Cranial osteology and phylogenetic relationships of a Late Triassic parareptile from the Chinle Formation of the American Southwest Rachel Johnson1 & Hans-Dieter Sues2 1. Transylvania University, Lexington, KY 2. Smithsonian Institution, National Museum of Natural History

Introduction Results Conclusions

Procolophonidae, a family of small to medium- Reduced premaxillary Articular low relative to Subfamily Scale: 1 bar= 1 cm Labial and lingual tooth count marginal dentary teeth sized parareptiles, emerged in the Permian, maxillary tooth cusps The MCZ specimens belong to Leptopleuroninae, survived the Permian-Triassic mass extinction, due to the absence of vomerine teeth, oblique ventral and diversified until the Triassic-Jurassic and dorsal surfaces of the dentary, and the articular extinction. This group was very widespread, with situated well below the dentary. fossils known from every continent. Typical Diet procolophonids are recognized by their small size, The deep dentary and pronounced coronoid process elongated orbits, and bulbous or bicuspid Dorsal view of Quadratojugal Posterior view of allowed for attachment of large jaw adductor molariform teeth. MCZ 9312 Anterior view Left lateral view spines Reduced MCZ 9313 Scale: 1 bar= 1 cm muscles. Uniquely cusped teeth allowed for MCZ 9312 and 9313 are two specimens of a number of chopping, while occlusal surfaces between maxillary maxillary, highly derived procolophonid that were found in Paired No vomerine dentary and dentary teeth provided a large area for crushing jugal teeth or the Owl Rock Member of the Chinle Formation in teeth and shearing. These features suggest a diet of spines denticles the American Southwest, dating to the Late primarily high-fiber plant material. Triassic. Phylogenetic Relationships 57 cranial, dental, and MCZ was most closely related to Hypsognathus skeletal characteristics Oblique ventral, from the Newark Supergroup in eastern North dorsal faces America. Their only difference is in the presence of from Cisneros (2008) were Ventral view Close-up of dentition Right lateral view of dentary Palatal view coded in 25 taxa of maxillary monocuspid teeth in Hypsognathus which Procolophonidae. Only 26 Photographs of MCZ 9312 and 9313, highlighting the most derived characteristics found in members of the subfamily Leptopleuroninae are absent in MCZ specimens. This shows a rare link of these cranial and dental between the east and west of present-day North characteristics could be America that is rarely displayed in the fossil record. Procolophonid of the Leptopleuroninae applied to and coded for subfamily in its habitat. Reconstruction by the MCZ specimens. Douglas Henderson. Deep occlusal MCZ Maxillary Parsimony analysis in TNT (Tree Analysis Using depression Hypsognathus monocuspid New Technology) was utilized to create a teeth absent Libognathus Constricted Abajo phylogenetic tree for this family (Goloboff et al. maxillary tooth 2003). Implicit Enumeration, a branch-and-bound Enlarged cervices Geographic distribution of closely algorithm that provides exact trees, was used in premaxillary Geographic Relationships related North American procolophonids the analysis, and all characters were equally incisors Two leptopleuronines, Libognathus, from the weighted. Collapsing rule 1 was employed, which Widely Dockum Group (Texas), and the Abajo skull, from collapses all branches that are ambiguous or separated the Owl Rock Member of the Chinle Formation cusps unsupported. (Utah), are related to the MCZ specimens. Only one Strict consensus tree of 29 most Most parsimonious tree of 25 taxa; dentary of Libognathus was found, but it shares a Single parsimonious trees. Includes all 26 excludes Libognathus due to deep dentary and large coronoid process with MCZ prominent taxa. Statistics: tree length= 115 incompleteness. Statistics: tree Research Questions steps, consistency index= .713, specimens. The Abajo skull shares a lack of dentary length= 114 steps, consistency retention index= .837. index= .719, retention index= .841. maxillary monocuspid teeth and a flattened snout. 1. To which subfamily do these skulls belong? incisor 2. What characteristics support this Labiolingually expanded Only synapomorphy is postfrontal contact with classification? Procolophonidae References Acknowledgments dentary teeth both the frontal and parietal 3. What are these specimens’ relationships to Prominently Family Cisneros, J. 2008. Phylogenetic relationships of Thank you to Elizabeth Cottrell, Gene Hunt, procolophonid parareptiles with remarks on and Virginia Power for coordinating the other procolophonids? bulbous teeth Leptopleuroninae Synapmorphies include absence of vomerine their geological record. Journal of NHRE program, and to the National teeth or denticles, oblique ventral and dorsal Systematic Palaeontology. 6(3):345-366. Science Foundation for its funding. Thank 4. What do the dentition and cranial features Subfamily Goloboff, P., J. Farris, and K. Nixon. 2003. T.N.T.: Tree you to Farish Jenkins for collection of surfaces of the dentary, and articular situated Analysis Using New Technology. Program specimens and Harvard University’s and documentation, available from Museum of Comparative Zoology for suggest about its lifestyle and diet? well below the alveolar margin of the dentary authors and www.zmuc.dk/public/phylogeny. Photograph of unique dental features in MCZ 9312 loaning them to Hans Sues at NMNH.