Cranial Anatomy of the Late Triassic Phytosaur Machaeroprosopus, with the Description of a New Species from West Texas

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Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas

Article in Earth and Environmental Science Transactions of the Royal Society of Edinburgh · September 2012 DOI: 10.1017/S1755691013000364

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Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas

Axel Hungerbühler, Bill Mueller, Sankar Chatterjee and Douglas P. Cunningham

Earth and Environmental Science Transactions of the Royal Society of Edinburgh / Volume 103 / Issue 3-4 / September 2013, pp 269 - 312 DOI: 10.1017/S1755691013000364, Published online: 07 October 2013

Link to this article: http://journals.cambridge.org/abstract_S1755691013000364

How to cite this article: Axel Hungerbühler, Bill Mueller, Sankar Chatterjee and Douglas P. Cunningham (2013). Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 103, pp 269-312 doi:10.1017/S1755691013000364

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Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas Axel Hungerbu¨hler1, Bill Mueller2, Sankar Chatterjee2 and Douglas P. Cunningham2 1 Mesalands Community College, 911 S. Tenth Street, Tucumcari, NM 88401, USA. Email: [email protected] 2 Division of Paleontology, Museum of Texas Tech University, Box 43191, Lubbock, TX 79409, USA.

ABSTRACT: The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with bevelled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital–parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redon- dasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus.

KEY WORDS: Dockum, Norian, Pseudopalatus, Redondasaurus

Phytosaur skulls are abundant in the Upper Triassic Chinle skull of M. jablonskiae from the Petrified Forest. Other than Formation in the southwestern United States, especially those that, the most informative overall studies of a pseudopalatine of pseudopalatine phytosaurs, the most derived clade of phy- phytosaur from North America to date remain Camp’s (1930) tosaurs that includes various species that have been referred account on M. tenuis and Mehl’s (1922) description of M. to Pseudopalatus Mehl, 1928 and Redondasaurus Hunt & Lucas, andersoni. Parker & Irmis (2006) defined a node-based clade 1993. As a rough estimate, more than 75 skulls of these two for the Pseudopalatinae following Hungerbu¨hler (2002). They genera have been recovered over the last hundred years in Ari- defined the clade as Nicrosaurus, Mystriosuchus, Pseudopalatus, zona, Colorado, New Mexico, Texas and Utah. This number Redondasaurus, and all the descendants of their last common represents approximately one-third of all phytosaur skulls ancestor. known from North America. Given the abundance, it is strik- Here we present a detailed description of the cranial anatomy ing how little information is available about the detailed cra- of the genus Machaeroprosopus on the basis of three skulls. The nial anatomy of this group. The seminal paper on phytosaur excellent preservation of the specimens provides a wealth of new skull morphology is still Camp’s (1930) study based on obser- morphological information on previously debated anatomical vations on the types of Smilosuchus gregorii (Camp 1930) and structures, in particular relating to the braincase and the palate, Smilosuchus adamanensis (Camp 1930). Because the configura- both regions of the skull that are either frequently inaccessible tion of the skull elements in many specimens of pseudopalatine or rarely preserved because of their fragile nature. Moreover, phytosaurs, among them almost all type specimens, is rather two of the specimens represent a new species of Machaeropro- imperfectly preserved, the majority of accounts deal more sopus. They provide additional evidence for sexual dimorphism with the general appearance of the skull rather than with osteo- in phytosaurs, and their unusual combination of characters has logical details (Cope 1881; Huene 1915; Hunt & Lucas 1993; important implications for the taxonomy of North American Long & Murry 1995; Lucas et al. 2002). More recent accounts pseudopalatine phytosaurs. of older collections from Arizona (Heckert & Lucas 2000) and Taxonomic note. Parker et al. (2013 (this volume)) demon- New Mexico (Zeigler et al. 2002a, 2003b) and recently discov- strate that Pseudopalatus Mehl, 1928 is a junior synonym of ered, well-preserved material of pseudopalatine phytosaurs Machaeroprosopus Mehl, 1916. We argue below that there from the Petrified Forest Member of the Chinle Formation are good reasons to consider the genus Redondasaurus Hunt and the Redonda Formation of New Mexico (Heckert et al. & Lucas, 1993 a junior synonym of Machaeroprosopus as 2000; Zeigler et al. 2002b, 2003a) similarly provide few detailed well. Consequently, in the text we refer to all nominal species osteological data. Parker & Irmis (2006) have provided, to date, that are currently included in Pseudopalatus and Redondasau- the most detailed cranial description of a North American rus as species of Machaeroprosopus. We provisionally follow pseudopalatine phytosaur, with their description of the partial Stocker (2010) in using the genus-group names Leptosuchus

6 2013 The Royal Society of Edinburgh. doi:10.1017/S1755691013000364 270 AXEL HUNGERBU¨ HLER ET AL. Case, 1922 sensu strictu, Smilosuchus Long & Murry, 1995 onisciform actinopterygian, a temnospondyl amphibian, the and Pravusuchus Stocker, 2010 for taxa that were traditionally aetosaur Typothorax, the rauisuchid Postosuchus, the poposau- part of a more inclusive concept of Leptosuchus. roid Shuvosaurus and a theropod dinosaur (Cunningham et al. Institutional abbreviations. AMNH, American Museum of 2002). Natural History, New York, NY; CM, Carnegie Museum of Natural History, Pittsburgh, PA; GPIT, Palaöntologische Sammlung, University of Tu¨bingen, Germany; NHMUK, 2. Systematic paleontology The Natural History Museum, London, UK; NMMNH, New Archosauriformes Gauthier, Kluge & Rowe, 1988 Mexico Museum of Natural History and Science, Albuquerque, Phytosauria Jaeger, 1828 sensu Nesbitt 2011 NM; PEFO, Petrified Forest National Park, AZ; SMNS, Phytosauridae Jaeger, 1828 sensu Doyle & Sues 1995 Staatliches Museum fu¨r Naturkunde Stuttgart, Germany; Pseudopalatinae Long & Murry, 1995 sensu Parker & Irmis 2006 TTU, Museum of Texas Tech University, Paleontology Divi- Machaeroprosopus Mehl, 1916 sion, Lubbock, TX; UCMP, University of California, Museum of Paleontology, Berkeley, CA; UMMP, Museum of Paleon- Synonyms. Arribasuchus Long & Murry, 1995; Pseudopalatus tology, University of Michigan, Ann Arbor, MI; UMo, Uni- Mehl, 1928; Redondasaurus Hunt & Lucas, 1993. versity of Missouri, Department of Geological Sciences, Ver- Type species. Belodon buceros Cope, 1881. tebrate Paleontology Collection, Columbia, MO; YPM Yale Diagnosis. Pseudopalatinae that are tentatively distinguished Peabody Museum, New Haven, CT. from the other pseudopalatine phytosaur genera Nicrosaurus and Mystriosuchus by several derived character states: ventrally convex suture of the maxilla with the premaxilla and nasal (also 1. Geological setting of the Patricia Site (locality in Leptosuchus and Smilosuchus ssp.); exposure of supratem- number TTU VPL 3870) poral fenestra on skull roof reduced to narrow slit or entirely closed (also in Angistorhinopsis ruetimeyeri (Huene 1911): Upper Triassic strata of the Dockum Basin are exposed along Huene 1922); distinct subsidiary opisthotic process of squa- the eastern escarpment of the Southern High Plains in the mosal (also in Pravusuchus Stocker, 2010); lateral corner of Texas Panhandle, and continue along the western escarpment posttemporal fenestra formed by squamosal, rather than by and the Pecos River Valley in eastern New Mexico. Researchers union of squamosal and paroccipital process; base of paro- from New Mexico (e.g., Lucas & Hunt 1989; Lucas et al. 1994, ccipital process of opisthotic expands posteriorly in a sinuous 2001) and Texas (Lehman 1994a, b; Lehman & Chatterjee 2005; curve, resulting in the exoccipital pillar being in extension of Martz 2008) advocate two competing stratigraphic schemes. We midline, rather than the posterior rim of the paroccipital pro- note that this debate is largely about priority and nomenclature, cess, and the posterior outline of the posttemporal fenestra being and both stratigraphic schemes agree that the units relevant oblique rather than parallel to the axis of paroccipital process here, the upper portion of the Cooper Canyon Formation in (also in Leptosuchus, Smilosuchus and Pravusuchus ssp.); basioc- Texas and the Bull Canyon Formation in New Mexico, are cipital condyle receded under supraoccipital shelf and obscured equivalents in time. We follow the stratigraphic nomenclature in dorsal view (also in Leptosuchus, Smilosuchus and Pravusu- as proposed by Lehman (1994a). Accordingly, the Dockum chus ssp.); vomers on anterior half of interchoanal septum flat Group of Texas includes, in ascending order, four mappable and broad, rather than narrow and sharp. The validity of these units: the Santa Rosa Sandstone, the Tecovas Formation, the apomorphic characters as synapomorphies of Machaeropro- Trujillo Sandstone and the Cooper Canyon Formation (upper sopus needs to be tested by a more comprehensive phylogenetic Cooper Canyon of Martz 2008). A fifth and uppermost unit of analysis. the Dockum Group, the Redonda Formation, is restricted to Distribution. Restricted to the uppermost units of the Triassic eastern New Mexico and seems to grade eastward and south- of the southwestern USA (the stratigraphic nomenclature fol- ward into the upper part of the Cooper Canyon Formation. lows Parker & Martz (2011) for Arizona; Lucas (1993, 1997) The strata forming the Trujillo Sandstone and Cooper and Heckert & Lucas (2000) for New Mexico; and Lehman Canyon Formation represent a thick (maximum more than (1994a) for Texas): Upper part of the Sonsela Member (Parker 150 m) alluvial depositional sequence, separated from the un- & Irmis 2006; Parker & Martz 2011), Petrified Forest Member derlying Tecovas Formation by a locally angular uncon- (Heckert & Lucas 2002; Parker & Martz 2011), and Owl Rock formity. The basal part of the Trujillo Sandstone consists of Member (Kirby 1989; Heckert & Lucas 2000; Parker & Martz thick, multistoried and laterally-extensive fluvial channel-sand 2011) of the Chinle Formation of Arizona; Bull Canyon bodies that reflect multiple phases of channel incision, lateral (Hunt 2001), Rock Point (Lucas & Hunt 1992), and Redonda migration and aggradation. The Trujillo Sandstone grades (Hunt & Lucas 1993) Formations of north-central and eastern and intertongues upward with an increasing proportion of New Mexico; Cooper Canyon Formation of West Texas fluvial flood-plain mudstone, and thus the overlying Cooper (Lehman & Chatterjee 2005; this study). Canyon Formation is largely mudstone-dominated. Inter- bedded fluvial channel sandstone units in the Cooper Canyon Machaeroprosopus lottorum sp. nov. Formation mostly reflect single phases of channel migration (Figs 2–5, 7, 11–15, 18, 20–23) and aggradation, and so tend to be single-storied. Holotype. TTU-P10076, cranium. The Patricia Site TTU VPL 3870 served as an example for Paratype. TTU-P10077, cranium, only referred specimen. vertebrate bone accumulation in channel facies (Lehman & Type locality. TTU Vertebrate Paleontology Locality 3870 Chatterjee 2005). The site is located about 13 km southwest (exact locality data reposited at TTUP), 13 km South of Post, of Post, in Garza County. Vertebrate fossils, along with car- Garza County, Texas. bonaceous plant remains, occur here within the upper part of Type horizon. Upper part of the Cooper Canyon Formation, the Cooper Canyon Formation, in channel deposits of fine- Dockum Group, Upper Triassic. grained sandstone and green mudstone (Fig. 1). Age. Norian, Late Triassic. The most abundant fossils collected from this site are phyto- Distribution. Restricted to type locality saurs, representing more than 90% of the identifiable remains. Diagnosis. Machaeroprosopus lottorum is diagnosed by four In addition TTU VPL 3870 yielded isolated remains of a palae- characters which we interpret as autapomorphic for the taxon: NEW MACHAEROPROSOPUS FROM WEST TEXAS 271

Figure 1 Patricia Site TTU Vertebrate Paleontology Locality 3870, Garza Co., Texas: (A) view of Site 1C, the locality of TTU-P10074; (B) composite section of Locality 3870, with depositional interpretation and the stratigraphic position of phytosaur specimens. Arrows indicate the position of the two characteristic conglomeratic beds that bracket the main fossiliferous strata.

(1) lateral rim of naris broad, flat, and rugose; (2) supratem- supraoccipital complex; in addition, from M. mccauleyi by (1) poral fenestra fully closed in dorsal aspect, forming a shallow a shorter antorbital fenestra; (2) a parietal ledge that is twice as semicircular indentation into the skull roof (parietal, postorbi- wide; and lateral walls of the parietal–supraoccipital complex tal and squamosal) with strongly bevelled rim that continues that are (3) thick-based and (4) low; in addition, from M. onto the parietal; (3) free section of postorbital–squamosal buceros by a gently sloping rather than sinuous outline of the bar (equalling in Machaeroprosopus the length of the dorsal rostral crest in the morph with extended rostral crest; from surface of squamosal) short; (4) strongly developed horizontal both M. gregorii (Hunt & Lucas 1993) and M. bermani (Hunt medial laminae of palatines, that almost close the posterior & Lucas 1993) by a shorter and higher posttemporal fenestra; section of the palatal vault in ventral view. in addition, from M. gregorii by (1) a high posterior process of Differential diagnosis. In addition to the autapomorphic fea- the squamosal with elevated dorsal surface; (2) a bulging lateral tures, M. lottorum is distinguished from other species referred surface of this process; (3) a deep, rather than shallow supra- here to Machaeroprosopus by a number of characters that we occipital shelf framed by squamosal processes of the parietals assess as systematically important. The systematic validity of that are (4) sloping rather than vertical in their ventral section; other variable features (see Table 1 and Appendix) is problem- and (5) the squamosal forming the lateroventral rim of the post- atic because they differ in referred specimens from the type temporal fenestra by developing of a lamina onto the parocci- specimens (e.g., naris elevation: Camp 1930; Zeigler et al. pital process. M. lottorum differs from M. jablonskiae by having 2002a, b, 2003b) or they evidently vary within the hypodigms a lateral ridge on the squamosal, a knob-like tip on the of other pseudopalatine taxa (see Hungerbu¨hler 1998). Ma- squamosal, a rectangular outline of the parietal–supraoccipital chaeroprosopus lottorum differs from all species of Machaero- complex, low lateral walls of the parietal–supraoccipital com- prosopus except M. gregorii by a comparatively broad dorsal plex, and a beveled rim of the supratemporal fenestra that surface of the squamosal; from both M. buceros (Cope 1881), continues onto the parietal. A distinction from M. andersoni in which we include M. pristinus (Mehl 1928) and M. tenuis Mehl, 1922 is more difficult because of the incompleteness of Camp 1930, and from M. mccauleyi (Ballew 1989) by (1) the the holotype of this species, but M. andersoni does not show absence of a prenarial groove; (2) the lateral ridge of the squa- the autapomorphic characters 1, 2, and 4 of M. lottorum, pos- mosal being absent on the posterior process i.e., the dorsal and sesses a rounded, un-crested palatal ridge, and the maxillary lateral surfaces of the process grade into each other; (3) a short furrow is absent. and low rather than long and extensive flange of the squamosal; Etymology. In honur of John Lott and Patricia Lott Kirk- and (4) a rectangular rather than round top of the parietal– patrick for their continuous support of this project. 272 AXEL HUNGERBU¨ HLER ET AL.

Table 1 Character-taxon matrix used in the analysis of the phylogenetic position of Machaeroprosopus lottorum and TTU P10074. 0 ¼ primitive character state; 1, 2, 3 ¼ derived character states; A ¼ character states 0 or 1; B ¼ character states 0 and 1; ? ¼ missing data.

Character

1 11111 11112 22222 22223 33333 33334 4 Taxon 12345 67890 12345 67890 12345 67890 12345 67890 1

Outgroup taxa Nicrosaurus kapfﬁ 11220 11001 10000 10100 02000 00000 00000 00000 0 Mystriosuchus planirostris 00000 00010 00000 02010 20011 10021 03010 20200 0 Mystriosuchus westphali 10000 10020 00000 02110 02011 10021 03010 20200 0 Ingroup taxa and specimens Machaeroprosopus mccauleyi ?0211 10111 10010 20111 12022 21011 00100 02001 0 Machaeroprosopus pristinus 00101 00010 10111 21111 21012 210?? ?1011 022?0 ? Machaeroprosopus buceros 10220 0?020 1??21 2??11 20222 2?0?2 ?1111 0?11? ? Machaeroprosopus gregorii 00A00 0???? ?0121 21000 01200 03022 13111 112?? ? Machaeroprosopus bermani 11211 11121 10000 11111 B1012 13012 120?? 1?211 1 Machaeroprosopus jablonskiae ????? ??0?? ???0? 12000 12011 ?1112 1?00? ????? ? TTU-P10074 00000 01111 00111 21110 10222 12011 12011 02201 0 TTU-P10076 00101 01110 11100 22000 10122 12122 12011 02111 1 TTU-P10077 11211 01120 11121 12000 1AA22 12122 ?2011 ??211 1

2.1. Material and preservation site and most likely belongs to this specimen. The cranium is entirely freed of matrix. The length is 815 mm from the anterior 2.1.1. TTU-P10076 (Figs 2, 3). Complete, 945 mm-long, break of the premaxillae to the tip of the sqamosals; the total slender-snouted and gracile cranium, including the most com- length is estimated to be 900 mm. plete and informative dentition of a specimen of Machaeropro- sopus known to date. The specimen was found lying on the left 2.2. Description of Machaeroprosopus lottorum sp. nov. side and slightly tilted onto the skull roof, with the right pos- The description of the cranial anatomy of Machaeroprosopus terior portion of the postorbital region broken up and scat- lottorum focuses on TTU-P10076, one of the best preserved tered down the hill slope. Compaction resulted in a shearing skulls of this genus available to date. Additional information of the skull to the right side, which affected in particular the from TTU-P10077 is inserted at the appropriate places. The narial region and the right postorbital region. The left side of shape of a phytosaur skull traditionally is the more important the skull is thus flattened and appears more extended visually, part of its anatomy for comparative and phylogenetic pur- the right side is verticalised. The right paroccipital process is poses, and most previous studies focused on characters of the crushed and was pushed dorsally. The right postorbital region general skull morphology rather than on osteological details. was not reassembled with the cranium until after the descrip- For this reason, we feel justified in giving separate accounts tion, to allow easy access to the braincase; it is not included in of the external skull morphology, the major skull openings the figures. The cranium including the dentition is entirely and important external structures that extend over several freed of matrix. cranial elements. Structures that are restricted to single skull 2.1.2. TTU-P10077 (Fig. 4). Almost complete, 1040 mm- elements are described with the individual bones. long, robust cranium with a massive snout (altirostral sensu Hunt 1989, 1994). The skull was found dorsal side up and the 2.3. External skull morphology occipital aspect partially was exposed, which explains the loss of the left squamosal and parts of the paroccipital processes 2.3.1. Rostrum. In phytosaurs, the prenarial area includes and quadrates. The posterior portion of the narial region and the rostrum with the highly variable prenarial crest, if present. the skull roof are crushed, and the entire skull is sheared to the The area is shaped differently in the two specimens of M. right side. The skull deck was removed in pieces, prepared, lottorum, and both differ from that in TTU-P10074. In the and reassembled to its original shape. Similarly, the articular slender-snouted (dolichorostral) TTU-P10076 (Fig. 5) and parts of both quadrates are kept separate from the skull. TTU-P10074 (Fig. 6), the rostrum is wider than high, flattened With exception of the rostrum, the skull is in parts strongly semicircular in outline, and narrows only insignificantly in fragmented and the fragments are friable, the damage having anterior direction in the premaxillar section. The rostrum is been enhanced by root penetration. The fragments had to be almost imperceptibly curved upwards. In dorsal view, the out- fixed in their present distorted position before the matrix could line is triangular with concave ventral rims of the maxillaries. be removed from the dorsal surface. On the ventral side, both A slight constriction marks the articulation of the premaxilla tooth rows were fully exposed, but the palatal area is only pre- with the maxilla on the rostrum. pared in broad outlines. In TTU-P10076 (Fig. 7), the prenarial area drops steeply Machaeroprosopus sp. over a distance of 35 mm at an angle of 75 from the nares. (Figs 6, 8, 10, 16–17, 19) A kink in the profile marks the point where the slope starts to level out in a gradual steady way, being level at 210 mm in 2.1.3. TTU-P10074. Almost undistorted slender-snouted front of the nares. The posterior one fourth of the slope is cranium (dolichorostral sensu Hunt 1993, 1994), lacking the rounded, but narrow in cross-section, and visually demarcated anteriormost section of the rostrum because of surface exposure. from the ventral part of the rostrum by two lateral depressions A section of a right premaxilla including the alveoli pm4 (4th below the narial cone. Anteriorly, the top surface increasingly premaxillary alveolus) through pm6 was recovered later at the grades into the rostrum, but is still distinguished visually by NEW MACHAEROPROSOPUS FROM WEST TEXAS 273

Figure 2 Stereopairs of the dorsal and ventral aspects of the skull of Machaeroprosopus lottorum TTU-P10076. Scale bars ¼ 100 mm. narrow extensions of this depression. It is only in the anterior of the naris, situated 205 mm above the alveolar plane, at the one fourth that the slope merges with the rostrum to a semi- gentle angle of 20 in a slightly undulating line to about the circular cross-section as in TTU-P10074. midpoint of the rostrum. Here, at a height of 80 mm, the slope The left side of the prenarial area of TTU-P10077 (Fig. 4) changes fairly abruptly to continue at 3–4 to a point 140 mm is dislocated ventrally for 12 mm in front of the nares, but is in front of the tip of the rostrum, where the now 50 mm-high undistorted otherwise. It slopes from the elevated anterior rim crest ends in a step. In the anterior half of the crest, the ﬂanks 274 AXEL HUNGERBU¨ HLER ET AL.

Figure 3 Machaeroprosopus lottorum TTU-P10076: reconstruction of the skull in (A) ventral, (B) dorsal, (C) lateral and (D) occipital views. Scale bars ¼ 100 mm. NEW MACHAEROPROSOPUS FROM WEST TEXAS 275

Figure 4 Stereopair of the dorsal aspect of the skull of Machaeroprosopus lottorum n. sp. TTU P-10077. Scale bar ¼ 100 mm. are constricted by two large, triangular depressions, which temporal fenestra. In TTU-P10077, the posterior rim of the separate the vertical top of the crest from the steeply sloping groove is drawn out to an extensive, laterally projecting alveolar portions of the maxilla and premaxilla. The outline flange. The groove is bounded posteriorly by a series of three of the depression corresponds exactly with the prenarial ridges, which extend oblique to the long axis of the groove. section of the nasal, and is characterised furthermore by the Each of the ridges is separated by a distinct groove running deepest sculpture of the entire skull. In the anterior half, the into the infratemporal fenestra. TTU-P10076 lacks a differen- crest grades into the steeply sloping flanks of the rostrum, tiated infraorbital area (Fig. 7) and shows only a very faint resulting in a triangular cross-section. The top of the crest is groove. narrow and sharp in front of the nares, but expands and be- 2.3.3. Parietal–supraoccipital complex. (Supraoccipital shelf, comes more rounded anteriorly. Figs 9, 10) In posterior view, the shape of the parietal– 2.3.2. Infraorbital area. The area just ventrally to the supraoccipital complex in both TTU-P10076 and TTU-P10077 orbits, formed by the orbital process of the postorbital, the is rectangular, with a broad, horizontal parietal ledge. The posterior section of the lacrimal behind the preorbital ridge lateral wall of the supraoccipital shelf, formed by the descend- and the orbital process of the jugal and leading into the pre- ing squamosal processes of the parietals, are vertical and, only infratemporal shelf, is distinguished in TTU-P10077 from the in the ventral third of the complex they turn to the horizontal surrounding surface by the different surface sculpture. Most of in a posterolateral direction in a gentle, steady curve. The the area is smooth, and forms a conspicuous strip set deeper supraoccipital shelf, including the supraoccipital and two than the flank of the naris and the preorbital area. A distinct lamella of the parietals, slopes continuously downward and feature is a narrow and deep groove along the rim of the infra- posteriorly at an angle of 45; the shelf is thus an inclined 276 AXEL HUNGERBU¨ HLER ET AL.

