Marasuchus

Marasuchus (meaning "Mara crocodile") is a genus of basal dinosauriform archosaur, sometimes regarded as a junior synonym of Lagosuchus. Both are small bipedal dinosauriforms based on 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 based on 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 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.

Conversely, 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.

Specimens referred to the genus Marasuchus possessed some, but not all of the adaptations which traditionally characterized dinosaurs. For example, its proportions indicate that it was likely bipedal as in early dinosaurs. Also, it shared certain specific characteristics with that group, most relating to the hip and the head of the femur. Nevertheless, it lacked certain dinosaur-like features such as a perforated acetabulum, and it had several plesiomorphic ("primitive") features of the ankle.