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Home , Archosauriformes, Archosauromorpha, Protoavis, Sankar Chatterjee, Silesaurus, Tanystropheidae

ISSN 0326-1778 (Impresa) ISSN 1853-6581 (En Línea)

HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24

DESCRIPTION OF A MULTITAXIC BONE ASSEMBLAGE FROM THE UPPER POST QUARRY OF (), INCLUDING A NEW SMALL DINOSAURIFORM

Descripción de una asociación multitaxones del Triásico Superior de Post-Quarry de Texas (Grupo Dockum), incluyendo un nuevo taxón de pequeño basal

Volkan Sarıgül1, Federico Agnolín2,3 and Sankar Chatterjee1

1Museum of (Box 43191), Lubbock, Texas 79409, USA. [email protected], [email protected] 2Fundación de Historia Natural Félix de Azara, Departamento de Ciencias Naturales y Antropología, Universidad Maimónides, Hidalgo 775 (C1405BDB), Ciudad Autónoma de Buenos Aires, Argentina. [email protected] 3Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Av. Ángel Gallardo 470 (C1405DJR), Ciudad Autónoma de Buenos Aires, Argentina.

5 SARIGÜL V., AGNOLÍN F. AND CHATTERJEE S.

Abstract. A bone assemblage composed of intermixed small cranial and postcranial fragments from the Post Quarry of Texas, USA, is described. The skeletal elements represent multiple individuals of different taxa, including a partial dorsal column assigned to campi and an incomplete dentary referred to a new and of a small-sized basal dinosauriform. Ankylothecodont dental implantation of the dinosauriform dentary bears strong resemblance to silesaurids. A fragmentary archosauromorph braincase is another intriguing element of the assemblage; it displays a striking contrast of a derived otoccipital on a plesiomorphic basioccipital. Poor preservation prevents more conclusive taxonomic assignments for the rest of the skeletal elements. The observed attrition and entangling in this bone assemblage reflect the complexities of the Dockum land taphonomy.

Key words. Upper Triassic, Texas, Post Quarry, bone assemblage, , Dinosauriformes.

Resumen. Una asociación ósea de diminutos fragmentos craneanos y postcraneanos de diferentes individuos es aquí descripto. Los especímenes provienen de la bien conocida localidad fosilífera del Triásico Tardío de Post Quarry, Texas, USA. Los elementos esqueletarios pertenecen a diversos archosauromorfos y saurios, incluyendo una columna vertebral parcial asignable a Vancleavea campi y un dentario referido a un nuevo género y especie de pequeño dinosauriformes basal. Implantación anquilotecodonte de los dientes en el dentario indica afinidades fuertes con . Un basicráneo fragmentario de arcosauromorfos constituye un elemento curioso de la asociación. Este ejemplar exhibe un marcado contraste entre un otoccipital muy derivado y un basioccipital con rasgos plesiomórficos. La pobre preservación de la mayor parte de los elementos esqueletarios impide asignaciones taxonómicas más acotadas. El grado de desgaste y la mezcla de esta asociación osteológica reflejan las complejidades de la tafonomía de los tetrápodos terrestres de Dockum.

Palabras clave. Triásico Tardío, Texas, Post Quarry, asociación de elemento óseos, Sauria, Dinosauriformes.

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INTRODUCTION recovered from the Post Quarry are usu- ally associated (Lehman and Chatterjee, The Post Quarry (MOTT 3624, formerly 2005; Martz et al., 2013), attritional speci- the Miller Quarry) is perhaps the most mens represented by one or few elements productive quarry of the also occur as much as the partially com- Dockum Group of Texas, in terms of num- plete skeletons. In some cases, as the one bers and taxonomic diversity. introduced here, scattered and damaged of many iconic Dockum vertebrate elements are intermingled, making attri- like temnospondyl Rileymillerus cosgriffi bution of each element to a specific taxon Bolt and Chatterjee, 2000, pseudosuchians complicated. Such interesting discoveries smalli Parker, 2005, Pos- provide additional data for the taxonomic tosuchus kirkparticki Chatterjee, 1985 and diversity and taphonomic interpretation of inexpectatus Chatterjee, 1993, the Post Quarry, a relatively small quarry silesaurid smalli Chatterjee, with an area less than a hundred square 1984 and the controversial texen- meters (Chatterjee, 1985). sis Chatterjee, 1991 were discovered in this famous bonebed, as well as many other specimens referred to temnospondyls, the- Location and Geological Settings rapsids, , , basal cro- codylomorphs and dinosauromorphs (e.g., The widely exposed Upper Triassic ter- Chatterjee, 1983; Long and Murry, 1995; restrial sediments in eastern New Mexico Lehman and Chatterjee, 2005; Nesbitt and and western Texas, namely the Dockum Chatterjee, 2008; Nesbittet al., 2009a; Martz Group, yield one of the richest et al., 2013; Sarıgül, 2016, 2017a). Although land tetrapod faunas in the world. The Post it was noted that the vertebrate fossils Quarry is located about 15 km south to the