Figure 5 Machaeroprosopus lottorum TTU-P10076, skull in dorsal view. Scale bar ¼ 10 cm. Abbreviations: aof ¼ antorbital fenestra; f ¼ frontal; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; m ¼ maxilla; n ¼ nasal; na ¼ naris; o ¼ orbit; p ¼ parietal; pl ¼ parietal ledge; pm ¼ premaxilla; pn ¼ paranasal; po ¼ postorbital; pof ¼ postfrontal; prd ¼ preorbital depression; prf ¼ prefrontal; q ¼ quadrate; qj ¼ quadratojugal; sm ¼ septomaxilla; soc ¼ supraoccipital; sp.p ¼ squamosal process of parietal; sq ¼ squamosal; sq.pl ¼ squamosal platform; stf ¼ supra-temporal fenestra. plane, neither curved and levelling out terminally as in Nicro- choana, the surface of the groove widens gradually and deepens saurus and most specimens of Machaeroprosopus, nor vertical to form the rounded concave prechoanal area. In the centre of as in Mystriosuchus, Machaeroprosopus bermani and Machaer- the prechoanal area, the prechoanal section of the vomers is oprosopus gregorii. raised slightly to a broad elevated structure. The alveolar ridge 2.3.4. Palate. (Fig. 11.) On the ventral surface of the ros- parallels the tooth row medially, so closely that, in parts of the trum of TTU-P10076, the raised alveolar ridges enclose a ﬂat, premaxilla, a concave indentation is formed opposite each wide interpremaxillary groove. About 50 mm anterior to the alveolus. The ridge is asymmetrical, with vertical lateral and NEW MACHAEROPROSOPUS FROM WEST TEXAS 277

Figure 6 Machaeroprosopus sp. TTU-P10074, postnarial part of the skull in dorsal view. Scale bar ¼ 10 cm. Abbreviations: aof ¼ antorbital fenestra; aofo.j ¼ jugular antorbital fossa; f ¼ frontal; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; m ¼ maxilla; n ¼ nasal; na ¼ naris; o ¼ orbit; opo.sq ¼ opisthotic process of squamosal; p ¼ parietal; pl ¼ parietal ledge; po ¼ postorbital; pof ¼ postfrontal; prd ¼ preorbital depression; prf ¼ prefrontal; q ¼ quadrate; qj ¼ quadratojugal; soc ¼ supraoccipital; sq ¼ squamosal; stf ¼ supra-temporal fenestra.

sloping medial rims. On the premaxilla and the anterior part of centre of the palatine. The palatine ridge extends anteriorly the maxilla, the ridge is broad, reaching a maximum width of into the convex round, tapering tip of the element, and poste- 15 mm opposite maxillary alveolus 9 (m9). Here, an outward riorly into the overhang over the palatal vault to merge with kink in the anterior third of the maxillary tooth row (opposite the medial side of the pterygoid flange. These elevations frame m12) effectively splits the alveolar ridge in two structures. The an elongated depression, in which lies the suborbital fenestra. alveolar ridge continues along the diverging tooth rows, stand- The midline of the semi-cylindrical palatal vault is elevated for ing out as a much more prominent structure on the palate 50 mm above the crest of the palatal ridge. The opening be- because of its now much diminished width. The height of the tween the two halves of the palatal plane is 22–26 mm wide alveolar ridge also decreases rapidly, and it merges with the below the choana and the anterior half of the palatal vault. palatal plane in the posterior quarter of the maxilla (roughly Because of the extensive overhang of the palatines, the palatal opposite m19). A second sharp, but narrow and low ridge, on vault is actually much wider (60 mm). Posteriorly, the exposure or parallel to the premaxilla–maxilla suture splits from the of the palatal vault is constricted severely in TTU-P10076. The alveolar ridge and runs straight across the slope of the pre- width increases posteriorly to 65 mm because of the divergence choanal area, converges slightly with the midline and dis- of the palatines. With the emergence of the pterygoid flange appears towards the raised prechoanal area. (the ventral ramus of pterygoid and ectopterygoid, plus the The choanal and postchoanal palate is subdivided into two posterior tip of the palatine) out of the walls of the palatal tiers: the lower tier of the horizontal palatal plane (including vault and the horizontal overhang of the palatine, both hori- the palatine and the palatal parts of maxilla and ectoptery- zontal tiers merge into a unified vertical structure. goid); and the dorsally arched, higher tier, which includes the choana (the choanal process of the maxilla, the interchoanal 2.4. Skull openings septum i.e., the anterior part of the vomers and the vertical dorsal ramus of the palatine), followed by the palatal vault 2.4.1. Nares and associated structures. The nares of all (the posterior part of the vomer and the arched anterior ramus specimens are considerably elevated above the centre of the of the pterygoid). skull roof (for 15 mm in TTU-P10076). The septomaxilla The palatal plane is morphologically dominated by two ele- forms most of the internarial septum and the anteromedial vations: the fading alveolar ridge and the raised ridge on the rim of the naris; an additional bony element, named here the 278 AXEL HUNGERBU¨ HLER ET AL.

Figure 7 Machaeroprosopus lottorum TTU-P10076, skull in left lateral view. Scale bar ¼ 10 cm. Abbreviations: aof ¼ antorbital fenestra; ect ¼ ectopterygoid; f ¼ frontal; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; lsp ¼ laterosphenoid; m ¼ maxilla; n ¼ nasal; n(r) ¼ right nasal; opo.sq ¼ opisthotic process of squamosal; pl ¼ parietal ledge; pm ¼ premaxilla; pn ¼ paranasal; pn(l) ¼ left paranasal; pn(r) ¼ right paranasal; po ¼ postorbital; pof ¼ postfrontal; pop.opo ¼ paroccipital process of opisthotic; pp.sq ¼ posterior process of squamosal; prf ¼ prefrontal; pt ¼ pterygoid; q ¼ quadrate; qj ¼ quadratojugal; sm ¼ septomaxilla; sm(l) ¼ left septomaxilla; sm(r) ¼ right septomaxilla; sopo.sq ¼ subsidiary opisthotic process of squamosal; sq ¼ squamosal; sq.pl ¼ squamosal platform. paranasal, occupies the anterolateral border to a variable extent and, for about 20 to 30 degrees, upward; the orbits are not (see below), and the nasal forms most of the lateral and the turned anteriorly to any degree, and thus there is no indication entire posterior rim. of binocular vision. With to exception of the broad and The subrectangular naris of TTU-P10076 (Fig. 12C) is long smooth ventral rim, the orbital rim is sharp and raised above (83–85 mm), but narrow, reaching a maximum width of 15 mm the surrounding skull surface, forming a conspicuous, 10 mm- close to the posterior border. It extends about 10 mm anterior broad, less sculptured zone around the opening. The elevation to the level of the anterior rim of the antorbital fenestra. Ante- is particularly strong at the posterodorsal corner, in the form riorly, the naris is indented as a distinct, 20 mm-deep and 5 of an extensive hump, especially pronounced in TTU-P10074, mm-broad, V-shaped outlet (Fig. 12C, ‘nou’). The anterior- and along the anterior rim. This anterior orbital ridge causes most section of the lateral rim is thin and sharp. The lateral the preorbital depression (Fig. 6, ‘prd’), here, in contrast to rim is straight and slopes slightly in anterior direction, the an- the pseudopalatine phytosaur Mystriosuchus (GPIT 261/001; terior rim being 11 mm lower than the posterior. In both TTU- Hungerbu¨hler 2002), actually a series of smaller, deep pits P10076 and TTU-P10077, most of the rim is squared in dorsal separated by bridges of the surface sculpture. The ridge con- aspect and deeply rugose by predominantly transverse, irregu- tinues ventrally to the anterior corner of the antorbital fenestra lar grooves, suggesting the presence of a cartilaginous structure onto the lacrimal, where it marks the anterior border of the less (Fig. 12). The narial cone seems to be slightly constricted at sculptured infraorbital area. midlength, and shows two symmetrical, ﬂat and broad depres- 2.4.3. Antorbital fenestra and antorbital fossa. In TTU- sions below the anterior third, which enhances the cone-like P10076, the antorbital fenestra is surrounded anterodorsally appearance of the narial bulb. The internasal septum is thin, by the dorsal, and ventrally by the ventral processes of the posteriorly with a sharp edge that grades into a smoothly maxilla, the lacrimal posterodorsally, and the jugal posteriorly rounded but still narrow rim anteriorly. The dorsal rim is and posteroventrally (Figs 7, 12A, B, 13). The opening is oval, straight throughout and situated a few mm below the lateral with an angular rather than round posterior corner. In the un- rims of the nares. deformed openings, the long axis, which is positioned at a low A raised central prenarial hump anterior to the nares, includ- angle with the axis of the skull, measures 106 mm, the short ing parts of the internarial septum, or a pair of paramedian axis 435 mm; the size is comparatively small for phytosaurs, prenarial grooves extending onto the rostrum out of the narial with reference to naris length. The ventral edge is prominent outlets, are absent in M. lottorum and TTU-P10074. and sharp, whereas the dorsal rim is broadly rounded and 2.4.2. Orbit and preorbital ridge. The orbit is surrounded deep. TTU-P10076 (as is Machaeroprosopus sp. TTU-P10074) by the prefrontal anterodorsally, the frontal dorsally, the post- is among the few specimens of pseudopalatine phytosaurs that frontal posterodorsally, the postorbital posteriorly, and the show remnants of an antorbital fossa. The anterodorsal part lacrimal ventrally (Fig. 13). The jugal is excluded from the of the fossa appears as a small depression on the lateral face orbit in both specimens of M. lottorum and TTU-P10074. of the maxilla (Figs 7, 8, 12A; ‘aofo.ml’). Further posteriorly, The undeformed orbit is oval, with a conspicuous straight the dorsal process of the maxilla and the anterior process of and ﬂat ventral rim and a long axis directed anteroposteriorly the lacrimal are folded over, forming the broad dorsal rim of (Fig. 2). The plane circumscribed by the opening faces laterally the antorbital fenestra, but continue as a steeply medioventrally NEW MACHAEROPROSOPUS FROM WEST TEXAS 279

Figure 8 Machaeroprosopus sp. TTU-P10074, postnarial part of the skull in left lateral view. Scale bar ¼ 10 cm. Abbreviations: aof ¼ antorbital fenestra; aofo.ml ¼ maxillo-lacrimal antorbital fossa; ect ¼ ectopterygoid; f ¼ frontal; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; m ¼ maxilla; n ¼ nasal; opo ¼ opisthotic; opo.sq ¼ opisthotic process of squamosal; pm ¼ premaxilla; pn ¼ paranasal; po ¼ postorbital; pof ¼ postfrontal; pp.sq ¼ posterior process of squamosal; ppr.sq ¼ parietal process of sqamosal; prf ¼ prefrontal; pt ¼ pterygoid; q ¼ quadrate; qj ¼ quadratojugal; sm ¼ septomaxilla; sm(l) ¼ left septomaxilla; sm(r) ¼ right septomaxilla; sq ¼ squamosal. sloping plane, a 15 mm-deep maxillo–lacrimal antorbital fossa spanning the entire indentation. Thus, the supratemporal open- as overhang over the antorbital fenestra proper (Fig. 12A, C). ing is in M. lottorum and TTU-P10074 effectively closed on the In addition, there is a distinct jugular fossa in the posteroven- skull roof, and all three specimens are more derived than the tral corner extending along the posterior rim of the antorbital deeper, slit-like, straight or medially curved openings seen in opening, in the form of a narrow, thin lamella medial to the the type specimens of M. buceros, M. mccauleyi, M. jablonskiae lacrimo–jugular rim of the antorbital fenestra, both of which and M. andersoni. The maximum length of the opening to the enclose a deep, V-shaped recess (Fig. 12C, ‘aofo.j). posterior extent of the paroccipital process is 85 mm, of which 2.4.4. Supratemporal fenestra. The supratemporal fenestra the posterior 50 mm are completely recessed below the hori- is bounded by the parietal anteriorly, the postorbital and the zontal surface of the squamosal (i.e., under the dorsal sulcus; medial lamella of the squamosal laterally, the parietal ledge Figs 9, 10) and are not visible in dorsal view. The supratem- medially, and the sloping squamosal process of the parietal poral fenestra opens thus almost exclusively to the rear. and the horizontal parietal process of the squamosal posteriorly 2.4.5. Infratemporal fenestra. The infratemporal fenestra (Fig. 13). Because of the elongated squamosal, the posterior rim is bounded by, clockwise from the orbit, the postorbital, squa- is actually positioned posterolaterally, and it is depressed on the mosal, quadratojugal and jugal (Fig. 13). The opening roughly undeformed right side for 36–42 mm below the level of the skull forms a parallelogram with a concave dorsal rim, the antero- roof, or for about 30% of the skull height. In all specimens, the dorsal corner being located below the centre of the orbit. The anterior rim of the fenestra is shallow, but broad compared to fenestra extends far forward in TTU-P10077 (and TTU- other species previously referred to Pseudopalatus. It forms a P10074; Fig. 8), the anteroventral corner being 10 mm in front semicircular, 13 mm-deep excavation in TTU-P10076 (Fig. 5) of the anterior orbital rim, but terminates level with the orbit in that hardly indents the skull roof proper, i.e., the parietal. The TTU-P10076 (Fig. 7). excavation is, rather, caused by the projection of the parietal 2.4.6. Posttemporal fenestra. The posttemporal fenestra of ledge to the rear. In both TTU-P10076 (Figs 5, 9) and TTU- TTU-P10076 is short and oval, with a ﬂat dorsal rim, 27 mm P10077, the rim is distinctly bevelled, the ventral edge almost by 11 mm wide (Fig. 9). The opisthotic–squamosal suture is 280 AXEL HUNGERBU¨ HLER ET AL.

Figure 9 Machaeroprosopus lottorum TTU-P10076, skull in occipital view. Scale bar ¼ 50 mm. Abbreviations: boc ¼ basioccipital; bpt.bsp ¼ basipterygoid process of basisphenoid; bpt.pt ¼ basipterygoid process of pterygoid; bsp ¼ basisphenoidal part of parabasisphenoid; cr ¼ central ridge of quadrate; ds ¼ dorsal sulcus; ect ¼ ectopterygoid; eoc ¼ exoccipital; fl.sq ¼ squamosal flange; fm ¼ foramen magnum; f.pat ¼ facet for proatlas; fq ¼ quadrate foramen; itf ¼ infratemporal fenestra; j ¼ jugal; la.p ¼ lamina of parietal; lc ¼ lateral condyle of quadrate; m ¼ maxilla; mc ¼ medial condyle of quadrate; nc ¼ narial cone; opo.sq ¼ opisthotic process of squamosal; p ¼ parietal; pl ¼ parietal ledge; po ¼ postorbital; pop.opo ¼ paroccipital process of opisthotic; pp.sq ¼ posterior process of squamosal; ppr.sq ¼ parietal process of squamosal; pro ¼ prootic; ptf ¼ posttemporal fenestra; ptof ¼ pteroccipital fenestra; ptr.q ¼ pterygoid ramus of quadrate; q ¼ quadrate; qj ¼ quadratojugal; qr.pt ¼ quadrate ramus of pterygoid; r ¼ recess; soc ¼ supraoccipital; sopo.sq ¼ subsidiary opisthotic process of squamosal; sp.p ¼ squamosal process of parietal; stf ¼ supra-temporal fenestra; vr.pt ¼ ventral ramus of pterygoid; vs ¼ ventral sulcus. located in the angular medial corner of the fenestra. The pari- of the palatal vault. Thus, the choana expands from 9 mm to etal process of the squamosal forms the entire dorsal rim of 15 mm in width, and the plane of the opening is bent in the the posttemporal fenestra, the paroccipital process of the opis- vertical plane. thotic two thirds and an extension of the squamosal the lateral 2.4.9. Suborbital fenestra. In TTU-P10076, the area of the third of the concave ventral rim. The fenestra is set somewhat suborbital fenestra is fractured on the right side and the left oblique with respect to the axis of the paroccipital process: the side is cracked and the palatine telescoped underneath the pala- lateral corner is located deeper, and the lateral section of the tal section of the maxilla. The suborbital fenestrae are well- fenestra is thus strongly roofed over by the parietal process of delineated (Fig. 11). The suborbital fenestra lies on the palatal the squamosal. The rounded lateral rim grades smoothly into plane between the maxilla and the palatine, about 10 mm be- the ventral sulcus. hind the choana (Fig. 14, ‘sf’). The opening is reduced com- 2.4.7. Foramen magnum. (Fig. 9.) The foramen magnum pared to that of non-pseudopalatine phytosaurs, and appears is a transversely oval opening (TTU-P10076: 21 mm by 155 as a narrow oval fenestra 17 mm by 7 mm wide, with pointed mm). The supraoccipital shelf overhangs the foramen mag- anterior and posterior corners. The maxilla forms the anterior num by 15 mm in both specimens. The condylar parts of the and the ectopterygoid the posterior half of the lateral rim, exoccipitals extend posteriorly, resulting in a concave poste- while the palatine borders the opening laterally. rior edge of the exoccipital pillars, and thus forms a distinct, 2.4.10. Subtemporal fenestra. (Fig. 11) According to the slightly concave platform in front of the foramen. less deformed right side, the subtemporal fenestra of TTU- 2.4.8. Choana. (Fig. 11.) The undistorted subrectangular P10076 is the large ventral, anteroposteriorly elongated opening left choana is 73 mm in TTU-P10076, and thus subequal in of the adductor chamber. The shape is subrectangular with an length with the naris. The posterior rim is exactly below the oblique, posteromedially trailing margin and posteriorly slightly posterior rim of the naris, but the anterior rim extends further converging walls. It is bordered anteriorly by the broadly forward. Because of the vaulting of the prechoanal palate, the rounded palatal part of the ectopterygoid, and medially by the anterolateral rim of the choana formed by the maxilla is curved ventral surface of the pterygoid–quadrate plate (predominantly upward and, at the same time, widens in a broad lateral recess, the pterygoid ramus of the quadrate). The quadrate forms the being slightly overhung by the anterior section of the palatine. posterior margin and the jugal the lateral margin, with the In the posterior two thirds, an extensive vertical lamella of the quadratojugal contributing to the posterolateral corner. palatine forms a lateral wall. The palatine and the vomers also 2.4.11. Interpterygoid vacuity. The interpterygoid vacuity form the posterior rim. The interchoanal septum formed by the is reduced to a roughly 35 mm-long, roughly heart-shaped vomers is a 9–11 mm-broad, flat or slightly convex ventral opening (Fig. 14). On the roof of the palatal vault, the vacuity plane, the ascending medial walls of the choana converge at indents the pterygoids in a 10-mm long, tapering slit. The con- each other and the septum becomes much narrower internally. cave lateral rims are formed by the basipterygoid processes of At midlength, the septum narrow considerably and curves the pterygoids. The notch between the basipterygoid processes upward in a step-like fashion to level out on the deeper level of the parabasisphenoid marks the posterior limit. NEW MACHAEROPROSOPUS FROM WEST TEXAS 281

Figure 10 Machaeroprosopus sp. TTU-P10074, skull in occipital view. Scale bar ¼ 10 mm. Abbreviations: boc ¼ basioccipital; bpt.bsp ¼ basipterygoid process of basisphenoid; cr ¼ central ridge of quadrate; eoc ¼ exoccipital; ﬂ.sq ¼ squamosal ﬂange; fm ¼ foramen magnum; fq ¼ quadrate foramen; la.p ¼ lamina of parietal; lc ¼ lateral condyle of quadrate; l.sq ¼ lamella of squamosal onto paroccipital process of opisthotic; mc ¼ medial condyle of quadrate; opo.sq ¼ opisthotic process of squamosal; p ¼ parietal; po ¼ postorbital; pop.opo ¼ paroccipital process of opisthotic; pp.sq ¼ posterior process of squamosal; ppr.sq ¼ parietal process of squamosal; ptf ¼ posttemporal fenestra; ptof ¼ pteroccipital fenestra; ptr.q ¼ pterygoid ramus of quadrate; q ¼ quadrate; qj ¼ quadratojugal; qr.pt ¼ quadrate ramus of pterygoid; soc ¼ supraoccipital; sopo.sq ¼ subsidiary opisthotic process of squamosal; stf ¼ supra-temporal fenestra; vr.pt ¼ ventral ramus of pterygoid; vs ¼ ventral sulcus.

2.4.12. Pteroccipital fenestra. (Fig. 9) The pteroccipital of fairly long slits. Because of the dorsal expansion of the fenestra is a narrow, predominantly ventrally- and somewhat maxillae, the posterior section of the premaxillae is developed posteriorly-facing passage between the pterygoid–quadrate as a narrow extension on the top of the rostrum. Posteriorly, plate and the braincase. It is crescentic in outline, with straight each element splits into two tapering processes: a broader and lateral and convex medial rims. As an estimate, the length is shorter medial process along the median plane that is wedged 70 mm and the maximum width is 20 mm, although the latter for 13 mm between the septomaxillae, and a larger, narrower is somewhat exaggerated by deformation in all specimens. The process that extends for about 20 mm on the lateral side of passage is framed laterally by the dorsal rim of the pterygoid– the crest between the septomaxilla and the nasal (Fig. 12A, C). quadrate plate, anteriorly by the lateral edge of the basiptery- The opposite is the case in TTU-P10077 (Fig. 15). The dorsal goid process of the parabasisphenoid, and medially by the (medial) process is narrower, non-tapering, and 37 mm long, of anterior wall of the stapedial groove and the base of the which 20 mm are represented by a thin prong along the midline. paroccipital process. The stout ventral (lateral) process is twice as broad, subequal in length, extends horizontally below the septomaxilla, and forms 2.5. Individual elements an anteroventrally sloping suture with the nasal. Moreover, a deep and narrow furrow, in parts resembling an almost closed 2.5.1. Premaxilla. The elongated subrectangular terminal channel, extends for 75 mm on both sides on the premaxilla, in rosette of the premaxillae is longer than wide, terminating by extension of the ventral septomaxilla–premaxilla contact. Such a slight constriction (Fig. 11). It is only moderately expanded a groove has not been identified before in, and is not homologue laterally, being 47 mm wide, with a width of the rostrum of 31 with, the prenarial groove of other phytosaurs, which extends mm at the constriction. The premaxillae curve ventrally to a out of the nares on the septomaxillae and nasals. moderate degree in front of pm3, the tip being situated 24 The interpremaxillary groove (Fig. 11), starting between mm below the level of the alveolar plane (Fig. 7). In anterior both pm5, is rounded in cross-section anteriorly, but rapidly view, the total height of the terminal rosette is subequal to the develops into a flat-bottomed channel posteriorly. The un- width (445 mm). The slender rostrum widens gradually from paired foramen incisivum is located on a central mound be- 33 mm at pm5 to 46 mm at the end of the premaxillae; there is tween pm3 and pm4. Anteriorly and laterally, there is a series an almost imperceptible lateral convexity along the last five of three (left) and two (right) nutritious foramina. A conspi- premaxillary alveoli. cuous pair of foramina that open posteriorly is situated in the The suture between the premaxillae is present as a groove bottom of the interpremaxillary groove at the level of pm8 on the anterior surface of the rosette and along most of the (Fig. 11). The palatal surface of the premaxilla extends into a dorsal surface of the rostrum, but the bones are fused without thin, tapering palatal process that runs on the maxilla (illus- an external trace over the distance of 90 mm in the anterior trated in TTU-P10074, Fig. 16A, ‘pap.pm’) and reaches the section above pm3 to pm9 (Fig. 5). A well developed longitu- tip of the choana, overlapping the vomer medially (Fig. 11). dinal groove with a rectangular cross-section is present on the 2.5.2. Maxilla. The maxilla appears on the lateral surface, lateral surface of the rostrum between pm10 and pm18, about forming two sharp, anteriorly-pointing, subequally long prongs 10 mm above the alveolar plane (Fig. 7). Anteriorly and pos- that interdigitate with the premaxilla (Fig. 7). Posteriorly, the teriorly, the groove is dissociated into an array of short grooves suture curves more and more dorsally, until the maxilla extends or depressions. In a somewhat irregular pattern, foramina in the over two thirds of the height of the prenarial area and levels out grooves and depressions enter into the rostrum, on average at into the narrow dorsal process above the antorbital fenestra, every second tooth position. Some foramina take on the shape firmly sutured by a strongly serrated suture with the nasal. In 282 AXEL HUNGERBU¨ HLER ET AL.

