Abstract
BackgroundArgentinean 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 FindingWe 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/SignificanceOur 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.
Highlights
Basal sauropodomorphs are non-sauropod sauropodomorphs that diversified and spread to most continents from the Late Triassic through the Early Jurassic, and constitute the first global radiation of herbivorous dinosaurs [1,2]
The lateral surface of the ascending process of Leyesaurus bears a rounded ridge throughout its entire dorsoventral length, a feature that is absent in all other basal sauropodomorphs
The new taxon described in the present work increases our knowledge of basal sauropodomorphs, in particular our understanding of the diversity of Massospondylidae
Summary
Basal sauropodomorphs are non-sauropod sauropodomorphs that diversified and spread to most continents from the Late Triassic through the Early Jurassic, and constitute the first global radiation of herbivorous dinosaurs [1,2]. The Brazilian record includes Saturnalia tupiniquim [3,4,5] from the Carnian Santa Maria Formation; and the possible basal sauropodomorph Guaibasaurus candelariensis [6,7,8] and Unaysaurus tolentinoi [9] from the Carnian-Norian Caturrita Formation. We report a partial skeleton of a new basal sauropodomorph from the upper levels of the Quebrada del Barro Formation that has implications for our understanding on the diversity of massospondylid sauropodomorphs in South America and for the supposed age of this stratigraphic unit. 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. 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
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