Apatosaurus:  Almost everybody's favorite dinosaur is Apatosaurus which was once known as Brontosaurus, the "Thunder Lizard".

Genus Name: Apatosaurus ("deceptive lizard")
Type Species: * A. ajax (Marsh, 1877) 
Length: 69-85 feet (21-26 meters) 
Weight: 10-40 tons 
Time: 155-145 million years ago (Late Jurassic) 
Place: Colorado, Oklahoma, Utah, Wyoming 
Diet: plant-eater (herbivore)