Michelle R. Stocker, Sterling J. Nesbitt, Katharine E. Criswell, William G. Parker, Lawrence M. Witmer, Timothy B. Rowe, Ryan Ridgely & Matthew A. Brown (2016)
A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives.
Current Biology (advance online publication)
Following the end-Permian extinctions, crown-group reptiles underwent an extensive diversification. From this radiation, archosauromorphs (reptiles closer to birds and crocodylians than to squamates) preserve one of the most diverse and disparate fossil records within Reptilia. The oldest and best-documented terrestrial record of this archosauromorph diversification in North America is the Late Triassic Otis Chalk assemblage. This assemblage includes an exceptional range of disparate cranial morphologies, dental modifications, and overall bauplans. Common clades in this assemblage are phytosaurs, with hyper-elongated and narrow rostra that have invoked statements of convergence with extant crocodylians, and armored aetosaurs, resembling the Cretaceous tank-like ankylosaurian dinosaurs. Reevaluation of the Otis Chalk assemblage (Supplemental Information) has illuminated further examples of convergent morphology, such as a shuvosaurid similar to Effigia that mimics the ornithomimid “ostrich-dinosaurs”. Exemplifying this extreme morphological convergence, we present here a new dome-headed taxon from the assemblage, which further illustrates the extraordinary range of morphological disparity present early in the Late Triassic.