Marasuchus

Marasuchus (meaning "Mara crocodile") is an early genus of dinosauriform archosaur, one of the closest relatives of dinosaurs. It is sometimes regarded as a junior synonym of Lagosuchus (which would make Marasuchus an invalid later name for Lagosuchus fossils). Both names have been applied to small bipedal dinosauriform fossils from the same time and place: the Late Triassic (early Carnian stage) of what is now La Rioja Province, Argentina. If valid, Marasuchus contains a single species, Marasuchus lilloensis. Marasuchus lilloensis was originally designated as Lagosuchus lilloensis in 1972. It was named for a few well-preserved dinosauriform fossils stored at PVL, a museum in San Miguel de Tucuman. L. lilloensis is the second named species of Lagosuchus, a contemporary archosaur described from a smaller and more fragmentary fossil the previous year. A 1994 study argued that the first species, Lagosuchus talampayensis, has insufficient fossil material to justify its continued use. In response, the same study gave the better-preserved PVL fossils a new genus: Marasuchus. On the other hand, a 2019 study redescribed the original material of Lagosuchus and came to the opposite conclusion: that it was valid and not readily distinguishable from Marasuchus lilloensis. This suggests that Marasuchus lilloensis is a junior synonym of Lagosuchus talampayensis, since it was a later name applied to the same animal. Marasuchus and Lagosuchus fossils possessed some, but not all of the adaptations which traditionally characterized dinosaurs. For example, its proportions indicate that it was probably bipedal (walking on only its hindlimbs), like early dinosaurs. Most of its specific dinosaur-like traits relate to the hip and the head of the femur (thigh bone). Nevertheless, it lacked certain dinosaur-like features such as a perforated acetabulum (open hip socket), and it had several plesiomorphic ("primitive") features of the ankle. Marasuchus was roughly the size of a pigeon,...