New insights on the phylogenetic and biogeographic relationships of basal Sauropodomorpha

APALDETTI, CECILIA; BITTENCOURT, JONATHAS ; MARTÍNEZ, RICARDO N.

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Instituto y Museo de Ciencias Naturales UNSJ

?Prosauropods? are a grade of herbivorous/omnivorous dinosaurs that traditionally include most non-sauropod sauropodomorphs. Earliest representatives of this group date back to the end of Carnian, and after reaching a nearly global distribution, ?prosauropods? disappeared before the end of Jurassic. Despite recent advances, the phylogenetic relationships among basal sauropodomorphs are still controversial. The analysis of Yates (2007), which has been largely accepted in more recent studies, supports the clade Plateosauria, comprising typical ?prosauropod? families as Plateosauridae (Plateosaurus Meyer + Unaysaurus Leal, Azevedo, Kellner and Da Rosa), Riojasauridae (Riojasaurus Bonaparte + Eucnemesaurus Hoepen), Massospondylidae (Lufengosaurus Young + Coloradisaurus Bonaparte + Massospondylus Owen) plus Anchisauria and its stem-taxa. An alternative phylogenetic hypothesis (Upchurch et al. 2007) assembles Plateosaurus, Riojasaurus and Coloradisaurus into Plateosauridae, and this latter with Massopondylus and Lufengosaurus into Plateosauria. We perform a new analysis of a previously modified version of the Yates (2007) dataset, adding the reassessment of some taxa and resulting in a different phylogenetic scheme. Plateosauridae is shown as a more restrict clade, including only the species formerly ascribed to the genus Plateosaurus, from Europe, whereas Unaysaurus is found in a new basal massopod clade that also includes Sarahsaurus Rowe, Sues and Reisz and Ignavusaurus Knoll. Massospondylidae is mostly represented by taxa from Southern Hemisphere. Seitaad Sertich and Loewen, recently described from the Early Jurassic of North America, resulted as closely related to Anchisauria. Previous phylogenetic scenarios in which the plateosaurids comprise species from both Europe and South America are problematic, as an exclusive faunal sharing between these areas is not supported by geological and biostratigraphic evidence. A bayesian biogeographic analysis over the geographical distribution of sauropodomorphs within the original phylogenetic frameworks of Upchurch et al. (2007) and Yates (2007) suggests that dispersal across Pangaea would explain the occurrence of plateosaurids in those areas. Yet, the lack of unambiguous plateosaurid representatives in North America and Africa contradicts this scenario, hinting at spurious phylogenetic signal. Alternatively, the close relationship of the South American ?prosauropods? with taxa from connected areas fits better to the available biostratigraphic data. Indeed, our results suggest some provincialism in the Late Triassic evolution of sauropodomorphs. Plateosauridae is restricted to northern Pangaea, whereas basal Massopoda inhabited predominantly the southern hemisphere, achieving a global distribution during the Early Jurassic.