Evolution102

Bird skulls evolved more slowly than the skulls of their dinosaur ancestors. Credit: Ryan Felice

In Evolution 101, BRT discussed the incredible skull diversity of Frogs, in this blurb its bird skull variation even though their theropod ancestors seems to have had a decided edge in that department based on recent findings.

To whit.

What the researchers found was that dinosaurs evolved 1.5 to three times faster than birds in all regions of the skull. After the mass extinction event brought the Mesozoic era to a close and ushered in the Cenozoic era, birds diversified. But they did so far more slowly than their Mesozoic dinosaur forerunners. “Their rate of morphological change declines just as they are taking off as a radiation,” Goswami says.

Why the sudden deceleration? Goswami thinks it reflects a shift in priorities for skull function. Whereas dinosaur skulls have elaborate display and fighting structures and complex feeding mechanisms that require large areas for jaw-muscle attachment, bird skulls are mostly dedicated to housing and protecting the animals’ comparatively large brain, she explains.

It all centers on flight ...

The discovery that bird skulls resulted from relatively low evolutionary rates “is essentially opposite from what we know of the rest of the skeleton,” observes Stephen Brusatte of the University of Edinburgh in Scotland, another outside expert. “Previous studies, including one of my projects, showed that bird skeletons evolved faster than nonbird skeletons. What this means, I think, is that the origin of birds was driven by rapid and remarkable changes to the skeleton: particularly turning the arms into wings for flight. The heads were less important in this transition, and they probably lagged behind the rest of the skeleton.” Early on in their evolution, birds seem to hit on a head design that worked for them, with such features as a beak, big eyes and and a large brain, he says. “Birds didn’t need to radically change any of these things in order to adapt to different niches.” Instead, Brusatte suggests, “after birds split off from other dinosaurs and went into the skies, they adapted to new niches by changing their body sizes, wing shapes and flying styles more than their heads.”

Awesome. :)