Artículos de revistas
Bird embryos uncover homology and evolution of the dinosaur ankle
Fecha
2015Registro en:
Nature Communications | 6 : 8902 | 2015
DOI: 10.1038/ncomms9902
Autor
Ossa Fuentes, Luis
Mpodozis Marín, Jorge
Vargas Milne, Alexander
Institución
Resumen
The anklebone (astragalus) of dinosaurs presents a characteristic upward projection, the 'ascending process' (ASC). The ASC is present in modern birds, but develops a separate ossification centre, and projects from the calcaneum in most species. These differences have been argued to make it non-comparable to dinosaurs. We studied ASC development in six different orders of birds using traditional techniques and spin-disc microscopy for whole-mount immunofluorescence. Unexpectedly, we found the ASC derives from the embryonic intermedium, an ancient element of the tetrapod ankle. In some birds it comes in contact with the astragalus, and, in others, with the calcaneum. The fact that the intermedium fails to fuse early with the tibiale and develops an ossification centre is unlike any other amniotes, yet resembles basal, amphibian-grade tetrapods. The ASC originated in early dinosaurs along changes to upright posture and locomotion, revealing an intriguing combination of functional innovation and reversion in its evolution.