Figure 1 - Field properties of the Post Quarry. A, location map of the Post Quarry with the Dockum Group exposures marked in grey (modified after Chatterjee 1991); B, a photograph displaying the general view of the quarry and predominant red mudstones (Photo credit: Bill Mueller). The white arrow in the photograph indicates the main fossiliferous horizon of the step-like platform at the lower part of the hill.

HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 7 SARIGÜL V., AGNOLÍN F. AND CHATTERJEE S. town of Post in Garza County, in western instead, they are found concentrated in a Texas (Figure 1A) and placed in the upper distinct horizon of ca. 30 cm. in thickness part of the lower unit of the Cooper Can- (Figure 1B), except the Protoavis specimens yon Formation, referring to a new tri-par- which were collected around a meter above tite stratigraphic framework established (Chatterjee, 1991; Martzet al., 2013). for Garza County (Martz, 2008; Martz et al., 2013). However, this claim is not fol- lowed based on the fact that no difference MATERIALS AND METHODS in lithostratigraphy is detected between the previously described Tecovas Formation in Garza County by Lehman and Chatterjee Discovery and preparation (2005) and the newly demonstrated unit, of the specimens and thus it is suggested the employment of the former nomenclature (Bill Mueller, In the summer of 1993, some delicate fos- personal communication, 2016). Whatever sils within a small mudstone block were the name is, this basal lithostratigraphic found by Soumya Chatterjee, the elder son unit is mainly composed of red coloured of , in the main fossilifer- floodplain mudstones with few intercalat- ous horizon of the Post Quarry and were ing lacustrine deposits and happens to be jacketed for preparation in the laboratory. a direct correlate for the Tecovas Formation This mudstone block yielded tiny and in- in northern Texas and in New Mexico (Fig- termingled bone fragments that are poorly ure 1B). The collected tetrapod fossils are preserved, including a partial braincase, an not homogeneously dispersed within the incomplete dentary, few articulated cervi- fluvial mudstones of this particular quarry; cal vertebrae associated with an incomplete

Figure 2 - The original field sketch of the bone assemblage that is redrawn from Sankar Chatterjee’s field book and each element is labeled separately with a voucher number in accord with the provided diagnosis. The unknown bone fragment is assumed to be an astragalocalcaneum by Sankar Chatterjee and it is said to be shattered while exposing and now lost.

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and distorted left , some articulat- logenetic affinities of TTU-P11254b. We ed postcervical vertebrae with an attached included the specimen within the compre- bone fragment, distal end of a left , hensive phylogeny published proximal end of a left , distorted right by Nesbitt (2011) with the modifications tibia and and two procoelous ver- by Nesbitt et al. (2017) and the re-scoring tebrae found attached to few fragmentary of carried out by Agnolin and shafts (Figure 2). These fragments were Rozadilla (2017) (Appendix 1). Pseudolago- prepared under a binocular microscope suchus and are considered as and then the same elements underwent a synonymous and fused in a single terminal more elaborate second preparation phase based on Arcucci, (1997, 1998), and work in of cleaning and scrapping. Each bone progress based on newly collected material possesses an individual voucher number (Novas et al., 2015). Character 174 of Nes- (TTU-P11254a-i) and is reposited at the bittet al. (2017) is modified here as follows: Museum of Texas Tech University collec- Character 174: Tooth implantation: (0) tions. free at the base of the tooth; (1) teeth fused to the base by fibrous tissues which form a bulbosity; (2) teeth fused to the base by thin Phylogenetic analysis bony ridges. The resulting data matrix is composed The phylogenetic analysis here is per- by 419 characters and 93 taxa. The phylo- formed with the aim to elucidate the phy- genetic analysis was performed using TNT

Figure 3 - The phylogenetic placement of TTU-P11254b. The cladogram reflects the consensus of the 260 most parsimonious trees of 1391 steps. Consistency index= 0.353, retention index= 0.770. Numbers on branches indicate Bremer values.

