Osteoderms in Anurans

Dermal ossifications-- osteoderms- are more common in anurans than has been gen- erally acknowledged. In the hylid Phyllomedusa bicolor osteoderms are located in the dermis, cover the dorsal surface of the head and body, and are scattered on the lateral and ventral surfaces and the limbs. Each osteoderm consists of a vascularized bony basal plate (0.1 mm thick) from which bony lamellar spines protrude into the epidermis. The dorsal body osteoderms are approximately 3 mm2 in area. Similar osteoderms are present in Phyllomedusa vaillanti and Gastrotheca weilandii. In the pelobatid Megophrys nasuta osteoderms are present in the dorsal body skin and although comparable to the osteoderms of Phyllomedusa in size and shape they are histologically very dif- ferent. Megophrys osteoderms are avascular and composed of calcified collagen bundles in an orderly three-dimensional arrangement. The leptodactylid Hylactophryne augusti also has small bony osteoderms in the skin of the dorsum. They differ from the hylid osteoderms and resemble Megophrys osteoderms in being avascular and having a matrix composed of horizontal and vertical bundles of collagen. Larger dermal bony dorsal plates are present in Lepidobatrachus and Ceratophrys (Leptodactyl- idae) and in Brachycephalus (Brachycephalidae). Anuran osteoderms are structurally different from, and not homologous with, caecilian dermal scales. Given the histological differences among the various anuran osteoderms and the taxonomic diversity (Hylidae, Pelobatidae, Leptodactylidae, and Brachycephalidae), osteoderms appear to have been independently evolved a number of times within the Anura. It is suggested that the term dermal scale be restricted to the bony scale of fishes and caecilians, and osteoderms be used to denote the dermal scutes of anurans and reptiles. Textbooks on vertebrate anatomy clearly state that amphibians, with the