Camarasaurus ( ) is a genus of sauropod dinosaur that lived during the Late Jurassic, between 155 and 145 million years ago, in North America. Named by Edward Drinker Cope in 1877, it contains four species: C. supremus, C. grandis, C. lentus, and C. lewisi. The name Camarasaurus means , referring to the hollow chambers, known as pleurocoels, in its cervical vertebrae. Over 530 specimens have been excavated in sedimentary rocks of the Morrison Formation, including several complete skeletons. It is among the best understood dinosaurs.
A medium-to-large sauropod, C. supremus is estimated to have been long and to have weighed 42.3 tonnes, whereas C. lentus was only around long. It was a bulky sauropod with a proportionally wide rib cage. The skull was proportionally larger and more strongly built than in other sauropods, with powerful jaws allowing for high bite forces. The teeth were spoon-shaped and formed a continuous cutting edge. It had 13–14 teeth in each side of the upper jaw and 13 teeth in each side of the lower jaw, which were rapidly replaced. Camarasaurus was named during the Bone Wars, a rivalry between paleontologists Edward Drinker Cope and Othniel Charles Marsh. Marsh assigned many species to his genus Morosaurus, including M. lentus and M. grandis, which are now assigned to Camarasaurus.
Camarasaurus is a member of the group Macronaria. Some paleontologists have grouped Camarasaurus with taxa like Tehuelchesaurus and Lourinhasaurus in the family Camarasauridae, whereas others consider it as the only member of Camarasauridae. Camarasaurus was probably a selective feeder that fed at a height of . Known specimen range from a presumed embryo to an individual that probably reached 40 years of age, one of the highest ages reported for an individual dinosaur. Camarasaurus also lived alongside dinosaurs like Stegosaurus, Allosaurus, and Brachiosaurus.
History
Discovery and naming
thumb|left|Field photograph of the first Camarasaurus specimen in 1877, which was collected by Oramel W. Lucas The first Camarasaurus bones were discovered by David Baldwin, one of Marsh's collectors, in early 1877 in [[Garden Park, Colorado|Garden Park, Colorado, near a peak now known as 'Cope's Nipple'. Baldwin found the bones while visiting the discovery site of a fossil that locals had identified as a fossil bird, and which he aimed to secure for Marsh (who later described it as Hallopus, a crocodylomorph). Neither Baldwin nor Marsh were interested in collecting the dinosaur bones. Shortly after, the same bones were discovered by the local teacher Oramel W. Lucas during a hunting trip. Lucas then wrote to Cope, who offered him payment for excavating the fossils. The name Camarasaurus means "chamber lizard", from the Greek kamara and sauros , alluding to the internal chambers of the vertebrae that, according to Cope, were "lighter in proportion to their bulk than in any air-breathing vertebrate". Lucas and his brother, Ira H. Lucas, continued to sent additional bones of the new dinosaur to Cope until 1884 that together represent most of the skeleton. The eight vertebrae originally described by Cope (the type material of C. supremus, on which the species is based on) are probably from two individuals. They are catalogued under the specimen number AMNH 5760, which also encompasses other Camarasaurus fossils discovered by O. W. Lucas.
Probably in early 1879, John A. Ryder created a life-sized drawing of the reconstructed skeleton under the direction of Cope. In 1885, the naturalist Charles Frederick Holder published a drawing of a living Camarasaurus, which might be the first life restoration of a sauropod. The neck, tail, and limbs are depicted as very slender, and the snout features a short trunk.
