Field of Science

Paleohistology of Rauisuchid Osteoderms

Yes, I am still in Argentina. I'd planned on posting a little more, especially since I visited Ischigualasto National Park and spent some hours prospecting in the Ischigualasto Formation (it did not disappoint) but I've been up to my eyeballs in aetosaur specimens and trying to keep myself fed (meals take a long time here), so forgive me. Meanwhile here is a paper I've been waiting on for awhile now regarding osteoderm histology of rauisuchids with comparisons to some other archosaur groups as well.

Scheyer, T. M. and J. B. Desojo. 2011. Palaeohistology and external microanatomy of rauisuchian osteoderms (Archosauria: Pseudosuchia). Palaeontology (advance online publication) DOI: 10.1111/j.1475-4983.2011.01098.xhttp://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2011.01098.x/abstract

Abstract - The presence of postcranial dermal armour is plesiomorphic for Archosauria. Here, we survey the external microanatomy and histology of postcranial osteoderms (i.e. dorsal paramedian and caudal osteoderms) of rauisuchians, a widely distributed assemblage of extinct predatory pseudosuchians from the Triassic. The osteoderms of eight rauisuchian taxa were found to be rather compact bones, which usually lack significant bone remodelling or large areas of cancellous bone. The presence of highly vascularized woven or fibrolamellar bone tissue deposited in the core areas indicates higher growth rates during earlier life stages, whereas a more compact parallel-fibred bone matrix indicates reduced growth rates in later development. This pattern of change corroborates earlier studies on long bone histology. With the exception of a bone tissue found in the sample of Batrachotomus kupferzellensis, which might be the result of metaplastic ossification, the general mode of skeletogenesis is comparable with intramembraneous ossification. The lack of cancellous bone tissue and remodelling processes associated with bone ornamentation, as well as the predominantly intramembraneous mode of ossification, indicates that rauisuchian osteoderm formation differs profoundly from that of the osteoderms of the only extant pseudosuchian lineage, the crocodylians.

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