The first metriorhynchoid crocodyliform from the Aalenian (Middle Jurassic) of Germany, with implications for the evolution of Metriorhynchoidea

Abstract

Thalattosuchia, a clade of Mesozoic aquatic crocodyliforms, were the only archosaurs that ever became fully adapted to marine ecosystems. They are represented by two clades, the semiaquatic teleosauroids and the metriorhynchoids, which include fully pelagic forms. So far, little is known on the early evolutionary history of Metriorhynchoidea and data are sparse, especially from the early Middle Jurassic. Opisuchus meieri gen. et sp. nov. a metriorhynchoid crocodyliform from the early Aalenian (early Middle Jurassic) of southern Germany, is described here. It is one of the most complete specimens of a non-metriorhynchid metriorhynchoid, and the best-preserved thalattosuchian described from the Aalenian. The new taxon is represented by a nearly complete skull, which has a unique combination of characters distinguishing it from other species of Metriorhynchoidea. It displays a mosaic of plesiomorphic and apomorphic morphological features that sheds new light on early metriorhynchoid evolution. This taxon is an important puzzle piece, which will help to better track the mosaic character distribution in Thalattosuchia.