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1.1 (Goloboff et al., 2008). All characters outgroup. This situation is attributed to the were equally weighted and treated as unor- fragmentary condition of the fossil remains dered. Heuristic searches were performed and thus, we opt not to include Technosau- after 1000 replicates of WAG+TBR, saving rus in the phylogenetic analysis performed 100 trees per replicate. The phylogenetic here. analysis resulted in the recovery of 260 Most Parsimonious Trees (MPTs), of 1391 steps, with a consistency index of 0.353, SYSTEMATIC PALAEONTOLOGY and a retention index of 0.770 which are summarized using a strict consensus tree Sauria McCartney, 1802, sensu Gauthier, (Figure 3). Kluge and Rowe 1988 We also intend to include the new dino- Huene, 1946, sensu sauriform taxon with the coeval silesaurid Benton, 1985 Technosaurus smalli in a phylogenetic analy- Gauthier, Kluge and sis (see scorings of T. smalli in Appendix 2). Rowe 1988 The new dinosauriform taxon and T. smalli Vancleavea campi Long and Murry, 1995 are both recovered as silesaurids when they Referred specimen. TTU-P11254a, partial are individually included to the analysis. vertebral column and a piece of osteo- However, it results a more complicated pic- derm. ture when T. smalli and the new dinosauri- Description and remarks. The partially form taxon are included together; both taxa preserved vertebral column comprises are nested within a polytomy where Eu- seven vertebrae and each possess parkeria capensis is found as the immediate shallow lateral excavations on the side,

Figure 4 - Partial postcervical vertebrae and attached fragment of Vancleavea campi (TTU-P11254a). Abbreviations: exc, lateral excavations; os, attached osteoderm fragment; poz, postzygapophysis; pr, paramedian ridges; prz, prezygapophysis.

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a feature shared with many archosauro- tion sensu Martz, 2008), collected from the morphs (Figure 4). Although the specimen main thin, fossil-rich horizon that is situat- is severely compressed mediolaterally, ed about 8 meters below the top of the for- two paramedian ridges are on ventral side mation (Martzet al., 2013). The Post Quarry are conspicuous on some vertebrae. Pres- horizon corresponds to (Sarıgül, ence of two paramedian ridges is an auta- 2017b). pomorphy of the dorsal centra of Vanclea- Diagnosis. A minute silesaurid distin- vea campi; however, it is noted that these guishable from all other members of the ridges occur on the caudal vertebrae of except Asilisaurus kongwe Nesbitt et al., V. campi as well (e.g. Nesbitt et al., 2009b). 2010 by having smooth and conical dentary Concurringly, an independent examina- teeth that have no expansion or curvature tion of the specimen concludes that the above the root. S. aenigmaticus differs from vertebrae represents part of the postcer- A. kongwe in having a Meckelian groove re- vical series of Vancleavea and the attached stricted to ventral margin of the dentary. Be- unrecognizable piece of bone is an amal- cause the anterior portion of TTU-P11254b is gamation of Vancleavea dermal armor (Bill not preserved, it remains unknown whether Mueller, personal communication, 2015). the dorsal margin of the anterior dentary of S. aenigmaticus is convex as in that of A. kon- gwe. Similarly, apical sides of the preserved Archosauriformes Gauthier, Kluge and teeth of S. aenigmaticus are mostly obliter- Rowe 1988 ated and cannot be compared with the teeth Dinosauriformes Novas, 1992 of A. kongwe that possess weakly serrated Silesauridae Langer, Ezcurra, Bittencourt carinae at the tip of each crown. and Novas, 2010 Description and remarks. The dentary frag- Soumyasaurus gen. nov. ment is a slender and transversely narrow element with an elliptical cross-section. The Etymology. Coined by Sankar Chatterjee lateral side is almost featureless except for to honour his elder son Soumya for his dis- the presence of several neurovascular fo- covery of the specimen. ramina (Figure 5A). Few lingual pits at the species. Soumyasaurus aenigmaticus, alveolar margin are detected on the medial sp. nov.; see below. side, and a narrow Meckelian groove runs Diagnosis. As for species, see below. the length of the dentary on the ventral mar- Stratigraphic and geographic range. As for gin (Figure 5B). Four erupted teeth are pre- species, see below. served, however, there are about 11 closely spaced alveoli, making the dentary tooth Soumyasaurus aenigmaticus gen. nov., sp. nov. count of 15 or more (Figure 5C). Charac- teristic grooves and foramina implying the Etymology. Species name represents the presence of a keratinous in silesau- nature of the specimen, derived from the rids (e.g., Dzik, 2003; Langer and Ferigolo, Latin word “aenigma” that means “enigma 2013) are lacking on the edentulous end or riddle”. and this portion is interpreted as the pos- . TTU-P11254, partial left dentary. terior end of the tooth row. The Meckelian Type locality. Post Quarry (MOTT 3624), groove also tapers towards the counter di- Garza County, Texas. rection of the edentulous portion, indicat- Type horizon. Tecovas Formation (or the ing that TTU-P11254b probably represents lower unit of the Cooper Canyon Forma- a left side dentary (Figure 5B-C).

