Jurassic sauropods from Patagonia and sauropod faunal replacement in the Jurassic.

POL, D.; RAUHUT O. W.; CARBALLIDO, J. L.

Congreso; 4th International Paleontological Congress; 2014

The main diversification of sauropod lineages dinosaurs happened during the Jurassic, but especially the pre-Late Jurassic sauropod record is still rather poor. Thus, the origin of the Late Jurassic and Cretaceous sauropod faunas is still poorly understood. In South America, pre-Cretaceous sauropod dinosaurs are mainly known from the Cañadón Asfalto Basin of Central Patagonia. Within this basin, two geological units have yielded sauropod remains, the Cañadón Asfalto Formation and the Cañadón Calcáreo Formation. From the latest Early to early Middle Jurassic Cañadón Asfalto Formation, two sauropod taxa have been described so far, the basal eusauropods Patagosaurus and Volkheimeria. Two further taxa of sauropods are represented by so far undescribed material. Phylogenetic analysis demonstrates that all of these taxa are basal, non-neosauropod sauropods, representing at least three distinct lineages. The Late Jurassic (Oxfordian-Kimmeridgian) Cañadón Calcáreo Formation has yielded two taxa of sauropods, the basal macronarian Tehuelchesaurus and the dicraeosaurid Brachytrachelopan. Furthermore, fragmentary remains indicate the presence of a brachiosaurid titanosauriform and a diplodocid. Thus, the taxonomic composition of the sauropod fauna from the Cañadón Calcáreo Formation is markedly different from that of the Cañadón Asfalto Formation, but remarkably similar to roughly contemporaneous faunas from the Morrison Formation of North America, various units in Europe, and the Tendaguru Formation of Tanzania. These records show that a sauropod assemblage formed by basal macronarians, basal titanosauriforms, and diplodocids had been established by the Kimmeridgian at the latest both in Gondwana and western Laurasia. The Middle Jurassic sauropod fossil record indicates that up to the Bathonian sauropod assemblages were dominated by basal eusauropods (non-neosauropodan sauropods), this indicates a rapid sauropod faunal turnover from the Middle to the Late Jurassic. Taking into account palaeogeographical reconstructions, this faunal replacement probably happened between the Bathonian and the beginning of the Oxfordian, in a geologically short period of less than five million years. enviar mensaje