Morosaurus and the Bone Wars
On March 7, 1877, the railway employee William Harlow Reed found fossil bones south of Como Station, Wyoming, on a hill that would become one of the first and most important dinosaur localities: Como Bluff. Together with his colleague William Edward Carlin, Reed sent some of the bones to Marsh, including some tail vertebrae, a dorsal (back) vertebra, and two limb bones. Although Reed and Carlin had identified the bones of those of the ground sloth Megatherium, Marsh recognized their dinosaurian nature and sent his assistant Samuel Wendell Williston oversee and assist with collecting. Later in the same year, after further preparation of the fossils, Marsh moved A. grandis to Morosaurus, as M. grandis. He also named another, larger species of Morosaurus, M. robustus, based on an ilium from the same quarry. In 1878, Marsh wrote that his Morosaurus "must have been very sluggish in all its movements", and that "its brain was proportionately smaller than in any known vertebrate". Its type specimen, YPM 1910, was mounted at the Yale Peabody Museum fossil hall in 1930 and was one of the first nearly complete sauropod skeletons to be found, consisting of: the vertebral column from the second cervical to the eighth caudal, a cervical rib, the left scapula, the right coracoid, humeri, the left radius, ilia, the left ischium, the right pubis, the left hindlimb and left pes, and the right tibia. a suggestion supported by later authors. Riggs synonymized M. impar, the type species, with M. grandis and further suggested that Morosaurus and Camarasaurus were synonyms. However, the suggestion that Morosaurus and Camarasaurus were generic synonyms was not formalized until later research. In 1925, American researcher Charles W. Gilmore mistakenly synonymized C. grandis with C. impar despite the former being named first. The competition to mount the first sauropod skeleton specifically was the most intense, with the American Museum of Natural History (AMNH), Carnegie Museum of Natural History (CM), and Field Museum of Natural History (FMNH) all sending expeditions to the west to find the most complete sauropod specimen, In 1899, AMNH field workers Walter Granger and Peter Kaisen unearthed a complete Camarasaurus skull, mandible, and associated cervical vertebrae in rock layers at Bone Cabin Quarry, Wyoming, the first discovery of a nearly complete Camarasaurus skull. In 1905, a plaster skull based on the Camarasaurus skull found at Bone Cabin Quarry and based on a skull later referred to Brachiosaurus was mounted on a skeleton of Brontosaurus, In 1909, American fossil hunter Earl Douglass of the CM uncovered an extensive deposit of dinosaur fossils at what is now the iconic Dinosaur National Monument near Jensen, Utah. In 1914 during excavations at the Monument, Douglass unearthed a nearly complete skull and skeleton of a juvenile C. lentus still preserved in articulation. In 1925, this skeleton was then described by Charles W. Gilmore who supported the claim that Morosaurus is a synonym of Camarasaurus, a position supported by other authors. The generic name Cathetosaurus lewisi comes from the Greek κάθετος (kathetos meaning "vertical"), in reference to its supposed ability to stand upright, and (' meaning "lizard"), and the species name is in honor of Arnold D. Lewis, a fossil preparator and field worker. In 2013, paleontologists Octavio Mateus and Emanuel Tschopp argued in a conference abstract that Cathetosaurus is a distinct genus, and New Mexico, extending the northeastern and southern range of the genus. The New Mexican remains were found in the Summerville Formation, indicating Camarasaurus lived outside of the Morrison Formation. Compared to other sauropods, it was relatively bulky with a wide ribcage. The neck and tail were comparatively short and the skull large. Due to its relatively long forelimbs, it was slightly taller at the shoulders than at the hips.
Skull
thumb|C. supremus skull
The skull was larger and more strongly build than in other sauropods, with massive upper and lower jaws. As in the contemporary Brachiosaurus, the (nostril) was enlarged, resulting in an arched forehead. but the skull of Camarasaurus was more rounded and short-faced. When viewed from above, the snout was rounded and slightly tapering, different to the rectangular snout of Diplodocus. The skull was almost rectangular when viewed from the back and higher than wide.
Postcranium
thumb|Forefoot (above) and hind foot (below) skeletons of the specimen "E.T."
