A Lower to Middle Jurassic Terrestrial Vertebrate Assemblageand its Implications for the Post-Triassic Radiation of Tetrapods

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PI will study the implications of an exceptional Lower or Middle Jurassic vertebrate assemblage for the diversification of terrestrial tetrapods following the mass extinction(s) at the end of the Triassic. The vertebrate assemblage, from the La Boca Formation, Huizachal Canyon, Tamaulipas, Mexico, affords a unique test of whether rapid adaptive radiation, commonly inferred to follow mass extinctions, occurred in post-Triassic global vertebrate faunas. Preliminary work indicates that: a)based upon vertebrate biostratigraphy, the age of the assemblage (which includes new taxa) is ambiguously Lower or Middle Jurassic; and b)the assemblage accumulated under unique depositional conditions, in a structurally complex setting that hinders simple lithostratigraphic correlations. To integrate the Huizachal assemblage into a reconstruction of post-Triassic tetrapod diversification, PI will a)study the systematic paleontology of the assemblage, including a phylogenetic characterization; b)establish a lithostratigraphy for Huizachal Canyon involving the reconstruction of sedimentary environments; and c)constrain the age of the Huizachal assemblage by means other than vertebrate biostratigraphy. Having accomplished these prerequisites, they will integrate results into phylogenetically-based compilations of post-Triassic terrestrial diversity, to test the idea that the early Jurassic was characterized by a rapid radiation of terrestrial vertebrates.