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Figure 5 - Incomplete dentary referred to a new basal dinosauriform, Soumyasaurus aenigmaticus gen. nov., sp. nov. (TTU-P11254b). A, lateral view; B, medial view; C. dorsomedial view. Abbreviations: a, alveolus; ede, edentulous portion; mg, Meckelian groove; lp, lingual pit; nf, nutrient foramen. Hatches signify damaged portions.

Presence of ankylothecodont teeth, Silesauridae. Silesaurid teeth are ankylosed which means the teeth are fused at the base to their sockets by fibrous tissues which to the dentary bone (Nesbitt, 2011, char- creates a collar-like structure around the acter 174) is the main unambiguous syn- tooth base as in , and apomorphy shared by S. aenigmaticus and Diodorus (Dzik, 2003; Kammerer et al., 2012;

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Figure 6 - Dentary of the Technosaurus smalli holotype (TTU-P9021). A, lateral view; B, medial view; C, dorsal view. A close-up view of the dentition is provided for the lateral view including a separate 1 cm scale. For abbreviations, see Figure 5

Langer and Ferigolo, 2013), contrasting the of the dentary is missing in both taxa. Be- condition of other ankylothecodont archo- sides the obvious size difference, the major sauromorphs where the teeth are strongly contrast between the two taxa is the dental attached to their base by bony ridges (e.g. morphology. The lower jaw dentition of T. Ezcurra, 2014). Another feature shared by smalli comprises triangular and possibly tri- S. aenigmaticus and other silesaurids except cuspid teeth with unpronounced denticles Asilisaurus kongwe is the Meckelian groove on the dental edge and faint striations on restricted to the ventral border on the me- crown surface; a structure which is clearly dial side of the dentary (Nesbitt, 2011, char- different from that ofS . aenigmaticus. acter 152; Dzik, 2003; Ferigolo and Langer, Dentition of S. aenigmaticus is also very 2007; Nesbitt et al., 2010; Kammerer et al., different from the other silesaurids with 2012). The anterior tip of the dentary is not typical leaf-shaped teeth (Dzik, 2003; Kam- preserved; thus, it is not possible to discern merer et al., 2012; Langer and Ferigolo, whether it is rounded or tapers anteriorly 2013). Although they differ in the position (Nesbitt, 2011, character 155). of the Meckelian groove, the dentary teeth Technosaurus smalli is the only other sile- of A. kongwe probably offers the best com- saurid described from the same quarry parison for the dentition of Soumyasaurus with a holotype consisting of a premaxilla than any other silesaurid in both size and and an incomplete dentary (e.g., Chatterjee, morphology. However, teeth of A. kongwe 1984; Nesbitt et al., 2007) (Figures 6A-C). T. possess a serrated carina (Nesbitt et al., smalli and S. aenigmaticus share the typical 2010, Figure 1), but this feature cannot be silesaurid synapomorphies of having a sile- detected in those of S. aenigmaticus since saurid-type ankylosed dentition and a ven- the apical portions of the preserved teeth trally restricted Meckelian groove. The tip are either missing or severely damaged.