The vertebral column consisted of 12 cervical (neck), 12 dorsal (back), and five sacral (hip) vertebrae. The tail was composed of 53 caudal vertebrae the two specimens that preserve a complete tail (CM 11338 and GMNH 101). Most of the volume of the dorsal and cervical vertebrae was made up by air sacs which were connected to the lungs. These air sacs filled extensive excavations in the vertebrae that gave Camarasaurus its name (). The cervical and dorsal vertebrae were (concave at the rear and convex at the front) and had large excavations on their sides called . The upper end of the shoulder blade was expanded. In the hip, the pubis was massive, while the shaft of the ischium was slender, curved, and its end was not expanded. The articulation surface between the pubis and ischium was long. Such a fleshy pad was absent in the forefoot, as shown by skin skin impressions preserved close to the palmar (rear) surface of the metacarpals of the Camarasaurus specimen SMA 0002 ("E.T."). The skin impressions also indicate that the second to fourth fingers of the forefoot were together wrapped in tissue. Patches of skin impressions are also preserved on the hind limbs of "E.T.", where they mostly show hexagonal scales that were between in diameter. One year later, with the description of Amphicoelias, Cope used the families Camarasauridae and Amphicoelidae, the former showing opisthocoelous vertebrae (vertebrae that are concave at the back) and the latter amphicoelous vertebrae (vertebrae that are concave on both ends). Also in 1877, Marsh named the genus Morosaurus, which he placed in the Atlantosauridae, together with his genera Atlantosaurus and Apatosaurus. Marsh later classified Morosaurus in a sauropod family of its own, Morosauridae.
Camarasauridae has historically been in wide use. For example, in a 1990 review, John Stanton McIntosh recognized two subfamilies within the family: Camarasaurinae, containing Camarasaurus, Aragosaurus, Euhelopus, and Tienshanosaurus, and Opisthocoelicaudiinae, containing Opisthocoelicaudia and Chondrosteosaurus.
Since 1998, Camarasaurus is generally classified as a basal (early diverging) member of the sauropod group Macronaria, which is opposed to another major group of sauropods, Diplodocoidea. Within Macronaria, Camarasaurus is placed outside of the group Titanosauriformes, which comprise the majority of genera. several studies used both names, with Camarasauromorpha excluding some very basal members of Macronaria.
Below is a simplified cladogram from Pedro Mocho and colleagues (2014), which recovered Camarasauridae as including Camarasaurus, Tehuelchesaurus, and Lourinhasaurus, three genera of Late Jurassic sauropods:
thumb|260x260px|Photo of [[Edward Drinker Cope, the describer of Camarasaurus, to the right of a C. supremus cervical vertebra]]
Currently recognized species
thumb|Scale diagram of three known species of Camarasaurus
Four species are commonly recognized: C. supremus, C. grandis, C. lentus, and C. lewisi.
Other species that were previously assigned to Camarasaurus have since been moved to other genera. Morosaurus agilis was named in 1889 by Marsh on the basis on a partial skull and three vertebrae, but was described as a new genus of dicraeosaurid under the name Smitanosaurus in 2020. Morosaurus marchei was named in 1897-98 by Henri Sauvage on the basis of a tooth and an incomplete tail vertebra found in the Alcobaça Formation of Lisbon, Portugal. The vertebra was later found to be of a theropod, while the tooth is from an indeterminate macronarian sauropod. Apatosaurus alenquerensis was named in 1957 by Lapparent and Zbyszewski on the basis of a partial postcranial skeleton from the Lourinha Formation in Lourinha, Portugal. It was tentatively placed in Camarasaurus by McIntosh in 1990, but was granted a new genus in 1998, Lourinhasaurus. In 1998, Anthony Fiorillo analysed microscopic pits and scratches on the tooth surfaces and concluded that adult Camarasaurus consumed coarser foods than the contemporary Diplodocus. Juvenile Camarasaurus, in contrast, appeared to have consumed the same soft foods as adult Diplodocus. Modern herbivorous mammals with rounded snouts are often selective feeders that feed on particular plants that are less abundant but nutritious, while wide-snouted species are non-selective feeders that feed on less nutritious but abundant food in bulk. Based on this observation, John Whitlock argued in 2011 that the round-snouted Camarasaurus and Brachiosaurus were selective feeders while the square-snouted diplodocids and rebbachisaurids were bulk feeders. The sturdy construction of the skull also suggests that it was able to resist greater stresses during feeding than other sauropods. In a 2017 study, Kayleigh Wiersma and Martin Sander described a patch of soft tissue covering parts of the lower jaw and teeth of a Camarasaurus specimen nicknamed "E.T.". This impression appears to have been the animal's gums, indicating that the tooth crowns were partly enclosed by gums. Such gums may explain why sauropod tooth rows are often found intact even when isolated from the jaws. These authors also suggested that the gums could have been covered by a horny beak, which could have helped with cutting vegetation while protecting the teeth. The presence of such a beak is consistent with the presence of small foramina (openings) and grooves on the outer surfaces of the jaws that would have contained blood vessels in life. while some later authors assumed a nearly vertical, swan-like neck. In 1999 and 2005, Kent Stevens and Michael Parrish analyzed how the neck vertebrae connected to each other in neutral pose, and concluded that the necks of Camarasaurus and other sauropods were typically held straight with a slight downwards slope. In 2009, Mike Taylor and colleagues showed that in modern animals, necks are usually extended and therefore curved upwards, suggesting that the same was true for sauropods. In a 2007 study, Paul Sereno and colleagues suggested that the head of Camarasaurus was habitually inclined downwards by about 15°, based on the orientation of the semicircular canals in the inner ear, which housed the sense of balance. Taylor and colleagues argued that in this posture, the occipital condyle would have faced downwards, requiring that the front part of the neck was steep, and possibly close to vertical.
