The diplodocus is an extinct genus of the diplodocus sauropod dinosaur-a great, long-necked animal with a whip-like tail and four limbs. Its front limbs are shorter than the hind limbs, creating a mainly horizontal posture. Diplodocus remains are among the most easily identifiable and well studied dinosaur fossils found in the middle to upper Morrison Formation, which was formed about 154 to152 million years ago during the late Jurassic period in the geological timescale. This specimen, excavated in the summer of 2001, is 145 million years old and was collected on private lands in the Big Horn Basin.