The evolutionary origin of metamorphosis in tetrapods: clues from palatal osteohistology in temnospondyls

The aim of this project is to study the evolutionary origin of metamorphosis in the amphibian lineage. Lissamphibians (i.e., salamander, frogs, and caecilians) are the only extant tetrapods that metamorphose, but it is still not clear whether metamorphosis is unique of this clade or if it evolved during the Palaeozoic in their putative ancestors, the dissorophoid temnospondyls. To date, metamorphosis cannot be inferred unequivocally for this fossil group because of the lack of complete ontogenetic series. In this project, we propose to infer metamorphosis in temnospondyls in a novel way: testing whether their palatal bones show histological signals of remodelling, a process that occurs in pterygoids and vomers during metamorphosis in salamanders. To do so, we propose to study using synchrotron x-ray imaging the ontogenetic changes in cranial bones at the histological level in a range of salamander taxa with different life cycles and compare them to key temnospondyl species.