Anatomía vertebral de los dinsaurios dicraeosauridae de la formación mulichico (cretácico inferior): descripción, comparación y consideraciones filogenétcas

Abstract

The vertebral anatomy of three presacral vertebrae (a mid-cervical vertebra, an anterior dorsal vertebra, and a posterior dorsal vertebra) of a possible new species of a Dicraeosauridae sauropod dinosaur are described. The specimens were collected in levels of the Mulichinco Formation (Valanginian, Lower Cretaceous), Neuquén Basin, Patagonia, Argentina. In this work, the more important characters of the possible new species are described, including possible autopomorphies. Also, comparisons with another Dicraeosauridae dinosaurs are provided, and the synapomorphies of the different clades included are recognized. The material here studied seems to be more related to Amargasaurus than to other species of the family. The importance of the dicraeosaurids from Mulichinco regarding their chronostratyigraphical record are commented upon, as well as the diversity and paleogeographic distribution of this fossil fauna. The new dicreaeosaurid materials here described allow us to expand our knowledge of the Lower Cretaceous sauropods from South America, being the first Valanginian record of this sauropod family wordwide. This group had a rather cosmopolitan distribution along the Upper Jurassic, and would have been more diversified in Gondwana. By the Lower Cretaceous, this group seems to be exclusively Gondwanian, recorded only in the Argentinean Patagonia. The outstanding preservational condition of the fossils here described is interpreted as the result of a particular taphonomic history. The dicraeosaurids show a trend toward small body masses, neck shortening and well developed hemispinal processes, which are significant from a paleoecological point of view.