An Enigmatic Small Neosuchian Crocodyliform from the Woodbine Formation of Texas.

Abstract

New discoveries at the Arlington Archosaur Site (AAS), a Cenomanian (Late Cretaceous) locality in north-central Texas, are filling gaps in our knowledge of mid-Cretaceous Appalachian ecosystems, which remain poorly characterized. The AAS is notable because it preserves a diverse crocodyliform record. As seen in other sites that preserve four or more crocodyliform taxa, the species present at the AAS exhibit different snout shapes and body sizes, indicating that this high diversity of sympatric species was likely sustainable due to niche partitioning. Here we describe Scolomastax sahlsteini gen. et sp. nov., a new species of crocodyliform from the AAS, currently known from a partial right mandibular ramus. This species differs from other crocodyliforms in possessing features associated with durophagy or omnivory, including a shortened mandible, reduced tooth count, heterodonty, a dorsally expanded surangular, and enlarged attachments for jaw adductor muscles. Our phylogenetic analysis places this new taxon within Eusuchia as a member of Paralligatoridae and sister taxon to Paralligator gradilifrons. Scolomastax sahlsteini extends the record of paralligatorids into the Late Cretaceous of North America. This discovery represents the first appearance of this clade on the poorly known landmass of Appalachia, supporting a biogeographic connection between North America and Asia in the Early Cretaceous prior to completion of the Western Interior Seaway. However, relationships among other endemic crocodyliforms and tree instability within Paralligatoridae suggest further analysis is needed to resolve phylogenetic and biogeographic relationships (http://zoobank.org/urn:lsid:zoobank.org:pub:DC114471-6687-4BB5-8FAE-96F7278B1DAF). Anat Rec, 303:801-812, 2020. © 2019 Wiley Periodicals, Inc.