Why do we show a bird even though we have no fossils?

painting of a Cretaceous bird

Cretaceous bird. Click to zoom.

We know birds were widespread during the Cretaceous because bird fossils have been found in Early Cretaceous and older rock at sites around the world, including sites in North America. But bird bones are delicate, and well preserved bird fossils are rare except in some unusual sites. For these reasons, scientists do not think the failure to find bird fossils in the Cretaceous deposits near Washington, D.C. is evidence that there were no birds here.