A Nestling Bird from the Lower Cretaceous of Spain: Implications for Avian Skull and Neck Evolution

A feathered skeleton of a Lower Cretaceous enantiornithine bird from Spain indicates that the modified diapsid skull of modern birds did not evolve until late in their evolution: Basal birds retained an essentially primitive diapsid design. The fossil provides data clarifying long-standing debates on the cranial morphology of the basalmost bird, Archaeopteryx . It also reemphasizes the notion that the early morphological transformations of birds were focused on the flight apparatus. This fossil was a nestling and suggests that early postnatal developments in the Cretaceous enantiornithine birds and those in their extant counterparts are comparable.