Figure 11 Machaeroprosopus lottorum TTU-P10076, skull in ventral view. Scale bar ¼ 10 cm. Abbreviations: boc ¼ basioccipital; bsp ¼ basisphenoidal part of parabasisphenoid; ch ¼ choana; ect ¼ ectopterygoid; ipv ¼ interpterygoid vacuity; itf ¼ infratemporal fenestra; j ¼ jugal; lc ¼ lateral condyle of quadrate; m ¼ maxilla; mc ¼ medial condyle of quadrate; o ¼ orbit; opo ¼ opisthotic; pal ¼ palatine; pm ¼ premaxilla; pt ¼ pterygoid; ptf ¼ posttemporal fenestra; ptof ¼ pteroccipital fenestra; q ¼ quadrate; qj ¼ quadratojugal; sq ¼ squamosal; v ¼ vomer. NEW MACHAEROPROSOPUS FROM WEST TEXAS 283

Figure 12 Machaeroprosopus lottorum TTU-P10076: details of the narial area in (A) lateral left view; (B) lateral right view; (C) anterolateral left view. Scale bars ¼ 50 mm. Abbreviations: aof ¼ antorbital fenestra; aofo.j ¼ jugular antorbital fossa; aofo.ml ¼ maxillo–lacrimal antorbital fossa; f ¼ frontal; f.pn ¼ facet for paranasal; g ¼ groove; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; m ¼ maxilla; n ¼ nasal; nou ¼ narial outlet; o ¼ orbit; pis ¼ preinfratemporal shelf; pm ¼ premaxilla; pn ¼ paranasal; po ¼ postorbital; prd ¼ preorbital depression; prf ¼ prefrontal; sm ¼ septomaxilla.

TTU-P10077 (Fig. 15), the maxilla bulges distinctly along the restricted width of 11 mm. TTU-P10077 (and Machaeroprosopus posterior part of the premaxilla and the nasal in a strongly sp. TTU-P10074) show a peculiar sturdy prong of the maxilla convex suture. This section of the element is extremely thin, into the premaxilla in front of the apex of the suture. The prong being 2 mm thick medio-laterally in TTU-P10074 (Fig. 16A). is absent in TTU-P10076, and the nasal–maxillary suture is The base of the dorsal process is marked by a concavity of almost straight (Fig. 12). The surface of the much higher ven- the nasal-maxillary suture, and the process continues with a tral process is vertical and extends far posteriorly, forming two 284 AXEL HUNGERBU¨ HLER ET AL.

Figure 13 Machaeroprosopus lottorum sp. nov.: schematic reconstruction of the skull and the conﬁguration of the cranial elements in (A) ventral, (B) dorsal, (C) lateral and (D) occipital views. Scale bars ¼ 100 mm. NEW MACHAEROPROSOPUS FROM WEST TEXAS 285

Figure 14 Machaeroprosopus lottorum TTU-P10076: (A) right palate in ventral view; (B) with pterygoid ﬂange removed, showing the steinkern of the sinus between ectopterygoid and palatine. Scale bars ¼ 50 mm. Abbre- viations: ch ¼ choana; ect ¼ ectopterygoid; g ¼ groove; ipv ¼ interpterygoid vacuity; m ¼ maxilla; pal ¼ palatine; pt ¼ pterygoid; sf ¼ suborbital foramen; si ¼ sinus; vr.ect ¼ ventral ramus of ectopterygoid; vr.pt ¼ ventral ramus of pterygoid.

Figure 15 Machaeroprosopus lottorum TTU P-10077, left anterial narial and prenarial region. In the interpretive drawing, the right side is not shown. Scale bar ¼ 50 mm. Abbreviations: m ¼ maxilla; n ¼ nasal; pm ¼ premaxilla; pn ¼ paranasal; sm ¼ septomaxilla. 286 AXEL HUNGERBU¨ HLER ET AL.

Figure 16 Machaeroprosopus sp. TTU-P10074: (A) cross-section through the rostrum 75 mm in front of the nares, view in anterior direction. Transverse break-surfaces unshaded, arrows indicate position of sutures on the outside; (B) counterpart of the right dorsal part of the same section to show the sutural conﬁguration, view in posterior direction; (C) right prenarial area in lateral view. Scale bars ¼ 10 mm. Abbreviations: ac ¼ alveolar canal; ar ¼ alveolar ridge; c.pm ¼ premaxillary cavity; cv.m ¼ maxillary cavern; cv.n ¼ nasal cavern; m ¼ maxilla; m12 ¼ alveolus 12 of maxilla; m14 ¼ alveolus 14 of maxilla; n ¼ nasal; pap.pm ¼ palatal process of premaxilla; pm ¼ premaxilla; sm ¼ septomaxilla; sm(l) ¼ left septomaxilla; sm(r) ¼ right septomaxilla.

opposite to alveoli m4 to m12 and heads obliquely on a ridge over the prechoanal depression, straight towards the anteromedial corner of the choana. This choanal process extends, sloping to the midline and posteriorly because of the concavity of the prechoanal palate, between the tip of the palatine laterally and the palatal process of the premaxilla and the vomer medially. It forms the anterior rim of the choana, and continues below the palatine on the lateral side of the opening for 21 mm; i.e., for one fourth of the choana length. The contribution of the maxilla to the choanal rim is thick and rounded, and the anterolateral rim is concave, resulting in a broadened lobate expansion of the anterior part of the choana below the tip of the palatine. The suture with the palatine runs parallel to the alveolar rim in the elongate depression of the palatal plane to the suborbital fenestra. The maxilla continues along the base of the ectopterygoid, overlapping the bone, straight towards the anterolateral corner of the subtemporal fenestra, and ends in a blunt tongue lying ventrally on the ectopterygoid–jugal complex. 2.5.3. Septomaxilla. The sutural configuration of the im- Figure 17 Machaeroprosopus sp. TTU-P10074, cross-section through mediate prenarial area is difficult to interpret in the slender- the rostrum 195 mm in front of the nares, view in anterior direction. snouted TTU-P10076 because of fractures, intense superficial Scale bar ¼ 10 mm. Abbreviations: ac ¼ alveolar canal; ar ¼ alveolar damage, the sculpturing and the lamellate interdigitation of ridge; c.pm ¼ premaxillary cavity; ipmg ¼ interpremaxillary groove; the constituent elements. The septomaxilla forms much of the m ¼ maxilla; m2 ¼ alveolus 2 of maxilla; pm ¼ premaxilla. internarial septum and extends forwards, wedged between the paranasal, the nasal and the premaxilla. The septomaxillae are asymmetrically developed on the inter- thirds of the antorbital rim, and meets the jugal in a subvertical nasal septum of TTU-P10076 (Fig. 12C). Thirty mm behind the suture, the ventral section of which trails obliquely toward the anterior rim of the naris, the suture between the septomaxillae jugal notch. drops vertically on the right flank of the septum, which is, from On the ventral surface, the suture between maxilla and pre- this point backwards formed by the left septomaxilla alone. The maxilla appears laterally to alveolus m1, curves closely in front suture with the nasal appears on the septum 27 mm in front of around the alveolus and extends posteriorly in the lateral edge the posterior rim, running horizontally, and ascends to the of the alveolar ridge (Fig. 11). It crosses the ridge obliquely dorsal surface right at the posterior rim of the opening. NEW MACHAEROPROSOPUS FROM WEST TEXAS 287

Figure 18 Machaeroprosopus lottorum TTU-P10076, left side of the braincase. For details of the otic region, see Figure 24. Scale bar ¼ 50 mm. Abbreviations: cp.ps ¼ cultriform process of parasphenoid; ept ¼ epipterygoid; eptp.pt ¼ epipterygoid process of pterygoid; g ¼ groove; hypg ¼ hypophyseal gap; pqg ¼ palatoquadrate groove; ptr.q ¼ pterygoid ramus of quadrate; qr.pt ¼ quadrate ramus of pterygoid; V ¼ trigeminal foramen; VII ¼ foramen for facial nerve.

In the anteriormost section of the naris, the septomaxilla sutural contact on the left side of TTU-P10076, and the obli- forms a laterally concave flange, the floor of the narial outlet, que course over the dorsal rim of the naris (Fig. 12C). The pos- and abuts against the paranasal. Externally, the septomaxilla terior extent is restricted to the anterior one fourth of the side of extends as a thin strip forwards along the midline, apparently the naris in TTU-P10076. In TTU-P10077, the nasal is detached intensively covered by the paranasal. The element triples in from the paranasal along the posterior section of the suture line width in front of the paranasal and seems to terminate 70 and crushed down, and extends externally along the anterior mm in front of the naris, at about the level of the anterior third of the naris. A cross-section of the narial rim reveals tip of the nasal (TTU-P10076, right side; Fig. 12C). Surface (Fig. 15, inset) that the nasal underlies the paranasal and damage to the bone on the left side reveals several parallel reaches forward to a point 15 mm behind the anterior corner suture lines (Fig. 12A, C) that mark the intensive interdigita- of the naris. This suggests that the extent of the paranasal tion with the underlying premaxilla, as in Smilosuchus gregorii may vary by expanding over the nasal. The element seems to UCMP 27200 (Camp 1930). On both sides, the sutures be- be present also in TTU-P10074, according to a sigmoidal suture tween the septomaxilla and the paranasal extend out of the line on the left side that separate the anterior third of the naris through the narial outlets, separating two 4 mm narrow lateral narial rim from the nasal (Fig. 8). elements. The septomaxillae widen to 9 mm at 75 mm in front 2.5.5. Nasal. The nasal is an extensive element that forms of the nares (gradually on the right side, abruptly at a point much of the interorbitonasal area and the narial cone. Ante- 40 mm in front of the naris on the left side), extending further riorly, the nasal is wedged as a thin, tapering prong between forward than the nasal. The length of the septomaxilla of TTU- the convex maxilla and the posteriormost section of the pre- P10077 compares with that of TTU-P10076, but the element is maxilla, terminating 75 mm in front of the naris (Fig. 7). The much broader. It is still 14 mm wide at the anterior end, where bone expands, however, much deeper internally below the pre- it broadly interdigitates with the dorsal process of the premaxilla and the dorsal process of the maxilla, meets its coun- maxilla, and a bulge of the lateral rim down the flank of the terpart along the midline, and forms much of the roof of the rostral crest results in a maximum width of 28 mm. large antorbital cavity here (Fig. 12B); similarly, a thin wedge 2.5.4. Paranasal. An additional discrete skull element is of the nasal is exposed in TTU-P10076 between the septomax- outlined clearly in the anterior lateral corner of the nasal open- illa and the posterior lateral process of the premaxilla (Fig. ing of TTU-P10076 (Fig. 12) and TTU-P10077 (Fig. 15). We 12A, C). In this region, the nasal contains a broad, dorsoven- refer to this element as the paranasal bone. It forms the thick, trally-compressed cavern that extends into the base of the pre- pillar-like anterior rim of the naris and the anteriormost part of maxilla. The cavern extends posteriorly at least to a point 75 the narial flank. The element is triangular in outline, with a mm in front of the naris, and communicates with the antorbi- blunt, ventrally pointing tip. The medial side lies on the septo- tal cavity by means of narrow canals (Fig. 16A, B). The nasal maxilla and forms the lateral wall of the narial outlet. Later- forms the posterior three fourths of the lateral rim and the ally and posteriorly, it is overlapped by the nasal, forming entire posterior rim of the naris, but seems to contribute little a short squamal suture, as evidenced by the partially exposed to the internasal septum. Posterior to the nares, the width of 288 AXEL HUNGERBU¨ HLER ET AL.

Figure 19 Machaeroprosopus sp. TTU P-10074, postnarial part of the skull in dorsal view. Scale bar ¼ 10 mm. Abbreviations: aof ¼ antorbital fenestra; aofo.j ¼ jugular antorbital fossa; f ¼ frontal; itf ¼ infratemporal fenestra; j ¼ jugal; l ¼ lacrimal; m ¼ maxilla; n ¼ nasal; na ¼ naris; o ¼ orbit; opo.sq ¼ opisthotic process of squamosal; p ¼ parietal; pl ¼ parietal ledge; po ¼ postorbital; pof ¼ postfrontal; prd ¼ preorbital depression; prf ¼ prefrontal; q ¼ quadrate; qj ¼ quadratojugal; soc ¼ supraoccipital; sq ¼ squamosal; stf ¼ supra-temporal fenestra.

the nasal is restricted by the lacrimal, but in particular by the prefrontal posterolaterally to two processes that contact the frontal 10 mm in front of the orbit. 2.5.6. Frontal. Both frontals, are cross-shaped, as is typical for phytosaurs (Fig. 5). The subequally long anterior and posterior processes are wedged between the nasals and prefrontals, and the parietals and postfrontals, respectively. There is a remarkable left–right asymmetry in TTUP-P10076 (as is in TTU-P10074) regarding the length of these posterior processes. The orbital wing of each element expands laterally and dorsally to the centre of the raised dorsal rim of the orbit; both frontals thus enclose a depressed concave interorbital area. The interfrontal suture is located on a low and broad elevation along the midline of the skull. 2.5.7. Prefrontal. The prefrontal is about 15timeslonger than the postfrontal. The element restricts the width of the posteriormost section of the nasal anteromedially and the anterior process of the frontal medially on the dorsal plane of the skull (Fig. 5), and extends onto the lateral side to form the anterodorsal and entire anterior rim of the orbit. At the level of the ventral rim of the orbit, the prefrontal meets the lacrimal; the suture is convex in TTU-P10076 (Fig. 7). Figure 20 Machaeroprosopus lottorum TTU P-10077, left bases of parietal–squamosal bar and paroccipital process: (A) dorsolateral 2.5.8. Lacrimal. The lacrimal is an elongated, but low ele- view; (B) section along indicated crack. Scale bar ¼ 10 mm. Abbrevia- ment. The high anterior process forms the posterior section of tions: epi ¼ epipterygoid; opo ¼ opisthotic; p ¼ parietal; pro ¼ prootic; the dorsal antorbital rim, including the inclined dorsal antorbital ptf ¼ posttemporal fenestra; soc ¼ supraoccipital; sq ¼ squamosal. NEW MACHAEROPROSOPUS FROM WEST TEXAS 289

Figure 21 Machaeroprosopus lottorum TTU-P10076, right side of the braincase with right temporal region removed. Scale bar ¼ 50 mm. Abbreviations: boc ¼ basioccipital; bpt.bsp ¼ basipterygoid process of basisphenoid; bsp ¼ basisphenoidal part of parabasisphenoid; cp.lsp ¼ capitate process of laterosphenoid; cp.psp ¼ cultriform process of parasphenoid; dl.pt ¼ dorsal lamina of pterygoid; ect ¼ ectopterygoid; eo ¼ epiotic; eoc ¼ exoccipital; ept ¼ epipterygoid; eptp.pt ¼ epipterygoid process of pterygoid; f ¼ frontal; hypg ¼ hypophyseal gap; ic ¼ foramen for cerebral branch of internal carotid; j ¼ jugal; jg ¼ jugular groove; (l) ¼ left; lsp ¼ laterosphenoid; mc ¼ medial condyle of quadrate; mdf ¼ median foramen (of laterosphenoid); opo ¼ opisthotic; opo.sq ¼ opisthotic process of the squamosal; p ¼ parietal; pal ¼ palatine; pl ¼ parietal ledge; po ¼ postorbital; ppr.sq ¼ parietal process of squamosal; pro ¼ prootic; ps ¼ presphenoid; ps.p ¼ parasphenoid process; pt ¼ pterygoid; ptf ¼ parasphenoid process; ptr.q ¼ pterygoid ramus of quadrate; q ¼ quadrate; qj ¼ quadratojugal; qr.pt ¼ quadrate ramus of pterygoid; (r) ¼ right; r ¼ recess; rg ¼ rugosity (of laterosphenoid); sg ¼ stapedial groove; stf ¼ supra-temporal fenestra; vp.lsp ¼ ventral process of laterosphenoid with projection; III ¼ foramen for n. oculomotorius;IV¼ foramen for n. trochlearis;V¼ trigeminal foramen for n. trigenimus;VII¼ foramen for n. facialis.

fossa (Fig. 12B). The process tapers slightly anteriorly to meet antorbital fossa is exclusively in the jugal (Fig. 12C). The jugal and interdigitate with the dorsal process of the maxilla at about forms here a thin lamina, 8 mm medial to the the posterior rim midlength of the antorbital fenestra. The lacrimal is bounded of the antorbital fenestra, that ascends parallel to the rim. The dorsally by the posterior section of the nasal, and the prefrontal maximum width of the lamina is 7 mm. With the outer rim of in a distinctly convex suture at the level of the ventral rim of the the antorbital fenestra, it encloses a recess that leads into an orbit, which results in a dorsally-directed prong between the ascending groove. A preinfratemporal shelf is present, but nasal and the prefrontal. The lacrimal forms the anterior half poorly deﬁned in TTU-P10076. In the anteroventral corner of (TTU-P10076) of the ventral orbital rim, and does not contrib- the infratemporal fenestra, the jugal holds a deep, posteriorly- ute to the anterior rim. Because of extensive fragmentation, no facing oval recess enclosed by the bases of the quadratojugal information is preserved regarding the opening of the lacrimal process and the jugal process of the ectopterygoid. The orbital canal, which in phytosaurs is usually placed internally in the process is slender, and extends along the lacrimal in an anteroventral corner of the orbit, at or close to the joint of ascending, slightly serrated suture to contact the postorbital lacrimal and prefrontal (Case 1929; Camp 1930; Case & White about 25 mm below the orbit in a posterodorsally trailing 1934; Witmer 1997; Senter 2002). The ventral process is absent suture. The jugal is thus excluded from the orbit. Posterome- in TTU-P10076 (Fig. 7), and does not contribute to the antor- dially, the orbital process forms much of an extensive, 25 mm- bital fenestra. broad medially-directed ﬂange along the postorbital–jugal bar, 2.5.9. Jugal. (Fig. 7) The maxillary process of the jugal and thus a deep, posteriorly-facing area developed as the ante- is short and high. There is no jugal notch developed at the rior wall of the infratemporal fenestra. The jugal continues maxilla–jugal suture, but only a slight concavity of the ven- high up to about mid-height of the orbit, overlapping the post- tral rim. The jugal contributes only to about one fourth of orbital in a broad tongue. the ventral rim of the antorbital fenestra. The posteroventral 290 AXEL HUNGERBU¨ HLER ET AL.

Figure 22 Machaeroprosopus lottorum n. sp., reconstruction of the braincase in right lateral view. Scale bar ¼ 50 mm. Abbreviations: ap.pro ¼ anterior projection of prootic; boc ¼ basioccipital; bsp ¼ basisphenoidal part of parabasisphenoid; cr.pro ¼ crista prootica; dl.pt ¼ dorsal lamina of pterygoid; eo ¼ epiotic; eoc ¼ exoccipital; Figure 23 Machaeroprosopus lottorum TTU P-10076, cross-sections f ¼ frontal; fo ¼ foramen ovalis; hyp.g ¼ hypophyseal gap; ic ¼ fora- of left epipterygoid: (A) 14 mm above base; (B) 28 mm above base. men for cerebral branch of internal carotid; jg ¼ jugular groove; l ¼ Arrows point in anterior direction. Scale bar ¼ 1 mm. lacrimal; lsp ¼ laterosphenoid; mdf ¼ median foramen (of laterosphenoid); mf ¼ metotic foramen; opo ¼ opisthotic; p ¼ parietal; po ¼ postorbital; pof ¼ postfrontal; pro ¼ prootic; ps ¼ presphenoid; broad hump on the postfrontal marks the highest point of the psp ¼ parasphenoid; psp.p ¼ parasphenoid process; r.lsp ¼ recess orbital rim (Fig. 8), and thus of the skull roof. in laterosphenoid; sq ¼ squamosal; stg ¼ stapedial groove; tg.lsp ¼ 2.5.12. Parietal. The parietals extend forward to the level triangular gap of laterosphenoid; vp.lsp ¼ ventral process of laterosphenoid with projection; III ¼ foramen for n. oculomotorius;IV¼ of the posterior rim of the orbits, forming a short transverse foramen for n. trochlearis;V¼ trigeminal foramen for n. trigeminus; interdigitating suture with the frontals (Fig. 5). Anterolaterally, VII ¼ foramen for n. facialis; XII ¼ foramen for n. hypoglossus. the parietal meets the postfrontal in a concave suture. Laterally, the bone is in contact with the postorbital, and it forms the The quadratojugal process is low, being 24 mm high at its entire anterior rim of the strongly reduced supratemporal fen- base, and only expands a little on the ventral side until it is estra posteriorly. In TTU-P10074 (left side, Fig. 6), it extends enclosed, and topped, by the lateral and medial lamina of the slightly farther posterior along the medial rim of the postorbi- quadratojugal. The ventral rim sharpens posteriorly and almost tal–squamosal bar. In the centre of the parietals, there are two reaches the lateral condyle of the quadrate (Fig. 11). The dorsal oval depressions situated symmetrically along the midline, pos- rim is flattened and merges anteriorly with the area of the pre- terior to a marked central hump on the interparietal suture. In infratemporal shelf; posteriorly, the anterior process of the Mystriosuchus westphali GPIT 261/001 and Smilosuchus gre- quadratojugal rides on the flattened surface of the jugal. gorii UCMP 27200, such an elevation marks a dome-like exca- 2.5.10. Postorbital. In dorsal view, the postorbital appears vation of the internal side of the parietals that is confluent with stout and truncated in comparison to other phytosaur taxa the brain cavity (Camp 1930; Hungerbu¨hler 1998). This struc- (Fig. 5). This is because of the short squamosal process of the ture has been interpreted as evidence for a pineal organ (Camp postorbital that forms the anterolateral rim of the supratem- 1930; Langston 1949) or, alternatively, as the cartilaginous tips poral fenestra. The process extends over only one fourth of of the supraoccipital in the otherwise ossified skull roof (Roth the length of the postorbital–squamosal bar, which is mainly & Roth 1980). The central skull roof terminates posteriorly formed by the elongated squamosal. The postorbital reaches with the conjoined parietal extensions that form a rectangular forwards along the parietal and the postfrontal to form the parietal ledge overhanging the supraoccipital shelf for 25 mm centre of the posterior rim of the orbit. The crescentic orbital (Fig. 9). The corners of the ledge are extended into two poste- process extending downward and forward is low, but strongly riorly-pointing prongs, which are dorsoventrally flattened. In expanded transversally, being twice as broad as high. It is the cavity below the ledge, the parietals bear two symmetrical wedged as a thin but long prong between the lacrimal and the pits close to the midline, probably the origin of strong tendons jugal (Fig. 7), rather than extending along the infratemporal of parts of the epaxial musculature (Anderson 1936). The cor- fenestra and meeting the lacrimal anteriorly and the jugal ven- ners of the cavity below the parietal ledge are deeply sculp- trally. The postorbital also contributes little to the anterior tured with ridges, protuberances and grooves, which provide rim of the infratemporal fenestra externally, although it ex- further insertion points for musculature. tends downward on the medial rim of the postorbital flange The squamosal processes of the parietals form almost verti- to about mid-height of the infratemporal fenestra (Fig. 7). cally descending walls around the supraoccipital, then curve hor- 2.5.11. Postfrontal. The postfrontal is the smallest element izontally while diverging posterolaterally, and the pointed tips exposed on the skull roof (Fig. 5). It is almost semicircular in finally meet and overlap the parietal processes of the squamosals. shape. The convex edge is surrounded, from front to back, by An exception is the left side of TTU-P10077, in which the squa- the frontal, the parietal and the postorbital, and the concave mosal process of the parietal does not reach the squamosal on edge forms the posterodorsal rim of the orbit. A conspicuous the dorsal face of the opisthotic process, but terminates in a NEW MACHAEROPROSOPUS FROM WEST TEXAS 291

