New embryological and palaeontological evidence sheds light on the evolution of the archosauromorph ankle

BONA, PAULA; EZCURRA, MARTÍN D.; FERNANDEZ BLANCO, MARÍA VICTORIA

Brisbane

Encuentro; 79th Annual Meeting of the Society of Vertebrate Paleontology; 2019

The homology and evolution of the archosaur ankle is a controversial topic that has been deeply studiedusing both fossil and extant evidences. In stem-archosaurs, the astragalus and calcaneum form theancestral proximal tarsus and a single ossification composes the centrale series. In more recent stemarchosaurs,the centrale is incorporated to the proximal row contacting laterally the astragalus. This boneis subsequently lost as an independent ossification before the split between birds and crocodyles, but theevolutionary fate of this element remains mostly unexplored. Here, we combine embryological andpalaeontological data and morphogeometric analyses to test the hypothesis of loss of the centrale or,alternatively, its incorporation into the archosaurian astragalus. Our results support that the centrale hasbeen incorporated into the archosaur astragalus and contradict the presence of a tibiale in bird embryos.The latter bolsters previous embryological studies that have concluded that the tibiale never develops inamniotes.