Camarasaurus lewisi is a species of sauropod dinosaur from the Upper Jurassic of the United States. It was named by James A. Jensen in 1988. C. lewisi was originally placed in its own genus, Cathetosaurus, but in 1996 it was reclassified as a species of Camarasaurus; most researchers since have considered it to be one of the four valid species of Camarasaurus. Two unpublished studies have since argued that the genus Cathetosaurus should be reinstated, whereas two other studies have argued that C. lewisi may be a junior synonym of another species of Camarasaurus. Description C. lewisi is the smallest species assigned to Camarasaurus; despite representing a very old individual, the holotype specimen is roughly 26% smaller than C. supremus, with a humerus long. The possible C. lewisi specimen SMA 0002 also represents a fully mature individual, but is exceptionally small, with a humerus only long. It is possible that the size difference reflects sexual dimorphism. Frank Seebacher estimated the length of C. lewisi as and mass as 11.7 tonnes, whereas Gregory S. Paul estimated the length of C. lewisi as and mass as 10 tonnes. C. lewisi was relatively long-necked compared to most specimens of Camarasaurus. In 1996, six traits were indicated distinguishing C. lewisi from other species. The bifurcated vertebrae of the neck and back have a narrow but deep cleft incising the tops of the neural spines, resulting in a V-shaped transverse profile instead of the U-shaped profile typical of Camarasaurus species. The bifurcation continues to the sacrum, instead of ending in the middle of the back as is typical of Camarasaurus. The first sacral vertebra is more strongly "sacralised" and the fifth, last, sacral vertebra is less strongly sacralised than typical in Camarasaurus. The costal plate of the sacrum is more strongly developed than typical of Camarasaurus, even compared to very old individuals of these. The ilium is rotated to the front and below, relative to the longitudinal axis of the sacrum. In the rear chevrons the rear facets make a steep angle of 60° with the horizontal plane while the front facets are placed horizontally. However, several of these characteristics may reflect the old age of the specimen, rather than distinctive characteristics of the species. It would then be a "ontogimorph". Mateus and Tschopp proposed three diagnostic characteristics for C. lewisi present in the holotype: the pelvis is rotated anteriorly, such that the pubis projects