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The name Crurotarsi is derived from the Latin word crus (lower leg) and the Greek word tarsos (ankle). It refers to the specialized articulation (a crurotarsal joint) between the lower leg (specifically the fibula) and the ankle (specifically the calcaneum) which is present in the skeletons of reptiles such as suchians and phytosaurs.
The thin tibia and fibula (lower leg bones) of aphanosaurs do not possess unique traits to the same extent as the femur. However, they are also shorter than the femur. These proportions are rare among early avemetatarsalians, but more common among pseudosuchians and non-archosaur archosauriformes.
The name Pseudosuchia was originally given to a group of superficially crocodile-like prehistoric reptiles from the Triassic period, but fell out of use in the late 20th century, especially after the name Crurotarsi was established in 1990 to label the clade (evolutionary grouping) of archosaurs encompassing most reptiles previously identified as pseudosuchians.
The earliest lineages of Crocodylomorpha are placed into the paraphyletic "Sphenosuchia", which are characterized by slender bodies with elongate legs. The oldest known crocodylomorph is Trialestes , known from the Late Triassic (Carnian-Norian) of Argentina, around 231–225 million years ago, [ 6 ] the last groups of "sphenosuchians ...
"Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. [2] Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs.
Ornithosuchidae is an extinct family of pseudosuchian archosaurs (distant relatives of modern crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like chimpanzees), meaning that they had the ability to walk on two legs for short periods of time.
P. kirkpatricki compared to a human. Postosuchus was one of the largest carnivorous reptiles during the late Triassic. The length of the paratype is estimated up to 3.5–4 m (11–13 ft) long, [3] and an individual of such length would have measured 2 metres (6.6 ft) tall at the head when stood upright and weighed around 250–300 kilograms (550–660 lb). [4]
The hypothesized leg musculature of P. gracilis, with leg bones (top), superficial muscles (middle), and deep muscles (bottom). When M. G. Mehl first named Poposaurus in 1915, he described it as "a well-muscled creature light in weight, possibly bipedal in gait occasionally, and most assuredly swift in movement."