HISTORIA NATURALNA OSTEODERM I INNYCH SKOSTNIEÑ ORAZ ZWAPNIEÑ SKÓRNYCH CZWORONOGÓW – STRUKTURA, ROZWÓJ, FUNKCJA I EWOLUCJA.

The skin of many tatrapods is supported by bone structures termed osteoderms. Osteoderms were present in the skin of the first tetrapods that appeared in the Devonian, and were inherited after their fish ancestors. During evolution, osteoderms were lost in many tetrapod lineages. They also appeared de novo several times, for examples, at least five times in amniotes. Osteoderms are present in six families of anuran amphibians, where they are located mainly on the dorsal side of the body. Bony structures also support skin of crocodiles and lizards. Osteoderms were highly developed also in ankylosaurs and stegosaurs, as two lineages of dinosaurs. Skin bones also form the turtle carapace and the armor of extinct placodonts. Among synapsids, osteoderms were present in two Permian species, and among mammals only in extant armadillos and extinct glyptodonts and ground sloths. Osteoderms were lost in such tetrapods as snakes, amphisbaenians, pterosaurs and birds, and most of amphibians and mammals. Osteoderms probably gave rise to gastralia, i.e. the abdominal ribs present in crocodiles, tuatara and many extinct amphibians and reptiles, that protect the guts from damage. In addition to osteoderms, in the skin of many modern amphibians, calcifications, such as lamina calcarea and dermal scales in Apoda, are present. Such calcifications do not contain bone tissue and therefore are not classified as osteoderms, but may have developed through their reduction. Comparative analysis reveals that osteoderms are a plesiomorphic feature of tetrapods, and their loss and reappearance make osteoderms a suitable subject of studies on evolutionary plasticity. [ABSTRACT FROM AUTHOR]