahedral in shape, ventrally associated articulating with paired proatlantal elements. The with the basal plate of the parasphenoid. The rest of postzygapophyses are comparably more prominent the footplate contacts the fenestra ovalis. This con- and horizontally directed. The atlantal neural arches figuration is common within Temnospondyli and may are fused to the centrum with no distinguishable have been mobile in a pump-handle fashion (Bolt & suture, as observed in Doleserpeton (Bolt, 1969, Lombard, 1984). 1977b) and Amphibamus (Carroll, 1964a; Daly, 1994). The body of the centrum is unipartite, consisting of one or more fused elements. A distinct, laterally con- LOWER JAW stricted body and ventral keel are typical features of The lower jaw is represented by fragmentary material rachitomous intercentra and suggest that the atlantal (OMNH 73281) consisting of the anterior-most por- intercentrum is at least one of the contributing ele- tions of the dentary, precoronoid, and splenial (Figs 9, ments to the centrum. The centrum appears subrect- 10). The dorsal surface of the dentary is smooth, angular in lateral view and dorsolaterally expanded housing a large fang and a replacement pit medially. beneath the neural arches. This expanded area may The posterior extent of the bone is missing, making consist of the intercentrum and neural arches fusing an exact count of dentary teeth impossible. The to the atlantal pleurocentra that are otherwise dentary sutures with the precoronoid along a distinct absent. Anteriorly, the bicondylar articulating surface dorsal depression, where a large foramen is present of the centrum aligns almost perfectly with the occipi- posterior to the dentary fang. A dense patch of small tal condyle of the skull. The tight fit between the atlas teeth occupies a narrow band along the dorsal surface and the occipital would have probably restricted the of the precoronoid. Ventromedially, the precoronoid range of movement about this joint, if not prevented contacts the splenial along a deep, anteroposteriorly it altogether. directed groove. The groove continues anteriorly, The axis is a tall, broad multipartite element. The deflecting dorsally and creating a medially situated stout axial neural arches contact the broad, postero- gap in the sutural surface of the symphysis. The laterally protruding transverse processes but remain symphysis consists mainly of the dentary with unfused to the centrum. The prezygapophyses are smaller posterior contributions from the splenial and directed anterolaterally to articulate with the atlantal precoronoid. neural arches. The postzygapophyses are notably OMNH 52365 preserves the posterior corner of the elongate in comparison to the prezygapophyses and lower jaw (Fig. 11). The surangular and articular are directed posterolaterally. The axial neural arches fuse robust, forming the articulating surface of the lower dorsally, forming the broad, rugous axial neural jaw. Medially, a greatly interdigitated suture sepa- spine. The lateral surfaces of the neural spine are rates the surangular from prearticular and angular. concave, narrowing anteriorly to wedge between the The para-articular foramen is visible on the postero- atlantal neural arches. Dorsally, the neural spine medial surface of the prearticular. thickens greatly before tapering to a pyramidal point. The wedge-like axial intercentrum is present but displaced posteriorly. As in Ach. cumminsi the axial AXIAL SKELETON intercentrum is considerably smaller than those of Slightly disarticulated anterior vertebral elements the following cervical vertebrae (Williston, 1909). No were recovered in close association with OMNH pleurocentra are visible. 73281 (Fig. 12), including the atlas-axis complex and The third cervical vertebra appears mostly com- portions of the third and fourth vertebrae. Several plete but disarticulated. The slightly bulbous dorsal fragments of tall, wing-like cervical ribs flank the tip of the neural spine is damaged. A dorsoventrally vertebral column on either side. Although each struc- directed groove runs along the anterior face of the ture appears to be in its correct relational position, spine. Ventrally, the groove bifurcates to meet the each vertebral element has been rotated counter- strongly anteromedially directed prezygapohyses.