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The inclusion of S. aenigmaticus in the tubera (Figures 7B-C). Each basal tuber dis- data matrix of Nesbitt et al. (2017) resulted plays slight excavations on the lateral side in its nesting within the basal dinosauri- (Figures 7C-D). The sphenoidal contribu- form clade Silesauridae. With the aim to tion to the basal tubera, if any present, can- test the robustness of tree topology, Bremer not be detected. supports are calculated for each node. The The left lateral side comprise a large sec- support of major archosaur , as Or- ondary tympanic opening (i.e., fenestra nithodira, Dinosauriformes, and Cruro- pseudorotunda) encapsulated by the fused tarsi is relatively low (Bremer support = exoccipital-opisthotic complex (oto-occip- 1), as previously recognized and discussed ital or otoccipital), which is dorsolaterally by Nesbitt (2011). The clade Silesauridae + pierced by a foramen that possibly transmit- Soumyasaurus also has a Bremer support = 1. ted a segment of the occipital vein, similar to The inclusion of Soumyasaurus within Sau- what is identified on the opposite side of the rischia, to Dinosauria or The- braincase (Figures 7C-D). The bony frame ropoda results in a tree of a length of 1392. around the fenestra pseudorotunda is a dis- This implies that a single step may change tinguishing character of extant , the position of S. aenigmaticus. Thus, S. ae- and TTU-P11254c represents few of the fos- nigmaticus is attributed to Silesauridae, but sil examples in which this gracile structure with some degree of uncertainty. is preserved (Gower and Weber, 1998). The floor of the fenestra pseudorotunda- main Sauria McCartney, 1802, sensu Gauthier, tains a direct connection between the cranial Kluge and Rowe 1988 cavity and the vagus foramen at the occipital Archosauromorpha Huene, 1946, sensu side, from where the vagus (X) and accesso- Benton, 1985 ry (XI) cranial nerves are carried along with Gen. et sp. indet. the posterior jugular vein (Figures 7C-D). In Referred specimens. TTU-P11254c, partial anterior view, the otic capsule possesses a braincase; TTU-P11254d, cervical verte- distinct crescentic groove on its anterome- brae; TTU-P11254e, left scapula. dial border (Figure 7E). Description and remarks. The braincase Although the fused exoccipital-opisthot- is poorly preserved, and the intimately ic complex of TTU-P11254c is described fused bones complicate the demarcation in many archosauriforms (e.g., Gower and of each element. The is Sennikov, 1996; Currie, 1997; Gower and obliterated under the collapsed roof of the Weber, 1998; Gower, 2002), a posterior di- braincase; the only putative feature visible version of the vagus foramen evolved inde- at this area is a damaged foramen which pendently in crocodilians by the emergence might be related to a segment of the occipi- of a secondary lamina (Klembara, 2005), tal vein (Figure 7A). The occipital in neotheropods by the projection of the is round in posterior view and the basioc- metotic strut (e.g., Currie, 1995; Sampson cipital probably forms most of the occipital and Witmer, 2007; Fiorillo et al., 2009), and condyle with limited contribution of exoc- possibly in by the posterior ossi- cipitals as in most saurians (Figure 7A). The fication of the braincase (e.g., Bennett, 1991; condylar neck is ventrally constricted at the Kellner, 1996). The posterior shift of the base, a condition that is also very apparent vagus foramen in TTU-P11254c is reminis- in lateral view, and then the basioccipital cent to the condition described in neothero- flares again to form a pair of medially well- pods, where the presence of a well-devel- separated and anteroposteriorly long basal oped metotic strut results in separation of

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Figure 7 - Partial braincase of an undetermined archosauromorph (TTU-P11254c). A, posterior view; B, ventral view; C, left lateral view; D, left ventrolateral view; and E, anterior view. Abbreviations: bc, brain cavity; bt, basal tubera; eo, exoccipital; fm, foramen magnum; fov, foramen for occipital vein; fpr, fenestra pseudorotunda; ic, crista interfenestralis; oc, occipital condyle; op, opisthotic; vf, vagus foramen; IX., foramen for glossopharyngeal nerve. Hatches signify damaged parts. The arrows refer to the diversion of the vagus foramen.

the vagus nerve. However, this separation pseudorotunda is topologically suitable for results in a laterally diverted transmission being the perilymphatic foramen, and the instead of a direct one from the endocranial small foramen situated at the posterior side cavity recalls that of non-avian theropods possibly represents the glossopharyngeal (e.g., McClellan, 1990; Currie and Zhao, (IX.) nerve foramen. The glossopharyngeal 1993; Currie, 1995; Rauhut, 2004; Samp- nerve always leaves the braincase laterally son and Witmer, 2007) rather than that of from the metotic foramen or the fenestra modern like Rhea and Aquila. It is pseudorotunda; however, a separate exit also noted that the vagus nerve emerges for this particular nerve is observed in ju- from the occiput via a direct transmission venile stages of some modern birds which from the braincase floor in one specimen turned into an ossified notch or a foramen referred to (Fiorillo et al., 2009). in adult phase as in the subarctic ge- Moreover, the upper section of the fenestra nus Fulmarus (Walker, 1985).

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Figure 8 - (TTU-P11254d) and left scapula (TTU-P11254e) assigned to undetermined archosauromorphs. A, left lateral view of cervical vertebrae; B, lateral view of left scapula. Abbreviations: ac, process; gle, ; hyp, hypapophysis; poz, postzygapophysis; prz, prezygapophysis. Hatches signify damaged parts.

