Sample Page

Camarasaurus (/ˌkæmərəˈsɔːrəs/ KAM-ər-ə-SOR-əs) is a genus of sauropod dinosaur that lived during the Late Jurassic, between c. 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 ‘chambered lizard‘, 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 23 m (75 ft) long and to have weighed 42.3 tonnes, whereas C. lentus was only around 15 m (49 ft) 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 2 to 5 m (6 ft 7 in to 16 ft 5 in). 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.

Camarasaurus was discovered during the Bone Wars, a feud between two American paleontologists, Othniel Charles Marsh and Edward Drinker Cope, that led to a surge of fossil discoveries in the Western US in the late 19th century.^[1] The first Camarasaurus bones were discovered by David Baldwin, one of Marsh’s collectors, in early 1877 in 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.^[1] The first fossil that Cope received from Lucas was the jaw of a theropod, which Cope named Laelaps trihedrodon in a brief publication.^[1] The second shipment from Lucas contained one cervical (neck vertebra), three dorsals (trunk vertebrae), and four caudals (tail vertebrae) of a much larger animal, described by Cope as “the largest or most bulky animal capable of progression on land, of which we have any account”.^[2]

Cope gave these fossils the name Camarasaurus supremus in another quickly written 1877 publication.^[2] The name Camarasaurus means “chamber lizard”, from the Greek kamara ‘chamber‘ and sauros ‘lizard‘, 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”.^[3] 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.^{[4]: 484 [5]: 33} For decades after its discovery, Camarasaurus supremus would remain a relatively obscure taxon compared to the more complete and more extensively figured sauropods discovered by Cope’s opponent Othniel Marsh.^[6]: 251 Cope’s collection was acquired by the American Museum of Natural History, and was then described in greater detail by Henry Fairfield Osborn and Charles Craig Mook in 1921.^[6] 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.^{[6]: 260 [4]}

Probably in early 1879, John A. Ryder created a life-sized drawing of the reconstructed skeleton under the direction of Cope.^[7][1] The drawing was 68 ft (21 m) in length and based on known Camarasaurus bones as well as the reconstructed limbs Morosaurus grandis published by Marsh a few months earlier.^[7] Little was known of the skull at the time, and since most modern reptiles are carnivorous, it was assumed that the same applied to Camarasaurus. Consequently, the hypothetical skull bore long, carnivorous teeth.^[1] This drawing is the first skeletal reconstruction of a sauropod ever made, although it was only published by Mook in 1914, at a much smaller scale of 1/100 natural size.^[7][8] 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.^[9][10]

Figures of the cervical (neck) vertebrae (top), a composite skull reconstruction (right), and ribs (left) of C. supremus from Osborn and Mook (1921)

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 major dinosaur sites: Como Bluff.^[11] Together with his colleague William Edward Carlin, Reed sent some of the bones to Marsh, including some articulated 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.^{[5]: 34 [11]: 34} In December 1877, Marsh described the bones (YPM 1901) as a new species of his previously established genus Apatosaurus, A. grandis.^{[12][5]: 34}

Williston was staggered when seeing the locality, reporting “magnificently preserved” dinosaur bones “scattered for 6 or seven miles”.^[11]: 28 In late 1877 and early 1878, Marsh received several shipments of bones from the same quarry, now known as YPM-Marsh Quarry 1. Besides many additional bones of the original A. grandis individual, these contained a partial skeleton of a second, similarly sized individual (YPM 1905). Parts of these skeletons were mixed up, and some bones cannot be reliably assigned to either.^[5]: 34 The shipments also contained a sacrum (YPM 1900), which Marsh described as a new genus and species, Morosaurus impar, in 1878.^{[5]: 34 [13]} The name Morosaurus name comes from the Greek Μόρος (moros meaning “stupid”), in reference to its small brain size compared to its body size, and σαυρος (sauros meaning “lizard”).^[14] Later 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”.^[15]: 514 He also moved A. grandis to Morosaurus, as M. grandis, and named another, larger species of Morosaurus, M. robustus, based on an ilium from the same quarry.^{[5]: 34 [15]} Marsh later realized that M. grandis and M. impar were the same species but did not publish this finding.^[15]

Morosaurus lentus was named by Marsh in 1889 on the basis of a juvenile sauropod skeleton that was found at Como Bluff.^[16][17] 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,^[18] 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.^[19][18]

