Osteoderm histology of Proterochampsia and Doswelliidae (Reptilia: Archosauriformes) and their evolutionary and paleobiological implications. (2nd February 2015)

• Record Type: Journal Article
• Authors: Cerda, Ignacio A.; Desojo, Julia B.; Trotteyn, María J.; Scheyer, Torsten M.
• Is Part Of: Journal of morphology. Volume 276:Number 4(2015:Apr.)
• Page Start: 385
• Page End: 402
• Publication Date: 2015-02-02
• Subjects: Morphology -- Periodicals; Physiology -- Periodicals; Anatomy -- Periodicals; 571.3
• DOI: 10.1002/jmor.20348
• Languages: English
• ISSNs: 0362-2525

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>Postcranial osteoderms are commonly developed in the major lineages of Archosauriformes, including forms such as proterochampsids and doswelliids. Here, we survey the histology of osteoderms of the doswelliids <italic>Archeopelta arborensis</italic> and <italic>Tarjadia ruthae</italic>, and the proterochampsids <italic>Chanaresuchus bonapartei</italic> and <italic>Pseudochampsa ischigualastensis</italic> to understand better the morphogenesis of these skeletal elements. Whereas, the Doswelliid osteoderms possess a trilaminar organization, in which two cortices (external and basal) can be differentiated from an internal core of cancellous bone, these elements are compact structures in proterochampsids. The osteoderms of <italic>P. ischigualastensis</italic> are avascular and they consist entirely of parallel‐fibered bone. Conversely, the osteoderms of <italic>C. bonapartei</italic> are well vascularized structures composed of zones of woven‐fibered bone and annuli of parallel‐fibered bone. The rather simple microstructure observed in <italic>P. ischigualastensis</italic> osteoderms suggests that these elements grew at a constant, low rate. Compared with proterochampsids, doswelliid osteoderms possess a more complex histology, which appears to be linked to variations in the growth rate during the osteoderm formation and also to the development of the external ornamentation. A comparison of our findings with the results of earlier studies on other archosauriforms (phytosaurs and pseudosuchians) reveals that the general osteoderm histology of doswelliids bears a closer resemblance to that of phytosaurs and pseudosuchians than the proterochampsid osteoderm microstructure. If all archosauriform osteoderms are homologous structures, the closer resemblance of doswellid osteoderm microstructures to that of phytosaurs and pseudosuchians is in agreement with the hypothesis that doswellids are more closely related to archosaurs than proterochampsids. J. Morphol. 276:385–402, 2015. © 2015 Wiley Periodicals, Inc.</p> </abstract>