The right shoulder blade of the specimen CM 11338 is inclined by approximately 45° with respect to the horizontal. Gilmore, in his 1925 monograph, argued that this specimen reflected the original orientation of the bone, and consequently, his skeletal reconstruction was slightly taller at the hips than at the shoulders. This finding contradicted the 1921 reconstruction of Osborn and Mook, which showed a much steeper shoulder blade, resulting in an animal that was taller at the shoulders than at the hips and with the base of the neck higher above the ground. Gilmore's interpretation of a low-angled shoulder blade subsequently became widely accepted for sauropods in general. In a 2007 study, Daniela Schwarz and colleagues compared the anatomy of the shoulder girdle with that of modern animals and concluded that Osborn and Mook's original interpretation of a steeply inclined (60–65°) shoulder blade and a consequently higher shoulder was correct. Therefore, this fusion is not pathological but might be an adaptation for stiffening the tail. Rothschild and Berman argued that the fusion was a sexually dimorphic feature that occurred only in the males or only in the females. In males, it could have supported whip-lash motions with the tip of the tail during fights with other males. In females, the stiffening could have helped with arching the tail to allow for copulation. In another 2008 study, Nicole Klein and Martin Sander found that individuals of similar age tend to fall into two size classes that might represent different species or sexual dimorphism.
Life history
In 1883, Marsh reported the fragmentary skeleton of a very small sauropod discovered at Como Bluff, which he estimated at about in body length. Based on the small size and the incomplete ossification of the bones, Marsh argued that it must have belonged to an embryo. In 1896, Marsh assigned the specimen to a new species, Pleurocoelus montanus, without further comment, but probably because of the very large pleurocoels (excavations) in the vertebrae. Although a small juvenile, there is no evidence that this specimen is indeed an embryo as proposed by Marsh. The first definitive sauropod embryos and eggs were described from the Argentinian locality Auca Mahuevo in 1998.
As in other dinosaurs, juveniles had proportionally larger heads, shorter necks and tails, and shorter limbs than adults. although the limbs were overall more robust in adults. A 2017 study by Woodruff and Foster estimated the specimen GPDM 220 was probably about 30 years old, and maximally 35 years old, at the age of death. The specimen "E.T." was even older. In a 2014 study, Katja Waskow and Sander estimated that this specimen reached sexual maturity at an age of 18 or 19 years and its full size at 40 years. As of 2024, GPDM 220 and "E.T." are amongst the oldest dinosaur individuals identified, even though representing relatively small individuals. Dinosaurs might have grown throughout most of their lives. In 2021, Bruce Rothschild and Florian Witzmann determined that of 13 analyzed Camarasaurus specimens, 2 had probably reached full size, as indicated by the closure of vascular openings on the articular surfaces of long bones that provided nutrients for bone growth.
Metabolism
Dinosaurs have traditionally been assumed to be cold-blooded ectotherms that depend on environmental temperatures. Since the 1960s, evidence has been presented that dinosaurs instead were homoiotherm (capable of maintaining constant body temperatures) or even endotherm (having an increased metabolism capable of maintaining elevated constant temperatures). Juvenile sauropods were probably endotherms, enabling their rapid growth, while fully grown individuals may have had decreased metabolic rates as body temperature could be maintained by body mass alone.