The postzygapophyses remain only partially pre- acetabular notch. A large laterally directed obturator pared, with articulating surfaces orientated postero- foramen is present. The right femur is complete and laterally. A single, ventrolaterally directed, transverse is in articulation with the right pelvis, and resembles process is visible. Posteriorly, the distal surface of the the described femur of Ach. cumminsi (Williston, transverse process is broad and flat, and would have 1909; Olson, 1941). The proximal and distal heads are articulated with the wide cervical ribs. The intercen- expanded, whereas the shaft is gently concave. The trum is disarticulated but lies in close association long fourth and internal trochanters of the adductor with the rest of the third cervical vertebra. It is blade are robust, with a thin intertrochanteric ridge roughly crescentic and wedge-shaped in lateral view. bordering a deep oval concavity. A deep adductor crest Another intercentrum, presumably belonging to the runs along the entire flexor surface of the femur, fourth cervical vertebra is pressed against the poste- terminating near the fibular condyle. The distal head rior surface of the third cervical intercentrum. Only a is all that remains of the left femur, which sits in single unpaired and disarticulated pleurocentrum is close association with an articulated tibia, fibula, and visible. It is unclear what particular vertebra this elements of the pes. element contributed to. The tibia (Fig. 14) has a greatly expanded femoral head with a well-developed cnemial crest and trough. The slender shaft appears circular in cross-section, APPENDICULAR SKELETON broadening distally to meet the convex articular facet. OMNH 52545 represents a complete right humerus The fibula is almost as long as the tibia. Its proximal (Fig. 13). The humerus is a massive element with and distal ends are about equal in width. Both ends flared proximal and distal ends orientated at approxi- are slightly directed toward the tibia by a medially mately right angles to each other. The shaft is concave curvature of the shaft. Following the descrip- laterally constricted and appears somewhat subrect- tion of the pes of Ach. cumminsi (Williston, 1909; angular in cross-section. Distally, a well-developed Schaeffer, 1941), the tibia and fibula articulate with a ectepicodyle and entepicondyle dominate the extensor proximodistally elongate intermedium (Fig. 14) along surface. A convex radial condyle is positioned on the the medial surfaces of their distal ends. Distal to the anteroventral surface of the flexor side. Proximal to intermedium is the wide, concave fourth centrale. The this area, a prominent supinator process comes to a wedge-shaped tibiale flanks the tibia, rotated slightly blunt point. A supinator process has been observed out of position. A small bone possibly representing a not only in other trematopids where the area is pre- centrale or tarsal sits out of place, displaced by the served (Williston, 1909; Olson, 1941; Dilkes & Reisz, distal end of the right femur. Next to this bone are 1987; Dilkes, 1990), but is also present in Eryops, two broken unidentified phalangeal elements. A seymouramorphs, and diadectimorphs (Pawley & single element of the pes located next to the right Warren, 2006). Moreover, the development of a supi- pelvis has suffered pyrite damage and may represent nator process has been correlated with the degree of the first centrale. ossification of the humerus and is at least suggestive of a terrestrial lifestyle (Pawley & Warren, 2006). A posteriorly directed, anterior humeral keel joins the DISCUSSION supinator process to a roughly oval attachment area for the pectoralis muscle alongside a distinct deltoid PHYLOGENETIC ANALYSIS crest. Proximally, the humeral articulating surfaces A review of previous studies involving trematopid are well developed and slightly convex. relationships reveals that the family has typically OMNH 73514 represents the pelvic girdle and been analysed in two ways. Although each approach extremity of Ach. dunni (Fig. 14). Both sides of the affirms both the monophyly of Trematopidae and its pelvic girdle are partly exposed in lateral view with position as the sister group of Dissorophidae, subtle no discernable sutures separating the ilium, ischium, differences in methodology have resulted in varying and pubis. Most of the iliac blade is missing on the perceptions of trematopid interrelationships. left pelvis, although the rest of the element appears Firstly, cladistic analyses of trematopid ingroup intact. The right pelvis is missing portions of the relationships have been assessed using a single taxon ischium and pubis and has a large crack running as the outgroup while also excluding aberrant forms along its surface. Any preserved structures dorsal to from the analysis altogether. Dilkes (1990) was first the ventral margin of the acetabulum remain to show that Anconastes, Phonerpeton,andAcheloma obscured by matrix housing the hindlimb. Both pelves formed a monophyletic sister-group to Amphibamus are broad, thin bones. The acetabulum is triangular (Amphibamus (Anconastes (Phonerpeton, Acheloma))). in outline, bordered dorsally by a strongly developed Ecolsonia and Actiobates were not included in that transverse pelvic ridge and posterior supra- study at the time because they were generally con-