Figure 24 Machaeroprosopus lottorum TTU-P10076, otic area of the braincase in right lateral view. Scale bar ¼ 50 mm. Abbreviations: boc ¼ basioccipital; bsp ¼ basisphenoidal part of parabasisphenoid; d ¼ depression; eoc ¼ exoccipital; fm ¼ foramen magnum; fo ¼ foramen ovalis; f.pat ¼ facet for proatlas; jg ¼ jugular groove; lr ¼ lateral ridge sensu Gower & Walker (2002); mf ¼ metotic foramen; ol ¼ opisthotic lamella; pit ¼ pit sensu Camp (1930) in stapedial groove; plt ¼ platform of anterior wall of stapedial groove; p.psp ¼ parasphenoid process; pr ¼ projection; pr.lsp ¼ anteroventral process of the laterosphenoid; prs ¼ presphenoid; r ¼ recess; stg ¼ stapedial groove; v ¼ trigeminal foramen. broad end sutured to the supraoccipital (Fig. 20). The squa- posterior section of the rim of the medial lamella is squared mosal processes that form the lateral walls of the supraoccipi- and the anterior section is rounded (Fig. 9), in contrast to a tal shelf and ride on the supraoccipital are low and stockily thin and sharp rim in TTU-P10077. Both specimens show a built, with a broad base that narrows rapidly to a sharp rim. natural depression on the central medial part of the free post- They send a thin crescentic lamina onto the supraoccipital, orbital–squamosal bar (e.g., Fig. 6), which enhances the ele- both laminae together covering about one quarter of the sur- vated appearance of the posterior process. face of the shelf. The descending flange of the parietal anterior The posterior process of the squamosal projects far beyond to the squamosal process extends forwards, forming about half the extremity of the paroccipital process. Although almost of the lateral surface of the braincase, and meets the lateros- identical in absolute length, the length of the posterior process phenoid, epiotic, and opisthotic in a straight oblique suture of the squamosal in proportion to postorbital length is moderate (Fig. 18). in the larger skull TTU-P10077 (39 mm) than in TTU-P10076 2.5.13. Squamosal. A major distinction between M. lotto- (45 mm), which falls in the same longer relative size class as rum TTU-P10076 and TTU-P10077 on the one hand, and TTU-P10074. The overall shape of the process is, however, all other nominal species of Machaeroprosopus including similar in all specimens. It forms a massive, broad, but in par- Machaeroprosopus sp. TTU-P10074 on the other is the shorter ticular vertically expanded structure called the terminal knob length of the free postorbital–squamosal bar i.e., the distance of the squamosal by Ballew (1989). The process is considerably between the tip of the squamosal and the anterior rim of the narrower as the parietal–squamosal bar, which leads to a sinu- supratemporal fenestra, which corresponds largely to the max- ous (in other specimens angular) curvature of the medial rim of imum length of the squamosal, in proportion to the distance the postorbital–squamosal bar (Figs 5, 19; indeterminate in between the anterior rim of the supratemporal fenestra and TTU-P10077 because of incompleteness). The medial side of the orbit. The relative (and absolute) maximum width of the the knob is flattened and confluent with the flat medial rim of squamosal in the anterior third to midlength of the element is the parietal–squamosal bar, the lateral side is convex and also larger in M. lottorum than in TTU-P10074 and in other bulgy. The verticalisation of the terminal knob results in a dor- species of Machaeroprosopus, with the exception of M. gregorii sal surface sculptured with faint pits and grooves that is signifi- and M. bermani. The width increase is due to the expansion cantly raised above the level of the postorbital–squamosal bar. of the medial lamella of the squamosal. In TTU-P10076, the The knob forms the posterior border of a lanceolate area on 292 AXEL HUNGERBU¨ HLER ET AL. the horizontal face of the squamosal that show the typical pital process along the inner side of dorsal rim of the ptery- sculpture of anastomosing blunt ridges and elongated grooves goid–quadrate plate, i.e. the quadrate ramus of the pterygoid. in TTU-P10074 and TTU-P10076 (Fig. 5), but is almost un- The quadratojugal process is a broad vertical extension that sculptured in TTU-P10077 (Fig. 4). Both TTU-P10076 and articulates with the quadrate head medially. At the base of the TTU-P10077 show large, irregularly shaped pits, suggestive of upper one third of the infratemporal fenestra, the quadratoju- insertions of tendons, on the lateral face of the ventral base of gal process juts out to form a laterally facing facet for the the posterior process (Fig. 7). quadratojugal, which results in a narrow horizontal platform The opisthotic process (Figs 7, 9; ‘opo.sq’) of the squamosal (Fig. 7). The quadratojugal overlaps the quadratojugal pro- (descending process in Long & Murry 1995; hook-like process cess, leaving a thin tapering prong visible along three quarters in Mehl 1928), the origin of the m. depressor mandibulae pro- of the posterior rim of the infratemporal fenestra. Internally, fundus (Anderson 1936), projects downward for about 30 mm. the process extends broadly downward and covers a large area The vertical, slightly sinuous anterior margin forming the pos- of the quadratojugal. terior rim of the otic notch ends in two unequally sized prongs The sharp lateral edge of the postorbital–squamosal bar set transversally. The ascending posterior margin shows sev- continues as a prominent ridge beyond the infratemporal fen- eral protuberances and encloses an angle of 40 with the ante- estra, and outlines the base of the quadratojugal process as a rior margin (less steep with 55 in TTU-P10074), resulting in a depressed, smooth area, bordered ventrally by the horizontal triangular rather than hook-shaped outline of the process. The platform of the squamosal. This area includes a funnel-shaped smooth lateral surface is confluent with the area for the m. depression on the squamosal in extension of the infratemporal depressor mandibulae superficialis. The dorsal half of the medial fenestra, which was interpreted as the origin of the m. adductor face is braced against the extremity of the anterior side of the externus superficialis in Smilosuchus gregorii UCMP 27200 by paroccipital process of the opisthotic. The posterior surface Anderson (1936). In TTU-P10076, this depression extends and the lateral end of the paroccipital process merge to a single into a very faint groove that is cut off by the sculptured dorsal strongly rugose area that faces posteriorly. part of the lateral face of the squamosal. The ridge of the post- The thin parietal process extends exactly anteromedially orbital–squamosal bar is reduced to broad and low area, and (Fig. 9, ‘ppr.sq’). The lateral half is expanded posteriorly by a the dorsal and lateral surface of the squamosal grade smoothly thin lamella that forms a sharp posterior ridge running parallel into each other in the centre of the bone and on the posterior to and below the medial rim of the postorbital–squamosal bar. process. The smooth area for the m. depressor mandibulae super- A cross-section of the process is here teardrop shaped, with an ficialis above the opisthotic process of the squamosal is poorly extended sharp posterior rim. The broad base of the parietal defined in TTU-P10076. It terminates posteriorly in a concave process, the ventral and the medial surface of the squamosal vertical edge that connects the posterior process with the opis- body enclose the dorsal sulcus (‘ds’), which is the area of the thotic process of the squamosal, here called the squamosal adductor chamber that is open posteriorly because of the flange (Fig. 9, ‘fl.sq’). The flange is comparatively small and depression of the parietal–squamosal bar. The medial section of thick, but quickly thins out to a sharp edge that extends only the bar is twisted for about 90 around the long axis. The pos- over a short distance on the ventral side of the posterior process. terior ridge is gradually reduced in size leading to an oval Ventrally, above the opisthotic process, this edge is drawn out cross-section, shifts onto the dorsal surface, and merges with into a short, knobby posteroventral projection; the subsidiary the descending rim of the supraoccipital shelf. Medially, the opisthotic process of the squamosal (‘sopo.sq’). parietal process enters the corner of the supraoccipital shelf and 2.5.14. Quadratojugal. The quadratojugal has a triangular interdigitates with the supraoccipital, excluding this element outline (Fig. 7). Dorsally and posteroventrally, the quadratoju- from the posttemporal fenestra. The anteromedial extent of the gal articulates with the quadrate in two extensive joint surfaces parietal process is largely destroyed on the right side of TTU- above and below the quadrate foramen; the bone does not, P10076 and difficult to access on the left side as well as in however, contribute to the horizontal platform that is exclu- TTU-P10074, and accessible in TTU-P10077 only (Fig. 20). sively formed by squamosal and quadrate. The dorsal border Here, the squamosal sends a narrow, 2 mm, thin extension with the quadratojugal process of the squamosal has a sinuous that lies on the opisthotic onto the medial side of the braincase. outline and, below the quadratojugal, borders the ventral third The extension forms a marked ridge in continuation with the of the infratemporal fenestra. Anteriorly, the element is drawn anterior edge of the parietal–squamosal bar. It continues below out into an outer tapering sharp process that extends along the the anterior face of the squamosal process of the parietal, lying posterior half of the ventral rim of the fenestra. The anterior on the descending flange of the parietal, and makes contact process forms a well-marked offset ridge riding on the dorso- with the prootic. The parietal process forms the entire upper lateral edge of the jugal. Ventrally to the anterior process, the rim of the posttemporal fenestra. The ventral surface of the quadratojugal encloses the posterodorsal part of the jugal with base of the parietal process roofs over the paroccipital process a lateral and a more extensive medial lamina. The external of the opisthotic, and forms with the squamosal flange the ven- suture between the quadratojugal and the jugal runs from the tral sulcus. The squamosal is firmly sutured with the paroccipi- tip of the anterior process posteroventrally step-like towards tal process along the distinct lateral edge of the ventral sulcus the lateral condyle of the quadrate. The thin tapering medial (Fig. 9, ‘vs’). On the lateral side, a shallow triangular and rugose lamina extends along the centreline of the jugal over the poste- pit, probably the origin of a tendon, is separated from the ven- rior third of the infratemporal fenestra. The ventral edge of the tral sulcus by a broad, ventrally narrowing ridge. Anterome- quadratojugal is a broad, 25 mm-long rugose area lateral to dially, the squamosal develops a thin lamella that overlies the the posteroventral tip of the jugal and the medial condyle of posterior face of the paroccipital process forming the bottom the quadrate (illustrated also in TTU-P10074, Fig. 8). The con- of the vental sulcus. The lamella extends upon the dorsal sur- tribution of the quadratojugal to the rim of the subtemporal face of the paroccipital process and extends forward covering opening is a 2 mm narrow strip that connects the rugose area the opisthotic/quadrate suture. Thus, the squamosal does not with the medial lamina. only form the lateral corner of the posttemporal fenestra, but Posteriorly, the quadratojugal is drawn out into a deep and also the lateral one third of the ventral rim. It continues as a vertical, but blunt posterior ridge that defines both the lateral flat, broad process (pterygoid process sensu Mehl 1916) for a edge of the skull and the recess for the quadrate foramen (Fig. short distance anteromedially on the dorsal face of the parocci- 9). The posterior ridge curves outward, as does the entire ventral NEW MACHAEROPROSOPUS FROM WEST TEXAS 293 section of the quadratojugal, and disappears towards the ventromedial to the lateral edge at about midlength of the plate (Fig. lateral corner of the skull. The central area of the quadratojugal 11). The pterygoid ramus of the quadrate covers, as a triangle is sculptured with ridges, humps and even spike-like protuberan- with truncated anterior apex, about three quarters of the lateral ces, but the peripheral areas are smooth or undulating. There is face of the pterygoid–quadrate plate facing the adductor a deep, vertical depression anterior to the posterior ridge and the chamber, the suture between quadrate and pterygoid running anteroventral part of the quadratojugal shows a larger, but atop the dorsal edge. shallower horizontal depression which extends onto the jugal. Internally, a concave lateral flange extends forward onto the Medial to the posterior ridge, the quadratojugal is wrapped inner lamina of the quadratojugal. The quadrate bears four around the side of the quadrate and appears along the side on potential attachment areas for the adductor muscles: (1) the the posterior face of the skull. Here, the element forms much blunt, vaulted anterior edge of the flange running from the of the quadrate recess, but actually contributes only ventromedial rim of the quadrate foramen downward and outward, laterally to the rim of the quadrate foramen proper. A groove plus the steeply inclined plane of the flange that faces medially situated almost entirely on the quadratojugal extends ventrally and slightly anteriorly; (2) a marked oblique ridge in extension out of the quadrate foramen between the posterior ridge and of the lateral edge of the ventral surface of the pterygoid– the suture with the quadrate. quadrate plate towards the lateral condyle, and the area below 2.5.15. Quadrate. The quadrate is firmly inserted in the this and the horizontal ridge; (3) a horizontal ridge on the ventral side of the squamosal. The quadrate head curves back- central axis of the pterygoid–quadrate plate in extension of ward almost to the base of the paroccipital process, and the the lateral edge of the quadrate ramus of the pterygoid, and head is visible in lateral view as semicircular posterior exten- the area below, terminating on the lateral edge and the con- sion of the squamosal (Fig. 7). Lateral to the head, a 40 mm- cavity below the medial condyle: and (4) a central ridge on high vertical extension projects outward for 12 mm to form the ventral face of the pterygoid–quadrate plate, and a con- the dorsal articulation facet for the quadratojugal. The projec- cave area on the quadrate ramus in front of it. tion forms a horizontal platform of the cheek that is covered 2.5.16. Vomer. The vomers form the interchoanal septum by the quadratojugal process of the squamosal dorsally. Medi- (Fig. 11). The vomers are extraordinary broad in the anterior ally, the head articulates with the paroccipital process of the section (114 mm in TTU-P10076), but become narrower with opisthotic in a deeply serrated, obliquely transverse suture on the dorsal curvature of the septum at mid-length of the choana the posterior wall of the otic notch; thus, most of the external and are narrow and sharp in the anterior third. The sharp auditory canal lies within the quadrate. edge of the vomers continues as a crest for a short distance The neck of the quadrate is the narrowest part of the bone on the palatal vault. The contribution of the vomers to the medial to the quadrate foramen (Fig. 9). The foramen itself is palatal vault is minute and restricted to a rectangular, 7 mm- framed by the process for the quadratojugal articulation dor- long area along the midline and the posteromedial corner of sally and dorsolaterally, the neck medially, and the massive the choana. Anteriorly, both vomers form a simple, 33 mm articular part of the quadrate ventrally. A marked dorsome- long prong onto the prechoanal depression and are overlapped dially to ventrolaterally trailing ridge borders the recess of the by the premaxillae. quadrate foramen posteriorly and continues in a sinuous curve 2.5.17. Palatine. The ventrally exposed area of the palatine downward, forming the faint medial rim of the shallowing forms the medial section of the palatal plane along the choana groove between the quadrate and the quadratojugal. Towards and the palatal vault (Fig. 11). The anterior portion of the pala- the lateral condyle of the quadrate, the groove deepens to a tine lateral to the choana is tapering and strongly vaulted. The sharp slit exactly on the quadrate–quadratojugal suture. Be- apex of the convexity faces ventrally, forming an elevated tween the ridge and the neck of the quadrate, a broad shallow medial part of the palatal plane and a verticalised area that groove leads out of the quadrate recess and ventrally and overhangs slightly the anterior section of the choana. Anteri- medially in the direction of the medial condyle. Below the level orly, the palatine encroaches upon the maxilla, terminating in of the quadrate foramen, the quadrate flares out laterally, but a blunt prong about 10 mm in front of the anterior rim of the in particular medially (Fig. 11), to form the wide but narrow choana. The section below the choana and the anterior half of condylar area (TTU-P10076: 84 mm by 20 mm). The medial the palatal vault is distinguished by a prominent, medially in- condyle is almost flat and projects with a sharp rim laterally clined, ragged ridge. It demarcates sharply the now less con- and anteriorly. The lateral condyle is less extensive, more vex, horizontal palatal section from a vertical lamella, the dorsal bulbous and exposed in lateral view. The area in between is ramus of the palatine forming the lateral wall of the choana. anteroposteriorly constricted and bears an indistinct, obliquely The ventral area of the vertical and the entire horizontal lamella oriented central ridge, which is represented by a less promi- is covered with longitudinal ridges, oblique short pits and rugos- nent, blunt third condyle in TTU-P10074. ities. In the postchoanal section (Fig. 14), the palatine thins out The pterygoid ramus of the quadrate is a thin, vertical, tri- distinctly, the ridge merges into the ventral surface, and the ver- angular plate with truncated anterior apex that is closely ap- tical section is flexed ventrally, so that the bone is transformed plied to the lateral side of the quadrate ramus of the pterygoid into a horizontal, slightly convex structure with a sharp median (Fig. 18), forming a single unit, the pterygoid–quadrate plate. edge. This horizontal palatine lamella is extensive, both sides The plate is triangular with a horizontal ventral rim and an forming two lobes over the palatal vault that leave a narrow, anteromedially sloping dorsal edge (Fig. 9). The ventral part 12 mm-wide gap in between. The palatines thus cover here of the pterygoid–quadrate plate is folded medially to form a about 80% of the width of the vault, the closest approach to a horizontal ledge 25 mm deep at the base of the pterygoid pro- fully ossified secondary palate that has been observed in phyto- cess, which diminishes to 15 mm anteriorly. At the base of the saurs. In its posteriormost section, the palatine narrows and pterygoid ramus, at the level of the quadrate foramen, is a deep the medial rim curves outward. The element is applied as a vertical recess enclosed by the horizontal and vertical parts of thin rod to the medial side of the vertical pterygoid flange. A the pterygoid ramus, and the neck of the quadrate. The suture thin lamella extends dorsally onto the palatal vault; i.e., onto between the quadrate and the pterygoid on the medial face of the pterygoid. The exact extent of the lamella on the palatal the pterygoid–quadrate plate forms a broad triangle extending vault is indeterminable, but seems to be restricted to the ventral over the posterior half of the plate. On the ventral surface of parts of the wall, and is largely concealed under the overhang. A the ledge, the suture runs obliquely on a marked ridge from the narrow posterior extension of the bone is wedged between the 294 AXEL HUNGERBU¨ HLER ET AL. pterygoid and the ectopterygoid and almost reaches the rim of tral apex. The anterolateral and posteromedial rims are subvert- the pterygoid flange; this extension is absent in TTU-P10074. ical, and the longer anteroventral and shorter posteroventral The palatine also forms the posterolateral corner of the choana. rims are inclined towards each other and meet in a blunt corner. The suture with the pterygoid is vertical and disappears ven- The basipterygoid process of the pterygoid is a cup-shaped trally under the palatine overhang. posterior projection, attached with a broad base to the vaulted Posterolaterally, a deep groove is developed between the posterior rim of the palatal vault. The concave articular face is palatine and the ectopterygoid, ventrally along the insertion directed laterally, the slightly convex inner surface medially. of the bone with the pterygoid flange. The lateral rim of the The base of the quadrate ramus is stout and low. Here, the broadening palatine becomes sharp and lies on the ectoptery- ventromedial rim is raised to form a second, vertical articula- goid, both bones closing the groove and separating it from the tion with the basipterygoid process of the parabasisphenoid. suborbital fenestra. Anterior to the suborbital fenestra, the Above this joint, a plate-like vertical extension, the epiptery- palatine overlaps the maxilla in a suture that leads straight goid process, extends dorsally. The process is largely broken parallel the alveolar rim into the tip of the bone. off in TTU-P10074, but shows ragged edges in TTU-P10076 2.5.18. Pterygoid. The pterygoid may be subdivided into (Figs 18, 21, ‘ept.pt’), and must have been of considerable ex- four areas. Because of the development of a secondary palate, tent, because the remnants are 20 mm high and 15 mm long. the anterior or palatal ramus is verticalised and consists of (1) On the lateral side is a broad and shallow groove framed by the arched ventral section with a medial lip forming with its well-developed ridges (Fig. 18, ‘g’). It curves from the base of counterpart the dorsally closed palatal vault; and (2) a vertical the quadrate ramus in extension of the epipterygoid forward extension on top, the dorsal lamella, which is largely hidden and downward towards the ventral ramus and opens up to a from view between the palatal plane and the orbitonasal area. broad funnel (‘pqg’). Walker (1990) concluded that a similar The anterior process grades posteroventrally into (3) the ventral palatoquadrate groove in the sphenosuchian Sphenosuchus ramus (part of the pterygoid flange); and (4) the quadrate ramus most likely received the posterior extension of the cartilagi- extends posteriorly and laterally. nous palatoquadrate, which continued as epipterygoid ossifi- The palatal ramus extends anteriorly, forming the roof and cation. Posteriorly, the quadrate ramus expands dorsally, lying much of the lateral wall of the pterygoid vault to reach the medially on the pterygoid ramus of the quadrate, and is folded posterior rim of the choana between the vomer and the pala- over ventrally to participate in the horizontal platform of tine. This includes a vertical strut with a concave medial rim the pterygoid–quadrate plate (Figs 9, 21). The vertical and the 10 mm posterior to the choana that merges dorsally with the horizontal surfaces enclose a deep, cone-shaped recess on the wall of the palatal vault and supports the overhanging hori- medial face of the base of the quadrate ramus. On the medial zontal palatine like a shelf brace. Both pterygoids send out a face of the pterygoid–quadrate plate, the quadrate ramus medial lip, and they meet at the midline closing the roof of develops a dorsal process along the ascending dorsal rim, and the palatal vault. In the posterior half of the vault, the rims a ventral process that largely overlies the quadrate on the hori- of the lips are turned ventrally, and both are closely applied zontal platform and extends into the recess at the base of the to form a marked ridge. The vaulted rims diverge about 10 mm quadrate. By contrast to the morphology of the pterygoid ramus in front of the posterior rim of the vault, framing the anterior tip of the quadrate, the quadrate ramus is grooved on the ventral of the interpterygoid vacuity, and curve steeply downward to face by a raised medial and a ridge-like lateral rim, terminated form the basipterygoid process and grade into the posterior rim posteriorly by the oblique ridge of the pterygoid–quadrate su- of the ventral ramus. The dorsal laminae are largely concealed ture (Fig. 11). At the base of the quadrate ramus, the grooved below the orbitonasal region and only the posterior section is ventral face turns ventrally and laterally to merge with the open to description. This section includes an extensive, but pterygoid flange. This groove probably delimits an attachment only a fraction of a millimetre-thin lamina that extends slightly area for the jaw adductors in addition to those described on the inclined to the medial side upward, sheathing the base of the quadrate. cultriform process of the parabasisphenoid. The vertical poste- 2.5.19. Ectopterygoid. The ectopterygoid consists of the rior rim extends in alignment with the posterior rim of the pal- prominent ventral ramus directed posteromedially onto the atal vault and levels out horizontally at a level of about one- pterygoid flange, and the laterally directed palatal part (Fig. 11). third of the space between the palatal vault and the skull roof. The ventral ramus is verticalised by a twist along the long In the dorsal one-third, the rims of both laminae diverge in axis of the ectopterygoid, and underlies the ventral ramus of their course forward to enclose the cultriform process. As in the pterygoid. The ectopterygoid contribution of the pterygoid Mystriosuchus westphali GPIT 261/001(Huene 1911, fig. 4), flange is considerably thicker than the ventral ramus of the the dorsal laminae leave a narrow gap compared to that in pterygoid, and effectively the ectopterygoid represents the Smilosuchus gregorii UCMP 27200 (Camp 1930, fig. 34) and main structural support for the pterygoid flange. At the ante- Brachysuchus megalodon UMMP 10336 (Case 1929, fig. 17) rolateral base of the pterygoid flange in extension of the ante- that can be traced to at least the posterior end of the choana. rior rim of the subtemporal fenestra, the ectopterygoid wraps In extension of the posterolateral wall of the palatal vault, over the ventral ramus of the pterygoid, and appears as a the ventral ramus extends downward onto the pterygoid flange broad and rugose elevation on the lateral face of the pterygoid (Fig. 14A). The broad and comparatively thick base of the flange (Fig. 14A). The ventral and posterior rims of the ectop- flange above the level of the palatine is formed largely by the terygoid on the pterygoid flange are thickened and rugose, and pterygoid (Fig. 11), except for the anterolateral rim (ectopter- recessed below the pterygoid, indicating the presence of a ygoid) and parts of the medial surface (lamina of the palatine). cartilaginous cap around the edges of the flange. The broad, Below, the ventral ramus extends into a thinner, vertical lamina ridge-like anteromedial rim of the bone, exposed on the left that overlies the ventral process of the ectopterygoid, facing side because of disarticulation of the palatine, forms the lateral posterolaterally. This surface is smooth, and projects up to sev- wall of a groove between both elements (‘g’). The groove is 45 eral millimetres over the rim of the ectopterygoid all around the mm long and less than 5 mm broad. It leads into an elongated, pterygoid flange. In TTU-P10074, this lamina is particularly 16 mm-deep sinus preserved as a steinkern in TTU-P10076 (Fig. thin with sharp edges. The outline of the flange is angular rather 14B). The recess is enclosed between the ectopterygoid ventrally than rounded, forming an oblique (anterolateral to posterome- and the palatine part of the palatal vault medially and dorsally, dial) subrectangular base with an unequilateral triangular ven- and opens anterolaterally into the antorbital cavity. Anteriorly, NEW MACHAEROPROSOPUS FROM WEST TEXAS 295 the rim of the ectopterygoid sharpens, is extended medially and projections of the presphenoid, but leave narrow gaps to each extensively overlapped by the palatine. The ectopterygoid is projection. The upper rim approaches the floor of the optic only about 7 mm thick in the area between the groove and the nerve foramen. It is possible that a narrow fissure remains suborbital fenestra, and this might represent the roofed-over between the ventral sections of both halves of the projection posterior section of the slit-like suborbital fenestra, the plesio- through which the trough on the cultriform process communi- morphic character state. The ectopterygoid expands both verti- cates with the sella turcica, but the structure is too delicate to cally and horizontally into the stout and compact palatal part safely allow further mechanical preparation. In front of the that forms the robust posterior rim of the subtemporal fenestra, base of the parasphenoid process is a notch in the wall of the and meets the maxilla laterally and the jugal posterolaterally. parasphenoid trough that expands into a large, round foramen The jugal process of the ectopterygoid extends for at least 20 (this area is crushed on the left side). Ventrally, the base of the mm upward onto the jugal on the medial edge of the bone. cultriform process expands posterolaterally on each side onto The following account of the braincase elements, their con- the basisphenoidal portion of the braincase in a sharp and nectivities and structures is largely based on the accessible high, curved ridge that contacts the anterior pillar of the right side of TTU-P10076. For this section, if not indicated prootic and frames the sella turcica laterally. otherwise we refer to Figure 18 for illustration, and present a The hypophyseal area has been freed from matrix, but is reconstruction of the braincase in left lateral view in Figure 22. still difficult to access because of the parasphenoid processes 2.5.20. Epipterygoid. The ventral parts of both epiptery- of the cultriform process. The sella turcica is a conical pit deeply goids are preserved in articulation in TTU-P10076 (Figs 21, excavated into the basisphenoidal portion of the parabasisphe- 18). The element appears as an anteroposteriorly compressed noid, opening dorsally, below a comparatively high, vertical, rod that is 29 mm long and 5 mm broad. However, cross- anteriorly concave dorsum sellae. A subtriangular hypophyseal sections of the left epipterygoid show the rod to be a largely gap lies between the parabasisphenoid and the cultriform pro- hollow tube (Fig. 23). The base is curved anteriorly and cess ventrally and anteriorly, the presphenoid dorsally, and the merges with the base of the quadrate ramus of the pterygoid prootic posteriorly. As it most likely represents a cartilaginous to become the dorsal edge of the funnel-like depression. Because zone of the anterior portion of the braincase, it is a preserva- no suture is evident, both elements are most likely fused tional gap rather than a true fenestra as designated in Camp together. The epipterygoid encloses a laterally facing, vertical (1930) and Chatterjee (1978). The plane of the gap faces ante- recess with the epipterygoid process of the pterygoid situated rolaterally, and exposes the dorsum sellae and the uppermost posteriorly to the element, but does not touch the process or if part of the sella turcica. The prootic–parabasisphenoid suture so only with the medial edge at the base. continues horizontally over the dorsum sellae, and therefore 2.5.21. Parabasisphenoid and hypophyseal area. The para- much of the dorsum is formed by the prootic. The paired cere- sphenoid is not clearly distinguishable from the basisphenoid. bral branches of the internal carotids enter the bottom of the Only on the right side of TTU-P10076 (Fig. 21) does an as- sella turcica through the parabasisphenoid. The hypophyseal cending suture seem to be present close to the proximal part cavity communicates with the braincase cavity via a round cen- of the basipterygoid process, trailing toward the hypophyseal tral foramen in the dorsum sellae just below the presphenoid. gap. The entire area is also marred by cracks, but it seems The basipterygoid process is a column with a triangular that the parasphenoid extends as a thin sheet of bone onto cross-section, the blunt apex of which lies level with the plane the basisphenoid, and is partially broken away here. Otherwise, of the tubera (TTU-P10074) or slightly below (TTU-P10076). both elements may be fused over large parts of the braincase, Two vertical, flat facets occupy the entire height of the pro- and the complex is best regarded as a parabasisphenoid. cess: a lateral one with the base of the quadrate ramus of the On the exposed left side of TTU-P10076, the cultriform pro- pterygoid, and an anterolateral one with the cup-shaped basi- cess appears to be composed of two individual structures, pterygoid process of the pterygoid. The pterygoid thus enwraps separated by a horizontal suture, somewhat similar to the ini- the basipterygoid process of the parabasisphenoid on two sides, tial description for Mystriosuchus westphali GPIT 261/001 by with only the convex posteromedial face of the process being Huene (1911), subsequently found to be unsubstantiated free. Ventral displacement of the right basipterygoid process of (Hungerbu¨hler 2002). However, the left side, and the intact the parabasisphenoid relative to the left one in TTU-P10074 condition in TTU-P10074 indicates that this is a fracture that indicate that the joints were not fused, but potentially mobile. caused a slight ventral displacement of the upper section of the The shape of the articulation allows only vertical sliding move- cultriform process. The entire structure projects anteriorly from ments along the joint surfaces, provided that movement of both the base of the braincase in front of the sella turcica. The cultri- components was not restricted by other means. In ventral view, form process forms a narrow, parallel-sided rod bearing a hor- the base of each basipterygoid process is defined by a crescentic, izontal, trough-like excavation with very thin walls dorsally marked ridge on the postero-medial side. On both sides, the and a sharpened rim, which results in a ‘pointed U’-shaped ridges converge from the apices of the recesses between the (rather than the usual ‘V’-shaped) cross-section ventrally. The basipterygoid processes and the basioccipital tubera toward the height decreases gradually as the result of a concave ventral ventral extent of the parabasisphenoid below the cultriform pro- rim, and the process is enclosed and concealed anteriorly by cess. These ridges also outline the anterior extent of the central, the dorsal processes of the pterygoids. Impressions under the shallow, triangular median pharyngeal recess between both pro- dorsal process suggest that the cultriform process extends as a cesses. Each ridge forms the ventral rim of a groove that curves low but broad rod close to the dorsal rim of the processes into upward and forward around the base of the basipterygoid pro- the choanal