Abstract
BackgroundBasal sauropodomorphs, or ‘prosauropods,’ are a globally widespread paraphyletic assemblage of terrestrial herbivorous dinosaurs from the Late Triassic and Early Jurassic. In contrast to several other landmasses, the North American record of sauropodomorphs during this time interval remains sparse, limited to Early Jurassic occurrences of a single well-known taxon from eastern North America and several fragmentary specimens from western North America.Methodology/Principal FindingsOn the basis of a partial skeleton, we describe here a new basal sauropodomorph dinosaur from the Lower Jurassic Navajo Sandstone of southern Utah, Seitaad ruessi gen. et sp. nov. The partially articulated skeleton of Seitaad was likely buried post-mortem in the base of a collapsed dune foreset. The new taxon is characterized by a plate-like medial process of the scapula, a prominent proximal expansion of the deltopectoral crest of the humerus, a strongly inclined distal articular surface of the radius, and a proximally and laterally hypertrophied proximal metacarpal I.Conclusions/SignificancePhylogenetic analysis recovers Seitaad as a derived basal sauropodomorph closely related to plateosaurid or massospondylid ‘prosauropods’ and its presence in western North America is not unexpected for a member of this highly cosmopolitan clade. This occurrence represents one of the most complete vertebrate body fossil specimens yet recovered from the Navajo Sandstone and one of the few basal sauropodomorph taxa currently known from North America.
Highlights
The Early Jurassic (201.5–176 Ma) was an interval of major global climatic and biotic transition that included the diversification of many vertebrate groups
Among these were the sauropodomorphs, a diverse group of herbivorous dinosaurs that would remain among the dominant herbivores in many terrestrial ecosystems through the close of the Mesozoic, a period of more than 140 million years
The basal members of Sauropodomorpha, often referred to as the ‘prosauropods,’ achieved a nearly global distribution by the Early Jurassic, with taxa known from Africa [1,2,3,4,5,6,7,8,9], Antarctica [10], Asia [5,11,12,13,14,15], India [5]; North America [16,17,18], and South America [19,20]
Summary
The Early Jurassic (201.5–176 Ma) was an interval of major global climatic and biotic transition that included the diversification of many vertebrate groups. Among these were the sauropodomorphs, a diverse group of herbivorous dinosaurs that would remain among the dominant herbivores in many terrestrial ecosystems through the close of the Mesozoic, a period of more than 140 million years. In contrast to several other landmasses, the North American record of sauropodomorphs during this time interval remains sparse, limited to Early Jurassic occurrences of a single wellknown taxon from eastern North America and several fragmentary specimens from western North America
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