Although the otoccipital of TTU-P11254c represents a dinosauriform. Nevertheless, is highly comparable to that of non-avian TTU-P11254c might add to the large list of neotheropods as mentioned above, this characters interpreted to occur among the- portion displays a clear contrast with the ropods later in the have already plesiomorphic state of the basal tubera. In been convergently acquired by archosauro- non-avian theropods, the basal tubera are morph taxa during the Triassic. expanded ventrally and merged at the mid- The cervical vertebrae (TTU-P11254d) line for the most part, if not completely (e.g., and the scapula (TTU-P11254e) bear a Chure and Madsen, 1988, figure 8; Sereno close resemblance to archosauromorph and Novas, 1993; Currie, 1995; Sampson bones as well. The preserved cervical and Witmer, 2007). A possible explanation centra are anteroposteriorly elongate and for either TTU-P11254c represents a new transversely compressed, and they have a type of theropod or another example of well-developed ventral keel (Figure 8A). morphological convergence among Triassic Presence of prominent hypapophyses on archosauromorphs (e.g., Hunt, 1989; Nes- the cervicals is a plesiomorphic charac- bitt and Norell, 2006; Stocker et al., 2016) ter that is lost in many archosaur groups remains obscure because of the paucity of (Romer, 1956, Gauthier, 1986), but it is re- the available material. Recently, Piechowski tained in the middle cervical vertebrae of et al. (2018) have suggested avian-like traits spp. and (Nesbitt, on the braincase of Silesaurus opolensis Dzik, 2011, character 192). The scapula is found 2003 based on ventrally directed paroc- attached to the cervicals; it possesses a ro- cipital processes and reconstructed muscle bust and dorsoventrally expanded mor- attachments on the occipital side, even phology, differing from what is observed though the otoccipital of S. opolensis retains in lepidosauromorphs where the the plesiomorphic condition of having a lat- is the dominant element of the shoulder erally directed metotic foramen. Paroccipi- girdle (Romer, 1956) (Figure 8B). Howev- tal processes of TTU-P11254c are not pre- er, the poor preservation of these elements served, but the otoccipital is more derived offers any diagnostic features to pinpoint than that of S. opolensis which may indicate a taxon more inclusive than Archosauro- a closer relation to avians if TTU-P11254c morpha.

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Figure 9 - Limb bones (TTU-P11254f-h) and procoelous vertebrae (TTU-P11254i) found associated with some unrecognizable shafts (colored in grey). A-C, left femur (TTU-P11254f) in anterior, posterior and distal views; D-F. left tibia (TTU-P11254g) in anterior, posterior and proximal views; G. right tibia with attached proximal end of fibula (TTU-P11254h); H. two procoelous vertebrae intermingled with few limb bone shafts (TTU-P11254i). Abbreviations: cc, cnemial crest; fib, fibula; lc, lateral condyle; lco, lateral cotyle; mc, medial condyle; mco, medial cotyle; ns, damaged neural spine; poz, postzygapophysis; prz, prezygapophysis. Hatches signify damaged parts. The 1 mm scale is for (C) and (F).