region. At midheight of the cultriform process, cess toward the lateral face of the cultriform process. there is a blunt, ridge-like expansion below a narrow and faint The foramen for the cerebral branch of the internal carotid groove. Posteriorly, the trough of the cultriform process is is situated in the parabasisphenoid high up on the anterior closed against the sella turcica by a hook-shaped dorsal projec- face of the base of the tuber, anterior to the ridge in continuation formed by the parasphenoid processes (Fig. 24, ‘psp.p’). tion of the anterior wall of the stapedial groove. It opens into The delicate walls of the trough are extended dorsally here, a posterodorsally ascending, short groove that crosses this ridge. curve inward and are closely applied and meet in a sharp 2.5.22. Basioccipital and basioccipital tubera. The basioc- posterior edge, forming a flat, vertical, recurved hook. The cipital condyle is hemispherical (Figs 9, 10). The central normal parasphenoid processes are inserted between two anteroventral axis of the condylar surface points somewhat more ventrally 296 AXEL HUNGERBU¨ HLER ET AL. than posteriorly, being located a few millimetres below the noto- represented by a tongue of cartilage. The axis of the capitate chordal pit, but the condylar surface is far from facing postero- process is marked by a blunt subvertical ridge, the cotylar crest, ventrally as in most phytosaurs. Analysis of the bone texture aligned ventrally with the anteroventral process of the bone. indicates that the bases of the exoccipitals are functionally inte- Between the olfactory tube, the capitate process, the frontal, grated into the articular surface. The exoccipital–basioccipital and the postfrontal is a considerably large, but shallow recess sutures on the condyle are marked by two deep, slightly con- (also present, but much deeper in TTU-P10074) that continues cave grooves. A deep notochordal pit faces exactly posteriorly. forward as a groove along the frontal–laterosphenoid suture. From the pit, a deep vertical groove trails dorsally toward the A foramen at the bottom of the recess most likely represents joint exoccipital suture. The basioccipital neck is stout, rela- the exit of the vena cerebralis anterior (cf. Janensch 1936; tively broad, and smooth ventrally, i.e. without a central ridge. Walker 1990). The basioccipital tubera extend ventrally, but predominantly The posterior section of the laterosphenoid is wedged between laterally to a width of 80 mm as opposed to 27 mm at the the descending wall of the parietal posterodorsally and the basioccipital neck. The rugose tuberal surface is directed ven- prootic ventrally, and contacts the epiotic posteriorly. The hor- trally. The tubera form a confluent unit, the left and right side izontal suture with the prootic runs on a broad ridge that ter- of which is separated by a short and sharp ridge. A groove on minates anteriorly in a small, pyramidal, upward pointing pro- the lateral edge distinguishes the basisphenoidal contribution jection, situated entirely on the laterosphenoid. The suture is from the basioccipital contribution of the tubera. The paraba- indistinct and appears to be largely fused. sisphenoid forms about two thirds and the basioccipital one Anteriorly, the laterosphenoid forms the roof of the trans- third of the ventral surface of the tubera. A central tongue of versely kidney-shaped optical foramen (II). Paired crescentic the basioccipital, bearing the midline ridge, reaches the ante- grooves dorsally to the lateral lobes of the foramen probably rior rim of the tubera and separates both parabasisphenoidal received the epipterygoid (see below). The exit for the troch- halves. The basioccipital portion of each tuber projects farther learis nerve (IV) is in a small depression laterally and slightly laterally than the parabasisphenoidal portion to a blunt point, above the optical foramen. A small foramen of unknown affin- and is in addition even slightly recurved in TTU-P10074. The ities lies in the laterosphenoid just above the tip of the presphe- parabasisphenoidal portion is larger anteroposteriorly, with a noid in both TTU-P10076 and TTU-P10074. A narrow ventral rounded rectangular outline, and more rugose. The well distin- process of the laterosphenoid extends between the presphenoid guished muscle scars of the m. basioccipito-vertebralis (Anderson and the prootic into the roof of the trigeminal foramen (V). A 1936; in crocodylians, m. longus colli, Frey 1988) are oblong distinguished feature of this process is an anteroposteriorly flat- oval, positioned slightly oblique, and meet anteriorly at the tened, rectangular projection above the trigeminal foramen midline ridge. that is directed anterolaterally and ventrally (Fig. 24). The ven- 2.5.23. Laterosphenoid. TTU-P10076 preserves the com- tral rim of the process extends as a faint ridge onto the roof of plete anterior processes of the laterosphenoids, which enclose the trigeminal foramen, separating two passages out of the the olfactory tract of the brain that give rise to the olfactory opening. As interpreted by Camp (1930) for Smilosuchus gre- nerve (I). The laterosphenoid is here sutured to a sharp, prom- gorii, the ventral section of the laterosphenoid–prootic suture inent ventral ridge on the frontal, which continues beyond the probably runs in the deep, V-shaped cleft behind this projec- laterosphenoid forming the anterior internal rims of the orbit. tion. The anterior border of the ventral process with the pre- The laterosphenoids extend as an oval tube along the posterior trigeminal part of the prootic is marked by a vertical suture three quarters of the orbit, but do not reach the prefrontals as from mid-height of the presphenoid to the rim of the trigeminal in Smilosuchus gregorii UCMP 27200 (Camp 1930). The ventral foramen. However, the suture cannot be traced onto the inner symphysis of the anterior processes is somewhat broadened and wall of the opening, and the laterosphenoid and the prootic rugose, indicating the attachment of the interorbital septum, and seem to be partially fused. becomes a more prominent ridge toward the optic foramen. 2.5.24. Presphenoid. The presphenoid appears as a stout, There is no external evidence that the anterior process of the triangular element. It is unclear whether the element represents laterosphenoid consists of several sphenoidal elements, as postu- an unpaired ossification or two fused symmetrical elements, lated for Smilosuchus gregorii UCMP 27200 (Camp 1942), nor although the strongly damaged bone in TTU-P10074 does not is an ossification in the dorsal section of the interorbital septum reveal a median suture and favours the first interpretation. (as in Smilosuchus gregorii UCMP 27200: Camp, 1930; or as in The body of the element, a central, anteriorly sloping plat- M. jablonskiae PEFO 31207: Parker & Irmis 2006) detectable. form, forms the floor of the optic foramen. Two wing-like, ex- With the divergence of the internal orbital ridge in the anterior tremely thin dorsal processes, largely lying on the laterosphe- section of the orbit, the symphysis is separated by a narrow cleft, noid (TTU-P10076, left side), contribute to the lateral rims of and the olfactory tube opens anteriorly as a large round funnel. the optic foramen. Two stubby, rectangular processes point Just above the optical nerve is a single median foramen on a ventral and anterior, and terminate in small facets that face mound-like elevation, in a similar position as one in Smilosu- slightly outward (Fig. 24). These processes receive the dorsal chus (Camp 1930, figs 25, 37, ‘‘r’’). The anterior third of the projection of the cultriform process in between them. Two anterior process of the laterosphenoid, as well as a narrow small ventral processes extend along the laterosphenoid and zone below the frontal–laterosphenoid suture and the symphy- the hypophyseal section of the prootic in the direction of the seal area are slightly rugose to finely pitted, which may indicate anterior pillar of the prootic. The oculomotorius foramen that the ossification was not fully completed. (III) is situated between this process and the prootic. The prominent capitate process of the laterosphenoid arches 2.5.25. Prootic. The trigeminal foramen (V) is bounded upward and outward and meets the frontal at the anterior largely by the prootic, separating the anterior pillar of the ele- base of the process, the postfrontal and the postorbital in a ment from the posterior capsular portion, with a contribution central triple point, and the tip of the parietal posteriorly. At of the laterosphenoid to the roof. The foramen, which also the extremity, there is a shallow triangular gap between the gave exit to the vena cerebralis medialis and most likely the ab- laterosphenoid on the medial side, and the prefrontal, postor- ducens nerve (VI) (see discussion), is a large, vertical oval bital and parietal laterally (as in TTU-P10074; also noted in opening. It is 20 mm deep, with a shelf-like, concave ventral modern crocodylians: Iordansky 1973), suggesting that the rim and overall converging walls. The actual foramen into the capitate process was not fully ossified and the extremity was braincase cavity is about half as large as the external opening, NEW MACHAEROPROSOPUS FROM WEST TEXAS 297 and the deep walls might have enclosed and protected the tri- figuration of the elements is only in parts determinable, and geminal (Gasserian) ganglion. Two passages out of the trigemi- includes the posteriormost section of the prootic, the dorsal nal foramen can be reconstructed by osseous correlates and are parts of the parabasisphenoid and the basioccipital, the anterior indicated in Figure 21: one passage leading dorsally through section of the exoccipital, and the base of the paroccipital pro- the cleft between the anteroventral process of the laterosphe- cess and presumably the ventral ramus of the opisthotic. The noid and the ridge-like continuation of the external posterior foramen ovale and the metotic foramen lie in the lateral halves wall of the foramen. It probably transmitted the ophthalmic of these grooves, which continue anteromedially onto the base branch of the trigeminal nerve (V1), similar to the interpreta- of the basioccipital tuber. tion by Camp (1930) for Smilosuchus gregorii. The ophthalmic The stapedial groove is twice as broad as the jugular groove, branch most likely crossed the ridge of the capitate process and not divided into a stapedial and a tympanic fossa as figured through a groove between the base of this process and the for Smilosuchus gregorii UCMP 27200 (Camp 1930, fig. 37). anterolateral process of the laterosphenoid, to continue in a The foramen ovale is small and oval (long axis is 6 mm), situ- fainter groove upward and forward along the curvature of the ated close to the posterior rim opposite a small recess in the laterosphenoid. A second broader, anterodorsal exit is marked anterior wall. Anteromedially, the groove passes over a small, by a notch between the projection of the anteroventral process round depression and leads into a narrow passage caused by a of the laterosphenoid and the anterior pillar of the prootic. We platform-like bulge of the anterior wall with the traversing speculate that this notch indicates the course of the abducens prootic–parabasisphenoid suture. It widens abruptly to a broader nerve (VI). medial depression. Here, an elongated recess, which could also The anterior pillar of the prootic is stout, rises in a dorsal be a foramen, opens into the anterior wall (Camp 1930, fig. 37 direction lateral to the hypophyseal area to the level of the indicates a ‘pit’ in similar position for Smilosuchus gregorii). top of the dorsum sellae, and forms the expanded dorsal The anterior wall formed by the prootic is the most prominent flange of the dorsum. On the inner side, a curved ridge extends elevation. It shows a marked step above this ‘pit’ to continue to the base of the presphenoid as the dorsolateral rim of the as a lower, but sharp ridge forward and downward, until it dorsum sellae. The oblique suture with the clinoid process of curves laterally to merge with the lateral face of the basis- the parabasisphenoid enters the hypophyseal gap at midheight phenoidal portion of the tuber. (Fig. 21). On the base of the pillar, close to the ventral rim of It cannot be demonstrated for TTU-P10076 (or for TTU- the trigeminal foramen, is a finely ridged area from which the m. P10074) that the opisthotic forms a ventral ramus separating retractor pterygoidei arose (Walker 1990). A peculiar feature so the stapedial from the jugular groove. This ramus, termed the far not recognised in phytosaurs is an anterior triangular, flat opisthotic lamella (Walker 1990; Gower 1997, Hungerbu¨hler projection at the top of the anterior pillar. It is largely lost on 2002; crista paroccipitalis of Chatterjee (1978); descending the right side of TTU-P10076 (Fig. 21), but present on the left ramus of Stocker (2010)), is thin and sharp and continues side. In TTU-P10074, the size of a similar projection is con- anteromedially as a marked edge of the basisphenoidal por- siderable, with a length of 12 mm and a base height of 9 mm. tion of the tuber. The suture between the parabasisphenoid The capsular (post-trigeminal) exposure is large and extends and the basioccipital runs parallel to this ridge in the anterior below the laterosphenoid, as described above, meets the epiotic portion of the stapedial groove. posterodorsally, and extends ventrally and posteriorly along the The jugular groove is much narrower and somewhat deeper parietal and opisthotic, forming a thin superficial splint on the than the stapedial groove. The metotic foramen is a large and anterior edge of the base of the paroccipital process. On its long oval (15 mm by 5 mm) and occupies the entire mid-section ventral face, the prootic–opisthotic suture trails medially into of the jugular groove. The jugular groove continues as a slowly the stapedial groove and towards the opisthotic lamella, but is widening cleft onto the basioccipital. The posterior wall formed cut off by a large crack. Ventrally, the prootic–parabasisphe- by the exoccipital and the basioccipital (the equivalent of the noid suture crosses the extension of the stapedial groove be- lateral ridge (Gower & Walker 2002) or the subvertical crest tween the foramen ovale and the base of the tuber and turns (Gower 2002) of the exoccipital in pseudosuchians) is low, dorsally onto the anterior face of the opisthotic lamella; the broad and blunt. A broad anterior projection narrows the further course is obscured by damage. jugular groove below the metotic foramen, but the opening is The crista prootica runs subhorizontally parallel to and above clearly not subdivided into a foramen pseudorotunda and a the anterior edge of the paroccipital process towards the post- vagus foramen. Lateral to this projection and close to the eroventral rim of the trigeminal foramen. The posterior section metotic foramen, a single hypoglossal foramen (XII) exits the of the crista prootica is extended into a marked horizontal exoccipital in the dorsal portion of the posterior wall of the flange that is thick and blunt in TTU-P10076, but much sharper jugular groove. The hypoglossal nerves leave the braincase in TTU-P10074. The posterior section of the flange terminates thus in an anterior, rather than a lateral direction. abruptly, and the crista prootica faints quickly in anterior direc- 2.5.27. Opisthotic. The cochlear part of the opisthotic is tion in some distance behind the trigeminal foramen, so that the treated above. The complex internal configuration of the opis- structure resembles more a short overhang rather than a proper thotic here (see Camp 1930) and the external appearance on crest. The singular foramen for the facial nerve (VII) is a hori- the base of the paroccipital process is largely indeterminable zontal slit in the centre of the space between the edge of the in the specimens described here. anterior section of the crista prootica and the anterior lamella The paroccipital process of the opisthotic (Fig. 9) extends in of the stapedial groove. It is overhung by a convex ridge. This a posterolateral direction from the midline, both enclosing an ridge provides a short groove for the palatine branch of the angle of about 45–50. The base of the paroccipital process is facial nerve in anteroventral direction, and a much more pro- exceptionally broad. In ventral view, the process expands to the nounced and longer channel for the hyomandibular branch of rear in a sinuous curve, resulting in the oblique position of the the facial nerve, running in a posterior direction above the posttemporal fenestra with respect to the axis of the paroccipital anterior wall of the stapedial groove and overhung by the process of the opisthotic and the parietal–squamosal bar, re- flange of the crista prootica. spectively and, in the exoccipital pillar, being situated in exten- 2.5.26. Structures of the otic region. The complex mor- sion of the midline of the paroccipital process. phology of the region of the stapedial and the jugular grooves The lateral half of the paroccipital process is expanded in a is separately described and illustrated in Figure 24. The con- significantly ventral direction and the process is transformed 298 AXEL HUNGERBU¨ HLER ET AL. into a comparatively narrow, vertical structure. In M. lottorum half of each facet is situated on the supraoccipital, the lateral TTU-P10076 (Fig. 9) and TTU-P10077, it is abrupt with a half on the exoccipital. kink marked by a ventral prong, followed by a level ventral rim (oar-shaped paroccipital process sensu Ballew 1989), 2.6. Dentition whereas in TTU-P10074, the expansion is gradual (Fig. 10). TTU-P10076 is one of the very few specimens referable to The anterior face is braced against the quadrate and the entire Machaeroprosopus that provides substantial primary data on dorsal face slots into the squamosal and is covered anterome- the dentition. There are 48 teeth preserved in situ, out of which dially by a lamina of this element. Posterodorsally, the narrow 12 are fully erupted and complete enough for an identification lateral face abuts against the subsidiary opisthotic process of of the dental characteristics. Although there are some uncer- the squamosal. tainties because of gaps in the tooth row, this specimen allows 2.5.28. Epiotic. The epiotic is a separate ossification in the the determination of the diversity of the tooth morphologies dorsal part of the otic capsule that later in ontogeny fuses with and the onset of dental features within the premaxilla and the supraoccipital (e.g., Rieppel 1993). Because such a fusion maxilla series. The dental nomenclature follows the suggestions cannot be demonstrated in the specimens described, in con- of Smith & Dodson (2003). trast to the condition in M. jablonskiae PEFO 31207 (Parker The premaxilla contains 27 and the maxilla 24 tooth posi- & Irmis 2006), the epiotic is treated here as separate entity. tions, resulting in a total of 51. The spacing of the alveoli is The epiotic is exposed as a small, roundish area in the centre regular; premaxillary teeth are set in a distance of half an of the lateral face of the braincase. It is distinguished from the alveolar diameter, which decreases to one third between the surrounding parietal (posterodorsally), laterosphenoid (anteri- larger pm24 to pm26. There is a distinct, 12 mm-long dia- orly) and prootic (anteroventrally) by well-developed sutures. stema anterior to m1, which is largely on the premaxilla. M1 The epiotic is at the bottom of a well-defined, subrectangular through m3 are very close together, m4 through m16 are sepa- depression in an oblique position, much deeper and better rated by half an alveolar diameter, and posteriorly the inter- defined than in any other phytosaur. The depression opens alveolar space gradually decreases, being very close again anteroventrally onto the prootic by means of a broad channel. between the last seven maxillary alveoli. With the exception It almost certainly housed the exit of the vena capitis dorsalis, of pm1 and pm2, the alveoli are circular and differ only in although there is no foramen visible in TTU-P10076, TTU- size. Alveolus pm1 is labio-lingually oval (15 by 115mm). P10077 or TTU-P10074. M. jablonskiae has a vena capitis dor- The round, 10 mm-wide alveoli pm3 and pm4 face ventrally, salis foramen in the laterosphenoid close or at the junction rather than ventrolaterally. Posteriorly, the alveolar plane on with the supraoccipital in a similar depression (Parker & Irmis the premaxilla and the anterior section of the maxilla is in- 2006). Thus, the presence of this foramen is variable within clined for 30 relative to the horizontal plane (Fig. 17). Alveoli two species of Machaeroprosopus, but the taxonomic useful- pm5 through pm22 are even sized, with diameters of between ness of the character needs to be explored over a wider range 7 mm and 8 mm. The alveolar width increases to 9 mm in of taxa. pm23 through pm25, pm26 being again noticeably smaller 2.5.29. Exoccipital. The exoccipitals meet along the mid- (the size of pm27 is indeterminate). Alveoli m1 through m3 line and thus form most of the periphery of the foramen mag- get rapidly larger from 5 mm to 7 mm, followed by a gradual num and the cavity of the medulla oblongata. The exoccipital size increase to 105 mm in alveolus m23. The two last alveoli pillars are stout and broad, as the lateral face arches outward are significantly smaller. to merge with the paroccipital process. The element is fused to Regardless of their position, the teeth have several features the opisthotic, and even the contact with the supraoccipital in common. In fully erupted teeth, the crown-root line is con- above the foramen magnum seems to be fused in TTU-P10076. sistently situated 4–6 mm above the alveolar plane and in The exoccipital–opisthotic complex has a broad exposure on some specimens such as pm1 even substantially more. Hence, the lateral face of the braincase, with a slightly ascending suture the gum line must have been at about the level of the alveolar with the basisphenoid. ridges. Secondly, all teeth are smooth, without ornamentations 2.5.30. Supraoccipital. The outline of the supraoccipital seen in comparable phytosaur dentitions, such as wrinkles in on the centre of the supraoccipital shelf (Figs. 9, 10) is triangu- Rutiodon carolinensis (Emmons 1856) or fluting by widely lar, covered by concave sutures with the laminae of the squa- spaced ridges in Mystriosuchus planirostris (McGregor 1906; mosal processes of the parietals and truncated above by the Hungerbu¨hler 1998). Visible pseudostriae in the teeth of TTU- parietal, near the apex of the shelf 10 mm below the parietal P10076 are actually dense discontinuous arrays of cracks in the ledge. The inclined plane of the supraoccipital bears a faint enameloid. central ridge in its lower half. Laterally, the supraoccipital The first of the two enlarged premaxillary teeth (pm1 left) ex- narrows into a triangular prong toward the corners of the tends for 39 mm out of the alveolus, but the actual tooth crown shelf, and is truncated by strongly serrated sutures with the height (TCH) is 276 mm. The crown is steadily curved lin- squamosal. In TTU-P10076 and TTU-P10077, the element ex- gually. The cross-section is oval (fore–aft basal length (FABL): tends close to the posttemporal fenestra, but fails to reach this 95 mm; basal width (BW): 101 mm) with a rounded labial and opening. An unusual modification is present on the left side of a more pointed lingual side. A faint, unserrated lingual carina TTU-P10077 (Fig. 20): the supraoccipital appears on the dor- extends over the entire crown height. The premaxilla teeth pos- sal surface of the base of the parietal–squamosal bar, separat- terior to position pm4 are uniform in shape. Tooth crowns are ing the squamosal from the parietal by deeply interdigitating acarinate, slender and conical with an oval, labiolingually ex- sutures on this surface. tended base (in average, BW is 15 times as wide as FABL) The suture with the exoccipital/opisthotic complex is present that taper gradually to a round cross-section towards the apex. on the edge below the extremity of the shelf, trailing toward the The maximum crown heights are 24 mm (pm7) and 20 mm posttemporal fenestra. In TTU-P10076, the supraoccipital and (pm12). The basal part of the crown is straight. In the anterior exoccipital are fused above the foramen magnum. Two trans- positions, the apical half to one third of the crown is decidedly versely elongated, smooth humps above the foramen magnum curved in lingual direction; in more posterior positions the represent the facets for the proatlantes (Fig. 24). The condition curvature is less over only the apical one-third. This gives the in TTU-P10074, in which the proatlas articulations are rugose premaxillary teeth a kinked appearance. There are no teeth projections with a central concave facet, suggests that the medial preserved in the posteriormost enlarged premaxillary alveoli NEW MACHAEROPROSOPUS FROM WEST TEXAS 299 or in the anterior maxilla positions. Teeth in mid-position of somewhat steeper in front of the prenarial protuberances to the maxilla resemble premaxillary teeth, but are stouter (m7: the left and right of the midline, thus enhancing the pillar-like TCH 16 mm; FABL 66 mm; BW 74 mm) and less curved. appearance of these structures, but not along the midline; (ii) A faint, unserrated distal carina appears first in position m8. the prenarial area is generally rounded, and the top surface Starting with m11, the maxillary teeth are curved in a distal grades indistinguishably into the tooth-bearing section of the direction. M15 begins the transition to posterior maxillary teeth rostrum. with a serrated distal carina over the entire crown, and a mesial The smooth intraorbital area of TTU-P10074 is demarcated carina over the apical fourth of the crown. The cross-section posteriorly by a blunt ridge pointing laterally and posteriorly, is rounded with a distal edge, but the lingual side is flatter, which is an intermediate stage between the faint ridge of TTU- although still decidedly convex. One of the posteriormost max- P10074 and the projecting flange of TTU-P10077. illary tooth, m23, is stout (TCH 8 mm; FABL 94 mm; BW TTU-P10074 differs from M. lottorum in having a consider- 59 mm), with a triangular outline with two fully serrated car- ably narrower parietal ledge (26 mm versus 39 mm in TTU- inae. Because the mesial carina is more convex than the distal, P10076, at identical overall width of the skull table). The the crown axis is slightly recurved. In all four posterior maxil- squamosal processes of the parietals converge slightly towards lary teeth in which the serrations are preserved, the density the parietal ledge, resulting in an ‘inverted-U-shaped’ (sensu amounts to 4–45 denticles per mm on both carinae, measured Ballew 1989) frame around the supraoccipital shelf. In addi- at midheight of the crown. In contrast to teeth from similar tion, the slope of the squamosal processes of the parietals is positions in strongly heterodont phytosaur dentitions (e.g., only vertical close to the ledge, but slopes continuously at a Nicrosaurus kapffi SMNS 5727, Hungerbu¨hler 2000), posterior steep angle below. maxillary tooth crowns are biconvex, although the labial side is The exposure of the palatal vault is parallel-sided in TTU- much more vaulted, the carinae do not form distinct blades P10074, rather than severely constricted as in TTU-P10076, that are morphologically set apart from the central labial sur- and the undistorted choana is 83 mm longer than the naris. face of the crown, and these teeth do not show an imbricating The suborbital opening seems to have been much narrower in pattern. TTU-P10074 , and a lobate rim of the right palatine may indi- The nature of the dentition of TTU-P10077 must be largely cate that the suborbital fenestra was subdivided into several inferred from the alveoli. There are 24 premaxillary and 23 smaller foramina, as in the types of the pseudopalatine phyto- maxillary teeth, totaling 47. The terminal rosette contains saurs Mystriosuchus westphali (Huene 1911) or Machaeropro- two strongly enlarged teeth followed by two round, 11 mm- sopus andersoni (Mehl 1922). wide alveoli which are widely spaced and set high up on the TTU-P10074 differs from both specimen of M. lottorum in lateral side of the constriction facing ventrolaterally. Posterior several features of the narial area (Fig. 6): The centre of the to pm5, all alveoli are very closely spaced; being separated by narial cone is deformed to the right side, and thus the narial thin interalveolar septa with a maximum thickness of 3 mm. rims appear to be angular and the narial openings constricted Pm 5 is round, with a diameter of 5 mm, which increases to at midlength; in life, the shape of each naris was subrectangular an 115-mm labio–lingual width in pm8. From here, the shape with a more pointed anterior rim. The anterior rim is closed, of the premaxilla alveoli is transversely subrectangular, and although two narrow and shallow grooves extend out of the there are no size differences up to position pm23. The alveolar nasal openings. The sharp anterior narial rims are crescentic size changes abruptly to large dimensions in pm 23 and 24 pillar-like protuberances, between which the narial grooves (labio–lingual 17 mm, mesio–distal 16 mm), pm 24 is some- and the median suture of the septomaxillae pass onto the pre- what smaller (17mm by 135mm).Thissuggestsanabrupttran- narial area. The smoothly rounded lateral rim of the naris in sition to three large posteriormost premaxillary teeth. There is general slopes anteriorly; the rim is sinuous, the central section no diastema between premaxilla and maxilla. M1 to m7 are of the rim being levelled out, and thus the posterior rim is ele- strongly mesio-distally compressed, extremely closely spaced, vated for 10 mm above the anterior (Fig. 8). A similar condition and show a transverse subrectangular outline with the transverse in Mystriosuchus was termed a narial wing by Hungerbu¨hler axis pointing laterally and somewhat anteriorly. The dimensions (2002). The median suture on the septomaxilla runs in a deep increase gradually from 11 mm by 5 mm in m1 to 135mmby and narrow groove, present to about midlength of the inter- 105 mm in m7, which is the first oval maxillary alveolus. There narial septum. The internarial septum is narrow and sharp, is a greater size increase between m7 and m13 (17 mm by 155 without any significant increase in width anteriorly. mm). The alveoli are oval with the long axis oriented transver- 2.7.2. Internal structures of maxilla and septomaxilla. An sally. M14 to m21 are the largest alveoli in the dentition with extensive canal runs in the maxilla dorsal to the alveoli, prob- no size differences in the series, m20 being 18 mm by 15 mm ably transmitting blood vessels and nerves to supply the teeth long. The shape is broad oval, and the long axis is directed (Figs 16A, 17, ‘ac’). In the proximity of the choana, the pala- posteriorly and laterally. Alveoli m22 and m23 are smaller, tal section of the maxilla is extensively pneumaticised, show- the last one with an 115-mm short axis and a 14-mm long ing a central large cavern that is further subdivided by thin axis that points directly posteriorly. laminae and an array of accompanying smaller caverns or canals (Fig. 16A, ‘cv.m’). In TTU-P10074, the median suture 2.7. Skull morphology of Machaeroprosopus sp. between the septomaxillae and, in continuation, the premaxil- TTU-P10074 lae, is developed as a deep central groove all along the interna- TTU-P10074 differs in a number of character states from rial septum and over a distance of 145 mm anterior to the nares. Machaeroprosopus lottorum TTU-P10076 and TTU-P10077, Figure 16B shows details of the internal structure: a vertical and some structures are preserved in more detail than in these lamellae of the septomaxilla interdigitates with the under- specimens. lying premaxilla, among them a very thin, sheet-like lamella 2.7.1. External skull morphology. Two features on the ros- along the sagittal plane that reaches the deeper parts of the trum distinguish the dolichorostral TTU-P10074 from TTU- nasals. Internally, the septomaxilla contributes extensively to P10076: (i) the posterior section of the prenarial area slopes the roofs of the nasal and premaxillary cavities in Smilosuchus less steeply, at an angle of about 50 (Fig. 8). The slope is gregorii UCMP 27200 (Camp 1930, figs 22, 23, 25), but the 300 AXEL HUNGERBU¨ HLER ET AL. cross-sections of TTU-P10074 (Fig. 16A, B) are too far forward 3. Discussion of anatomical observations to show the ventral extent of the element for Machaeroprosopus. 