NEW EMBRYOLOGICAL AND PALEONTOLOGICAL EVIDENCE SHEDS LIGHT ON THE EVOLUTION OF THE ARCHOSAUROMORPH ANKLE

BONA P; EZCURRA M.D.; FERNANDEZ BLANCO M. V.

BRISBANE

Congreso; 79TH SVP ANNUAL MEETING; 2019

SOCIETY OF VERTEBRATE PALEONTOLOGY

The homology and evolution of the archosaur ankle is a controversial topicthat has been deeply studied using both fossil and extant evidences. In stemarchosaurs,the astragalus and calcaneum form the ancestral proximal tarsusand a single ossification composes the centrale series. In more recent stemarchosaurs,the centrale is incorporated to the proximal row contactinglaterally the astragalus. This bone is subsequently lost as an independentossification before the split between birds and crocodyles, but theevolutionary fate of this element remains mostly unexplored. Here, wecombine embryological and paleontological data and morphogeometricanalyses to test the hypothesis of loss of the centrale or, alternatively, itsincorporation into the archosaurian astragalus. Our results support that thecentrale has been incorporated into the archosaur astragalus and contradict thepresence of a tibiale in bird embryos. The latter bolsters previousembryological studies that have concluded that the tibiale never develops inamniotes.