Earliest Birds May Have Been Aquatic

Fossils from China's Gansu Province have shed new light on the early evolution of birds. The fossils show an bird-like species named Gansus yumenensis that lived about 110 million years ago, in the late Cretaceous. Gansus is only about 10-15 million years younger than feathered dinosaurs like Dilong paradoxus.

Artist's rendering of Gansus yumenensis

Gansus yumenensis lived most of its life in water, similar to loons, grebes, diving ducks, and alcids. It shares much of its bone structure with modern birds, and it could certainly fly.

Harris says Gansus shares many skeletal features with modern birds, including the knobby knees characteristic of underwater swimmers like loons and grebes. Moreover, he says, the preserved skin of the webbed feet shows the same microscopic structure seen in aquatic birds today.

"It was unexpected to find a bird this advanced in rocks this old," Harris said. "It tells us that the anatomical features we use to characterize modern birds evolved very quickly."

According to the researchers, Gansus is the oldest clearly established member of the subclass Ornithurae, the group most closely related to modern birds.

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Most fossil birds dating so far back belong to a different evolutionary lineage called opposite birds. The name stems from the fact that bones in their shoulders and feet fit together opposite from the way seen in birds today.

Opposite birds made up the dominant bird group of the Cretaceous Period (145.5 to 65.5 million years ago). They disappeared along with the dinosaurs when that period ended, leaving no modern descendants.

The most likely scenario now seems to be that most avian forms died at the end of the Cretaceous but that certain aquatic birds like the Gansus species survived. Modern birds - from ducks to gamebirds to songbirds - then evolved from these aquatic roots. Most of this early lineage has yet to be established, but it will be fun to watch where the bones lead us.