Following the Bone Wars, paleontologists also attempted to tackle the taxonomy of the many dinosaur genera named by Marsh and Cope.^[6][16] In 1898, Williston synonymized M. impar with M grandis,^[20] a suggestion supported by later authors.^[21][6][22] In 1901, American researcher Elmer Riggs concluded that of the five Morosaurus species named at the time, only three were valid: M. grandis, M. lentus, and M. agilis.^[23] Riggs synonymized M. impar, the type species, with M. grandis and further suggested that Morosaurus and Camarasaurus were synonyms.^[21] However, the suggestion that Morosaurus and Camarasaurus were generic synonyms was not formalized until later research.^[16] In their 1921 monograph on Camarasaurus, Osborn and Mook synonymized Morosaurus with Camarasaurus,^[6] an idea that has been accepted since.^[19][24] In 1925, American researcher Charles W. Gilmore mistakenly synonymized C. grandis with C. impar despite the former being named first.^[24] M. impar and M. robustus are now considered synonyms of C. grandis^[25][16] and M. agilis has since been moved to its own genus, Smitanosaurus.^[16]

After the end of the Bone Wars, many major institutions in the eastern United States were inspired by the depictions and finds by Marsh and Cope to assemble their own dinosaur fossil collections.^{[26]: 64–65, 105} 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,^{[26]: 1, 5} bring it back to the home institution, and mount it in their fossil halls.^{[26]: 1, 5, 247} In the mid-late 1890s, the AMNH and FMNH were the first to mount expeditions, finding sauropod material at Como Bluff and Fruita, Colorado respectively.^{[26]: 38–39, 117–118} This material, mostly consisting of limb bones, was referred to Morosaurus and led to new reconstructions of sauropod manus and pes structure.^[22][21] In the 1890s, Osborn also suggested that Morosaurus was a synonym of Camarasaurus.^[6][27] 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.^[28][29] In 1905, a plaster skull based on the Camarasaurus skull found at Bone Cabin Quarry and based on a skull later referred to Brachiosaurus^[30][31] was mounted on a skeleton of Brontosaurus,^[32][29] leading to a trend of mistakenly mounting Camarasaurus-like skulls on apatosaurine bodies. This was the first-ever mounted skeleton of a sauropod.^[29]

Around the same time as the AMNH, the CM was conducting its own fossil expeditions to quarries in Wyoming where it recovered several Camarasaurus specimens. However, paleontologists of the time assigned these fossils to Morosaurus instead of Camarasaurus.^[33][34] 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.^[35] 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.^[25][19] This skeleton is one of the best sauropod specimens known to science, with nearly every element preserved in articulation. Sometime prior to 1922, Douglass found another Camarasaurus skeleton at Dinosaur National Monument, however it remained in a plaster jacket for many years. In exchange for several fossils, money, and time to work with Gilmore, the National Museum of Natural History acquired the skeleton and several other fossils. This specimen was then prepared publicly at the Texas Centennial Exposition of 1936 before it was mounted in a death pose in the museum’s fossil hall in 1947. This skeleton would turn out to be the second most complete skeleton of Camarasaurus known.^[36][25] It too was referred to C. lentus by paleontologists.^[19][25]

In 1967, American researcher James Jensen collected a well preserved and articulated postcranial skeleton of Camarasaurus from Uncompahgre Hill in western Colorado which was then deposited at Brigham Young University under specimen number BYU 9740.^[37][38] This skeleton remained unprepared for many years and was not described until 1988, where Jensen described it as belonging to a new genus and species of sauropod, Cathetosaurus lewisi.^[38][37][39] The generic name Cathetosaurus lewisi comes from the Greek κάθετος (kathetos meaning “vertical”), in reference to its supposed ability to stand upright, and σαυρος (sauros meaning “lizard”). the specific name is in honor of Arnold D. Lewis, a fossil preparator and field worker.^[14][38] This original 1988 description was brief,^[38] but John McIntosh and colleagues extensively described BYU 9740 in 1996 where they determined that Cathetosaurus lewisi was a species of Camarasaurus,^[37] an opinion supported by many other authors.^[25][40][41] In 2013, paleontologists Octavio Mateus and Emanuel Tschopp argued in a conference abstract that Cathetosaurus is a distinct genus,^[39] but this was not supported by later research and phylogenetic analyses (studies of the interrelationships of organisms).^[41][42][40]

