X-Ray Computed Tomographic Reconstruction And Bone Histology Of The Aetosaur Coahomasuchus Chathamensis (Archosauria: Stagonolepididae) From The Upper Triassic Pekin Formation, Deep River Basin, North Carolina And A Re-Analysis Of Its Phylogenetic Relationships

Aetosauria is a clade of armored, quadrupedal archosaurian omnivores to herbivores known from Upper Triassic units globally. However, there remains debate about their: intra-clade relationships, internal skeletal structure, and patterns of growth. So I reanalyzed the recently described species Coahomasuchus chathamensis from the Sanford sub-basin of North Carolina. My phylogeny, with updated character scorings several aetosaurs, recovers Coahomasuchus in a polytomy with Aetosaurus and the Typothoracinae, in contrast with a recent analysis that recovered Coahomasuchus as labile. To better understand the interior skeleton of aetosaurs, I undertook the first CT reconstruction of an articulated aetosaur specimen. These scans revealed several previously unseen elements, including several articulated vertebrae and ribs and the left ulna. To better characterize growth in the clade, I undertook a histological examination of C. chathamensis, sampling a paramedian osteoderm from the holotype and five osteoderms and two incomplete limb bones from referred specimens. From these sections I estimated ages by using lines of arrested growth to determine that the sampled individuals ranged from two to eight years old. When compared to similarly sized aetosaurs, it can be inferred C. chathamensis was growing rapidly. The discovery reveals that the holotype of C. chathamensis is apparently a juvenile individual.