Camarasaurus was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America. Its fossil remains have been found in the Morrison Formation of Colorado and Utah, dating to the Late Jurassic epoch (Kimmeridgian to Tithonian stages), between 155 and 145 million years ago.
Camarasaurus presented a distinctive cranial profile of a blunt snout and an arched skull that was remarkably square. It likely travelled in herds, or at least in family groups.
The name means “chambered lizard”, referring to the hollow chambers in its vertebrae (Greek καμαρα/kamara meaning “vaulted chamber”, or anything with an arched cover, and σαυρος/sauros meaning “lizard”).
When the noted American paleontologist Edward Drinker Cope described Camarasaurus in 1877, he was obviously impressed by the hollow, box-like vertebrae in the neck. This feature made the neck much lighter and easier for the animal to carry, and it is this characteristic that gave the animal its name: “Chambered lizard.”
Camarasaurus was a stout, compact sauropod with a relatively short neck and short tail. The front legs were slightly shorter than the back legs. The head can be described as a bubble of air encased by thin struts of bone. Huge holes for the nostrils, eye sockets, and other skull cavities made the skull as light as possible but strong enough to withstand the bite forces from the doglike snout.
A fossil record exists of two adults and a 12.2-m-long (40 ft) juvenile that died together in the Late Jurassic epoch, around 150 million years ago (in northeast Wyoming, United States). Their bodies were assumed to be washed by a river in spate (flood) to their final resting place in alluvial mud. The scenario suggests that Camarasaurus traveled in herds or at least in family groups. At other sites, fossil camarasaur eggs have been found in lines, rather than in neatly arranged nests as with some other dinosaurs, which suggests that, like most sauropods, Camarasaurus did not tend its young.
Previously, scientists have suggested that Camarasaurus and other sauropods may have swallowed gastroliths (stones) to help grind the food in the stomach, regurgitating or passing them when they became too smooth. More recent analysis, however, of the evidence for stomach stones suggests this was not the case. The strong, robust teeth of Camarasaurus were more developed than those of most sauropods and were replaced on average every 62 days (M. D'Emic et al.), indicating that Camarasaurus may have masticated food in its mouth to some degree before swallowing. Other findings indicate that Camarasaurus spp. preferred vegetation different from other sauropods, allowing them to share the same environment without competing.
Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Griebeler et al. (2013) examined long-bone histological data and concluded that the Camarasaurus sp. CM 36664 weighed 14,247 kilograms (15.7 short tons), reached sexual maturity at 20 years and died at age 26.
Eagle et al. performed clumped isotope thermometry on the enamel covering the teeth of various Jurassic sauropods, including Camarasaurus. Temperatures of 32.4–36.9 °C (90.3–98.4 °F) were obtained, which is comparable to that of modern mammals.
The teeth were stumpy but strong – much more robust than the peglke teeth of other sauropods – and the jaws had a powerful bite. Camarasaurus was probably capable of dealing with a wider variety of tough plants, thereby giving it an advantage in mixed forests.
Camarasaurus is the most common sauropod in North America. A number of complete skeletons have been recovered, as well as numerous partial skeletons and isolated bones. Several specimens can be seen in the rocks of the dinosaur National Monument in Utah. As a result of these fossil finds, we now know more about Camarasaurus than we know about any other of the sauropod dinosaurs.
A Camarasaurus pelvis recovered from Dinosaur National Monument in Utah shows gouging attributed to Allosaurus.
In 1992, a partial C. grandis skeleton was discovered at the Bryan Small Stegosaurus Quarry of the Morrison Formation near Canon City, Colorado. This specimen preserved a partial right humerus catalogued as DMNH 2908 and associated vertebrae from the back and tail. In 2001, Lorie McWhinney, Kenneth Carpenter, and Bruce Rothschild published a description of a pathology observed on the humerus. They noted a juxtacortical lesion 25 by 18 cm wide made of bone that resembled woven fibers. Although woven bone forms in accessory dental bone, in other locations, it is a sign of injury or illness. The woven bone's "undulating fibrous bundles" were observed oriented in the direction of the m. brachialis. The lesion's fusion and lack of porosity at its near and far ends indicate the periostitis was inactive or healed. McWhinney and the other researchers argued that this injury would have been a continuous source of hardship for the animal. It would have exerted pressure on the muscles. This pressure would have compressed the muscles' blood vessels and nerves, reducing the range of motion of both the limb's flexor and extensor muscles. This effect would have hindered the mM. brachialis, m. brachoradialis, and to a lesser degree the m. biceps brachii to the lesion's position on the humerus. The researchers inferred that the inflammation of the muscles and periosteum would have caused additional complications in the lower region of the fore limb, as well. The lesion would also have caused long-term fasciitis and myosistis. The cumulative effect of these pathological processes would have moderate to severe effects on the ability of the limb to move and "made everyday activities such as foraging for food and escaping predators harder to accomplish."
The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as Barosaurus, Diplodocus, Apatosaurus, Brontosaurus, and Brachiosaurus. Dinosaurs living alongside Camarasaurus included the herbivorous ornithischians Camptosaurus, Gargoyleosaurus, Dryosaurus, Stegosaurus, and Othnielosaurus. Predators in this paleoenvironment included the theropods Saurophaganax, Torvosaurus, Ceratosaurus, Marshosaurus, Stokesosaurus, Ornitholestes, and Allosaurus, which accounted for up to 75% of theropod specimens, and was at the top trophic level of the Morrison food web. Camarasaurus is commonly found at the same sites as Allosaurus, Apatosaurus, Stegosaurus, and Diplodocus.
Other organisms in this region included bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, and several species of pterosaurs such as Harpactognathus and Mesadactylus. Early mammals present were docodonts (such as Docodon), multituberculates, symmetrodonts, and triconodonts. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.