A new basal sauropod dinosaur from the middle Jurassic of Niger and the early evolution of sauropoda.

Kristian Remes,Ignacio Fierro,Ralf Kosma,Francisco Ortega,Oumarou Amadou Ide,José Manuel Marín Ferrer,Ulrich Joger,Abdoulaye Maga,Niger Project Snhm ,Project Paldes

doi:10.1371/journal.pone.0006924

Abstract

BackgroundThe early evolution of sauropod dinosaurs is poorly understood because of a highly incomplete fossil record. New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification.Principal FindingsA new sauropod from the Middle Jurassic of Niger, Spinophorosaurus nigerensis n. gen. et sp., is the most complete basal sauropod currently known. The taxon shares many anatomical characters with Middle Jurassic East Asian sauropods, while it is strongly dissimilar to Lower and Middle Jurassic South American and Indian forms. A possible explanation for this pattern is a separation of Laurasian and South Gondwanan Middle Jurassic sauropod faunas by geographic barriers. Integration of phylogenetic analyses and paleogeographic data reveals congruence between early sauropod evolution and hypotheses about Jurassic paleoclimate and phytogeography.Conclusions Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line. The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time. Jurassic climatic zones and phytogeography possibly controlled early sauropod diversification.

Highlights

The Sauropoda were the dominant herbivores in Mesozoic terrestrial ecosystems for at least 120 million years during most of the Jurassic and Cretaceous
Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line
The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time

Summary

Introduction

The Sauropoda were the dominant herbivores in Mesozoic terrestrial ecosystems for at least 120 million years during most of the Jurassic and Cretaceous. In concert with their gigantism [1], this success is unsurpassed by any other group of terrestrial tetrapods. The number of known sauropod genera has almost doubled over the last decade, the early evolution of this group is still only poorly understood. This is in part because discoveries from the Early and Middle Jurassic are sparse, especially outside Asia. New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification

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Conclusion