You learned about dinosaurs in school.
Maybe you have seen them in a museum.
But how much do you really know about these animals? Were dinosaurs just big reptiles? For years, scientists thought dinosaurs were big, dumb, and cold-blooded -- in other words, just giant reptiles.
Some dinosaurs were huge.
But many were about the size of modern-day birds or dogs.
Were dinosaurs warm- or cold-blooded? Paleontologists are not sure.
But they believe some were intelligent.
Of course, no dinosaur was as smart as a human or even a monkey.
However, some smaller dinosaurs, like the two-meter (six-foot) Troodon, had fairly large brains.
Was Tyrannosaurus rex a powerful predator? Some scientists think the opposite is true.
In the movies, T.
rex is often a speedy giant, but in fact, this dinosaur could not run very fast.
Physically, it was too large.
In reality, T.
rex probably moved as fast as an elephant.
Also, T.
rex had very small arms.
Without strong legs or arms, this dinosaur probably wasn't a powerful hunter.
It may have been a scavenger instead, only eating animals that were already dead.
Did an asteroid kill the dinosaurs? An asteroid hit Mexico's Yucatan Peninsula about 65 million years ago.
It created a 180-kilometer (110-mile) wide crater called "Chicxulub.
" M any believe this asteroid caused the extinction of the dinosaurs.
But even before this, dinosaurs were already dying out around the world, for many reasons.
At the end of the Cretaceous period the global climate was changing: the Earth's temperature was getting colder.
Are all dinosaurs now extinct? Dinosaurs completely disappeared about 65 million years ago.
However, scientists believe modern-day birds are descendants3 of certain dinosaurs.
If this is true, then dinosaurs' relatives are still walking and flying among us!