Maraapunisaurus

thumb|Comparison of Maraapunisaurus (left) with the rebbachisaurids Rebbachisaurus (center) and Histriasaurus (right). thumb|Neural spine of Maraapunisaurus as drawn by E.D. Cope with parts labeled. The key rebbachisaurid features are the spinopostzygapophyseal laminae that extends dorsomedially from the postzygapophyses to join and form the postspinal lamina, and the pneumatic neural spine and arch. Other rebbachisaurid features include the rather simple ("attenuated") structure of the neural spine and the respective inclinations of the centrodiapophyseal lamina and the postzygodiapophyseal laminae. Maraapunisaurus is a genus of sauropod dinosaur from the Late Jurassic Morrison Formation of western North America. It contains one species, Maraapunisaurus fragillimus, which was originally named Amphicoelias fragillimus. It has sometimes been estimated to be the largest dinosaur specimen ever discovered. Based on surviving descriptions of a single fossil bone, scientists have produced numerous size estimates over the years; the largest estimate M. fragillimus to have been the longest known animal at in length with a mass of . However, because the only fossil remains were lost at some point after being studied and described in the 1870s, evidence survived only in contemporary drawings and field notes.

More recent studies have made a number of suggestions regarding the possibility of such an animal. One analysis of the surviving evidence, and the biological plausibility of such a large land animal, has suggested that the enormous size of this animal were over-estimates due partly to typographical errors in the original 1878 description. More recently, it was suggested by paleontologist Kenneth Carpenter that the species is a rebbachisaurid, rather than a diplodocid sauropod. He therefore used Limaysaurus instead of Diplodocus as a basis for size estimates. This resulted in a smaller, animal, and he dismissed the idea that there must have been typographical errors. Since then, somewhat larger size estimates have been made, placing Maraapunisaurus at 70 ―120 tons in mass and long, which still makes Maraapunisaurus the third longest animal to have ever lived behind Bruhathkayosaurus and Supersaurus specimen BYU 9024, as well as having the tallest and largest neural spine out of any animal ().