 |
 |
 |
 |
 |
 |
|
|
|
• Evolutionary Essentials
Birds Emerge
Dinosaurs are the ancestors of birds. The first dinosaurs walked on Earth around 230 million years ago. Over time, they became dramatically diverse. One group, called theropods (THAY-ro-pods), were the only group of carnivorous (meat-eating) dinosaurs. Birds are theropod dinosaurs.
We know birds are dinosaurs because:
 |
Birds have the defining dinosaur feature: hipbones with openings in the sockets.
|
|
When scientists look closely at bird skeletons and dinosaur skeletons, they count more than 100 features in common.
|
 Specifically, we know birds are theropods (the dinosaur group that also includes Tyrannosaurus) because among dinosaurs, birds share the most features with certain theropods.
One thing sets birds apart from their closest dinosaur relatives: their forelimbs are longer than their hind limbs. And longer forelimbs make better wings.
Scientists have two theories about how flight might have evolved in dinosaurs:
|
Bird ancestors were agile runners, and feathered, flapping arms provided lift as they leapt to catch prey.
|
|
Bird ancestors were tree climbers, and they glided to the ground or from tree-to-tree aided by wing-like arms.
|
To learn more about the relationship between birds and dinosaurs, meet Dr. Pete Makovicky in our Featured Scientists section.
Or continue to Flowering Plants Emerge. >>
|
|
|
|
|
|