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 NEW LOWER PERMIAN TREMATOPID 807 sidered as a dissorophid or juvenile, respectively. The present study undertakes the first comprehen- Sumida et al. (1998) performed a similar cladistic sive phylogenetic analysis of Trematopidae examin- analysis when describing Tambachia, heavily basing ing all valid and aberrant forms of the group along the choice of character states and outgroups on the with the new taxon within the broader context of work of Dilkes (1990) and Daly (1994). They con- dissorophoid relationships. The data matrix used by cluded that the monophyletic Trematopidae consisted Schoch & Rubidge (2005) provided the framework for of two sister groups comprised of Tambachia and our phylogenetic analysis. Twenty-four informative Anconastes in one clade, and Acheloma and Phoner- cranial characters were utilized from this matrix peton in the other (Amphibamus (Tambachia, Ancon- and another 30 were added from the literature astes)(Acheloma, Phonerpeton)). As in earlier works, (Appendix 2). Five taxa were selected for outgroup Sumida et al. (1998) used only Amphibamus for out- comparisons. Sclerocephalus haeuseri is a well group comparisons and left Ecolsonia and Actiobates described lower tetrapod known from abundant out of that analysis, despite growing evidence that material (Schoch, 2003; Schoch & Rubidge, 2005). neither form could be considered a dissorophid (Daly, Micromelerpeton credneri was included as a repre- 1994). sentative of basal dissorophoids. Eoscopus lockardi Secondly, trematopids have been included in larger (Daly, 1994) and Micropholis stowi were used to rep- scale phylogenetic studies of dissorophoid and temno- resent the two sister clades comprising Amphibami- spondyl relationships. Although Ecolsonia and Actio- dae (Schoch, 2003). Exquisite material of the bates have also been included in most of these cases, recently described Cacops morrisi (Reisz et al., 2009) character coding for trematopids has often been based was available and used to represent Dissorophidae. primarily on only the best known forms, excluding The trematopids Ach. cumminsi, Anconastes vesper- more than half of the potential members of the family sus, Phonerpeton pricei, Tambachia trogallas, Actio- from analysis. Daly (1994) included Trematopidae in bates peabodyi, and Ecolsonia cutlerensis formed the her analysis of amphibamid relationships along with ingroup along with Ach. dunni. A total of 53 cranial Ecolsonia. The analysis placed Ecolsonia outside characters was used in the analysis. Character Trematopidae; however, although several different coding for Ecolsonia, all trematopid taxa except trematopid taxa were discussed, character coding for Actiobates, and Cacops was based on first hand the group as a whole was based largely on Acheloma. observations (Appendix 1). Coding for all other taxa Subsequent authors followed this trend, coding char- was based primarily on the data matrices of Schoch acters for trematopids using only Acheloma and & Rubidge (2005), Ruta & Bolt (2006), and published Phonerpeton (Ruta, Jeffery & Coates, 2003; Schoch & descriptions as cited. A parsimony analysis was per- Rubidge, 2005; Anderson et al., 2008; Fröbisch & formed using PAUP 4.0b10 (Swofford, 2003) and Reisz, 2008). The purposes of these studies were not MacClade 4.08 (Maddison & Maddison, 1992). All to examine trematopid ingroup relationships; still, analyses were performed using a branch-and-bound the approach maintained monophyly for trematopids, search with all characters equally weighted and allowing the clade to be effectively utilized for out- unordered. Bremer support and bootstrap values group comparison. However, resolution within the were calculated to determine the robustness of group was lost through this method and the diversity nodes. The analysis resulted in one single most par- existing within Trematopidae as highlighted by simonious tree with a tree length of 99 steps, con- Sumida et al. (1998) remained unaccounted for. As a sistency index of 0.66, and rescaled consistency result, forms such as Ecolsonia and Actiobates failed index of 0.44 (Fig. 15). to cluster with derived trematopid taxa like Ache- The Olsoniformes (Dissorophidae, Trematopidae) loma, and fell outside the clade. forms a clade supported by three unambiguous syna- Ruta et al. (2007) included all valid trematopid pomorphies (16, 19, 20). Two additional steps are taxa, as well as Ecolsonia and Actiobates into a super- required to collapse the node. It is supported by a tree of temnospondyl relationships. The results bootstrap value of 66%. showed that Actiobates grouped with the trematopids The monophyly of Trematopidae is supported by Anconastes and Tambachia, whereas Ecolsonia fell four unambiguous synapomorphies (39, 41, 42, 44) within Dissorophidae. Conversely, the analysis of dis- and includes all previously valid trematopids along sorophoid relationships conducted by Huttenlocker, with Actiobates and Ecolsonia. The clade is strongly Pardo & Small (2007) indicated that Ecolsonia shared supported by a Bremer value of 5 and bootstrap value a more recent common ancestor with trematopids of 82%. Members of Trematopidae are defined by the than dissorophids. Although the study did not resolve presence of an elongated external naris (39); canini- trematopid ingroup relationships, data from Ache- form teeth (41); an inflection of the prearticular along loma, Phonerpeton, Tambachia, and Actiobates were the medial rim of the adductor fossa (42); and a considered when coding characters for Trematopidae. median vomerine septum (44).

