Apatosaurus is one of the most celebrated members of the giant group of dinosaurs known as the sauropods. These animals walked on 4 huge legs and had long necks and tails which sometimes measured as long as a football pitch. During the time of the American 'Bone Wars' when paleontologists were racing to publish more and more new species of dinosaurs from the American West, an exceptionally complete Apatosaurus post-cranial skeleton was incorectly described by O.C.Marsh as Brontosaurus, meaning thunder-lizard. Soon after this publication however, it was correctly assigned to the pre-existing genus Apatosaurus when scientists resolved that it the two specimens were from the same animal.
Sauropods were the largest land animals that ever lived on our planet and their leg bones can be impressively long. Our apatosaur femur drives this point home, measuring over 6' in length.