The brontosaurus was believed to be a long-necked, leaf-eating, tiny-headed dinosaur. The brontosaurus is not real. (Of course, if you want to live your live as a brontosaurus lover, you have my full support. I just want you to know the truth.)
...I know. This is hard to take, but as the result of scientific discoveries since the late 80s--when my deep, abiding love for the nonexistent entity began--has proven that what you and I think of as the brontosaurus is really the apatosaurus.
At some point, during my early childhood, the brontosaurus became the brachiosaurus—which might be different than an apatosaurus; when I was little the brontosaurus and the brachiosaurus were the same dinosaur—became a brontosaurus with a bump (and sometimes nostril as a brachiosaurus) on its head:
We are left with the apatosaurus. From Wikipedia:
Apatosaurus (pronounced /əˌpætɵˈsɔrəs/), including the popular but obsolete synonym Brontosaurus, is a genus of sauropod dinosaur that lived about , during the Jurassic Period (Kimmeridgian and Tithonian ages). It was one of the largest land animals that ever existed, with an average length of 23 m (75 ft) and a mass of at least 23 metric tons (25 short tons).No one is more sorry than I, Old People.
Apatosaurus article, Wikipedia