Paracrocodylomorpha

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. ==Description==

Unambiguous synapomorphies Under Nesbitt (2011)'s revised interpretation of the clade's components, only two unambiguous synapomorphies (derived distinguishing traits) were found for Paracrocodylomorpha. The tip of each pubis (forward-pointing hip bone) expands into a structure known as a pubic boot. In addition, metatarsal II (the foot bone which connects to the second-innermost toe) is at least as long if not longer than metatarsal IV (the foot bone which connects to the outermost toe). More basal pseudosuchians such as aetosaurs, ornithosuchids, Gracilisuchus, and Ticinosuchus lack these two traits. This posture is well known in loricatans (apart from sprawling crocodylomorphs) and basal poposauroids, but it is also known in aetosaurs. Aetosaurs may have acquired this posture independently, but if not, it cannot be considered a synapomorphy of Paracrocodylomorpha. Advanced poposauroids lack an outward-leaning ilium, but also possess a specialized supraacetabular crest which forces the acetabulum to face downward, resulting in the retention of a 'pillar-erect' posture. Some paracrocodylomorphs also have a pubis which contacts the ischium (rear-pointing hip bone) only slightly compared to earlier pseudosuchians. In poposauroids other than Qianosuchus and Lotosaurus, this trait is exaggerated to the point that the two bones don't even touch each other. The proximal portion of the femur (thigh bone) in some paracrocodylomorphs also possessed derived features compared to earlier taxa. Like many other archosaurs, the femoral head is tilted about 45 degrees outwards and backwards. The inner/rear face of the head possesses two large bumps (tubera), one more inward than the other. In non-paracrocodylomorph pseudosuchians, the more outward/rearward one (the posteromedial tuber) is larger, but in poposauroids and most loricatans, they are equal in size. However, Prestosuchus, one of the most basal loricatans, had a larger posteromedial tuber. Nevertheless, even more basal loricatans such as Mandasuchus had tubera of equal sizes, indicating that the situation in Prestosuchus was an anomaly. The femoral head may also have possessed a straight groove on its upper side in the earliest paracrocodylomorphs. This final trait is known in poposauroids and a few loricatans more basal than Fasolasuchus, but it is also unknown in Ticinosuchus and present in Nundasuchus so it may have predated Paracrocodylomorpha. ==Phylogeny==

According to Parrish (1993), this clade was nested within Rauisuchia, a group of crurotarsans that once included only extinct Triassic forms but is now generally regarded as paraphyletic. Rauisuchia traditionally included the families Rauisuchidae 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 showing the phylogenetic relationships in Parrish's 1993 study: In addition, several putative poposaurids such as Postosuchus and Teratosaurus were found to be rauisuchids. Sterling J. Nesbitt in 2011 found a similar topology, including Rauisuchidae and "Prestosuchidae" ( the latter of which he found to be polyphyletic) within Paracrocodylomorpha. The closest relative of Paracrocodylmorpha to not qualify as a member of the clade is Ticinosuchus, a large predator once considered to qualify as a prestosuchid. The composition of Paracrocodylomorpha generally follows the analysis of Nesbitt (2011) in other recent studies. }} ==References==