Field of Science

Dispersal as a Key Factor in Early Dinosaur Diversification of North America and the Myth of a 'Cosmopolitan' Dinosaur Fauna in the Early Mesozoic

New and available free from the Royal Society website. Popular news story here.

Rowe, T. B., Sues, H.-D., and R. Reisz. 2010. Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon. Proceedings of the Royal Society B, First Cite. doi:10.1098/rspb.2010.1867 

Abstract - Sauropodomorph dinosaurs originated in the Southern Hemisphere in the Middle or Late Triassic and are commonly portrayed as spreading rapidly to all corners of Pangaea as part of a uniform Late Triassic to Early Jurassic cosmopolitan dinosaur fauna. Under this model, dispersal allegedly inhibited dinosaurian diversification, while vicariance and local extinction enhanced it. However, apomorphy-based analyses of the known fossil record indicate that sauropodomorphs were absent in North America until the Early Jurassic, reframing the temporal context of their arrival. We describe a new taxon from the Kayenta Formation of Arizona that comprises the third diagnosable sauropodomorph from the Early Jurassic of North America. We analysed its relationships to test whether sauropodomorphs reached North America in a single sweepstakes event or in separate dispersals. Our finding of separate arrivals by all three taxa suggests dispersal as a chief factor in dinosaurian diversification during at least the early Mesozoic. It questions whether a ‘cosmopolitan’ dinosaur fauna ever existed, and corroborates that vicariance, extinction and dispersal did not operate uniformly in time or under uniform conditions during the Mesozoic. Their relative importance is best measured in narrow time slices and circumscribed geographical regions.


  1. Sarahsaurus was originally reported to have palatal teeth back when it was the Kayenta Massospondylus, but the new article doesn't mention them at all. I can only assume they were misidentified at first (Sereno said they were fish teeth in 2007), but if so it's frustrating that the mistake was just ignored since future researchers won't know what to make of the original report.

  2. I also looked for mention of the palatal 'cones/spikes' (see photo in original paper) in the diagnosis of Sarahsaurus, to notice the same thing as Mickey.

    But, Rowe et al don't describe or illustarte the original Kayenta 'Massopondylus'(material at Havard) material here, only referring it to Sarahsaurus. The new material, which includes the type of Sarahsaurus has a skull with jaws closed, so i simply assume the palate region was obscured. Wasn't there a report of similar projections on the palate of Eoraptor?

    It would be interesting to see if a detailed study & comparison of the original Kayenta "Massospondylus" skull supported its referral to Sarahsaurus.

  3. I'm only familiar with the TMM holotype material that Tim Rowe was working on, but as can be seen by the article, there is a referred specimen from the MCZ. I'm assuming this is why Hans Sues and Robert Reisz where included on the final paper. I believe they were working on the MCZ material and clearly they must believe they have the same taxon.

    Regarding the presence of palatal teeth, you will need to ask Hans Sues or Robert Reisz, as I'm not sure how much description from the MCZ material was used in the final article.

    You are correct that Eoraptor purportedly possesses palatal teeth.

  4. Jay,

    You are incorrect. The braincase and postcrania belong to TMM 43646-2. But the skull Rowe et al. describe and figure is the MCZ 8893 specimen that was originally described by Attridge et al. 1985 as Massospondylus.


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