Recent research from the University of Chicago and the University of Missouri shed new light on how the evolution of skull flexibility in dinosaurs led to the diverse array of modern birds we see today. The research team, including graduate student Alec Wilken and Associate Professor Casey Holliday, Ph.D., studied how skulls, jaw muscles, and feeding mechanics changed during the transition from dinosaurs to birds for over ten years.
The team performed computed tomography scans of fossils and skeletons of modern birds and related reptiles, such as caimans and alligators, to create 3D models. These scans allowed them to calculate the mechanics of the skulls and jaws in action. "We see this cascade of changes that happened along the dinosaur to bird transition," Holliday said.
One of the main differences between modern birds and other animals is cranial kinesis—the ability to move different parts of the skull independently—which allows birds to move their upper beaks relative to their braincases. "Cranial kinesis allows modern birds to enlarge their palates, enabling them to eat a wider variety of foods and use their beaks as multifunctional tools," the researchers found.
As brain and skull sizes increased in non-avian theropod dinosaurs, the muscles shifted to different positions, allowing the palate to separate and gain mobility—a characteristic that gave modern birds an evolutionary advantage by affecting the mechanics of their joints. "A large part of it hinges upon when birds evolved a relatively large brain. Just like in humans, bigger brains drive a lot of changes in the skull," Holliday stated.
The extra torque from cranial kinesis helps birds crack nuts and seeds. "In some ways, the beak functions like a surrogate hand, but being able to move the palate around while eating is also mission critical to helping them acquire food and survive," Wilken said.
However, this flexibility makes it much more difficult to determine how the pieces of their skulls work together. "You also have to think about how muscles pull on the joint, what kind of rotation they cause, and how other joints in the head limit the mobility," Wilken explained. "We can reconstruct the joint and look at it from all angles, but that doesn't mean you know how it moves," he added.
"I think cranial kinesis may become a key distinction between modern birds and their more dinosaur-like ancestors," Holliday believes, according to Scientias. As paleontologists discover more about dinosaurs, the dividing line between them and modern birds becomes murky. "Scientists used to think feathers were the key distinction between dinosaurs and birds, but now we know that many true dinosaurs also had feathers," the researchers noted.
The similarities between modern birds and small theropod dinosaurs like velociraptors are striking, blurring the line between dinosaurs and modern birds. "Birds are technically dinosaurs and are descended from them," the study pointed out. Flight evolved more than once among different dinosaur species, and many well-known dinosaurs could fly.
The article was written with the assistance of a news analysis system.