Deciphering the evolution of metamorphosis in amphibians through exceptional 300-million-year-old organ soft tissue preservations

Metamorphosis in extant amphibians is unique among vertebrates Its evolutionary origin remains poorly known, i.e. when metamorphosis first appeared and whether it is a derived feature of extant amphibians or whether it has been inherited from a common ancestor. The fossil preservation of soft tissues (i.e., intestines, eyes) is extremely rare. We propose to fill this gap by investigating with high resolution and contrast the exceptionally preserved 3D anatomy of some of the earliest known amphibians, discovered in a fossil site near Montceau-les-mines (France) including complete developmental sequence and soft tissues known to transform during metamorphosis. This project aims at applying synchrotron microtomography to attest changes of the intestines that could reflect a diet shift and change soft the eyes linked to different visual capacities. This comparative analysis will be crucial for understanding the evolution of metamorphosis at a critical time in amphibian evolution.