THE MORPHOLOGICAL EVOLUTION OF THE PHYTOSAURIA: REEVALUATING EARLY MEMBERS OF THE CLADE

Phytosaurs are a well-known Triassic group with a near-Pangean distribution. This cosmopolitan distribution, combined with morphological disparity spanning the Late Triassic, led to this clade being key to biostratigraphic and biochronologic correlations. Members of Phytosauria superficially resemble living crocodylians, exemplifying morphological convergence as well as possible ecological similarities. These similarities are most easily seen in derived phytosaurs near the end of the Late Triassic, though information is slowly accumulating on the timing and sequence of acquisition of those features. Recent work on a new Middle Triassic phytosaur from China indicated that the characteristic elongated rostrum of phytosaurs appeared after the cranial and postcranial modifications associated with enhanced prey capture, predating a similar general trend of morphological change observed in the evolution of crocodylians and their close relatives. Reevaluation of specimens from Germany, India, the American west, and the eastern US revealed a single Pangean clade early in the group’s history, and reassessment of specimens from the Newark Supergroup indicate the presence of a basal phytosaur in the Newark Supergroup rather than all phytosaurs from eastern North America being referable to an endemic Rutiodon. This suggests that the early evolution of the group was more complex than previously realized and reinforces the need to continue exploring the early evolution of the clade.