Camarasaurus lentus is an extinct species of sauropod dinosaur that lived during the Jurassic period in what is now the western United States. It is one of the four valid species of the well-known genus Camarasaurus. C. lentus fossils have been found in Wyoming, Colorado, and Utah. It is the species of Camarasaurus found in Dinosaur National Monument and the middle layers of the Morrison Formation. Camarasaurus lentus is among the best-known sauropod species, with many specimens known. A juvenile specimen of C. lentus, CM 11338, is the most complete sauropod fossil ever discovered. Description Like other sauropods, Camarasaurus lentus was a large, long-necked quadruped. It closely resembled other species of Camarasaurus in its anatomy, and in particular was very similar to C. supremus. It was of moderate size for the genus, being similar in size to C. grandis, 20% smaller than C. supremus, and slightly larger than C. lewisi. Gregory S. Paul estimated its length as and mass as 15 tonnes. The skull of C. lentus was typical for Camarasaurus; distinguishing traits between the skulls of different Camarasaurus species are not known. The anterior dorsal vertebrae of C. lentus have low, broad neural arches, similar to C. supremus but unlike the taller, narrower anterior dorsal neural arches of C. grandis. The anterior caudal neural spines of C. lentus lack the abrupt, T-shaped expansion found in other species of the genus. The pelvis of C. lentus is rotated relative to the sacrum so that the preacetabular blade of the ilium points slightly downward, as in C. lewisi, but seemingly unlike C. supremus. C. lentus may exhibit sexual dimorphism in the structure of its dorsal vertebrae. History of study The holotype specimen of Camarasaurus lentus was collected from Quarry 13 at Como Bluff, Wyoming, and stored at the Peabody Museum of Natural History under the catalog number YPM 1910. The specimen consisted of a partial posterior skull, mandibles, and the majority of the postcranial skeleton, the most complete Camarasaurus skeleton found during the Bone Wars. In 1889, Othniel Marsh described it as a new species, which he named Morosaurus lentus. The skeleton was later mounted in the Peabody Museum Hall in the 1930s, and remained mounted until the 2020s. Marsh used the name Morosaurus for many species now assigned to Camarasaurus. Camarasaurus had been named by his rival Edward Drinker Cope, and the two genera were recognized as synonymous in the