The term "brontosaur" is being used here informally to refer to the dinosaurs known scientifically as sauropods (soar-oh-pods). Since Brontosaurus is a famous example of the dinosaurs belonging to this group (and is known to virtually everybody) it was felt that the term "brontosaur" would be more accessible to readers who are not yet knowledgeable amateurs in the science.
Brontosaurs (sauropods) were the giants of the dinosaur world. They had huge bodies, tree-like limbs, very long necks, and (comparatively) small heads. The teeth were generally weak and peg-like, indicating a vegetarian diet and the nostrils often opened up onto the top of the head.
Owing to their size, it was once supposed that brontosaurs spent most, if not all of their lives, partially submerged in water in order to support their weight. More recent interpretations, however, have brontosaurs walking freely about on land. Brontosaurs were quadrupeds (walked on all four legs) although it has been imagined by some that they could have reared up onto the hind legs occasionally.
Brontosaurs arose from primitive ancestors known as Prosauropods ("Pro" = before). A well-known example of this is Plateosaurus (Plat-ee-oh-soar-us), from the Late Triassic of central and northern Europe. Plateosaurus was about 16 to 33 feet long and probably was capable of walking on two feet as well as on all fours. Like its giant relatives, it had a long, pliable neck.
The navigation bar to your left will take you to pages that describe individual sauropod dinosaurs.