Thalattosuchia
Thalattosuchia is the name given to a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Crocodilia. The clade contains two major subgroupings, the Teleosauroidea and Metriorhynchoidea. Within Metriorhynchoidea, the Metriorhynchidae displayed extreme adaptions for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin. The oldest records of thalattosuchians date to the Sinemurian and Pliensbachian stages, represented by indeterminate remains from  Argentina, Chile, and India. The term Thalattosuchia was coined by Fraas in 1901. Various authors considered Thalattosuchia an infraorder or a suborder within "Mesosuchia". However, the term "Mesosuchia" is a paraphyletic group, and as such is no longer used. For consistency, the Thalattosuchia are here placed at suborder rank, although the order that contains it is unnamed. The exact phylogenetic position of Thalattosuchia is uncertain, with them either being interpreted as members of Neosuchia or basal members of Crocodylomorpha, with the similarities to neosuchians possibly being due to convergence. Since Buffetaut (1982) demonstrated the shared characteristics of the early forms  of Metriorhynchidae and Teleosauridae, Thalattosuchia has consisted of these two families. Some of the early members of Teleosauridae have been discovered in non-marine deposits. The systematics of the genus "Pelagosaurus" are confused, with differencing topologies placing it as either a teleosaurid, or as the sister taxon to a Teleosauridae + Metriorhynchoidea clade. Others considered "Pelagosaurus" to be a basal metriorhynchoid.