2.7.3. Jugal (Fig. 8). TTU-P10074 has a broad and stout Narial and rostral crest. Given the high variability in the shape ventral process of the lacrimal that contacts and forms a short of phytosaur rostra, it is necessary to define criteria for identi- distance of the ventral rim of the antorbital fenestra. A further fying a crest and to classify crests to eliminate a potential source distinction from M. lottorum is that a well-defined, crescentic, of confusion. For example, Zeigler et al. (2002a, 2003b) distin- bumpy ridge surrounds the preinfratemporal shelf. This large guish, in the Canjilon Quarry phytosaur assemblage, between a area is 35 mm by 17 mm and opens dorsally into the postorbital morph with a tall, longer and robust crest (M. buceros) and a depression. morph with an abrupt, distinct narial crest (M. pristinus). Most 2.7.4. Parietal. In TTU-P10074, the parietal ledge shows previous authors (e.g., Camp 1930; Gregory 1962; Ballew irregular vertical ridges rather than two distinct prongs (Fig. 1989; Long & Murry 1995) regarded specimens of M. pristinus 10). Two symmetrically placed, posteriorly directed rugose as crest-less phytosaurs. Stocker (2010) categorised phytosaur knobs are situated on the inner side of the squamosal processes crests as narial and rostral crests, a crest being any elevation of the parietal of TTU-P10074 just below the parietal ledge. that rises above the area anterior and posterior to it. Narial Similar structures are absent in TTU-P10076 and P10077, but crests were defined as dorsal elevations both anterior and pos- were reported for Mystriosuchus westphali (Hungerbu¨hler 2002). terior to the nares. Narial crests can be in form of a narial cone 2.7.5. Squamosal. In accordance with the total length of raised above the level of the remainder of the snout, but also the squamosal, the posterior process of the squamosal on the include prenarial crests, redefined as ‘‘no or very little change undeformed right side of TTU-P10074 projects far beyond in dorsal elevation of the area of the skull roof posterior to the extremity of the paroccipital process (58 mm). In contrast the nares, but a decrease in dorsal elevation of the rostrum an- to M. lottorum, the ridge of the postorbital–squamosal bar in terior to the nares’’ (Stocker 2010, supplementum, unpaginated). TTU-P10074 becomes broader and blunter, but continues pos- She subdivided rostral crests into four types: (1) premaxillary teriorly onto the posterior process (Fig. 8). Thus, the dorsal crests; (2) dorsoventrally undulating crests including ‘partial’ and lateral surfaces of the central section of the squamosal crests that do not extend anteriorly to the terminal rosette of are set at a distinct angle in this specimen. A narrow but dis- the premaxillae; (3) crests that are continuous, sloping steeply tinct groove extends in TTU-P10074 from the external adduc- to the terminal rosette; and (4) crests that are continuous at a tor depression backward. It peters out above the level of the level from the nares to the terminal rosette. opisthotic process. This groove demarcates an elevated zone We adopt here Stocker’s (2010) classification of phytosaur below, which merges with the bulging lateral surface of the crests. According to her criteria, all specimens described here posterior process. This comparatively broad zone is reminis- have narial crests because there are elevated areas anterior cent of the narrow, well-developed lateral ridge of the squa- and posterior to the nares or, in other words, the nares are sit- mosal typical of M. pristinus and M. buceros but, in contrast uated in a cone that is elevated above the surface of the snout. to these, the elevation does not extend onto the posterior pro- Both TTU-P10076 and TTU-P10077 have partial rostral cess in TTU-P10074. The smooth area for the m. depressor crests, i.e., elevations that rise above the surrounding rostral mandibulae superficialis above the opisthotic process of the surface but do not reach the anterior tip of the premaxillae. squamosal is distinctly demarcated by a horizontal bumpy over- However, Stocker’s categories do not describe the entire mor- hang in TTU-P10074. The parietal process of the squamosal of phological variation seen in pseudopalatine phytosaurs. Char- TTU-P10074 extends farther medially on the posterior face of acters such as visual demarcation from the tooth-bearing part the supraoccipital shelf, and expands dorsoventrally onto the of the rostrum in the form of a longitudinal furrow, depres- shelf (Fig. 10). In medial aspect, the entire rim of the medial sion, or a flattened ‘shelf’-area lateral to the crest, crest profile, lamella of the squamosal is developed as a vertical plane that or mediolateral thickness are not considered. TTU-P10076 has is demarcated dorsally and ventrally by prominent blunt ridges a very short partial rostral crest below the narial cone, which (Fig. 10). This contrasts with TTU-P10076, in which the rim is is outlined by two lateral depressions. TTU-P10077 shows a vertical in the posterior section only, and with the thin and much extended, undulating and, in the anterior portion, sharp sharp rim in TTU-P10077. The medial lamella in TTU-P10074 partial rostral crest, outlined laterally by large depressions. is also much more thickened by a prominent ventral bulge along Stocker (2010) probably defined the categories largely to accom- the entire medial rim of the postorbital–squamosal bar. modate leptosuchomorph phytosaurs, the primary subjects of 2.7.6. Palatine. Although the same structures of the palatal her study, and she discussed other variable crest features in the section of the palatine are principally present in TTU-P10074, description without incorporating them in the classification. We they are differently developed. The vault of the anterior section do not wish to modify or expand Stocker’s classification here; of the bone is less marked, its apex points ventromedially and this should be left to a comprehensive study of the crest mor- the palatine terminates level with the choana. The palatine ridge phology in all phytosaur taxa. In this study, we prefer a reduc- is lower, points ventrally and is restricted to the central area of tive approach to character construction (Wilkinson 1995), and the bone. The postchoanal parts of the palatines are parallel- compartmentalise rostral crests into four discrete characters sided, showing a much smaller palatine lamella that is curved (Table 1: characters 1, 3, 4, 5) that adequately and objectively upward rather than horizontal and thus overhangs only about describe the variation in crest morphology in Pseudopalatinae. two third of the width of the palatal vault. The palatine lamella Septomaxilla and paranasal. Two discrete ossifications are is significantly less sculptured. identified in the narial and immediate prenarial regions of 2.7.7. Supraoccipital (Fig. 10). A central ridge on the TTU-P10076, TTU-P10077 and, possibly, in TTU-P10074. supraoccipital shelf is absent in TTU-P10074 and the lateral Paired separate elements anterior to the nasal openings that tips of the supraoccipital terminate more medial to the postor- incorporate most of the internasal septum were first men- bital fenestrae. The sutures between the supraoccipital and the tioned by Meyer (1865) for Nicrosaurus meyeri NHMUK exoccipitals cross the edge of the suparoccipital shelf and pass 42745, later identified as septomaxillae by Huene (1909) in downward and inwards into the foramen magnum, forming a Mystriosuchus westphali GPIT 261/001 and, since then, con- 4–6 mm thin strip on the roof of the canal for the medulla firmed as being present in every phytosaur taxon. The topol- oblongata. ogy and the relationships with the premaxilla and nasal show that the medial element in the specimens described here is the NEW MACHAEROPROSOPUS FROM WEST TEXAS 301 same element, the septomaxilla. Sereno (1991), Senter (2002) Contribution of squamosal to lateral wall of braincase. An and Stocker (2010) questioned the homology of this bone be- anterior lamella of the parietal process of the squamosal, cause of topological, functional and phylogenetic incongru- that extends far onto the lateral wall of the braincase and con- ence with the septomaxilla. The arguments were that the sep- tacts the prootic in M. lottorum (Fig. 22), invalidates this feature tomaxilla in lepidosauromorphs (1) is not exposed on the skull as an autapomorphy for Mystriosuchus westphali (Hungerbu¨hler surface; (2) is located on the floor rather than the roof of the 2002). Parker & Irmis (2006) confused this character with the nasal passage; and (3) does contact the maxilla, unlike the sep- ‘squamosal flange’ (see description) and its distribution (char. tomaxilla in phytosaurs. We wish to point out that the exter- 26), but correctly stated that the anterior lamella is present, but nal nasal openings of phytosaurs are highly modified with re- does not reach the prootic in M. jablonskiae and in an isolated spect to shape, orientation and position, as is the configuration pseudopalatine braincase they referred to M. cf. pristinus. This of the nasal bones, the choana and the palate. It seems rather indicates that the anterior extent of the squamosal on the brain- unlikely that details of the topological relationships of a bone case is indeed variable within Machaeroprosopus and might be present in this region are not affected. The septomaxilla also a taxonomically informative feature. undergoes substantial evolutionary modifications in synapsids, Epipterygoid. Among phytosaurs, the morphology of the including a facial exposure (Wible et al. 1990). Senter (2002) epipterygoid is known in sufficient detail only for Smilosuchus argued that (4) the septomaxilla provides support for the vom- gregorii (UCMP 27200) and Mystriosuchus westphali (GPIT eronasal (Jacobson’s) organ, for which there is no independent 261/001). The epipterygoid of Machaeroprosopus differs in evidence in phytosaurs. The presence of a septomaxilla, how- general shape and, in particular, in the mode of articulation ever, is not necessarily correlated with the development of the with the pterygoid. As described by Camp (1930) and Huene vomeronasal organ in, for example, urodeles (Trueb 1993, table (1909, 1911) and based on own observations (AH pers. obs. 6.2) and it may have acquired this structurally supportive func- 2000, 2002), the epipterygoid is a much thinner element in tion only secondarily in squamates (Wible et al. 1990, fig. 1). Smilosuchus and Mystriosuchus, with sharp lateral and medial Finally, (5) a septomaxilla is apparently absent in any other edges. As far as preserved, the epipterygoid of Mystriosuchus archosauromorph except the much more basal Proterosuchus is a largely antero–posteriorly elongated rod, and only the (Senter 2002); i.e., there is no phylogenetic continuity via dorsal section is twisted and faces anterolaterally. Smilosuchus Erythrosuchidae and Euparkeria to phytosaurs. With respect and Machaeroprosopus share a derived feature, the transverse to this argument, we wish to point out that a usually delicate orientation of the epipterygoid with an anteriorly-facing side. intranasal element in groups in which the narial area has re- In the ventral section, the epipterygoid of Smilosuchus is dis- ceived little attention could have been easily lost by tapho- tinctly twisted along the vertical axis and develops a thin, pos- nomic processes, or overlooked. Hence, we see no sufficient teriorly-directed lateral flange, resulting in a deeply grooved reason to doubt the homology of the bone in question with posterior side of the element. The base of the epipterygoid is the septomaxilla in other tetrapods. We interpret the expansion bifurcated and wraps around the epipterygoid process of the of the septomaxilla, including an exposure of the bone on the pterygoid, the groove receiving the anterior edge of that pro- prenarial surface and the exclusion of the premaxilla and the cess. The epipterygoid process thus forms a firm buttress for nasal from the internasal septum, as an apomorphic develop- the epipterygoid. In all epipterygoids except Machaeroprosopus, ment of Phytosauria. a process extends posteriorly along the quadrate wing of the The lateral ossification situated in the anterolateral corner pterygoid, and the epipterygoid and the pterygoid are clearly of the naris between the nasal and premaxilla has no prece- unfused, separate elements. dence in amniotes. It certainly represents a neomorphic bone Primitively, the epipterygoid articulates dorsally with the that evolved within Phytosauria. We introduce the name para- parietal close to the skull roof, and this condition is retained nasal (from Greek ‘para’ – beside or alongside of ) for this ele- in the archosauriform Proterosuchus (Broili & Schro¨der 1934; ment. All other descriptions of phytosaur crania agree in that Clark et al. 1993). In more derived archosaurs, the dorsal in- the same space is occupied by the nasal. There is no evidence sertion of the epipterygoid, when ossified and preserved, proba- for a paranasal in any specimen of Nicrosaurus (Hungerbu¨hler bly shifted onto the laterosphenoid (Gower & Sennikov 1996). 1998), or Mystriosuchus (McGregor 1906; Hungerbu¨hler 2002), The exact location of the dorsal articulation of the epipterygoid and we are confident that such an ossification is absent in the with the braincase in Machaeroprosopus is uncertain. Chatterjee immediate outgroups of Machaeroprosopus hypothesised by (1978) interpreted a pit in the dorsal section of the laterosphe- Hungerbu¨hler (2002). As described for TTU-P10074, the pre- noid behind the capitate process as the epipterygoid facet in narial area is difficult to interpret in many specimens of Ma- Parasuchus hislopi; a comparable recess in P-10076 is here chaeroprosopus, and the sutural configuration was only con- identified as the exit of a blood vessel. In Smilosuchus gregorii, firmed in excellently preserved specimens. We suspect that a the epipterygoid inserts in a pit on the anterolateral face of the reexamination will reveal that the paranasal is much more laterosphenoid at the base of the capitate process (Camp 1930, common in Machaeroprosopus. For this reason, we do not sug- left side; in contrast to his figures 36, 38 and 39, only the base gest the paranasal as diagnostic for M. lottorum. In all three of the right epipterygoid is now preserved). There is a shallow specimens under study, the paranasal is correlated with a rugose depression in P-10076 in a similar position as in Smilo- columnar appearance of the anterolateral rim of the nares, and suchus gregorii. Were the epipterygoid to insert here, the ele- such morphology may represent an indicator for the presence ment would have been considerably recurved (unlike any of the element in other specimens. known epipterygoid in phytosaurs) and, for the spatial condi- tions, would have to have been buttressed by the anteroventral Braincase process of the laterosphenoid, thereby closing the exit of the Several features of the braincase and related structures of cleft behind this process to a foramen. An alternative insertion Machaeroprosopus are described here for the first time, or pre- is the crescentic groove on the ventral side of the anterior pro- vious description are confirmed for this taxon. Many of these cess of the laterosphenoid, above the optical foramen, which is features are, however, difficult to evaluate critically with respect exactly in extension of the preserved base of the epipterygoid, to homology and phylogenetic significance, in the absence of as it is in Mystriosuchus westphali (Hungerbu¨hler 2002, fig. 8). detailed studies in most phytosaurs. Gower (1997) suggested a pit in a similar position as an articulation of the epipterygoid of Erythrosuchus. We think this is the 302 AXEL HUNGERBU¨ HLER ET AL. most likely insertion of the epipterygoid. The posterior shift of substantially enlarged ‘optical foramen’ (e.g., Plateosaurus, the epipterygoid on the laterosphenoid in Smilosuchus gregorii Galton 1985). Reports of a presphenoid in other pseudosu- might be connected to the strong anteroposterior compression chian archosaurs are questionable. After repreparation of the of the braincase in this taxon. type specimen, the presence of a presphenoid in the rauisuchid In comparison to other phytosaurs, the epipterygoid of Postosuchus as reconstructed by Chatterjee (1985) is unsub- Machaeroprosopus shows several differences. First, it forms a stantiated, and should be regarded as a part of the anterodor- thick, rather than blade-like rod. The preservation as a hollow sal process of the prootic (Weinbaum 2011). The evidence for tube in TTU-P10076 suggests that only the peripheral parts of a presphenoid in Saurosuchus (Alcober 2000) was considered the epipterygoid were ossified, and the core may have been in- doubtful by Gower (2002) because the demarcation from the filled with matrix after decay of the cartilage. Secondly, the laterosphenoid seems to be a fracture, and the postulated ele- entire transversely expanded side of the epipterygoid faces ment borders, unlike a presphenoid, the trigeminal foramen. anteriorly and, in conjunction with the different orientation, the In addition, the ‘presphenoid’ of Saurosuchus (Alcober 2000, posterior basal process is reduced. Thirdly, the ossified epiptery- figs 7, 8) shows a process of the same shape and in the same goid is spatially decoupled from the epipterygoid process of the position as the anteroventral process in TTU-P10076, which pterygoid. The ragged outline of the free epipterygoid process is definitely part of the laterosphenoid (Fig. 22, ‘vp.lsp’). For suggests that the structure was topped by a significant cartila- ornithodiran archosaurs, the only presphenoid described is in ginous extension, and it might have taken the place of the Ceratosaurus (Madsen & Welles 2000), but there authors present epipterygoid in closing the primary skull wall. It might even too little information to allow a comparison. An element called represent an ossification within the palatoquadrate, rather than the presphenoid in troodontid theropods (Currie 1985) more a primary part of the pterygoid, which became fused with this likely represents, according to its spatial relationships, an ossi- dermal bone. fication of the ethmoidal series. Parasphenoid process. TTU-P10076 and P-10074 are the first On the basis of three specimens of Smilosuchus,Camp(1942) phytosaur skulls to preserve this delicate structure (Fig. 22, postulated that the area of the laterosphenoid as described for ‘psp.p’). Remnants seems to be also present in Smilosuchus other phytosaurs is actually subdivided into a laterosphenoid gregorii UCMP 27200 (AH pers. obs.), but were apparently sensu stricto, an anteriorly placed orbitosphenoid, and a ‘sep- omitted in Camp’s (1930, fig. 37) braincase reconstruction. tosphenoid’ enclosing the anterior part of the olfactory tract. From its shape and position, it is likely that at least the top He suggested that these three elements fuse through ontogeny part of the projections represents ossifications embedded in into a single element, and claimed that sutures only persist ex- the interorbital septum. ternally in juveniles, but are obscured by superficial bone layers Gower & Walker (2002, p.13) described a ‘‘subvertical prow in adult specimens. An orbitosphenoid in a corresponding of the parabasisphenoid’’ in front of the hypophyseal fossa for position to that of Smilosuchus was also identified in Mystrio- the aetosaur Stagonolepis robertsoni. They interpreted tenta- suchus westphali (Hungerbu¨hler 2002). tively a pair of foramina in the front section of the ‘prow’, as- For other archosaurs, an overview is given in Hungerbu¨hler sociated with horizontal ledges as exits of the orbital arteries (2002) and we restrict our comments to some supplementary out of the hypophyseal fossa. The description and illustration information. An orbitosphenoid ossification in front of the (Gower & Walker 2002, fig. 3) is essentially similar to the para- laterosphenoid is well established for plateosaurid (Galton 1985) sphenoid processes and the associated foramen in TTU-P10076, and a variety of theropod dinosaurs (e.g. Madsen 1976; Currie although there is no horizontal ledge. It is conceivable that the 1985; Currie & Zhao 1993; Madsen & Welles 2000). This is a orbital arteries emerged from the hypophyseal fossa between paired ossification, with the centre of the bone dorsal to the the parasphenoid processes and travelled into the orbital cavities optical nerve. A medially curved, thin ventral process usually via foramina in the ossified walls of the cultriform process (but extends downward to a certain degree, forming the lateral rim see discussion in Gower 2002). Otherwise, parasphenoid pro- of the optical foramen. The process may meet its counterpart cesses among archosaurs have only been noted for dromaeo- at the midline (e.g., Allosaurus fragilis, Madsen 1978; confirmed saurid and troodontid dinosaurs (Colbert & Russell 1969; Currie by AH pers. obs.), and the optical foramen is completely sur- 1985). rounded by the orbitosphenoids. Among pseudosuchian archo- Presphenoid and orbitosphenoid. Two elements in addition saurs, only Parrish (1994) reconstructed an orbitosphenoid in to the laterosphenoid and the prootic in the anterior braincase the braincase of the aetosaur Longosuchus, but his evidence have been reported as present for some phytosaur taxa. could not be confirmed by Gower & Walker (2002), nor was A discrete ossification below the optical foramen in phy- an orbitosphenoid identified in other taxa (Small 2002). tosaurs was first recognised and described as presphenoid by This survey shows that two elements may ossify in the ante- Camp (1930) in the type specimen of Smilosuchus gregorii rior section of the braincase of archosaurs around the optical (UCMP 27200). The presphenoid illustrated for the basal phy- nerve, in addition to and substituting the prootic or the later- tosaur Parasuchus hislopi in Chatterjee (1978) is not preserved osphenoid in this region. These bones are not homologue, as in the specimen, but was postulated on the basis of sutural fac- indicated by their topological incongruence. A dorsal element, ets on the laterosphenoids in accordance with Camp’s (1930) usually called the orbitosphenoid, is paired and centred above interpretation in UCMP 27200 (S. Chatterjee, pers. comm. the optical nerve, although it may extend downward along the 2002). A presphenoid is, however, present in another basal sides of the foramen. A ‘slender’ or ‘ventral process’ of the form, Paleorhinus scurriensis TTU-P8090 (Simpson 1998, named laterosphenoid in Euparkeria (Clark et al. 1993) is topologically ‘orbitosphenoid’; AH, pers. obs.). So far, most studies of the consistent with the ventral process of the orbitosphenoid in braincase in other taxa have failed to identify the element dinosaurs. A ventral ossification, the presphenoid, may ossify (Lees 1907; Mehl 1928; Case 1929; Case & White 1934; below the optical nerve, although a dorsal process may occupy Colbert 1947), and one of us questioned the existence of this the same position lateral to the optical nerve as the process of bone altogether (Hungerbu¨hler 2002). TTU-P10076 and TTU- the orbitosphenoid (or laterosphenoid). Whether these elements P10074 are, to our knowledge, the only other phytosaur skulls are equivalent ossifications of the orbitosphenoid and presphe- that show well-preserved presphenoids. noid (both names are based on ossifications in the mammalian Frequently, this area of the braincase is not ossified in arch- skull; Romer 1956) is in need of further study, but we retain osaurs, leaving a gap (e.g., Euparkeria;Clarket al. 1993), or a NEW MACHAEROPROSOPUS FROM WEST TEXAS 303 these names, which are well embedded in the literature, for the of Mystriosuchus, in connection with the supratemporal fenestra time being. and the temporal region, most likely do not represent ancestral TTU-P10076 and TTU-P10074 demonstrate the ossification states, but are reversals or independent developments in this of a distinct presphenoid in Machaeroprosopus lottorum.The highly derived lineage (see Hungerbu¨hler 2002). The close rela- occurrence of this element across various phytosaur clades tionship with the North American pseudopalatine phytosaurs (Paleorhinus, Smilosuchus and Machaeroprosopus)suggests has also been contested (e.g., Hunt 1994; Long & Murry 1995). that this element regularly ossified in phytosaurs. According For this reason, we include Nicrosaurus, represented by the type to Camp (1930), the presphenoid forms much of the anterior species Nicrosaurus kapffi (Meyer 1860), as an additional out- inner wall of the braincase, and is thus a much more extensive group that currently is well-supported as the most basal pseudo- element than it appears to be externally. Because there is no palatine phytosaur (Ballew 1989; Hunt 1994; Long & Murry unambiguous evidence for this element in other archosaurs 1995; Hungerbu¨hler 2002). (with the possible exception of the theropod dinosaur Ceratosau- rus; Madsen & Welles 2000), the ossification of a presphenoid is 4.3. The ingroup most likely an autapomorphy of Phytosauria. The evidence for Apart from the skulls described in this study, the ingroup a discrete orbitosphenoid in phytosaurs (and pseudosuchian includes the six North American pseudopalatine species that archosaurs) is meagre, in contrast to a more widespread occur- are regarded as valid in the most recent reviews (Ballew 1989; rence in dinosaurian archosaurs. Camp’s (1942) suggestions are Hunt & Lucas 1993; Long & Murry 1995, in parts; Hunger- intriguing and offer an explanation for the erratic observations bu¨hler 2002; Parker & Irmis 2006). Character states were of a discrete orbitosphenoid ossification in phytosaurs (and, coded by examining the holotype of each OTU only, to avoid more generally, in other archosaurs), but his evidence for a subjectivity that might result from including specimens a priori subdivision of the laterosphenoid needs to be confirmed in his in the hypodigm. specimens and across more taxa. Abducens (VI) foramen. In Parasuchus hislopi, the abducens Machaeroprosopus pristinus (Mehl 1928) nerve (VI) exits on the anterior face of the braincase on the Holotype. UMo 525, complete cranium suture between the prootic and the parabasisphenoid, at the Type horizon. Petrified Forest Member, Chinle Formation level of the lower one-third of the hypophyseal gap to the Type locality. unknown locality in Painted Desert, Petrified medial side and the trigeminal foramen to the rear (Chatterjee Forest National Park, Apache County, AZ (Irmis 2005) 1978, fig. 5a). There is a broader matrix-filled notch in the M. pristinus is the type species of Pseudopalatus Mehl, 1928. same position on the right side of TTU-P10076 (Fig. 21), but Personal inspection by one of us (AH 2000) revealed that the such a notch is clearly absent on the well-preserved left side specimen falls rather short from being ‘‘of better than average (Fig. 18). The structure on the right side is more likely to be preservation’’ (Mehl 1928, p. 7). The postorbital region of the the result of a partial separation of the prootic from the para- skull has evidently been assembled from numerous fragments, basisphenoid along their suture. Camp (1930) could not iden- and the shape and the proportions of some features in the tem- tify a separate abducens foramen for Smilosuchus gregorii poral region seem to be distorted. The nasal area and the left either, and assumed that the abducens nerve exited together squamosal are in parts, and the top of the parietal–supraocci- with the trigeminal nerve through the trigeminal foramen. pital complex fully, reconstructed in plaster. This raises the This could indicate that in derived phytosaurids (Smilosuchus, question of whether the morphology of these features in the Machaeroprosopus) the course of the abducens nerve out of holotype is real, deformational or artificial, and we regard the braincase has been modified relative to the plesiomorphic some of the data taken from Mehl’s (1928) drawings, or from pattern in basal phytosaurs. subsequent photographs (Long & Murry 1995, figs 40B, 41A, B), as unreliable. Some characters of the holotype are at vari- 4. Phylogenetic evaluation of Machaeroprosopus ance with those seen in other specimens that have been included in the hypodigm (Ballew 1989; Long & Murry 1995; lottorum Zeigler et al. 2002a, 2003b). What remains of the original palate does not support Mehl’s (1928) reconstruction of a fully ossified 4.1. Design and purpose of the parsimony analysis secondary palate, as already suspected by Camp (1930). The We assess the phylogenetic position of Machaeroprosopus lotto- characters for M. pristinus are scored ‘as is’ in the type specimen rum (TTU-P10076 and TTU-P10077) and Machaeroprosopus (Table 1), and those from reconstructed areas are scored as ‘in- sp. TTU-P10074 by parsimony analysis in the framework of determinate’. It might be necessary to reconsider some of the the systematics of North American pseudopalatine phytosaurs, scores that might have been affected by deformation (e.g., as suggested in the reviews of Ballew (1989), Hunt & Lucas characters 8, 17, 18) pending the results of a thorough reassess- (1993) and Parker & Irmis (2006). We emphasise that we do ment of the specimen. Zeigler et al. (2002a, 2003b) regarded M. not attempt a revision of the North American pseudopalatine pristinus as the female morph of M. buceros and thus a junior phytosaurs at this stage, for reasons given below. Conse- synonym of M. buceros. We chose the conservative approach quently, we rely on previous studies for the validity of the to retain M. pristinus for the analysis, also in order to test their OTUs, and the data matrix does not include shared derived interpretation as sexual morph by conducting a parsimony characters which exclusively support the monophyly of the analysis. M. pristinus was diagnosed by Ballew (1989) by five ingroup, but are uninformative with respect to ingroup inter- autapomorphies: (1) proportionally very long rostrum; (2) relationships. The conclusions of our analysis presented here are mound-shaped, convex and thickened nasals around nares; (3) tentative, and a more comprehensive analysis is in preparation. sharp descent of nasals on the rostrum; (4) homodont dentition; and (5) subcircular antorbital fenestra. 4.2. Choice of outgroups The trees are rooted and the ancestral states of the characters Machaeroprosopus buceros (Cope 1881) are identified by comparison with Mystriosuchus planirostris Holotype. AMNH 2318, cranium (Fraas 1896) and Mystriosuchus westphali Hungerbu¨hler & Type horizon. upper Petrified Forest Formation (Lucas et al. Hunt, 2000, which most parsimoniously form the sister-group 2002) to the ingroup (Hungerbu¨hler 2002). However, several features 304 AXEL HUNGERBU¨ HLER ET AL. Type locality. near Orphan Mesa, Rio Arriba County, NM poral fenestrae, that is characterised by the absence of a ‘ros- (Lucas et al. 2002) tral’ crest (Hunt & Lucas 1993, p. 193). Recently, Spielmann & AMNH 2318 is a poorly preserved skull (see Lucas et al. Lucas (2012) rediagnosed the species (in which they include M. 2002), which accounts for the amount of missing data. Origi- bermani) by, in addition to the supratemporal fenestra con- nally erected as Belodon buceros, over time the species was as- cealed in dorsal view: (1) reduced antorbital fenestra; (2) a signed to no less than five different genera until Parker et al. prominent pre-infratemporal shelf; (3) the septomaxilla form- (2013, this volume) determined that M. buceros is the type spe- ing the anterolateral half of the external naris; (4) rim of the cies of Machaeroprosopus. Long & Murry (1995) designated orbit thickened; (5) inflated posterior part of nasal; and (6) Belodon buceros as the type species for their genus Arribasu- thickened dorsal osteoderms. chus. Hunt (1993, 1994; Hunt in Hunt et al. 2002) considered Machaeroprosopus bermani (Hunt &Lucas 1993) the taxon a species of Nicrosaurus, because the type specimen shows a dorsolaterally compressed posterior process of the Holotype. CM 69727, cranium with strongly deformed man- squamosal, slit-like supratemporal openings, and the narial dible lacking the anterior half of the symphysis openings are situated below the level of the skull roof. How- Type horizon. ‘siltstone member’ of Chinle Formation ever, the squamosals show numerous similarities with those (Nesbitt 2011) or Rock Point Formation (Spielmann & Lucas of other species of Machaeroprosopus (see Table 1), including 2012) the dorsoventrally expanded posterior process, and we regard Type locality. Coelophysis Quarry, Rio Arriba County, the shape of the supratemporal fenestrae as ambiguous because NM; the skull was recovered above the actual Coelophysis of damage. The position of the nares was correctly identified by bonebed when the quarry was reopened in the early1980s and Hunt, although the narial rims are severely abraded and parts of the overburden was removed (D. Berman pers. comm. 2001). the narial area are crushed down. This represents, however, the The type specimen is only superficially prepared, and the plesiomorphic state of this character. The type specimen shares sutural configuration and details of some structures, such as no derived feature with the type species of Nicrosaurus, N. kapffi the posttemporal fenestra and the parietal–supraoccipital (Meyer 1860) to the exclusion of the other pseudopalatine taxa, complex, are currently obscured. M. bermani was originally and consequently we reject this assignment. Ballew (1989) diagnosed a species of Redondasaurus in possession of a ‘partial’ identified three autapomorphies, which are posttemporal fenes- rostral crest. Spielmann & Lucas (2012) regarded the holotype tra extending laterally above the opisthotic, labio–lingually as the male morphotype of M. gregorii, and consequently M. compressed posterior maxillary teeth with a mesial ridge, and bermani as a junior synonym of that species. a V-shaped rostral crest. Machaeroprosopus mccauleyi (Ballew 1989) 4.4. Methods and analytical procedures The character-taxon matrix and a list of the character states Holotype. UCMP 126999, cranium with mandible are presented in Table 1 and the Appendix, respectively. The Type horizon. Petrified Forest Formation data were subjected to a parsimony analysis using the software Type locality. Billings Gap, Apache County, AZ program PAUP 3.1.1 (Swofford & Begle 1993), run on a Ballew (1989) lists five autapomorphic characters in support PowerMac computer to produce the most parsimonious of the species: (1) squamosal with distinct triangular outline branching pattern. Multistate characters were left unordered, without knob-like process; (2) lateral portion of opisthotic and all characters were initially treated as equally weighted. thin and elongate; (3) posttemporal fenestra large because of The analyses employed the ‘exact’ branch-and-bound algo- a medial extension; (4) basioccipital head relatively large; (5) rithm (addition sequence ‘furthest’ and the option ‘collapse basioccipital neck relatively short. Hunt et al. (2006) suggested zero-length branches’ activated), which guarantees finding all two additional diagnostic characters: the lateral margins of the most parsimonious trees (MPTs). The data were organised skull flare at 60 in posterior view and the presence of a ‘com- and tree statistics were calculated in MacClade 3.07 (Maddison plete’ rostral crest. & Maddison 1997); TL increased by one step relative to PAUP Machaeroprosopus jablonskiae (Parker & Irmis 2006) because C21 for Machaeroprosopus bermani is treated as ‘polymorphism’. To evaluate the support of the individual branches Holotype. PEFO 31207, posterior part of skull roof and of the MPTs, three methods were employed. First, a bootstrap braincase analysis was performed (10000 replications; search settings as Type horizon. Jim Camp Wash beds of Sonsela Member, above) and, secondly, Bremer support was computed for each Chinle Formation node using the software Autodecay 4.0 (Eriksson 1998). Thirdly, Type locality. near Mountain Lion Mesa, Petrified Forest a number of subsequent runs were performed, in which several National Park, Apache County, AZ (Parker & Martz 2011). constraints were enforced upon the MPTs retained by the parsi- Parker & Irmis (2006) identified a bevelled edge on the mony analysis. The constraints included clades of terminal taxa antero-medial edge of the postorbital–squamosal bar as a that were not present in the MPTs from the initial analysis, but single autapomorphic character in support of the species. have been hypothesised by previous workers. The minimum number of additional steps required to produce such suboptimal Machaeroprosopus gregorii (Hunt & Lucas 1993) trees when compared to the MPTs without the constraint is then Holotype. YPM 3294, cranium used as a relative measurement for the probability, how far Type horizon. Duke Ranch Member, Redonda Formation the constraint clades represent a reasonable option to be con- Type locality. Shark Tooth Hill, Quay County, NM (Spiel- sidered in reconstructing the interrelationships of the taxa and mann & Lucas 2012). specimens. M. gregorii isthetypespeciesofRedondasaurus.Long& The initial run recovered six MPTs with tree lengths (TL) of Murry (1995) did not accept the validity of Redondasaurus and 127 steps, consistency indices (CI) of 0.5, retention indices referred M. gregorii to Pseudopalatus pristinus. In the type (RI) of 0.51, and rescaled consistency indices (RCI) of 0.25. specimen, the entire narial area, the left side of the snout, the An Adams consensus tree (Fig. 25A) shows that there is little anterior two thirds of the right premaxilla, and most of the congruence among the trees. The analysis indicates that not palate are missing. M. gregorii was diagnosed as a species of only M. mccauleyi and M. jablonskiae, but also M. bermani, Redondasaurus, therefore with dorsally concealed supratem- are basal pseudopalatine taxa, whereas M. pristinus, M. buceros, NEW MACHAEROPROSOPUS FROM WEST TEXAS 305

