Phytosauria

Abstract

Abstract Phytosauria is a nearly cosmopolitan clade of large, quadrupedal, carnivorous archosauriforms. They are known unambiguously from Late Triassic deposits, although the clade’s ghost lineage extends at least to the late Early Triassic. Their nares are uniquely located close to the orbits rather than anteriorly in the rostrum as in modern crocodylians, and the rostrum is formed by elongated premaxillae bearing many teeth. Phytosaurs have roughly triangular, ornamented paramedian osteoderms, rounder appendicular osteoderms, and a unique ‘gular shield’ assembled from multiple, irregular osteoderms under the throat. Phytosaurs are reconstructed as semi-aquatic because of their general similarity to modern crocodylians and common preservation in fluvial and shallow-marine deposits. Currently, over thirty species are recognized. New specimens continue to be collected, some representing new taxa. The taxonomic status of other named taxa is uncertain and requires re-investigation. Since their discovery, phytosaurs have been used as biostratigraphic and biochronological index taxa for correlating Late Triassic sediments worldwide. Recent systematic and taxonomic revisions cast doubt on some of those correlations. Our understanding of the evolution of Phytosauria is far from complete. With reevaluation of well-known specimens, rigorous and comparative morphological descriptions, and robust phylogenetic hypotheses of ingroup relationships, studies of phytosaurs can address larger palaeobiological questions.