In 1992, a nearly complete and articulated skeleton of C. grandis^[43] was collected by fossil hunter Jeffrie Parker and colleagues from a site near the Bone Cabin Quarry.^[44] This specimen (GMNH-PV 101) now resides at the Gunma Museum of Natural History in Gunma, Japan.^[25][45] Another well-preserved Camarasaurus specimen was found in 1992 at the Howe Quarry in Wyoming by Swiss field workers working for the Sauriermuseum Aathal in Zurich, Switzerland. The skeleton is one of the best known, with nearly every element articulated and skin impressions from the skull and hindlimb.^[46][40] The specimen, SMA 002, has not yet gotten a full identification, but has been suggested to be a specimen of C. lewisi.^[40] In 1996, several fragmentary remains of Camarasaurus were described from western South Dakota^[47] and New Mexico,^[48] 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.^[48] In 2005, the northernmost specimen, an incomplete skull and postcranial skeleton, of Camarasaurus was discovered in the Little Snowy Mountains of Montana.^[49]

As a sauropod, Camarasaurus had an elephant-like body with a long neck ending in a proportionately small skull, and extremely lightly build vertebrae of the trunk and neck that were in stark contrast to the massive, columnar limbs.^[50]: 11 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.^[51][52]

Camarasaurus was a medium to large-sized sauropod.^[25][51] The most common species, C. lentus, was about 15 m (49 ft) in length, and C. grandis and probably C. lewisi were comparable in size.^[53][51] The body weight of adult C. grandis has been estimated to be about 12.6 tonnes on average, ranging from 8.3 tonnes in the smallest to 16.6 tonnes in the largest specimen.^[51] In 2020, John Foster stated that the latest species, C. supremus, had bones about 50% longer than those of the smaller species.^[51] Although C. supremus is too incompletely known to allow for precise size estimates, it would have reached almost 23 m (75 ft) in length and 42.3 tonnes in weight if its body proportions were identical to those of the smaller species.^[51] American paleontologist Gregory S. Paul, in 2024, instead gave a length estimate of 18 m (59 ft) and a weight estimate of 24 tonnes for this species.^[52]

The skull was larger and more strongly build than in other sauropods, with massive upper and lower jaws.^[54][25][51] Skull length varied between individuals, ranging from about 46% to 58% of the length of the femur.^[55] As in the contemporary Brachiosaurus, the external naris (nostril) was enlarged, resulting in an arched forehead.^{[56][24]: 353} Both genera had a well-defined snout,^[57] but the skull of Camarasaurus was more rounded and short-faced.^{[51][58]: 194} 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.^[24]: 354

The largest openings that penetrated the skull were the external naris, the orbit (eye opening), and the infratemporal fenestra, which was located behind and below the orbit. These three openings were about the same size. The external naris was oval in shape, and the orbit was teardrop-shaped, tapering to a point at its lower end. The orbit contained a scleral ring, a ring of small plate-like bones around the pupil of the eye. The infratemporal fenestra was roughly triangular and tilted backwards at an angle of 30°. A small and pear-shaped antorbital fenestra was present between the external naris and the orbit. Even smaller was the supratemporal fenestra, which was present in the rear corners of the skull roof and mostly facing upwards. This opening was oval in shape and obliquely oriented.^{[5]: 6 [24]: 364–365 [54]}

The skull showed several autapomorphies (features not found in related genera). According to a 2004 review, these include the lacrimal (the bone that formed the front margin of the orbit), which was tilted forwards. The quadrate, a columnar bone at the rear of the skull, did not reach the infratemporal fenestra as its upwards-facing part was short. The quadratojugal bone, which formed the rear-bottom corner of the skull, reached upwards to make contact with the squamosal bone. The side surface of the lower jaw had an oblique groove running from the surangular bone forwards and downwards to the lower margin of the dentary bone.^[56]: 306

Known specimens had four teeth in each premaxilla (the front bone of the upper jaw), 9 to 10 teeth in each maxilla (the main bone of the upper jaw), and 13 teeth in each lower jaw.^[5] The teeth were spoon-shaped and formed a continuous cutting edge. The teeth increased in length, and became more symmetric, towards the tip of the snout. The teeth were tilted forwards and bent slightly inwards. The front edges of the teeth were more curved than the rear edges, and the teeth in the lower jaw were straighter and slightly less robust than those of the upper jaw. This makes it possible to determine whether an isolated tooth came from the left or right side of the jaw and whether it came from the upper or lower jaw.^{[19]: 490 [24]: 365–366 [40]}