Figure 25 (A) Adams consensus tree of six most parsimonious trees (MPTs) obtained by parsimony analysis of character-taxon matrix, Table 1. (B) Strict consensus tree of two MPTs after exclusion of characters 1, 3, 4 and 5. (C) Single MPT after successive approximate character weighting (SAWC). Left values represent bootstrap percentages >50; right values Bremer support.

M. gregorii and the specimens under study are positioned more measurement of fit, the RI was chosen and the baseweight was crownwards. set to 1000. SACW recovered a single tree, which was identical In an attempt to remove one potential source of non-taxo- to one of the two MPTs retrieved in the previous run (Fig. 25B). nomic variation, we tested the suggestions of sexual dimorphism A bootstrap analysis was undertaken and Bremer support was proposed by Zeigler et al. (2002a, 2003b) and excluded the char- calculated for the less inclusive data matrix, and mapped onto acters 1, 3, 4, and 5, which together describe the presence and the SACW tree (Fig. 25C). the shape of a rostral crest, and reran the analysis with the Both MPTs now show M. pristinus þ M. buceros,aswellas same settings. This resulted in a drop of the number of the TTU-P10076 þ TTU-P10077, as sister-taxa. (TTU-P10076 þ MPTs to two (Fig. 25B) with a TL of 109 steps and slightly TTU-P10077) þ M. gregorii, the type species of Redondasaurus, improved statistical values (CI 0.52; RI 0.55; RCI 0.29). For form a clade. TTU-P10074 is recovered as immediate outgroup further improvement, a series of runs were undertaken with to this clade, followed by (M. pristinus þ M. buceros) closer to successive approximations character weighting (SACW; see the root of the tree. Wilkinson & Benton 1996). In this method, the characters are re-weighted a posteriori according to a measurement of fit as determined by the previous run, and the data is then re-ana- 5. Conclusions on sexual dimorphism lysed. Re-weighting and re-analysing continues until the weight The exclusion of a set of characters (rostral crest presence and no longer changes, or identical trees are found in a consecutive morphology) that has been suggested to represent sexually di- run (Swofford & Begle 1993). Thus, character incongruences morphic features in pseudopalatine phytosaurs resulted in an that result in multiple MTPs are expected to be resolved by improvement of the resolution of the phylogenetic relationships. successively low-weighting of homoplastic characters. As a The initial hypothesis of Zeigler et al. (2002a, 2003b), on the 306 AXEL HUNGERBU¨ HLER ET AL. basis of 11 skulls from the Canjilon quarry, and similar evi- Sues 2001). The only morph within this clade with a short ros- dence from a phytosaur assemblage from the time-equivalent tral crest is Angistorhinus talainti (Dutuit 1977). In addition, Snyder quarry (Zeigler et al. 2003a) in north-central New Mex- both the basal phytosaurs and Angistorhinus include speci- ico was based on three lines of reasoning. First, taphonomic mens of ‘gracile’ and ‘robust’ built, which are traditionally studies of the Machaeroprosopus assemblages from the Canji- separated at species level (e.g. Paleorhinus bransoni vs. Paleo- lon and Snyder quarries (Hunt & Downs 2002; Zeigler 2003) rhinus sawini; Long & Murry 1995) or even as distinct genera found that both represent a snap-shot of a contemporaneous (Angistorhinus vs. Brachysuchus; Hunt 1994; Leptosuchus vs. population. Secondly, a morphological comparison of the Ma- Smilosuchus; Pseudopalatus vs. Arribasuchus; Long & Murry chaeroprosopus assemblages suggested to the present authors 1995). A similar distinction is seen in Machaeroprosopus lotto- that the only distinction between the specimens lies in the rum, with the ‘gracile’ TTU-P10076 with a short rostral crest shape of the rostral crest. Lastly, Zeigler et al. (2002a, 2003b) and the much more ‘robust’ TTU-P10077 with a long rostral argued that dimorphic structures in fossil vertebrates that crest. Thus, ‘gracile’ and ‘robust’ morphs might be interpreted were interpreted as sexually dimorphic are cranial structures as sexual variants of one taxon. However, we advise caution, suitable for visual display, and phytosaur crests fit this pattern. because robustness is difficult to define objectively and, also, An analysis of the Canjilon Quarry data, however, did not pro- and perhaps predominantly, subject to growth variation. Note duce a statistically significant signal, because of the small sam- here that the Canjilon phytosaur assemblage includes both ‘gra- ple size (K. Zeigler pers. comm. 2002). Irmis (2005) pointed cile’ smaller specimens (UCMP 34250) and substantially more out weaknesses of the sexual dimorphism hypothesis: other ‘robust’ larger specimens (UCMP 34256) of the crested morph possible explanations of dimorphism such as sympatric closely Machaeroprosopus buceros (Zeigler et al. 2002a, figs 3D, E, related species or resource polymorphism have not been ruled 4D, E). out; the hypothesis does not test apparent dimorphism in other (2) The genera Leptosuchus and Smilosuchus do not include phytosaur genera; and does not address the presence of third a clearly uncrested, or dolichorostral morph, with the excep- morphs such as M. mccauleyi and Smilosuchus gregorii, with tion of some smaller and probably juvenile specimens (Camp shorter, much broader, fully-crested snouts (brachyrostral type 1930). In those species within both genera which can be reli- of Hunt 1989). Hunt et al. (2006) suggested that sexual dimor- ably differentiated by characters of the temporal region (e.g., phism is expressed in M. mccauleyi by an increased robustness by several features of the squamosal and the configuration of the rostrum in males, but because their two ‘male’ voucher of the septomaxillae: Stocker 2010; A. Hungerbu¨hler unpub- specimens are significantly larger than the ‘female’ holotype, lished data), the pattern of crest development is highly vari- the more massive snout can be similarly well explained as an able and does not show a conclusive pattern. In most cases it advanced stage of ontogeny. is hard to see a dimorphic crest development, and we agree Our analysis lends further support for Zeigler et al.’s with Stocker’s (2010) findings that both the pattern of cresting (2002a, 2003b) hypothesis. It produced a similar result on the and the robust or gracile built of skulls are incongruent with basis of a parsimony analysis of a different data set, although the distribution of character states that are currently deemed M. pristinus and M. buceros differ evidently more than only in taxonomically significant within these taxa. rostral crest characters (see Appendix; the pairwise distance (3) Nicrosaurus and Mystriosuchus both include a crested between both specimens corrected for missing data is 0393, and partially crested or uncrested (again, broadly, but not abso- and M. pristinus and M. buceros are more distant to each oth- lutely correlated with ‘robust’ and ‘gracile’) morph. First, in er than, e.g., M. bermani from the crested skull TTU-P10077 contrast to Machaeroprosopus pristinus/buceros and M. lotto- [0389]). Moreover, the data is exclusively derived from the rum, these morphs differ evidently by more than merely the de- actual name-bearing rather than from referred specimens. We velopment of a rostral crest or by crest length. Contra Kimmig thus conclude that it is more likely that M. pristinus and M. (2009), we find it difficult to attribute all observed character buceros are two morphotypes of the same species than two differences (which also include, for example, the development separate species. This hypothesis is even better supported for of the narial openings and the shape of the squamosal; Hunger- M. lottorum TTU-P10076 and TTU-P10077. bu¨hler 1998, 2002) to intraspecific variation within a population. European and North American Upper Triassic deposits Secondly, there is evidence for the dimorphic development of have yielded contemporaneous phytosaurs that share numerous various cranial characters, both within the hypodigms of the characters, and differ in overall appearance mainly by the ab- fully crested Nicrosaurus kapffi and in Nicrosaurus meyeri with- sence, presence and the nature of a rostral crest and the general out or with small rostral crests (Hungerbu¨hler 1998). Thirdly, in build of the skull (see Hungerbu¨hler 2002, table 1). We restrict the case of Mystriosuchus, there is a marked discrepancy in the our conclusion on sexual dimorphic characters explicitly to M. numerical proportion of the two ‘morphs’: the uncrested, ‘gra- buceros þ M. pristinus and M. lottorum. Our main concern is cile’ Mystriosuchus planirostris is known from at least one dozen that the explanation as sexual morphs as suggested here, and skulls, not counting numerous additional cranial fragments, by Zeigler et al. (2002a, 2003b), might be less critically and whereas the ‘robust’ Mystriosuchus westphali with a premaxillary universally applied to all phytosaurs, as it was the case with crest is represented by the type skull, a partial rostrum, and some poorly-founded previous suggestions of sexual dimorphic fea- jaw fragments only (Hungerbu¨hler 2002). tures in phytosaurs (Camp 1930; Colbert 1947; for a critique In conclusion, we strongly urge restraint from rash nomen- see Ballew 1989), Indeed, Kimmig (2009) presented results of clatural acts on the basis of our and Zeigler et al.’s (2002a, b, a principal component analysis in support of sexual dimor- 2003a, b) findings without substantial supporting evidence. phism for M. buceros and M. pristinus, but also extended that interpretation onto the genera Leptosuchus (including Smilosu- chus and Pravusuchus sensu Stocker 2010), Nicrosaurus, and 6. Systematic conclusions Mystriosuchus. A brief survey indicates that the situation in other phytosaur taxa may be much more complex than it 6.1. Machaeroprosopus lottorum appears to be in Machaeroprosopus. TTU-P10076 and TTU-P10077 are identified as more closely (1) There are evidently no crested variants known for basal related to each other than to any other specimen or taxon in- phytosaurs (‘‘Paleorhinus’’) and no fully crested morph is cluded in the analysis. This is the strongest phylogenetic signal known for Angistorhinus (Rutiodon sensu Hungerbu¨hler & in the matrix, because the clade was found five out of six times NEW MACHAEROPROSOPUS FROM WEST TEXAS 307 from the initial run of the analysis, and it is supported by the (3) Machaeroprosopus gregorii and Machaeroprosopus bermani highest bootstrap and decay values in the ingroup (Fig. 25). do not form a monophyletic group in any MPT. Even when the rostral crest features are not considered, it required 6.2. TTU-P10074 three additional steps to force M. gregorii with M. bermani Despite the close temporal proximity and the occurrence at into a sister-taxon relationship (¼ Redondasaurus). This is the same site, TTU-P10074 is consistently confirmed as not particularly striking because, according to the original de- closely related to TTU-P10076 or TTU-P10077, both by parsi- scriptions of Redondasaurus gregorii and Redondasaurus mony analysis as well as by traditional comparative anatomy bermani, the presence or absence of a crest is the only dis- (Table 2). Because the range of variation for a given species of tinction between both species, and M. bermani is often Machaeroprosopus is currently unknown, we do not expand regarded as the ‘male’ morph of M. gregorii. This is not the diagnosis of either M. lottorum or M. buceros to incorpo- reflected in our data, and Machaeroprosopus gregorii is rate TTU-P10074, and refer to this specimen as Machaeropro- consistently interpreted as more derived than Machaero- sopus sp. This study also demonstrates that pseudopalatine prosopus bermani. phytosaurs from the same location within a very close temporal range are not necessarily conspecific, but may exhibit a In contrast to Long & Murry (1995), we concur with Hunt wealth of morphological differences when examined in detail. & Lucas (1993) and Spielmann & Lucas (2012) that Machaer- oprosopus gregorii (Hunt & Lucas 1993) represents a valid spe- 6.3. Machaeroprosopus cies. The validity of the taxon is supported by three characters: The diagnosis of Redondasaurus is given as ‘‘supratemporal (1) complete absence of an indentation of the supratemporal fenestra that are essentially concealed in dorsal view and whose fenestra into the skull roof (C27[4], shared with the type of Re- anterior margin only slightly emarginates the skull roof’’ and dondasaurus bermani); (2) dorsoventrally compressed posterior- ‘‘wide squamosal-postorbital bars’’ (Hunt & Lucas 1993, p. most portion of the squamosal with lateral rims that strongly 193). The first diagnostic character is here subdivided in three converge to each other (C24[0]); and (3) vertical rims of the distinct states (C27[2–4]), which can be unambiguously distin- parietal–squamosal complex surrounding a shallow, vertical guished in all specimens under study. Merging C27[(2-4] into supraoccipital shelf (C31[3]). The latter two traits are not pres- one character state and re-analysing the data does not change ent in any other nominal species of the ingroup. the number and topologies of the MTPs obtained. We quanti- fied the second character to score it objectively. Machaeropro- 6.4. Arribasuchus sopus lottorum corresponds to the original diagnosis of Redon- Long & Murry’s (1995) subdivision of North American pseu- dasaurus, and could be referred to this genus. However, we dopalatine phytosaurs into a gracile, crest-less Pseudopalatus, propose that Redondasaurus should be regarded as a junior and Arribasuchus with massive, crested skulls is unsubstanti- synonym of Machaeroprosopus for the following reasons: ated by our data. A minimum of nine additional steps (increase by 7%; TL 136), and even 15 steps when the rostral crest char- (1) A comparison and assessment of cranial characters in Table acters are included (increase by 14%; TL 123) is required to 2 shows that Machaeroprosopus lottorum bridges the mor- force the OTUs into a dichotomy of Pseudopalatus sensu phological gap between Redondasaurus (as defined by the Long & Murry (1995) (Pseudopalatus pristinus, Redondasaurus type species Redondasaurus gregorii) and Machaeroproso- gregorii, TTU-P10074 and TTU-P10076) on the one hand, and pus (as defined by the type species Machaeroprosopus bu- Arribasuchus (Pseudopalatus mccauleyi, Redondasaurus bermani ceros; the species that were formerly included in the junior and TTU-P10077) on the other. Hence, we regard Arribasu- synonym Pseudopalatus) with respect to the supratemporal chus as a junior synonym of Machaeroprosopus. fenestra, the parietal–supraoccipital complex, and some features of the squamosal. In addition, M. lottorum shows a combination of characters that are exclusively expressed 7. Prospectus either in Machaeroprosopus (¼ Pseudopalatus) (e.g., C25[2], The comparatively poor support for all nodes in the MPTs a laterally expanded terminal knob of the squamosal) or in recovered in the analysis indicates that the data matrix still Redondasaurus (e.g., C18[0], a wider postorbital-squamosal contains a significant amount of ‘noise’. We suspect that, like bar). Thus, the existence of a taxon like Machaeroprosopus those describing the rostral crest morphology, a number of lottorum makes a distinction between the genera Redonda- characters do not contain a phylogenetic signal, but represent saurus and Machaeroprosopus (¼ Pseudopalatus) de facto ontogenetic, sexual or even individual variation. These are dif- arbitrary. ficult to identify at present. An examination of a wider range (2) Machaeroprosopus (¼ Pseudopalatus) sensu Ballew (1989) of specimens and the correlation of character states with those constitutes a paraphyletic group in all trees. We explored suggested as sexually dimorphic, or with those correlated with the possibility of Machaeroprosopus (¼ Pseudopalatus) a proxy for individual age of the specimens, may help to iden- being monophyletic by rerunning the analysis under the tify and eliminate phylogenetically uninformative characters. constraint that only trees were withheld in which the type In addition, this study revealed a wealth of cranial characters species Redondasaurus gregorii formed the sister-group to with potential taxonomic significance, but only few of them all other taxa. The shortest suboptimal trees that comply could be included in the analysis and evaluated, either because with the constraint all show a clade of both species of Re- the character states are unknown for the majority of specimens, dondasaurus as a sister-group of the rest of the ingroup, or because the distribution is uninformative for the small num- and are five additional steps (TL 109) or 5% longer than ber of OTUs of this analysis. the MPTs; i.e., they contain a considerable amount of addi- A factor contributing to the uncertainty is the missing or tional homoplasies. Therefore, we consider a basal position ambiguous data for several species because of the incomplete- of Redondasaurus with respect to all other North American ness of their type specimens (Redondasaurus gregorii)orpoor pseudopalatine phytosaurs (¼ Machaeroprosopus) an un- preservation (Pseudopalatus pristinus, Pseudopalatus buceros). likely option. It became evident during the preparation of the data matrix 308 AXEL HUNGERBU¨ HLER ET AL.