Figure 15. Single most parsimonious tree of dissorophoid relationships derived from cladistic analysis using PAUP 4.0b10 with A, relevant synapomorphies mapped on (* indicates a synapomorphy that supports the clade, but appears elsewhere in the tree); B, bootstrap (bold numbers) and Bremer decay (italic numbers) values calculated for the analysis; TL, tree length; CI, consistency index; RC, rescaled consistency index. Acheloma dunni is highlighted in bold.

Within Trematopidae, Actiobates, Ecolsonia, Ancon- As an olsoniform, Ach. dunni falls within the group of astes,andTambachia form a clade based primarily on Palaeozoic amphibians considered to exhibit morpho- the contribution of the maxilla to the ventral margin logical specializations for life on land (Bolt, 1969; of the orbit in the absence of an l.e.p. and l.e.e. The Berman et al., 1987; Sumida et al., 1998; Dilkes & node collapses after an additional two steps and it has Brown, 2007; Markey & Marshall, 2007; Schoch, a bootstrap value of 75%. Anconastes and Tambachia 2009). Its tall, box-like skull with laterally positioned are strongly united by a Bremer value of 6 and orbits and lack of lateral line canals is comparable to bootstrap value of 77%. Interestingly, both Ecolsonia that of Early Permian terrestrial amniotes and other and Actiobates may share a more recent ancestor with olsoniforms (Dilkes & Brown, 2007; Reisz et al., Anconastes and Tambachia (the two trematopids 2009). Furthermore, well-ossified limb bones includ- often left out of analyses) than either does with Ache- ing a humerus with well-developed condyles and loma or Phonerpeton. This may account for instances prominent supinator process suggest that Ach. dunni in which Ecolsonia fell outside Trematopidae when possessed large muscles capable of holding itself up trematopid character coding was representative of on land (Pawley & Warren, 2006; Dilkes & Brown, only Acheloma or Phonerpeton. Furthermore, replace- 2007). What is known of the axial skeleton bears ment of the supratympanic shelf by dermal sculptur- similarities to that of other olsoniforms characterized ing along the dorsal rim of the otic notch has been by a well-ossified atlas-axis complex and presacral cited as a character uniting Dissorophidae (Daly, vertebrae contributing to a relatively short trunk 1994), and was used to argue the assignment of (Williston, 1909, 1910). Although many medium to Ecolsonia as a dissorophid (Berman et al., 1985). large temnospondyls similar in size to the olsoniforms However, this character cannot be valid because the were aquatic (Schoch, 2009), their relatively short recently described dissorophid Cacops morrisi (Reisz axial length and small tail would suggest that olsoni- et al., 2009) retains a supratympanic shelf along the forms were more suited for an amphibious to terres- dorsal border of its otic notch. trial lifestyle (Laurin, Girondot & Loth, 2004). The new trematopid recovered from Richards Spur Furthermore, the atlas-axis complex observed in Ach. clusters with Acheloma and indicates that we can dunni is robust like that of Diadectes (Sumida & place it with that genus, but as a new species. The Lombard, 1991). The atlas would have attached node uniting Ach. dunni and Ach. cumminsi is sup- firmly to the occipital condyles, and probably would ported by two unambiguous synapomorphies: vomer have provided support for the weight of the massive with raised crest lying mesial to choana (33-0); and skull in terrestrial environments. otic notch with nearly horizontal ventral margin (43). The function of the posterior expansion of the The node has a Bremer support value of 8 and boot- trematopid external narial opening has been the focus strap value of 98%. Acheloma dunni is distinguished of limited inquiry (Olson, 1941; Bolt, 1974c; Dilkes, from all other dissorophoids based on a single auta- 1991, 1993). Bolt (1974c) proposed that the posterior pomorphy: the presence of sculptured lateral expo- portion of the external naris developed in response to sure of palatal elements that are excluded from the the lateral expansion of a gland. Furthermore, as the ventral margin of the orbit. external naris expanded to accommodate the gland, Phonerpeton does not form a clade with Acheloma the narial flange may have developed its unique mor- as previous studies have suggested (Dilkes, 1990; phology to counteract stress concentrated on the