Pampadromaeus
Pampadromaeus is an extinct genus of basal sauropodomorph dinosaurs known from the Late Triassic Santa [Maria Formation] of the Paraná Basin in Rio [Grande do Sul], southern Brazil.
Discovery
Pampadromaeus is known only from the holotype specimen Museu de Ciências Naturais da Fundação Zoobotânica do [Rio Grande do Sul|ULBRA]-PVT016, a disarticulated, partial but well preserved skeleton from a single individual which includes most of the skull bones and the lower jaws; dorsal, sacral and caudal vertebrae; elements of the shoulder girdle and the forelimbs, an ilium and elements of the hindlimbs. It was collected in the upper Hyperodapedon biozone from the Alemoa Member of the Santa Maria Formation in the "Janner" locality, geopark of Paleorrota, dating to the Carnian faunal stage of the early Late Triassic, about 230–228 Ma ago. A U-Pb dating found that the Santa Maria Formation dated around 233.23 Ma, putting it 1.5 million years older than the Ischigualasto Formation, and making the two formations approximately equal as the earliest dinosaur localities.Description
Pampadromaeus was a small bipedal animal. It shows a mosaic of basal and derived traits. It differs from other sauropodomorphs by a combination of characters. Some of these are shared with members of the Theropoda: the premaxilla is pointed downwards forming a subnarial gap with the maxilla and the anterior-most teeth are unserrated; in the location where with theropods the fenestra promaxillaris is positioned, a small depression is present. Basal traits consist of a large skull, a short thighbone, the possession of just two sacral vertebrae and the presence of fifteen teeth in the pterygoid.There were four teeth in the premaxilla and about twenty in both the maxilla and the lower jaw for a total of eighty-eight. The teeth were large, elongated, lanceolate, slightly recurved, sharply pointed and coarsely serrated. The lower leg was much longer than the thighbone, indicating a cursorial lifestyle.
In 2022, Tito Aureliano and colleagues performed a micro-computed tomography scan on the postcranial skeletons of some of the earliest saurischian dinosaurs that lived during the late Carnian including the herrerasaurid Gnathovorax with sauropodomorphs Pampadromaeus and Buriolestes, which showed that the invasive air sac system was absent and that their bones were not pneumatised. These results indicate that pneumatisation in archosaur groups are not homologous, but are traits that Convergent evolution#Parallel [vs. convergent evolution|independently evolved] at least 3 times.