It's called a "deceptive lizard" because its bones look so much like the mosasaurus, a sea creature, and scientists thought, because it was so big, it lived part of the time in the water. They now know that isn't true.

Some scientists believe the Apatosaurus wasn't strong enough to lift its head to eat leaves off trees, simply because its neck was so heavy.

The Apatosaurus used to swallow stones to help it grind up plants in its stomach. It did not chew its food.

One set of Apatosaurus bones was first called a Brontosaurus. Now the name "Brontosaurus" is not used by scientists, who know that it was just a different type of Apatosaurus.