By Sean Henahan, Access Excellence

An international team of scientists working in the Spanish Pyrenees uncovered the fossilized remains of a bird hatchling dating to the Lower Cretaceous, approximately 130 million years ago. The researchers believe the bird hatchling falls between the very early Archaeopteryx (approximately 150 million years old) and the more modern fossil birds Hersperonis and Ichthyornis, both of which are approximately 85 million years old. The four inch long  hatchling is thought to be a new bird species classified as an Enantiornithes (a member of a diverse group of birds that were capable of flight and that arose in the Cretaceous Period).

Discoveries during the last seven years have more than tripled the number of  recognized early bird species. Nonetheless, the understanding of the evolution of the modern bird skull has not advanced significantly since the first complete fossil bird skull was found a century ago. The new fossil was found in a remarkably good state of preservation, particularly of the head and neck.

The discovery is already providing new information about the skull anatomy of early birds, and is shedding new light on the skull of Archaeopteryx, the earliest bird ever discovered. For example, the skull of this new hatchling contains teeth, which early birds shared with their reptile antecedents, but modern birds have since lost. In addition, openings surrounding the hatchling's braincase are larger than those of modern birds. This could indicate that its skull muscles were very different from modern birds and were almost fully reptilian. This also suggest that the hatchling's brain would have been significantly smaller than that of modern birds.

The hatchling specimen also include well-preserved  neck, wings, shoulders, and sternum sections, along with  evidence of feathers. The shoulder and wing reveal advanced anatomical features, suggesting that this bird had a much better mastery of flight than Archaeopteryx. This also reinforces the idea that the development of flight took precedence over any other anatomical system in early bird evolution, and that birds retained a skull very similar to that of a meat-eating dinosaur even after they evolved a sophisticated flight capacity, notes Luis Chiappe, from the American Museum of Natural History.

Also of interest, the neck and wing bones, and the area near where the jaw attaches to the skull, all display clusters of tiny holes, very similar to the pattern found in the nestlings of modern birds. This suggests the hatchling grew steadily and rapidly while young, like modern birds. The researchers believe that the bird would have grown more slowly were it to have reached adulthood, as previous research has indicated that, unlike adult, modern birds, primitive birds may have matured slowly and experienced seasonal growth cycles.

The combination of both advanced and primitive physical characteristics exhibited by the new hatchling fossil     provides a window onto the evolutionary transition between theropods and birds and provides further evidence for the position that modern birds are in fact short-tailed, feathered descendants of meat-eating dinosaurs, notes Chiappe.

The research appears in the June 6, 1997 issue of Science.