Bald heads reveal dinosaur ancestry

I took the feeders down this past spring to keep the bears away and instead have been scattering black oil sunflower seeds on the broad railing and picnic table on our porch. In the summer I was doing it at dawn, but now, with the shorter days, it's closer to 6. As soon as I step out on the porch I hear the Chickadees calling to each other, announcing that breakfast has arrived. They are landing even before I am finished. In a nearby tree I hear the resident Cardinal alerting his mate. They are a little bit more cautious and wait until after I have gone back inside.

The minutes of peaceful feeding usually end with the noisy arrival of a family of Blue Jays. They are molting in late August and every year one or two sorry-looking individuals show up bald - with few feathers, or may be just a stubble on their heads. Fortunately that's only a temporary state lasting about two weeks until the feathers have regrown.

Although adult, they often look immature because their large eyes are more characteristic of chicks:

Others have more reptilian features:

The naked heads remind us that their ancestors are dinosaurs, not mammals, and that their closest living relatives are the crocodiles. They usually reach maturity within 12 weeks, but retain the large eyes characteristics of juvenile dinosaurs.

In a study published in the journal Nature on 5/27/12 examining this curious fact the authors conclude that

"We have provided a powerful new example of how heterochronic changes, paedomorphic" (retaining juvenile characteristics) "and peramorphic" (early development of adult characteristics) "were crucial in the origin and evolution of birds. We further demonstrate that these changes were driven by an extreme degree of elaboration in vision-associated areas of the brain that parallels the olfactory elaboration of mammals, and possibly by the evolution of the face into a precision grasping mechanism as the hands were co-opted for flight."

There is a very readable illustrated summary of the study in ScienceDaily: Evolution of Birds Is Result of a Drastic Change in How Dinosaurs Developed