Sumida et al., 1998; Ruta et al., 2007). This contra- narrow antorbital bar during feeding and avert the diction has resulted from changes in the character potential loss of structural integrity in the rostrum. coding with respect to the presence of parasphenoid He cited the lateral expansion of the glandula nasalis dentition in Acheloma. Originally, Acheloma and externa (salt gland) found in living reptiles as the Phonerpeton were united based on the presence of an most likely candidate, suggesting that it may have internarial fenestra and a lack of teeth on the paras- helped the amphibians cope with the demands of phenoid. The internarial fenestra appears in an array living in terrestrial environments. However, within of other dissorophoids. Examination of the holotype of extant taxa, salt glands are found primarily in birds Ach. cumminsi along with the fact that dentition is and reptiles that are either marine or feed on vegeta- present on the parasphenoid of Ach. dunni resulted in tion with high potassium content; functioning prima- the collapse of the node uniting Phonerpeton and rily in ionic regulation rather than osmoregulation Acheloma. (Peaker & Linzell, 1975). Neither condition would appear to be met by the carnivorous, terrestrial trematopids. Regardless of whether or not the posterior SPECULATIONS ON HABITS AND LIFESTYLE expansion of the external naris was caused by the Acheloma dunni appears to represent a large, terres- enlargement of a salt gland, Bolt (1974c) concluded trial predator within the Richards Spur assemblage. that the typical trematopid elongated external naris

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 789–815 810 B. P. POLLEY and R. R. REISZ and narial flange could not be used as diagnostic ectopterygoid fangs in Ach. dunni would have characters for the family. He reasoned that in any undoubtedly resulted in different forces acting on the labyrinthodont, the expansion of any structure lateral palate and suborbital bar during feeding in compari- to the nasal cavity could result in an elongated exter- son to Ach. cumminsi. If Bolt (1974b) was correct in nal narial opening along with the subsequent devel- asserting that the l.e.p. counteracted stress associ- opment of a narial flange. The argument was later ated with feeding then the evolution of laterally used to support removing Ecolsonia from Trematopi- exposed palatal elements in Ach. dunni may relate to dae (Berman et al., 1985). forces ensued on the skull by the enlarged ectoptery- Conversely, Dilkes’ (1993) study of the cranial goid fangs. ontogeny of Phonerpton suggests that the narial Trematopids have generally been considered as ter- flange developed early in the postmetamorphic ontog- restrial predators (Olson, 1941; Dilkes, 1990; Markey eny of trematopids. In turn, the posterior expansion of & Marshall, 2007). Recent fossil evidence indicates the external naris occurred successively, correlating that large olsoniforms like Ach. dunni at least scav- with the growth of the premaxillary and maxillary enged on top predators and played a significant role caniniform teeth and probable changes in the areas of in their ecosystems (Reisz & Tsuji, 2006; Reisz et al., stress concentration in the skull. He argued that the 2009). Acheloma dunni is the largest described narial flange evolved as a terrestrial adaptation in species of the Richards Spur assemblage (Maddin dissorophoids, enhancing water conservation and et al., 2006) and displays a host of complex adapta- olfactory sensitivity by increasing the surface area of tions associated with specialized feeding habits. As the nasal capsule. Additionally, the flange may have such, Ach. dunni may represent the top predator of been modified in trematopids to also reinforce the the Richards Spur ecosystem. skull. Furthermore, Dilkes (1993) stated that the presence of a salt gland is equivocal and as seen in living reptiles, an expansion of such gland would not ACKNOWLEDGEMENTS necessarily result in the posterior expansion of the external naris. Although the true physiological func- We are grateful to D. Scott for assisting in preparing tion of the elongated external naris and narial flange and photographing specimens. Special thanks to B. is unknown, both Bolt (1974c) and Dilkes (1993) agree Dunn and M. Feese for their continuing efforts to that changes in forces acting on the skull during collect fossils from