The origin of the tetrapod wrist revealed by 3D virtual palaeohistology

When did tetrapods acquire a wrist? Was the wrist formation a gradual process or a rapid innovation during the fin-to-limb transition? We don’t know exactly. We know that the wrist forms from the aggregation of short bones but their emergence and evolution are still unclear. Bone microanatomy and microstructure is an excellent source of developmental information to address our questions, but the rarity of fossils and the destructiveness of sectioning techniques have rendered the histological investigation impossible. In order to fill our knowledge gap on the origin of this key joint region, we propose to image the appendages of 380-300-My-old unique stem tetrapods emblematic of the so-called fin-to-limb transition. Using a multiscale approach with propagation phase-contrast synchrotron microtomography, we will be able to collect data on key fossils to draw a complete picture of this great evolutionary event at the origin of the remarkable radiation of tetrapods worldwide.