Bone histology and bone compactness of fossil and recent xenarthran long bones

STRAEHL, F.R.; SCHEYER. T.M.; FORASIEPI, A.M.; SANCHEZ-VILLAGRA M.

Oxford

Simposio; 60th ANNUAL SYMPOSIUM OF VERTEBRATE PALAEONTOLOGY AND COMPARATIVE ANATOMY; 2012

University of Oxford

Xenarthrans include anteaters, sloths and armadillos, and also a wide array of fossil forms. Their ecomorphological diversity and physiological specializations such as low metabolic rate make the first broad-scale palaeohistological study of this group worthwhile. Previously, osteoderm histology was shown to provide some phylogenetic and functional signal in xenarthrans. In this study, we focus on the histology of fossil and recent long bones. Thin sections were analyzed qualitatively and quantitatively by means of bone compactness profiles. Dense Haversian tissue made up of several generations of secondary osteons was detected. In some samples, only up to three potential growth marks were identified. A similar structure of highly remodeled bone tissue was identified in long bones of extant sloths. Extant armadillos and anteaters, on the other hand, showed a lower degree of organization. Primary reticular bone tissue was very common, but some areas with only longitudinal vessels occurred. Bone compactness of humeri and femora were correlated, with generally higher values for humeri. Within-group variation in bone compactness was high and no clear pattern coupled with locomotion could be detected. In general, values were highest in anteaters for both humeral and femoral bone compactness. Additionally, femoral bone compactness was higher in anteaters and sloths than in cingulates. Thus, compactness of xenarthran long bones could potentially provide some phylogenetic signal.