Meeting Abstract
Following the end-Permian extinction, terrestrial vertebrate diversity recovered by the Middle Triassic and was dominated by reptiles. However, these reptilian clades, including archosaurs and their closest relatives, are not commonly found until ~30 million years later in Late Triassic deposits despite time-calibrated phylogenetic analyses predicting an early Middle or even Early Triassic divergence for those clades. One of these groups from the Late Triassic, Phytosauria, is well known from a near-Pangean distribution, and this easily recognized clade bears an elongated rostrum with posteriorly retracted nares and numerous postcranial synapomorphies, particularly of the pectoral girdle, that are unique compared with all other contemporary reptiles. Here, we recognize the exquisitely preserved, nearly complete skeleton of Diandongosuchus fuyuanensis as the oldest and basalmost phytosaur. The Middle Triassic age and lack of the characteristically-elongated rostrum fill a critical morphological and temporal gap in phytosaur evolution, indicating that the postcranial modifications of phytosaurs occurred prior to rostral elongation. The cranial modifications that are present in Diandongosuchus suggest early modifications for prey acquisition, paralleling the trend that is later observed in crocodylomorph evolution. Based on the paleogeographic location and possible marine paleoenvironment of Diandongosuchus, we hypothesize salt-water tolerance as the mechanism for Phytosauria’s pan-Tethyan distribution, adding to the growing body of evidence that the saltwater tolerance of birds and crocodylians was present in their most recent common ancestor and closest relatives.
