Tuesday, June 24, 2008

Dinosaur Behavior

There are many aspects of dinosaur biology that will always remain a mystery, because so many parts of these animals and many of their behaviors are not preserved in fossils. In most cases, all that remains are a few bones and teeth. Consideration of other fossils, such as footprints, eggs, and fossilized droppings (coprolites) provide additional clues.

How intelligent were the dinosaurs? The traditional theory is that they were very stupid. There is a strong connection between the size of an animal's brain compared to the size of its body, and its level of intelligence.Some dinosaur skulls have preserved hollows where the brain once was, revealing the approximate size and shape of the brain. In other cases, a lump of rock formed inside the fossilized skull, taking on the size and shape of the brain.The proportion of brain-body size for most dinosaurs is roughly the same as it is for living reptiles.

Stegosaurus had the smallest known brain for its body size of any dinosaur. It weighed 2 tons when it was full grown, but its brain weighed only 3 ounces and was about the size of a golf ball!

The brain of Stegosaurus was only 1/25,000th of the weight of the whole body (in a human, it is 1/50th).  It was once thought that this dinosaur must have had a second brain in its tail to control the rear half of its body.

Small and medium sized meat-eaters had the largest brains, and were therefore the most intelligent. Troodon and Velociraptor were probably about as intelligent as modern rats or parrots.

No fossils have been found of dinosaur eyes, because eyes are soft and squishy and therefore do not preserve easily. Most knowledge of their vision comes from studying the size and position of the hollows (called orbits) in the skulls where the eyes were located. Small-eyed dinosaurs could probably see well only during daylight. The orbits in dinosaur skulls are also similar to those of modern reptiles.

Many plant-eating dinosaurs had eyes on the sides of their heads, giving them good peripheral vision. Small meat-eaters had large eyes in the front of the face pointing forward, allowing them to see detail and judge distances.

The skeletons of baby dinosaurs reveal that their leg bones were not fully developed when they hatched. They therefore must have been confined to their nests for the first weeks of life. Their parents would supply them with food, water, and protection. In some species, the parents would also teach their young how to fight and hunt for prey.
Images of dinosaurs as good parents with family units have redefined how we think about these creatures: not as cold-blooded savages but as gentle creatures with caring instincts for their children. Perhaps much more "intelligent" than was originally supposed.

My previous posts on dinosaurs are available here.

There are a lot of great books on the subject. My favorite is National Geographic Dinosaurs, by Paul Barrett. Also quite good is the Illustrated Encyclopedia of Dinosaurs, by Dougal Dixon. The subject is universally interesting: invest in a good book for yourself or as a gift.

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