So called "non-avian theropod" dinosaurs from the Cretaceous had feathers, nests, laid eggs and roosted like birds. If they were so much like birds, why don't we just say they were birds?

A paper in the February issue of Medical Hypotheses argues that these "dinosaurs" could very well, in fact, have been birds. The group includes what are now called troodontids and oviraptorids.

All birds are technically avian dinosaurs, but there's still controversy over exactly how and when the first actual birds emerged.