Field of Science

Revision of the Basal Sauropodomorph Anchisaurus polyzelus

This is the latest paper in the ongoing debate regarding the taxonomic validity of Anchisaurus polyzelus (Sauropodomorpha: Anchisauria) and the referral of three other partial specimens from the Early Jurassic Portland Formation of Massachusetts and Connecticut.  Whereas, all workers now agree that the four specimens all belong to the same species, the debate has centered around the status of the type materials of A. polyzelus, because if they are not diagnostic, the next available name for this material is Ammosaurus major. Through reanalysis of the material Yates proposes seven autapomorphies diagnosing this material, including one of these also found in the holotype specimen of A. polyzelus.  Thus, Yates argues that A. polyzelus is valid, all four specimens can unambiguously be referred to it, and that Ammosaurus major is the junior synonym.  This paper also features a revised phylogentic analysis of the sauropodomorpha based on the reanalysis including repreparation of the skull found in one of the referred specimens.  Anchisaurus is recovered at the base of Anchisauria and outside of Sauropoda.

As this is about the 6th paper in a little more than a decade dealing with this, I am awaiting the next installment ;).

Yates, A. M. in press. A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus Marsh. Palaeontology. doi: 10.1111/j.1475-4983.2010.00952.x


Abstract: The taxonomic status of the sauropodomorph dinosaurs from the Newark Supergroup of north-eastern USA is reviewed. The inclusion of the three articulated skeletons from Wolcott’s Quarry, Manchester, Connecticut in a single species is supported. Despite claims to the contrary the Manchester skeletons can be referred to the species Anchisaurus polyzelus, which is based on a fragmentary specimen from Massachusetts. Two autapomorphies: dorsoventrally flattened ischial blades set at a low angle to each other and slender sacral ribs of the first sacral vertebra, link the holotype of A. polyzelus to the Manchester specimens. A revised diagnosis of the species and new skull reconstruction are presented. Recent anatomical observations of A. polyzelus indicate that several character states used to assess its phylogenetic position require revision. However, these are not sufficient to overturn previous cladistic analyses. A revised cladistic analysis continues to find support for Anchisaurus as a relatively derived basal sauropodomorph that lies outside of the clade Melanorosaurus + Sauropoda but is more closely related to it than to ‘core prosauropods’ such as Plateosaurus and Massospondylus.

2 comments:

  1. Hi Bill and thanks for featuring my paper, believe it or not I didn't know it had been published until I saw your post. Regarding the phylogenetic analyses. This analysis was not intended in anyway to be an up-to-the minute analysis of basal sauropodomorph phylogeny. Its only purpose was to assess the claims of Fedak and Galton (2007) that new data for Anchisaurus destabilised its position close to Sauropoda (or in it depending on what definition you are using). So I simply added this data to my old(ish) 2007 matrix. Indeed all of my recent analyses (e.g. Aardonyx and the upcoming second Spionkop taxon) are simply additions to this matrix - although I did overhaul some codings for the Aardonyx paper. In the meantime I am working on a very large very thorough rehaul of the whole shebang. I'm going back to as many original specimens as possible, scoring everything anew so that no old errors can creep into the new analysis, trying very hard to include every single proposed character that does vary in the ingroup and adding a host of new taxa (Seitaad, Lamplughsaura, Adeopapposaurus, Glacialosaurus, Pradhania and a couple of in press taxa)AND trying to document each character score for each taxon with at least a reference, if not a figure. Its a massive undertaking and I don't expect to be finished anytime soon.

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  2. Thanks Adam, that does sound like a major, but necessary undertaking.

    We need to find a sauropodomorph in the Chinle now to help shake things up some more.

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