Table 2 Assessment of characters of Machaeroprosopus lottorum n. sp. and Machaeroprosopus sp. TTU P-10074 in comparison with the type species of Pseudopalatus and Redondasaurus. Numbers in square brackets refer to characters listed in the Appendix.

Machaeroprosopus lottorum TTU assessment of Pseudopalatus (type Redondasaurus (type P-10076 and Machaeroprosopus assessment of TTU Character species P. pristinus) species R. gregorii) P-10077 lottorum TTU P-10074 P-10074 paranasal: presence probably absent unknown present indecisive present (?) indecisive distance antorbital short longer short as Pseudopalatus short as Pseudopalatus fenestra to naris postorbital bar narrow twice as broad as narrow as Pseudopalatus narrow as Pseudopalatus (dorsoventrally) Pseudopalatus free postorbital– long long comparatively diagnostic long squamosal bar: short length [17] postorbital– broad very broad very broad as Redondasaurus broad as Pseudopalatus squamosal bar: width relative to free length [18] postorbital– narrow (twice as high (as broad as narrow (twice as as Pseudopalatus narrow (twice as as Pseudopalatus squamosal bar: broad as high) high) broad as high) broad as high) width posteroventrally to orbit horizontal/vertical angular, well- rounded, grade into rounded, grade into as Redondasaurus postorbital– intermediate state surfaces of posterior separated by po-sq each other each other squamosal ridge process of bar ridge and broad zone squamosal form oblique plane at angle with both horizontal and vertical surface lateral postorbital– continues as marked merges with sculp- diminishes to broad, as Redondasaurus continues as intermediate state squamosal ridge: ridge all along ture above base of low area (scored as broader and lower extent onto poste- posterior process posterior process absent) ridge rior process of (i.e., absent) squamosal [19] lateral squamosal present, high, well- absent, area grades blunt and broad intermediate state broad zone with intermediate state, ridge [20] distinguished (forms into m. depressor edge (scored as ab- deep, rugose border more similar to ‘double ridge’ with mandibulae area sent), marked border to m. depressor Pseudopalatus postorbital– to m. depressor mandibulae area squamosal ridge) mandibulae area groove between distinct, continuous almost incipient, faint groove that intermediate state, narrow and sharp intermediate state, lateral postorbital– groove between broad depression peters out rapidly more similar to groove, terminates more similar to squamosal and ‘double ridge’ con- (groove absent) Redondasaurus in front of posterior Pseudopalatus lateral squamosal tinues well onto process ridges posterior process postorbital– thick, rounded and thick, squared but thin, squared (TTU as Pseudopalatus thick, squared with more similar to squamosal bar: not distinctly without distinct P-10076) to sharp mccauleyi distinct ridges Pseudopalatus medial rim [23] squared ridges (TTU P-10077) without ridges dorsal surface of terminally raised flat (dorsoventrally terminally raised as Pseudopalatus terminally raised as Pseudopalatus squamosal / dorso- (dorsoventrally compressed) (dorsoventrally (dorsoventrally ventral extent of expanded) expanded) expanded) posterior process of squamosal [24] lateromedial extent knob (laterally strongly converging knob (laterally as Pseudopalatus knob (laterally as Pseudopalatus of tip of squamosal bulging, medial side lateral and medial bulging, medial side bulging, medial side [25] flattened) rim flattened) flattened) supratemporal rounded rounded distinctly bevelled diagnostic rounded opening: anterior rim supratemporal slit-like; either completely absent semicircular notch intermediate state semicircular notch intermediate state opening: exposure narrow and [27] medially curved, or broader and straight as in holotype supraoccipital shelf: rounded (‘inverted rectangular rectangular as Redondasaurus rounded as Pseudopalatus outline [29] U-shaped’ sensu Ballew 1989) parietal ledge: width broad broad broad narrow as Pseudopalatus [30] mccauleyi parietal–sqamosal constant steep slope constant vertical top two thirds verti- intermediate state constant steep slope as Pseudopalatus bar: slope [32] cal, bottom third steep supraoccipital shelf: deep, curved with shallow, predomi- deep, with con- intermediate state deep, with con- intermediate state median line terminal horizontal nantly vertical tinuous slope tinuous slope component posttemporal short, higher broad, low short, higher as Pseudopalatus short, higherþ indecisive opening: size [36] broad, low palatine: horizontal parallel-sided, unknown broad horizontal diagnostic parallel-sided, dis- as Pseudopalatus lamella [41] distinctly upturned lamellae; narrow tinctly upturned palatal vault NEW MACHAEROPROSOPUS FROM WEST TEXAS 309 that the majority of the type specimens among Machaeropro- (11) Narial wing: present (0); absent, narial opening closed sopus are in need of reinvestigation, both to substantiate the anteriorly (1). current alpha-taxonomy of Machaeroprosopus and to obtain (12) Lateral rim of naris: narrow, rounded (0); flattened, reliable data for a phylogenetic analysis. rugose (1). Our analysis did not include three additional nominal taxa (13) Length of antorbital fenestra, relative to length of naris: of North American pseudopalatine phytosaurs. Two of them large, >2(0);moderatetosmall,<2(1). were not considered because they are generally accepted as (14) Depression and flange in postorbital bar: absent (0); ver- junior synonyms of taxa included in the analysis: Machaeropro- tically elongated depression, posterior rim of postorbital sopus tenuis Camp, 1930 as Machaeroprosopus pristinus (Ballew bar may form a rounded narrow strut (1); vertically elon- 1989; Long & Murry 1995), and Machaeroprosopus andersoni gated depression, posterior rim of postorbital bar forms a Mehl, 1922 as Machaeroprosopus buceros (Hunt 1993; Long & distinct flange (2). Murry 1995). However, these suggested synonymies were never (15) Anterior extent of infratemporal fenestra relative to orbit: substantiated by a thorough character analysis. anteroventral corner below anterior half of orbit (0); anteroventral corner distinctly in front of anterior rim of orbit (1). 8. Acknowledgements (16) Length of posterior process of squamosal in relation to First and foremost, we are grateful to John Lott and Patricia postorbital length: absent or very small (0); moderate, Kirkpatrick, for unlimited access to their land, generous finan- >45 (1); long, <45 (2). cial support and their interest in our work. Without their sup- (17) Length of free postorbital–squamosal bar: long, >2 (0); port and continuing enthusiasm, this project would not have moderate, between 15and2(1);short,<15 (2). Mea- taken place. Jeffrey Martz skillfully executed Figures 3 and sured as the index of the distance between the level of 13. AH wishes to thank the staff of the following institutions the edge of the parietal ledge and the tip of the squa- for help during procuring data used in this study: Mark Norell, mosal along the longitudinal axis of the postorbital– Peter Makovicky, and Alejandra Lara (AMNH), David Berman squamosal bar (to account for the variable length of the (CM), Spencer Lucas, Andy Heckert, and Alan Lehner and his supratemporal fenestra; for the ingroup, the distance is family (NMNNH), Kevin Padian, Mark Goodwin, and Pat largely identical to squamosal length) to the distance be- Holroyd (UCMP), Ray Ethington (UMo), and Lyn Murray tween the parietal ledge to the posteriormost point of the and Mary Ann Turner (YPM). He also gratefully acknowl- orbit. edges financial support by a HCM fellowship of the European (18) Width of squamosal: very broad, <2 (0); broad to narrow, Union (grant no. ERBCHBICT 930521), the Doris and >2 (1). Measured as the index of the distance between the Samuel Welles Fund (Berkeley), and research funds awarded to level of the parietal ledge and squamosal tip to the maxi- Hans-Dieter Sues (formerly Royal Ontario Museum, Toronto). mum width of squamosal in dorsal view. We wish to thank Richard Butler and in particular Michelle (19) Lateral ridge of postorbital–squamosal bar continues as Stocker for their thorough and constructive reviews. ridge onto posterior process of squamosal: absent (0); present (1). The apomorphic state is a correlated with an angular separation of the dorsal and lateral surfaces of 9. Appendix. List of characters used in the the squamosal on the posterior process. phylogenetic analysis (20) Ridge on lateral, vertical surface of squamosal: absent (0); present (1). Character states are polarised with respect to Nicrosaurus (21) Sculpture on dorsal surface of squamosal: fully sculp- kapffi as outgroup. Character states scored for TTU P-10074, tured (0); lanceolate shape, faint sculpture on terminal TTU P-10076 and TTU P-10077 are described in more detail knob (1); lanceolate shape, terminal knob smooth (2). in the descriptive part. (22) Outline of medial rim of squamosal along supratemporal fenestra and posterior process: sinuous (0); angular (1); (1) Shape of anterior half of rostrum: semicircular (0); trian- straight (2). gular (1). (23) Face of medial rim of squamosal along supratemporal (2) Ventral bulge of posteriormost section of premaxillae: fenestra and posterior process: entire rim rounded or absent (0); small bulge to marked dorsally convex expan- sharp (0); squared in posterior section (1); entire rim sion (1). squared (2). (3) Length of elevated crest: crest absent according to criteria (24) Dorsoventral expansion of posterior process of squamosal: given in text (0); crest over less than half of rostrum (1); strongly compressed (0); expanded, dorsoventrally high, crest over at least half of rostrum length (2). but at level with surface of postorbital–squamosal bar (4) Sagittal profile of prenarial area: steep to moderately (1); strongly expanded, distinctly raised over surface of steep slope (0); very gentle slope (1); sinuous, i.e., hori- postorbital–squamosal bar (2). zontal or convex outline with anterior slope (2). (25) Mediolateral expansion of posterior process of squa- (5) Individuality of rostral crest: crest absent or crest flanks mosal (terminal knob sensu Ballew, 1989): knob absent, grade into rostrum (0); crest morphologically set apart strongly converging medial and lateral rim of squamosal from rostrum by a depression, a paramedian groove, or a (0); knob present, with parallel or slightly tapering sides horizontal expansion of the ventral part of the rostrum (1). (1); knob present, with strong lateral bulge. (6) Ventral outline of maxillary rim: straight or concave (0); (26) Squamosal flange: absent (0); shallow, does not extent distinctly convex (1). along entire length of posterior process of squamosal (1); (7) Prenarial groove: present (0); absent (1). extensive vertical area, along entire ventral rim of poste- (8) Elevation of nares: below or at level with skull roof (0); rior process of squamosal (2). above level of skull roof (1). (27) Supratemporal fenestra on skull roof: fully open, about (9) Position of anterior rim of nares relative to anterior as broad as long (0); narrow straight or medially curved rim of antorbital fenestra: anterior (0); at level with (1); slit (1); short, semicircular indentation into skull roof, posterior (2). relatively broader than state 1 (2); fully closed, no inden- (10) Narial outlets: present (0); absent (1). tation into skull roof (3). 310 AXEL HUNGERBU¨ HLER ET AL. (28) Rim of supratemporal fenestra on skull roof: rounded Case, E. C. 1922. New reptiles and stegocephalians from the upper (1); bevelled (1). Triassic of western Texas. Carnegie Institution of Washington (29) Outline of top of parietal–supraoccipital complex: angular, 321,1–84. Case, E. C. 1929. Description of the skull of a new form of phytosaur ‘inverted V-shaped’ sensu Ballew (1989) (0); rounded, ‘in- with notes on the characters of described North American phyto- verted U-shaped’ sensu Ballew (1989) (1); rectangular (2). saurs. Memoirs of the University of Michigan Museums, Museum (30) Width of parietal ledge: acute (0); horizontal ledge, narrow of Paleontology 2,VIþ 56 pp. (1); horizontal ledge, broad (2). Case, E. C. & White, T. E. 1934. Two new specimens of phytosaurs from the Upper Triassic of Western Texas. Contributions from (31) Lateral prongs on parietal ledge: absent (0); present (1). the Museum of Paleontology, University of Michigan 4, 133–42. (32) Slope of lateral walls of parietal–supraoccipital complex: Chatterjee, S. 1978. A primitive parasuchid (phytosaur) reptile from constant moderate (0); constant steep (1); dorsal part ver- the Upper Triassic Maleri Formation of India. Palaeontology 21, tical (2); entire walls vertical (3). 83–127. 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MS received 26 January 2012. Accepted for publication 25 March 2013.

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