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What Is a Dinosaur? | Anatomy & Evolution | General Behavior | Where Did They Live? | Why Did They Go Extinct?

Anatomy & Evolution
General Dinosaur Anatomy | Dinosaur Evolution

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Because dinosaurs are also craniates (within vertebrates), they have a specialized head at the front of the body. This head contains the brain, an enlarged nerve organ at the front of the spinal cord that encompasses three sensory capsules. These capsules detect light, smell, and sound, relaying this information to the brain. The skull of a dinosaur, like your own, contains specific regions to house each of these sensory functions. Dinosaurs also had specific organs associated with each sensory capsule: eyes for sight, ears for hearing, and a nose for olfaction. Specialized nerves led out from the brain to various parts of the body, the paths of which can sometimes be seen in dinosaur skull bones.

As gnathostomes, dinosaurs had hinged jaws that could open and close the mouth. The scapula or shoulder bone of the forelimb was connected by muscles to the rib cage, but the pelvis or hip bone of the hind limb was firmly attached to the backbone. Semicircular canals in the inner ear helped the animal to maintain its balance. Dinosaurs also had dermal bones (such as armor, as well as the outer skull bones), another gnathostome characteristic.

Because dinosaurs are tetrapods, their limbs had feet and hands. The forelimb was suspended on the ribcage, but the pelvis was firmly attached to the vertebral column. Among tetrapods, dinosaurs are amniotes. Thus they produced hard-shelled eggs with gas-permeable shells, which had to be laid on land. They did not have gills at any stage in their lives, and their skin was probably dry and scaly rather than moist and permeable.

As diapsid reptiles, dinosaurs had two openings in the skull behind the eye, one near the skull roof and another near the jawline. As archosaurs, they had an extra opening in the skull between the nose and eye, and another in the lower jaw.

To Learn more about how Dinosaurs are related to other animals, please visit our Tree of Life Interactive

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