Members of Stegosauria (steg-oh-SAWR-ee-uh) were quadrupedal herbivores
with rows of plates running down their backs and spikes upon their tails.
The spikes were probably useful in discouraging predators; a stegosaur
could maneuver itself so that it could swat at a predator with its tail.
The purpose of the plates is less clear.
One suggestion for their purpose is that they were armor against carnivores,
but as such, they would have left great areas unprotected. They may have
been “radiators,” used by stegosaurs to collect the heat of the sun in
cool weather (assuming they were cold-blooded) or to radiate it away in
hot weather. Support from this idea comes from the finding of fine grooves
in the surface of the plates, grooves that could have held a network of
blood vessels. If blood vessels did run just below the stegosaur's skin
but above the bone, the plates would not have been very effective as armor.
There are eleven known kinds of stegosaurs. The best-known of them, Stegosaurus,
has been popularized incorrectly as a having "second brain".
In fact, all stegosaurs had a node in their spinal column near the hind
legs that was probably a mass of nerves to assist in the control of their