Richards Spur. This project, feeding played a key role in their development. The amongst countless others, would not have been pos- advent of the use of finite-element analysis in assess- sible without their generous donations to the Sam ing sutural stress responses to feeding forces (Ray- Noble Oklahoma Museum of Natural History. We are field, 2005) may provide promising insight into the thankful to D. Berman of the Carnegie Museum of purpose of these unique features. Natural History, Pittsburgh, PA; R. Ethington of the Modifications in sutural morphology in response to University of Missouri, Columbia, MO; M. Norell of changes in forces associated with feeding are also the American Museum of Natural History, New York, illustrated in the unique configuration of the l.e.p. NY; and M. Ryan of the Cleveland Museum of Natural and l.e.e. in Ach. dunni. Bolt (1974b) proposed that History, Cleveland, OH for allowing us access to the l.e.p. (and probably the l.e.e.) evolved in early various trematopid specimens for study. dissorophoids typically characterized by small skulls with large orbits. A thickening of the palatine and its subsequent migration into the circumorbital elements REFERENCES of a widening orbit would have provided mechanical support for compressive forces acting on the narrow Anderson JS, Henrici A, Sumida SS, Martens T, Berman DS. 2008. Georgenthalia clavinasica, a new genus and suborbital bar during feeding. However, unlike other species of dissorophoid temnospondyl from the early dissorophoids, Ach. dunni has small orbits and a tall Permian of Germany, and the relationships of the family suborbital bar comparable to that of Ach. cumminsi.A Amphibamidae. 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APPENDIX 1 Data matrix used for phylogenetic analysis including 12 taxa and 54 characters. ‘a’ represents polymorphic characters (0 and 1)

1 1111111112 2222222223 1234567890 1234567890 1234567890

Acheloma cumminsi 0110000?01 0011010111 10??001011 Acheloma dunni 3110000?01 0011010111 10?0001011 Actiobates peabodyi 2??000???0 0???1?111? 10?0010111 Anconastes vesperus 2??001??0? 001???0111 11?0000010 Cacops morrisi 1111000011 0111010111 1100000011 Ecolsonia cutlerensis 2110001000 0011010011 1100000011 Eoscopus lockardi 110000aa11 111110110a 1011000011 Micromelerpeton credneri 1?1000aa1a 00?1001000 1110000011 Micropholis stowi 1110111a11 11110a0000 1a10000011 Phonerpeton pricei a111000000 0011110111 1000001011 Sclerocephalus haeuseri 0000001000 0000000000 0000101000 Tambachia trogallas 21?0010?0? 0011010111 11??000?10

3333333334 4444444445 555 1234567890 1234567890 123

Acheloma cumminsi 1100001011 1111110000 002 Acheloma dunni 1100001011 1?11?10000 002 Actiobates peabodyi 0??????11? 1???010100 111 Anconastes vesperus 0??????010 1101?10100 111 Cacops morrisi 00110??001 0000201011 012 Ecolsonia cutlerensis 0110001010 1101210111 110 Eoscopus lockardi 101100?001 0000000010 110 Micromelerpeton credneri 10111??100 0000000000 000 Micropholis stowi 10110??000 0000000010 210 Phonerpeton pricei 0010001011 1101000010 011 Sclerocephalus haeuseri 10100??000 0000000000 000 Tambachia trogallas 0?100??110 1101010100 111

APPENDIX 2 palatine wedging between lacrimal and jugal to make contribution to skull roof and orbital Descriptions of characters used in phylogenetic analy- margin (1); maxilla contributes to orbital margin sis. Characters 1–24 are informative cranial charac- in the absence of lateral exposure of palatine (2) ters based on Schoch & Rubidge (2005). Characters (based on Sumida et al., 1998); lateral exposure of 25–38 are taken from Ruta & Bolt (2006). Characters palatine present and excluded from orbital 39–54 are from literature as cited. margin by jugal and lacrimal contact (3). 1. Laterally exposed palatine: palatine overplated 2. Dorsal quadrate process: quadrate having smooth by jugal and lacrimal with no lateral exposure (0); posterodorsal side in plesiomorphic state (0);

