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HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 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 TRIASSIC POST QUARRY OF TEXAS (DOCKUM GROUP), INCLUDING A NEW SMALL BASAL DINOSAURIFORM TAXON Descripción de una asociación multitaxones del Triásico Superior de Post-Quarry de Texas (Grupo Dockum), incluyendo un nuevo taxón de pequeño Dinosauriformes basal Volkan Sarıgül1, Federico Agnolín2,3 and Sankar Chatterjee1 1Museum of Texas Tech University (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 Vancleavea campi and an incomplete dentary referred to a new genus and species 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 tetrapod taphonomy. Key words. Upper Triassic, Texas, Post Quarry, bone assemblage, Sauria, 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 Silesauridae. 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. 6 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 NEW BASAL DINOSAURIFORM FROM TEXAS 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 fossil vertebrate 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. Holotypes introduced here, scattered and damaged of many iconic Dockum vertebrate fossils 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 Desmatosuchus smalli Parker, 2005, Pos- provide additional data for the taxonomic tosuchus kirkparticki Chatterjee, 1985 and diversity and taphonomic interpretation of Shuvosaurus inexpectatus Chatterjee, 1993, the Post Quarry, a relatively small quarry silesaurid Technosaurus smalli Chatterjee, with an area less than a hundred square 1984 and the controversial Protoavis 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, phytosaurs, aetosaurs, 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 Late Triassic 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 Sankar Chatterjee, 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. 8 HISTORIA NATURAL Tercera Serie Volumen 8 (1) 2018/5-24 NEW BASAL DINOSAURIFORM FROM TEXAS and distorted left scapula, 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 femur, hensive archosaur phylogeny published proximal end of a left tibia, distorted right by Nesbitt (2011) with the modifications tibia and fibula and two procoelous ver- by Nesbitt et al. (2017) and the re-scoring tebrae found attached to few fragmentary of Pisanosaurus carried out by Agnolin and shafts (Figure 2). These fragments were Rozadilla (2017) (Appendix 1). Pseudolago- prepared under a binocular microscope suchus and Lewisuchus 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 bitt et 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
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