34 - Histological Diversity of Lizard Osteoderms and the Identification of a Novel Skeletal Tissue

Poster Board Number: 34
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Co-authors:

Catherine Williams - Aarhus University; Arkhat Abzhanov - Imperial College London; susan Evans - University College London; Anthony Herrel - Muséum national d'histoire naturelle; Loïc Kéver - Muséum national d'histoire naturelle; Alexander Kirby - University College London; Arsalan Marghoub - University College London; mehran Moazen - University College London; Shreya Rai - Imperial College London; Ed Stanley - Florida Museum of Natural History; Matthew Vickaryous - University of Guelph

Abstract Body :Osteoderms are bone-rich elements that form within the dermis of various vertebrates including many species of lizard. Although lizard osteoderms are known to vary in size, shape, and body-wide distribution, details of their histological composition remain poorly understood. Here, we characterized the histological diversity of osteoderms from representative members of the lizard groups Gekkota (geckos), Scincomorpha (scincids, cordylids, gerrhosaurids), and Anguimorpha (anguids, Shinisaurus, helodermatids). For most lizards, osteoderms are primarily composed of bone. This includes taxon-specific contributions of organized bone (lamellar plus parallel-fibred bone), woven-fibred bone, and Sharpey-fibred bone. In addition, we determined that multiple unrelated lizard genera also develop a highly mineralized, collagen and cell-poor tissue located on the superficial-most surface of the osteoderm. This so-called capping tissue was previously considered restricted to only a handful of species. Like bone, capping tissue demonstrates taxon-specific histological variability. Although it has been likened to enamel on the basis of hardness, we show that capping tissue is capable of remodeling. Further, the histology of capping tissue demonstrates taxon-specific variability. We propose that capping tissue is a novel skeletal tissue type, and predict that for some species the composite structure of lizard osteoderms evolved for impact resistance.