quadrate with prominent dorsoposterior out- 15. Tabular size: Tabular narrower than postparietal, growth, the quadrate process (1). but reaching almost same size as latter (0); 3. Vomerine depression: ventral surface of vomers tabular minute and laterally constricted by flat and element divided into anterior and unique enlargement of otic notch (1). posterior portion by transverse ridges that may or 16. Tabular-squamosal: Tabular and squamosal may not bear transverse tooth row (0); single widely separated by supratemporal (0); squamo- unpaired depression in anterior portion of vomers sal meeting tabular, excluding supratemporal that may or may not house an opening (1). from otic notch (1). 4. Parasphenoid dentition: basal plate of parasphe- 17. Postparietal length: postparietal forming trans- noid bearing shagreen of small teeth (denticles) versely rectangular or quadrangular element (0); anteromedially (0); plate entirely smooth (1). postparietal abbreviated and reduced to narrow, 5. Parasphenoid denticle field: parasphenoid den- poorly ornamented strut at posterior margin of ticle field well established, with triangular skull table (1). outline and with apex reaching onto base of 18. Squamosal-supratemporal: suture between squa- cultriform process (0); denticle field greatly mosal and supratemporal nearly as long as expanded anteriorly to cover most of the cultri- supratemporal itself (0); foreshortened squamoso- form process (1). supratemporal suture reaching only one third or 6. Parasphenoid basal plate: basal plate roughly less of length of supratemporal (1). quadrangular, as long as wide (0); basal plate 19. Supratympanic flange (= semilunar flange in much shorter than wide, reaching about half the Schoch & Rubidge, 2005, terminology following width (1). Bolt, 1974a): squamosal continuously orna- 7. Vomerine denticle field: vomer covered with more mented around margin of otic notch (0); squamo- or less dense shagreen of teeth in addition to sal having dorsally exposed and ornamented area obligatory fang pair (0); shagreen confined to (supratympanic flange) stepping abruptly into juvenile stages and /or absent throughout ontog- steeply aligned, poorly ornamented portion (1). eny (1). 20. Semilunar flange (= supratemporal flange of 8. Vomerine fangs: vomer lacking fangs in its medial Schoch & Rubidge, 2005): supratemporal without portion, outside lateral tooth arcade, but having ventral projection into otic notch (0); supratem- smaller accessory teeth in that region (0); vomer poral forming marked ventral flange participat- with additional fang pairs posterior to mid- ing in medial bordering of otic notch (1). vomerine depression (1). 21. Prefrontal-postfrontal: prefrontal and postfrontal 9. Pterygoid-vomer: retention of suture between firmly sutured, excluding the frontal from orbital pterygoid (palatine ramus) and vomer (0); ptery- margin (0); both elements separated by frontal, at goid contacting only posterior-most portion of least dorsally (1). palatine and lacking suture with vomer (1). 22. Skull width: moderately wide skull with jugals, 10. Pterygoid flange: palatine ramus of pterygoid postorbitals, and medial skull roofing series merging continuously into basipterygoid ramus usually longer than wide (0); skull table and (0); palatine ramus broadening abruptly to form cheek overall broadened, most elements being as transverse flange (1). wide as long or wider (1). 11. Palatine, ectopterygoid: palatine and ectoptery- 23. Palpebral ossifications: ossifications in orbit goid much wider than maxilla (0); palatine and restricted to sclerotic ring (0); numerous palpe- ectopterygoid reduced to narrow struts not wider bral ossicles at medial margin of sclerotic ring than adjoining maxilla (1). (1). 12. Interpterygoid vacuity: interpterygoid vacuity 24. Stapes: stapes with pronounced dorsodistal cur- roundish or oval in outline (0); interpterygoid vature directed towards dorsally located otic vacuity greatly expanded laterally at mid-level notch (0); stapes abbreviated without dorsodistal (1). curvature, directed laterally towards vertically 13. Narial flange: ventral (inner) side of prefrontal, aligned otic notch (1). lacrimal, and nasal smooth (0); inner side of these 25. Absence (0) or presence (1) of a prefrontal-jugal bones forming complicated bar-like structure contact. (narial flange), permitting contact with antorbital 26. Maxilla extending posterior to the level of the bar (1). posterior margin of the orbit (0) or terminating at 14. Prefrontal process: prefrontal forming simple the level of such margin or anterior to it (1). suture with lacrimal laterally (0); prefrontal 27. Absence (0) or presence (1) of inward inflection of underplating lacrimal widely by means of ventral skull outline in dorsal view at the level of the prefrontal process contacting palatine (1). maxilla-premaxilla suture.

