LOCOMOTORY PECULIARITIES IN MESOEUCROCODYILIANS: THE CASE OF ARARIPESUCHUS

ZURRIAGUZ, VIRGINIA; APESTEGUIA, S.; LIO, GABRIEL

San Luis

Jornada; XXV Jornadas Argentinas de Paleontología de Vertebrados; 2010

Universidad Nacional de San Luis

Despite crocodilians are considered as amphibious predators, their past history contains abundant terrestrial forms. However, the situation in basal mesoeucrocodylians is difficult to evaluate. Common and diverse in southern continents, basal mesoeucrocodylians included several herbivorous to omnivorous forms with heterodont dentition, propalinal jaw movements, and an unprecedented purported burrowing behavior. Among them, the genus Araripesuchus is still poorly known. Particularly, an articulated specimen from Araripesuchus cf. buitreraensis was studied in order to understand its locomotor abilities. Stylopodium, zeugopodium and even the autopodium show straight and hollow shafts. Metatarsals are long and straight and distal epiphyses show lateral pits for proximal phalanges. The specimen is articulated and finely preserved, showing its dorsal osteoderms in position. However, gastral elements are absent, thus suggesting that it is not a preservational artifact. On the other hand, the long legs and a large, three to four vertebrae sacrum, suggest an improved stability in the gait and an upright posture in comparison to that of extant crocodylians. Further, the lightening of the torso, devoid of gastralia, with hollow bones, pneumatic vertebrae, and only bearing two lines of scutes, is balanced with a heavily armored closed tail, completely surrounded by six lines of scutes that changed the center of mass backwards. This allowed the animal some independence in forelimbs and perhaps an occasional uprising in a way comparable to some xenarthrans, also owners of a closed tail. The future disarticulation of tails will permit to confirm if differential height in caudal neural spines support this proposal.