Paracrocodylomorpha

Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorpha was named by paleontologist J. Michael Parrish in 1993, although the group is now considered to encompass more reptiles than his original definition intended. The most recent definition of Paracrocodylomorpha, as defined by Sterling Nesbitt in 2011, is "the least inclusive clade containing Poposaurus and Crocodylus niloticus (the Nile crocodile). Most groups of paracrocodylomorphs became extinct at the end of the Triassic period, with the exception of the crocodylomorphs, from which crocodylians such as crocodiles and alligators evolved in the latter part of the Mesozoic. Parrish (1993) defined Paracrocodylomorpha as the last common ancestor of "Poposauridae" and Crocodylomorpha and all of its descendants. He believed that Poposaurus and its allies were among the closest relatives of crocodylomorphs. Therefore, his definition was intended to exclude various groups of heavily-built Triassic pseudosuchians, collectively known as "rauisuchians". Weinbaum & Hungerbühler (2007) hypothesized that the relations of Pseudosuchians were reversed to those hypothesized by Parrish. They claimed that "rauisuchians" such as Postosuchus, Batrachotomus, and Saurosuchus were closer to crocodylians than Poposaurus was. They erected a subgroup within Paracrocodylomorpha which they called Paracrocodyliformes. This subgroup contained all pseudosuchians closer to those three "rauisuchians" (as well as the Nile crocodile) rather than Poposaurus. Nesbitt (2011) introduced the most recent and common definition of Paracrocodylomorpha in his broad phylogenetic analysis. His results supported Weinbaum & Hungerbühler (2007)'s claim that "rauisuchians" were closer to crocodylians than Poposaurus was. In fact, he found that crocodylomorphs were actually descended from the "rauisuchian" group, thus rendering "Rauisuchia" a paraphyletic grade of various reptiles leading to crocodylomorphs.