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Leyesaurus, new sauropodomorph from Lower Jurassic (?) of Argentina



From: Ben Creisler
bh480@scn.org

New in PLoS ONE:

Apaldetti, C,, Martinez, R,N,, Alcober, O,A,, & Po,l D, (2011) 
A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro
Formation (Marayes-El Carrizal Basin), Northwestern Argentina.
PLoS ONE 6(11): e26964. 
doi:10.1371/journal.pone.0026964
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0026964


Background
Argentinean basal sauropodomorphs are known by several specimens from
different basins; Ischigualasto, El Tranquilo, and Mogna. The Argentinean
record is diverse and includes some of the most primitive known
sauropodomorphs such as Panphagia and Chromogisaurus, as well as more
derived forms, including several massospondylids. Until now, the
Massospondylidae were the group of basal sauropodomorphs most widely spread
around Pangea with a record in almost all continents, mostly from the
southern hemisphere, including the only record from Antarctica.

Methodology/Principal Finding
We describe here a new basal sauropodomorph, Leyesaurus marayensis gen. et
sp. nov., from the Quebrada del Barro Formation, an Upper Triassic-Lower
Jurassic unit that crops out in northwestern Argentina. The new taxon is
represented by a partial articulated skeleton that includes the skull,
vertebral column, scapular and pelvic girdles, and hindlimb. Leyesaurus is
diagnosed by a set of unique features, such as a sharply acute angle (50
degrees) formed by the ascending process of the maxilla and the alveolar
margin, a straight ascending process of the maxilla with a longitudinal
ridge on its lateral surface, noticeably bulging labial side of the
maxillary teeth, greatly elongated cervical vertebrae, and proximal
articular surface of metatarsal III that is shelf-like and medially
deflected. Phylogenetic analysis recovers Leyesaurus as a basal
sauropodomorph, sister taxon of Adeopapposaurus within the
Massospondylidae. Moreover, the results suggest that massospondylids
achieved a higher diversity than previously thought.

Conclusions/Significance
Our phylogenetic results differ with respect to previous analyses by
rejecting the massospondylid affinities of some taxa from the northern
hemisphere (e.g., Seitaad, Sarahsaurus). As a result, the new taxon
Leyesaurus, coupled with other recent discoveries, suggests that the
diversity of massospondylids in the southern hemisphere was higher than in
other regions of Pangea. Finally, the close affinities of Leyesaurus with
the Lower Jurassic Massospondylus suggest a younger age for the Quebrada
del Barro Formation than previously postulated.


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