Wikipedia
Metriorhynchidae is an extinct family of metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period ( Bajocian - Valanginian stages) of Europe, North America and South America. Metriorhynchids are fully aquatic crocodyliforms. Their forelimbs were small and paddle-like, and unlike living crocodilians, they lost their osteoderms ("armour scutes"). Their body shape maximised hydrodynamy (swimming efficiency), as did having a shark-like tail fin.
Metriorhynchids were the only group of archosaurs (aside from seabirds) to become fully adapted to the marine realm, becoming pelagic in lifestyle.
The name Metriorhynchidae was coined by the Austrian zoologist Leopold Fitzinger in 1843. It contains two subfamilies, the Metriorhynchinae and the Geosaurinae.