The first dinosaurs stood up straight on just two legs. Upright bipedal posture distinguishes them from other reptiles.
The ancestral dinosaur stood and ran swiftly on the three-toed feet of its long hindlimbs. Its short arms were used more for grabbing and holding than for locomotion. The earliest dinosaur could raise its head up on a long, s-shaped neck for a greater field of vision.
dinosaurs (DYE-no-sorz): reptiles that stand up straight on two hind legs with three-toed feet
New features:
- s-shaped neck for lifting up head to increase visual field; also helps balance
- large hips increase area for attachment of leg muscles
- upright, bipedal stance on three toes of hind legs; legs are positioned directly beneath the body, not splayed out to sides
- large hips increase area for attachment of leg muscles
Coelophysis (see-lo-FYE-sis)
This early dinosaur was an eight-foot-long meat-eater that roamed tropical forests in the region we now call the American Southwest. Long legs and a lightly-built skeleton made Coelophysis an agile hunter of insects and small vertebrates, including reptiles such as lizard-like Trilophosaurus.
Dinosaurs' upright posture allows them to be more continuously active than reptiles with sprawling posture. They might not run faster -- some lizards can run very quickly -- but they can run fast for longer periods of time, supported by efficient lungs and hearts.
PICTURE CAPTIONS:
- Coelophysis
- Trilophosaurus
- upright dinosaur posture
- sprawling posture
- Diagram showing common ancestry and evolution of lizards, crocodilians, and dinosaurs from organisms with two holes in skull behind eyes. Evolution of crocodilians and dinosaurs is where vocalization and breathing while running branch off.