Bone Histology of Phytosaur, Aetosaur, and Other Archosauriform Osteoderms (Eureptilia, Archosauromorpha). Issue 2 (24th December 2013)

• Record Type: Journal Article
• Authors: Scheyer, Torsten M.; Desojo, Julia B.; Cerda, Ignacio A.
• Is Part Of: Anatomical record. Volume 297:Issue 2(2014:Feb.)
• Page Start: 240
• Page End: 260
• Publication Date: 2013-12-24
• Subjects: Anatomy -- Periodicals; Evolution (Biology) -- Periodicals; Morphology -- Periodicals; 571.3
• DOI: 10.1002/ar.22849
• Languages: English
• ISSNs: 1932-8486

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well‐developed osteoderms. Here we provide a comparative study on the microstructure of phytosaur (five taxa) and aetosaur (thirteen taxa) osteoderms. For outgroup comparison, we sampled osteoderms of the sister taxon to Aetosauria, <italic>Revueltosaurus callenderi</italic>, and the doswelliid <italic>Jaxtasuchus salomoni</italic>. Phytosaur, aetosaur, and <italic>Jaxtasuchus</italic> osteoderms are composed of a diploe structure, whereas the <italic>Revueltosaurus</italic> osteoderm microanatomy is more compact. The external cortex of phytosaurs, <italic>Revueltosaurus</italic> and <italic>Jaxtasuchus</italic> osteoderms is mainly composed of parallel‐fibered bone. In aetosaurs, the external cortex mainly consists of lamellar bone, with lines of resorption within the primary bone indicating successive cycles of bone erosion and deposition. The basal cortex in all the specimens is composed of parallel‐fibered bone, with the cancellous internal core being more strongly developed in aetosaurs than in phytosaurs. Woven or fibro‐lamellar bone was recorded in both phytosaurian and aetosaurian taxa, as well as in <italic>Jaxtasuchus</italic>. Structural fibers, which at least partly suggest metaplastic origin, were only recorded in the internal core of two phytosaurs and in the basal cortex of one aetosaur. Osteoderm thickness and cancellous to compact bone ratios appear to be subject to ontogenetic change. Minimum growth mark counts in osteoderms sampled indicate that some aetosaurs and phytosaurs lived for at least two decades. Bone microstructures are more uniform in phytosaur osteoderms and show a higher level of disparity among aetosaur osteoderms, and at least in the latter, histological features are potentially apomorphic for species/genus level. Anat Rec, 297:240–260, 2014. © 2013 Wiley Periodicals, Inc.</p> </abstract>