Last of an ancient lineage: Remains of the youngest and most Austral indisputable diplodocoid (Dinosauria: Sauropoda) ever recoreded, from the Upper Cretaceous Bajo Barreal Formation of central Patagonia

MARTÍNEZ, RUBÉN D.; CASAL, GABRIEL A.; LUNA, MARCELO; IBIRICU, LUCIO M.; CARDOZO, SONIA; LAMANNA, MATTHEW C.

Denver; Colorado

Congreso; SVP; Reunión anual de Paleontología; 2004

Society of Vertebrate Paleontology (SVP)

Associated remains of a sauropod dinosaur have been found in exposures of the Upper Cretaceous Bajo Barreal Formation of northern Santa Cruz Province, Argentina. Material includes an anterior and posterior dorsal vertebrae, four anterior caudal vertebrae (three of them articulated), a left scapula, ribs, and other elements yet to be discovered. The anterior dorsal vertebra has a forked neural spine, while the posterior dorsals have unforked neural spines. Dorsal centra have pleurocoels. The most anterior caudal have wing-like transverse processes and high neural spine that progressively widen dorsally. The distal end of the scapula is well expanded, but its width is less than twice the minimum width of the blade. Several of these features allow us to include this specimen within Diplodocoidea, the first non-rebbachisaurid diplodocoid from the Upper Cretaceous. Our present knowledge of the Bajo Barreal Formation permits us to recognize two different faunas within the unit. The older of the two is middle Cenomanian-Turonian in age, and contains abelisauroid and tetanuran theropods, a basal ornithopod, and at least two sauropod lineages: Titanosauria and Diplodocoidea. The younger fauna is Campanian?-Maastrichtian in age, and consists of Megaraptor-like theropods, an undescribed ornithopod, and the titanosaurian Aeolosaurus sp. Stratigraphic data demonstrate that the bed that produced the new diplodocoid overlies the older dinosaur-bearing levels of the Bajo Barreal Formation but is nonetheless older than the Campanian-? Maastrichtian beds. Because of this, the age of the new diplodocoid can be no younger than Turonian. The presence of this ancient sauropod lineage in Upper Cretaceous Patagonian continental assemblages dominated by titanosaurians could shed light on the last surviving diplodocoids, which may have been relicts of a former Pangean distribution that ended their long and successful history in geographically remote central Patagonia.