Saturday, May 17, 2008

A detailed description of Desmatosuchus

Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus

William Parker, PaleoBios 28(1):1–40, May 12, 2008

Abstract: A new specimen of Desmatosuchus from northeastern Arizona (MNA V9300) preserves almost the entire vertebral column, the pelvis, and the majority of the armor carapace, allowing for an unprecedented detailed description of the taxon. Articulation and reconstruction of the armor carapace demonstrates that previous reconstructions of Desmatosuchus are erroneous in the orientation and position of the lateral armor. Lateral plates of the anterior dorsal region possess low rounded knobs instead of developed spines. The dorsal flange of the lateral plates of the dorsal region is longer than the lateral or ventral flange making the carapace transversely wider than previously thought. As a result, previous reconstructions articulate the lateral armor not only backwards but also on the wrong sides of the body. Posterior presacral vertebrae are extremely robust and possess fused ribs and the last presacral vertebra has been fused to the sacrum, a character that may be taxonomically useful. A prefrontal bone is also present in Desmatosuchus, contrary to previous descriptions. Reinvestigation of the genus Desmatosuchus suggests that there are only two valid species, D. spurensis and D. smalli. The lectotype of Episcoposaurus haplocerus is referable to Desmatosuchus but indeterminate at the species level, and therefore represents a nomen dubium. Accordingly, D. spurensis is reinstated as the type species of Desmatosuchus and the new Arizona specimen is assigned to this taxon. Acaenasuchus geoffreyi, a purported juvenile form of Desmatosuchus, is not referable to Desmatosuchus.

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