belongs to Camarasauridae, a family of basal macronarian sauropods. It is one of four species of Camarasaurus widely regarded as valid, alongside C. supremus, C. grandis, and C. lewisi. Camarasaurus lentus has two junior subjective synonyms, Uintasaurus douglassi and Camarasaurus annae. Uintasaurus douglassi is the type species of Uintasaurus. Due to the close similarity between C. lentus and C. supremus, it has been at times debated whether C. lentus is distinct from the latter. Takehito Ikejiri has noted that, as the holotype of C. lentus is a juvenile, the features used to distinguish between different species in adults of the genus cannot be identified, and the specimen came from a part of the Morrison Formation where C. grandis is more typically found. As such, the holotype of C. lentus may actually be a specimen of C. grandis, rather than belonging to the species conventionally known as C. lentus. Paleobiology Ontogeny Camarasaurus lentus is known from several growth stages, so its ontogeny is relatively well-understood. As C. lentus grew, its neck lengthened. The extent of neural spine bifurcation may have increased with age; in the younger CM 11338, the first cervical vertebra to have a partially bifurcated neural spine is the seventh, whereas in the older YPM 1910, bifurcation begins with the fifth. The limb bones show nearly isometric growth, but become slightly slenderer with age. Paleoecology Camarasaurus lentus lived during the late Kimmeridgian and early Tithonian ages of the Jurassic in what is now the western United States. The Dinosaur Quarry of Dinosaur National Monument, one of the sites where C. lentus has been found, dates to between 150.91 and 150.04 million years ago. The range of C. lentus includes what is now Utah, Colorado, Wyoming, and possibly South Dakota. Camarasaurus lentus fossils have been found in systems tract B4 of the Morrison Formation, strata from which have been dated to times ranging from 151.88 Ma to 149.1 Ma. At this time, a large lake, Lake T'oo'dichi', covered an area around what is now the Four Corners area of the western United States. C. lentus is one of the sauropod species present at the Cleveland-Lloyd Dinosaur Quarry, a controversial site known for its dense accumulation of dinosaur bones and disproportionate abundance of the predatory theropod Allosaurus. One interpretation of the site is that it represents a drought assemblage. At the Cleveland-Lloyd Dinosaur Quarry, C. lentus has been found to coexist