A new titanosaur from ‘Rancho de Ávila’ (Río Negro) in the Bajo de la Carpa - Anacleto Formations boundary

SEBASTIÁN APESTEGUÍA; PABLO A. GALLINA

Buenos Aires

Jornada; XIX Jornadas Argentinas de Paleontologia de Vertebrados; 2003

Museo Argentino de Ciencias Naturales

During the Late Cretaceous, sauropods experienced a decrease in their high-level diversity. Titanosaurs, however, experienced an increase. By Santonian to Campanian times, Patagonian titanosaur diversity included the last amphyplathian-tailed taxa as well as the highest diversity of procoelous forms, including the first saltasaurines, probably originated in Northern South America. A new non-saltasaurine titanosaur was collected from ‘Rancho de Ávila’, the locality that provided by 1920’s a large collection of titanosaur bones housed in the Museo de La Plata. The new titanosaur includes a lower jaw with slender chisel-like teeth, a cervical vertebra, six dorsal vertebrae, an articulated series of eight mid-caudal vertebrae, humerus, metacarpals, femur, tibia and a fifth metatarsal. No osteoderms were collected. The new taxon, less slender than Antarctosaurus, is characterized by long and very well developed diapoprezygapophyseal laminae and paired spinoprezygapophiseal laminae in anterior dorsal vertebrae, that remain unfused for most of the neural spine, showing however, a complete prespinal laminae. This condition is also observed in MLP-Av2121, assigned by Huene to Laplatasaurus and DGM-‘A’ from Peirópolis. The specimen belongs to the uppermost levels of Bajo de la Carpa Formation, at the boundary with Anacleto. Although an enormous diversity of specimens belonging to stem-lineages have been collected in the last years from the Río Colorado Subgroup, both in Southern Mendoza and Northwestern Neuquén Provinces, most of them remain undescribed. By Santonian to Early Campanian times, in the previous stages to the Kawas Sea transgressive event, the  Patagonian titanosaur lineages seem to have reached a peak diversity for the Late Cretaceous.