^Sanz, José L.; Chiappe, Luis M.; Pérez-Moreno, Bernardino P.; Buscalioni, Ángela D.; Moratalla, José J.; Ortega, Francisco & Poyato-Ariza, Francisco J. An Early Cretaceous bird from Spain and its implications for the evolution of avian flight. Nature. 1996, 382 (6590): 442–5. doi:10.1038/382442a0.