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Robust sauropodomorph from Upper Triassic of Argentina

From: Ben Creisler

Another new paper:

Martin D. Ezcurra and Cecilia Apaldetti (2011)
A robust sauropodomorph specimen from the Upper Triassic of Argentina and
insights on the diversity of the Los Colorados Formation. 
Proceedings of the Geologists' Association (advance online publication)

The Late Triassic rocks document the first steps of the early dinosaur
evolutionary radiation. Although the oldest dinosaurs were not abundant in
their assemblages, sauropodomorphs achieved a wide taxonomic diversity and
high abundance towards the Triassic?Jurassic boundary. In South America,
this pattern is documented in the Ischigualasto-Villa Unión Basin of
northwestern Argentina, in which dinosaurs achieved a numerical dominance
over other tetrapods during the deposition of the upper levels of the late
Norian-Rhaetian Los Colorados Formation. In this contribution we enrich the
faunal list of this assemblage with the description of a new medium-sized
basal sauropod specimen with a very robust tibial morphology. This new
specimen differs from the other known sauropodomorphs described for the Los
Colorados Formation and increases the alpha-diversity recorded for this
group. A phylogenetic analysis recovered the new specimen at the base of
Sauropoda and closely related to Lessemsaurus, Antetonitrus, and other
basal sauropods. These results match with the high degree of robustness
observed in the tibia of the specimen reported here, which closely
approaches the morphology documented for other basal sauropods and departs
from the morphospace occupied by non-sauropod sauropodomorphs. A two step
pattern of tibia robustness increase is observed in the sauropodomorph
phylogeny, a pattern that coincides and could be related with the
acquisition of more habitual quadrupedal gait achieved by basal sauropods.

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