Paracrocodylomorpha is a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 of crurotarsan archosaur

Archosaur

Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...

s that includes crocodylomorphs and several closely related Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 forms. Erected in 1993, the clade usually contains early crurotarsan taxa like Poposauridae

Poposauridae

The Poposauridae are a family of large carnivorous archosaurs which lived alongside dinosaurs during the Late Triassic. They are known from fossil remains from North and South America...

 and Gracilisuchus

Gracilisuchus

Gracilisuchus is an extinct genus of tiny crurotarsan from the Middle Triassic. It was a suchian close to the ancestry of crocodiles, and was at one time thought to be a dinosaur, but this hypothesis has since been rejected...

. These groups are considered sister taxa of the clade Bathyotica

Bathyotica

Bathyotica is a clade of crurotarsan archosaurs that includes the superorder Crocodylomorpha and its sister taxon Erpetosuchus, a small Triassic suchian. Bathyotica was named in a 2002 phylogenetic study of Erpetosuchus...

, which includes Crocodylomorpha and Erpetosuchus

Erpetosuchus

Erpetosuchus is an extinct genus of crurotarsan from the Late Triassic. It was first described by E. T. Newton in 1894 for remains found in northeastern Scotland, with more remains found in the United States in recent years. Erpetosuchus is the sister-taxon to Crocodylomorpha.The type species of...

. While Erpetosuchus is widely accepted as the closest relative of crocodylomorphs, the relationship of more basal

Basal (phylogenetics)

In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 taxa like Poposauridae are unclear.

Description

Paracrocodylomorpha is diagnosed by several unique characteristics, or synapomorphies. A ring of bone surrounds a projection on the calcaneum, a bone of the ankle. A ridge on the calcaneum is also present in Paracrocodylomorpha that runs across its entire length on one side. A foramen, or hole, in the base of the skull between the basioccipital and basisphenoid bones acts as an opening for a cavity in the braincase.

Phylogeny

Paracrocodylomorpha was named by paleontologist J. Michael Parrish in 1993. Parrish defined Paracrocodylomorpha as the last common ancestor of Poposauridae and Crocodylomorpha and all of its descendants. This clade was nested within Rauisuchia

Rauisuchia

Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...

, a group of crurotarsans that once included only extinct Triassic forms but is now generally regarded as paraphyletic. Rauisuchia traditionally included the families Rauisuchidae

Rauisuchidae

Rauisuchidae is a group of large predatory Triassic archosaurs, and constitute advanced representatives of the larger group Rauisuchia. There is some disagreement over which genera should be included in the Prestosuchidae, which in Rauisuchidae, and which in the Poposauridae, and indeed whether...

 and Poposauridae to the exclusion of Crocodylomorpha, but Parrish found Poposauridae more closely related to Crocodylomorpha than to Rauisuchidae. This close relationship was recognized since the 1980s. The genus Gracilisuchus was also found to be a close relative of crocodylomorphs and poposaurids but was not placed within Paracrocodylomorpha. Below is a cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 showing the phylogenetic relationships in Parrish's 1993 study:
The validity of Paracrocodylomorpha has not been widely accepted. For example, a 2007 phylogenetic study found the rauisuchian families Rauisuchidae and Prestosuchidae

Prestosuchidae

Prestosuchids were a group of Triassic carnivorous archosaurs. They were large active terrestrial apex predators, ranging from around in length. They succeeded the Erythrosuchidae as the largest archosaurs of their time...

 to be more closely related to Crocodylomorpha than was Poposauridae. The authors erected the clade Paracrocodyliformes for the clade including Rauisuchidae, Prestosuchidae, and Crocodylomorpha.