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Sauria McCartney, 1802, sensu Gauthier, incomplete and distorted condition which Kluge and Rowe 1988 prevents a more detailed identification. Gen. et sp. indet. Referred specimens. TTU-P11254f, distal end of a left femur; TTU-P11254g, proximal DISCUSSIONS ON THE SKELETAL end of left tibia; TTU-P11254h, a fragmen- ASSOCIATION AND TAPHONOMY tary right tibia; TTU-P11254i, two procoe- lous vertebrae and fragmentary undeter- The elements of this particular bone as- mined shafts of bones. semblage seem to represent a single indi- Description and remarks. The thin-walled vidual at first glance since the composing limb bones are extremely long and slender elements were found side-by-side and each which is reminiscent to that of some basal bone in the assemblage represents a differ- ornithodirans such as and ent skeletal constituent in a misleading in- (Benton, 1999; Benton and Walker, situ position (Figure 2). Alternatively, the 2011), as well as that of pterosaurs (Sereno, preliminary conclusion by the eldest au- 1991a). But in a closer look, these limb bones thor that the assemblage is consisted of de- are anatomically inconsistent with that of rived dinosaurian fragments has been also any typical archosaurian (Figures 9A-G). a matter of speculation (see Sarıgül, 2014). The distal end of the femur does not bear a Instead, it is realized that the Post Quarry tibiofibular crest which is an archosauriform bone assemblage yields an accumulation of synapomorphy (Nesbitt, 2011, character various small sized skeletal elements per- 322), whereas twin concave facets (i.e. coty- taining to multiple individuals of different les) on the proximal tibia are comparable to taxa, after a detailed examination conduct- that of lepidosaurians like Clevosaurus (Fra- ed by the first author. The postcervical ver- ser, 1988). Moreover, the procoelous state of tebrae (TTU-P11254a) are ascribed to Van- the two severely damaged vertebrae (Figure clavea campi, TTU-P11254b represents a new 9H) is considered to be a characteristic of a silesaurid taxon Soumyasaurus aenigmaticus, large number of squamates (Romer, 1956), whereas remaining elements (TTU-P11254c- but also of many tanystropheids (Pritchard i) are too incomplete to be safely referable to et al., 2015) and the new basal archosauro- a specific taxon more inclusive than Archo- morph Ozimek volans Dzik and Sulej, 2016. sauromorpha or Sauria. Among the body el- The fragmentary shafts around the procoe- ements referred to Archosauromorpha, the lous vertebrae are missing both ends but braincase (TTU-P11254c) is recently attrib- their morphology is identical to that of other uted to the same taxon with TTU-P11254b described limb bones. Given that the pro- (Agnolin et al., 2016). This assumption is coelous vertebrae are attributed to the same based on the derived otoccipital portion taxon with the limb bones, these fragments which is endorsed by recent discoveries on may represent a small-sized lepidosauro- the convergently evolved avian-like traits in morph taxon or a basal archosauromorph basal dinosauriform braincases (Agnolin et related to Sharovipterygidae. A tanystro- al., 2016; Piechowski et al., 2018). However, pheid affinity, on the other hand, is less like- the resulting tree from an additional phylo- ly since the basal forms possess a sigmoidal genetic analysis including both the dentary femur whereas more derived forms still re- and the braincase is indistinguishable from tain the curvature at the distal end of femur that including the dentary alone; thus, the (Pritchard et al., 2015). All these elements association of these two elements cannot be are considered as saurian bones due to their strictly confirmed. The remaining elements

18 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 NEW BASAL DINOSAURIFORM FROM TEXAS

are too incomplete to be safely referable to collection of the Post Quarry includes fairly a specific taxon more inclusive than Archo- complete skeletons of Postosuchus kirkpat- sauromorpha or Sauria. Future discoveries ricki (holotype), Desmatosuchus smalli (holo- of more complete specimens or introduc- type) and coccinarum Cope, 1875 tion of new viewpoints would bring differ- (e.g., Chatterjee, 1985; Parker, 2005; Martz et ent and possibly more correct suggestions al., 2013). Yielding individuals from mul- about the affinity of these elements. tiple taxa and representation of each Voo- Addressing the taphonomic settings of the rhies group in the Post Quarry assemblage Post Quarry provides a better understand- emphasize a pre-mortem gathering of all ing of the perplexity of the TTU-P11254 as- the different taxa having various sizes and semblage. The highly diverse fossil concen- dietary habits and dying at the same place tration, including both juvenile and adult due to an unknown cause. Regardless what specimens of different taxa, covering a very the cause of death is, disarticulated state of small area was initially interpreted as a re- the skeletons in this autochthonous assem- sult of a rapid flood event (Chatterjee, 1985). blage suggests that the carcasses were ex- In contrast, some long-term process of bone posed to some physical and chemical deg- concentration was suggested afterwards for radation before the burial. the later dispersal of the disarticulated but This exposure interval was not long still associated skeletons with both delicate enough to induce a considerable loss of and robust pieces, of which the long axis of skeletal parts as described for the partial bones are usually found aligned in a certain skeletons; however, many Post Quarry direction (Lehman and Chatterjee, 2005). specimens are represented by a single or Mass mortalities caused by flooding are usu- few isolated elements, a situation reflecting ally monotaxic or paucitaxic (e.g., Norman, the complex taphonomy of this quarry. The 1987; Mazza, 2015), and as correctly pointed holotype of temnospondyl Rileymillerus cos- out by Lehman and Chatterjee (2005), -nei griffi is identified based on a and lower ther the mass mortality nor the disarticula- jaw (Bolt and Chatterjee, 2000); where the tion in the Post Quarry is caused by a flood- holotype of Shuvosaurus inexpectatus was ing event. However, a long-term accumula- originally described based on a fragmentary tion may not be the case for the Post Quarry cranium and as well (Chatterjee, since disarticulated skeletal concentrations 1993), prior to the complementation with display evident hydraulic sorting rather a postcranial skeleton (Long and Murry, than alignment when exposed to strong 1995). A massive skull and jaws that are al- currents. Based on a study on some mod- most a meter in length referred to Leptosu- ern-day mammals, skeletal components are chus sp. (TTU-P09234; Martzet al., 2013) rep- evaluated under three groups according resents the largest detached piece of a tetra- to their susceptibility to hydraulic trans- pod fossil of the Post Quarry. These three port; lighter bones like ribs and vertebrae examples and many other isolated cranial are classified under Group I and they were and postcranial fragments of different sizes shown to be more easily carried away com- and shapes (e.g., Chatterjee, 1983; Long and pared to Group II and III elements, where Murry, 1995; Nesbitt and Chatterjee, 2008; the former group mainly comprises long Martzet al., 2013; Sarıgül, 2016, 2017a) dem- bones and the latter is characterized by the onstrate the lack of selective preservation skull and mandible as heaviest elements of in the Post Quarry taphonomy, concurring the skeleton (Voorhies, 1969; Behrensmeyer, with the previous conclusion of the absence 1975). In contrast, the land tetrapod fossil of hydraulic sorting. The attritional state

HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 19 SARIGÜL V., AGNOLÍN F. AND CHATTERJEE S. of the skeletons is subject to speculation as multitaxic assemblage, including fragments well; however, skeletal elements may easily referred to Vancleavea campi, a new basal di- disappear by in-situ factors (e.g., decom- nosauriform taxon Soumyasaurus aenigmati- position, scavenging, trampling) or during cus and to various undetermined saurians. diagenesis, and the resulting attrition in the Dentary features of S. aenigmaticus are quite Post Quarry can be explained simply by comparable to what is observed in sile- non-preservation. saurids, where the overall tooth morphol- Although the current activity did not ogy resembles to that of Asilisaurus kongwe seem to be involved in mortality and dis- rather to what is observed in Technosaurus articulation phases, a gentle flooding like smalli. It is more difficult to assign the- re a seasonal inundation of a floodplain, is maining bones due to their fragmentary implied here as the factor that buried the condition; this is applicable even for the whole assemblage. Such gentle current can- braincase featuring a posteriorly diverted not create sorting in disarticulated skele- vagus foramen and a possible separate exit tons, but it might have been responsible for for the glossopharyngeal nerve situated on the preferential orientation of some of the a plesiomorphic basioccipital. The striking long bones, as well as for the entangling of combination of plesiomorphic and derived some lighter bone fragments belonging to features indicates that such traits were different taxa. Indeed, the isolated elements probably more widespread among archo- were found in closer association with differ- sauromorphs than previously thought. ent bones in some cases. For instance, skele- The recognized skeletal inconsisten- tal consistency of the silesaurid T. smalli was cies and intermixing of different bones in resolved after a long examination process TTU-P11254 assemblage bears close resem- and appears to be the closest example to the blance to another Post Quarry bone assem- TTU-P11254 assemblage. Departing from blage from which T. smalli is described, and the original diagnosis of Chatterjee (1984), both assemblages appear to be produced the holotype of T. smalli is now restricted by the same taphonomic processes of the to two anterior jaw fragments; whereas the Post Quarry. associated posterior jaw fragment now re- ferred to S. inexpectatus and the affinity of the other bones remain unresolved (Sereno, ACKNOWLEDGEMENTS 1991b; Hunt and Lucas, 1994; Irmis et al., 2007; Nesbitt et al., 2007; Martz et al., 2013). We would like to thank Zheng Zhong The entangled condition of the T. smalli and and Kendra Dean Wallace for preparing the TTU-P11254 assemblages may be a result of specimens and Bill Mueller for taking pho- the burial process. Nevertheless, the limited tographs of the specimens and sharing his discussion provided here cannot explain all personal data and observations. We thank the taphonomic modes observed in the Post M.D. Ezcurra, F.E. Novas and S.J. Nesbitt Quarry and a comprehensive study is still for their comments about the morphology needed on the subject. and systematics of early and dinosauriforms. We also thank F. Brissón Egli, G. Lio and N. Chimento for their en- CONCLUSIONS lightening comments on anato- my. The first author owes special thanks to A puzzling assemblage of tiny bones S.E. Evans and D.J. Gower for sharing their from the Post Quarry of Texas represents a knowledge on saurian braincases. Finally,

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APPENDIX 1. Scorings of Soumyasaurus aenigmaticus based on Nesbittet al. (2017) data matrix Soumyasaurus_aenigmaticus ?????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????1?0????????????000?0001????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????

APPENDIX 2. Scorings of Technosaurus smalli based on Nesbittet al. (2017) data matrix Technosaurus_smalli ?????[23]000?????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????????1?0???????????[01]02011011??????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????

24 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24