28. Presence (0) or absence (1) of a maxilla- 42. Inﬂection of the prearticular along the medial rim quadratojugal contact. of the adductor fossa: absent (0); present (1) 29. Parietals more (0) or less (1) than two and a half (Dilkes, 1990). times as long as wide. 43. Ventral border of otic notch: slopes posteroven- 30. Postparietal less than (0) or more than (1) four trally (0); nearly horizontal (1) (Dilkes & Reisz, times wider than long. 1987). 31. Postorbital not narrowing (0) or narrowing (1) to 44. Median vomerine septum: absent (0); present (1) an acute posterior point. (Dilkes & Reisz, 1987; Dilkes, 1990). 32. Absence (0) or presence (1) of condition: 45. Tabular process: short or absent (0); curves vomer with posterolateral ramus that extends gradually to meet robust quadrate process (1); posteriorly along the medial margin of the bent down sharply at approximately a right palatine. angle to the dorsal edge of the skull table and 33. Vomer with (0) or without (1) a toothed, raised fused to the quadrate process (2) (Dilkes & Reisz, crest running anteroposteriorly and lying mesial 1987). to the choana. 46. Stapedial foramen: absent (0); present (1) (Daly, 34. Palatine excluded from (0) or contributing to (1) 1994). the interpterygoid vacuity. 47. Knobby exostoses ornamenting the skull roof: 35. Absence (0) or presence (1) of condition: palatal absent (0); present (1) (Daly, 1994). ramus of the pterygoid forming a butt joint with 48. Subnarial lacrimal process: long (0); short (1) the posterior margin of the palatine, thus (Sumida et al., 1998). producing a continuous sheet of bone with the 49. Semilunar curvature of the squamosal along latter. ventral border of the supratympanic ﬂange: 36. Absence (0) or presence (1) of an exoccipital- absent (0); present (1) (Berman et al., 1985; tabular contact. Dilkes, 1990). 37. Absence (0) or presence (1) of an exoccipital- 50. Dorsal rim of occiput: smooth (0); ornamented (1). postparietal contact. 51. Ratio of preorbital length to postorbital length: 38. Jaw articulation lying posterior to (0), level with preorbital length greater than postorbital length (1), or anterior to (2) the posterior facets of the by greater than 10% (0); preorbital and postor- exoccipitals. bital lengths approximately equal (1); postorbital 39. External narial opening: uniform, oval shaped length greater than preorbital length by greater margin (0); posteriorly expanded with distinct than 10% (2). anterior and posterior regions giving external 52. Suborbital bar height: greater than 10% of the naris an overall ‘key-hole’ shape (1) (Dilkes, total midline skull length (0); less than 10% of the 1990). total midline skull length (1). 40. Internarial fenestra: present (0); reduced (1); 53. Minimum distance between otic notch and orbital absent (2) (Dilkes, 1990). margin: greater than 25% of the total midline 41. Marginal teeth: uniform in size (0); caniniform skull length (0); between 10 and 25% of the total teeth on premaxilla and maxilla (1) (Dilkes, midline skull length (1); less than 10% of the total 1990). midline skull length (2).