Sculptured dermal bones as osteological correlates of integumentary structure and physiology of basal tetrapods

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The physiological changes that occurred during the conquest of land by vertebrates in the Late Palaeozoic are poorly understood, since soft part preservation is exceptional in basal tetrapods. Because the integument determines major aspects in a vertebrate’s metabolism, a better knowledge of the integumentary structure in basal tetrapods will help to understand the transition from fish to tetrapod and from non-amniote to amniote. Dermal bones are well suited as osteological correlates for integumentary soft parts since they develop within the dermis and are penetrated by noumerous blood vessels, nerves, and anchoring fibres. The present project has shown that in contrast to the aquatic stem-tetrapods, metaplastic tissue and closely packed, mineralised Sharpey’s fibres are present in sculptured dermal bones of basal crown-group tetrapods. This indicates that these more terrestrially adapted animals attained a denser integument that was well integrated with the sculpture of the bone surface. The sculptural ridges protected the numerous vessels that opened to the outer bone surface. In the proposed extension, the relationships between dermal bone and the overlying integument in extant sculpture-bearing fishes, amphibians, and crocodiles will be clarified that serve as extant phylogenetic bracket of the fossil forms. In this way, the hitherto obtained implications for the skin of basal tetrapods are tested. It will be established whether there is a correlation between sculptural pattern, vascularisation of the sculptured bone surface, and presumed mode of life.