Some "Non-Avian Feathered Dinosaurs" May Have Been Birds

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.

An animal like Jinfengopteryx elegans


..may have had a lot more in common with birds like this ostrich

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

UC Berkeley's J. Lee Kavanau, the author of the paper, argues that there is ample evidence supporting that troodontids and oviraptorids were secondary flightless birds. These birds, like today's ostriches and emus, lost their ability to fly, but retained their feathers.

"This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits," Kavanau writes. "Because ratites also are secondarily flightless and tinamous are reluctant, clumsy fliers, the new evidence strengthens the view that troodontids and oviraptorids were secondarily flightless."

He also points out that "secondary flightlessness apparently favors paternal care of clutches of large, abundant eggs." That's been observed for both the "non-avian theropods" and today's flightless birds. A single ostrich egg, for example, can weigh around 3 pounds and is equivalent to about 24 chicken eggs.

Fossilized eggs aren't that uncommon, so studies on them, along with evidence on how they were cared for by their parents, could provide clues as to when the first actual birds emerged. It's interesting to me that troodontids and oviraptorids exhibited relatively sophisticated parenting, with males helping out. It's thought that the earliest eggs from bird or bird-like animals enjoyed only maternal care, with the co-parenting emerging later.

Birds and avian precursors could therefore have been around much earlier than presently believed. As it stands, the world's first known bird is thought to have been Archaeopteryx, which lived about 150 million years ago.