Fossils of those avians that gave rise to the modern bird lineage "are relatively rare in the Cretaceous," explains Matthew Lamanna of the Carnegie Museum of Natural History, co-author of a paper detailing the finds, published today in Science. But "when we mapped ecology onto our evolutionary tree, a pattern became apparent that species leading up to modern birds are mostly aquatic," Lamanna notes.
Excavators spent years splitting mudstone to find the Gansus remains. "[It was] like turning the pages of a book," Lamanna says. They were rewarded, however, with five exquisitely preserved skeletons of the ancient bird. The fossils even reveal impressions of feathers, webbed feet and other rare details, though none of the remains include a skull.
During Gansus's time, a group of birds called the Enantiornitheans--known as opposite birds because their wing joints are reversed compared to their modern relatives--dominated the skies. But the opposite birds perished along with the dinosaurs 65 million years ago. How Gansus's group--the ornithurans--persevered remained to be discovered. "It's hard to answer this question just based on bird fossils," says lead author Hai-lu You of the Chinese Academy of Geological Sciences. "We need more information on the paleoclimate."
The scientists also need more of G. yumenensis. "Gansus likely behaved much like its modern relatives, probably eating fish, insects and the occasional plant," says co-author Jerald Harris of Dixie State College of Utah. "[But] we won't have a definitive dietary answer until we find a skull."