The tail was held above the ground during normal locomotion.Apatosaurus had a single claw on each forelimb and three on each hindlimb.
To complete the mount, sauropod feet that were discovered at the same quarry and a tail fashioned to appear as Marsh believed it should – but which had too few vertebrae – were added.
In addition, a sculpted model of what the museum thought the skull of this massive creature might look like was made.
Marsh distinguished the new genus Apatosaurus from Atlantosaurus on the basis of the number of sacral vertebrae, with Apatosaurus possessing three and Atlantosaurus four.
Two years later, Marsh announced the discovery of a larger and more complete specimen at Como Bluff, Wyoming.
To lighten its vertebrae, Apatosaurus had air sacs that made the bones internally full of holes.
Like that of other diplodocids, its tail may have been used as a whip to create loud noises. Apatosaurus lived about 152 to 151 million years ago (mya), during the early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, and Utah in the United States.The cervical vertebrae of Apatosaurus are less elongated and more heavily constructed than those of Diplodocus, a diplodocid like Apatosaurus, and the bones of the leg are much stockier despite being longer, implying that Apatosaurus was a more robust animal.The femora of Apatosaurus are very stout and represent some of the most robust femora of any member of Sauropoda.The tibia and fibula bones are different from the slender bones of Diplodocus but are nearly indistinguishable from those of Camarasaurus. The foot of Apatosaurus has three claws on the innermost digits; the digit formula is 3-4-5-3-2.He gave this specimen a new name based on the conventions of his age and the relatively sparse fossil record available at that time.