Calcified Integumentary Structures in Anurans

Although often overlooked, the integument of many vertebrates is reinforced by skeletal elements. In anurans these calcified structures include osteoderms, bone‐rich elements, and the lamina calcarea, a calcified, acellular layer that lacks collagen. We investigated the histology of anuran integument with a special focus on taxa developing skeletal elements. When present, the lamina calcarea forms a thin but discrete horizon at the interface between the superficial and deep dermis. This layer is rich in glycosaminoglycans (GAG) and is structurally unlike bone and cartilage. In contrast, anuran osteoderms are composed of cellular bone with limited GAG. A partial ontogenetic series of the tree frog Phyllomedusa bicolor provides the first details of anuran osteoderms development. In P. bicolor osteoderm development begins as a cluster of small calcified centres localized over the head. With continued body growth, osteoderms become larger in size and become distributed across the dorsal and ventral surfaces of the body, and across the limbs. The leaf litter frog Brachytarsophyrys cariensis is unusual in developing both osteoderms (on the dorsal body surface) and a lamina calcarea (on the ventral body surface). Our data shows that anuran integument has the ability to form skeletal elements and suggests that these elements arose in multiple anuran lineages. Grant Funding Source : NSERC