Pathologies
Multiple instances of pathologies (injuries or diseases) have been recorded in Camarasaurus specimens. In 1996, McIntosh and colleagues described pathologies in thirteen vertebrae of the complete tail of the C. grandis specimen GMNH-PV 101. In two of these vertebrae, the neural arch failed to completely develop, a developmental defect known as spina bifida – the first reported example of this condition in dinosaurs. In the 40th tail vertebra, only half of the neural arch had formed, leaving the spinal cord partly unprotected. At least five vertebrae show bone outgrowths around the joints of the vertebral centra, indicating osteoarthritis (degenerative joint disease). Five consecutive tail vertebrae (49 through 53) are pathologically fused into a single structure.
A specimen from Bone Cabin Quarry showed erosions in the (joints between vertebrae) in four out of twenty tail vertebrae. In 2002, Rothschild and colleagues identified these pathologies the oldest fossil evidence for inflammatory arthritis. In 2001, Lorrie McWhinney and colleagues described a periostitis, an injury of the periosteum (the outer layer of bones), in a humerus assigned to C. grandis. This injury involved parts of the bone to be fractured or torn off, possibly due to stress or repeated excessive exertion of muscles. The subsequent healing process caused a tumor-like mass protruding from the bone surface. The injury would have been long-term and may have impaired the movement of the forelimb and caused a limp. In 2016, Emanuel Tschopp and colleagues described five different types of pathologies in the bones of the fore- and hind feet of SMA 0002 ("E.T."). Such co-occurrence of different pathologies in a single individual is rare and might be due to the advanced age of the individual. The pathologies include a deep pit interpreted as osteochondrosis as well as various types of bony overgrowths, one of which was interpreted as osteoarthritis. Bony shelves extending above the front articular surfaces of the phalanges of the hind feet and were interpreted as enthesophytes caused by the insertion of tendons. These may have formed due to excessive use of the claws during life, possibly due to scratch-digging. A single tail vertebra from the Summerville Formation of New Mexico has been assigned to the genus by Adrian Hunt and Spencer G. Lucas in 1993, but this occurrence was not recognized in a subsequent review. which was questioned by subsequent studies.
Camarasaurus is known from over 530 specimens, including isolated bones and about 50 partial skeletons. It is the most common dinosaur of the Morrison Formation and, due to its abundance, one of the best-understood sauropods. As of 2022, 27% of sauropod specimens from the Morrison that could be assigned to a genus were Camarasaurus specimens. Most identifiable specimens of Camarasaurus belong to one of two species, C. grandis and C. lentus; C. supremus, and especially C. lewisi, is much rarer. Even though complete necks are rarely found in sauropods, five specimens of Camarasaurus preserve all or nearly all of the cervical vertebrae. Juvenile sauropod specimens are generally uncommon as their smaller size reduces their preservation potential. As of 2005, 44% of the sauropod specimens found in the Morrison Formation that are smaller than 50% of adult size are from Camarasaurus.
Paleoenvironment and migration
The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons. In 2011, Henry Fricke and colleagues analyzed the relative abundance of oxygen isotopes (δ<sup>18</sup>O values) of both Camarasaurus teeth and carbonate rocks across the Morrison basin. δ<sup>18</sup>O values vary geographically depending on factors such as aridity and altitude. Because the values obtained from the teeth differ from those obtained from the rocks they were found in, Fricke and colleagues concluded that the Camarasaurus must have migrated between the Morrison basin and the high-altitude areas in the west to avoid the basin's dry season. This migration would probably have been seasonal and over a distance of .
As of 2024, a total of 25 sauropod species are recognized from the Morrison Formation. Allosaurus accounted for 70 to 75 percent of theropod specimens and was at the top trophic level of the Morrison food web. Other vertebrates that shared this paleoenvironment included ray-finned fish, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs such as Hoplosuchus, and several species of pterosaur like Harpactognathus and Mesadactylus. Shells of bivalves and aquatic snails are also common. 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 in otherwise treeless settings (gallery forests) with tree ferns, and ferns, to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.