The vertebral column consisted of 12 cervical (neck), 12 dorsal (back), and five sacral (hip) vertebrae.^{[51][59]: 81} The tail was composed of 53 caudal vertebrae the two specimens that preserve a complete tail (CM 11338 and GMNH 101).^[60]: 5 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 (‘chambered lizard‘).^{[61]: 14–15 [62]} The cervical and dorsal vertebrae were opisthocoelous (concave at the rear and convex at the front) and had large excavations on their sides called pleurocoels.^{[24]: 370 [59]: 76} The neural spines (the top parts of the vertebrae) of the shoulder region were split, and the left and right halves formed a U-shape when viewed from the front or back. In the hip region, the neural spines were not split, short, and fan-shaped when viewed from the front or back.^{[51][5]: 37} The neural spines of the second to fifth sacral were often fused together.^[5]: 37 The cervical vertebrae had very slender and elongated cervical ribs that overlapped multiple preceding vertebrae.^{[24]: 374 [51]}

The left and right halves of the shoulder girdle were probably connected at the front of the trunk by the coracoids.^[63]: 40 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.^{[51][5]: 37} The forelimb was slender, and the humerus was about 77% the length of the femur (upper thigh bone). In contrast, the hindlimb was massive, and the tibia (shin bone) was about 60% the length of the femur. Camarasaurus is one of few sauropods that preserve the wrist, which in this genus consisted of only two bones, the ulnare and the radiale.^{[25][56]: 290} As in other macronarians, the five metacarpals were long, with the third metacarpal reaching one third of the length of the humerus.^{[5]: 37 [56]: 290} As typical for sauropods, the metacarpals were vertical and arranged in a tube-like fashion. The fingers were strongly reduced, with the thumb consisting of two phalanges (finger bones), including a claw that was slanted sidewards. The remaining digits possibly consisted of one phalanx, and lacked claws.^{[24]: 379–380 [56]: 290} In the ankle of the hind foot, the calcaneum was small and rounded.^[5]: 37 As in other sauropods, the hind foot had five digits, consisting of 2, 3, 4, 2, and 1 phalanx, respectively. The first three toes had recurved claws that were strongly flattened side-to-side.^[56]: 295

Footprints show that the hind feet of sauropods were supported by a large, fleshy pad akin to that of elephants.^[64]: 146 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 6 and 18 mm (0.24 and 0.71 in) in diameter.^{[46]: 42, 54} In 2015, Tschopp and colleagues created models of the fore- and hind feet based on “E.T.” to produce hypothetical footprints, showing that the prints of the hind feet were almost four times larger than those of the forefeet. Fossil trackways of sauropods can be “narrow-gauged” or “wide-gauged”, depending on how close the tracks are to the trackway midline; Camarasaurus might have had an intermediate gauge. So far, tracks have not been confidently assigned to Camarasaurus.^{[46]: 54–55}

In 1877, Cope described Camarasaurus as a new genus of dinosaur, and compared it with several genera that would later be classified as sauropods, including Cetiosaurus, Bothriospondylus, and Ornithopsis.^[65] 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).^[66] Also in 1877, Marsh named the genus Morosaurus, which he placed in the Atlantosauridae, together with his genera Atlantosaurus and Apatosaurus.^[13] Later in the same year, Marsh named the new suborder Sauropoda, with Atlantosauridae as its only family, because “they differ so widely from typical Dinosauria”.^[15] Marsh later classified Morosaurus in a sauropod family of its own, Morosauridae.^[67] Morosaurus and Morosauridae have since been synonymized with Camarasaurus and Camarasauridae, respectively, as the latter names were published earlier.^[68]

Camarasauridae has historically been in wide use.^[69]: 1555 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.^[7] However, the family is now often restricted to Camarasaurus itself, leading some researchers to reject it as redundant.^[69][70]

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.^{[71][57]: 461} Alternatively, the name Camarasauromorpha has been used to unite Camarasaurus and Titanosauriformes;^[72]: 9 several studies used both names, with Camarasauromorpha excluding some very basal members of Macronaria.^{[57]: 461 [73]} Camarasauromorpha has not been universally accepted.^[73]

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:^[74]

Four species are commonly recognized: C. supremus, C. grandis, C. lentus, and C. lewisi.^[42] C. supremus, named in 1877 by Cope, is the type species (the species the genus is based on). C. grandis was named in 1877 and C. lentus in 1889. C. lewisi was originally described as a distinct genus, Cathetosaurus, in 1988, but reclassified as a species of Camarasaurus in 1996.^[38][59] Some researchers have suggested that Cathetosaurus might be reinstated as a distinct genus,^[75][42] whereas others have suggested that C. lewisi should be assigned to C. grandis or to C. sp. (of uncertain species).^[25][76]

Most Camarasaurus specimens cannot be assigned to any particular species;^[77] species identification is complicated due to within-species variation and the often imprecise relative dating of localities.^{[25]: 370–371} The two most common species, C. grandis and C. lentus, can be distinguished based on the neural arches of the frontmost dorsal vertebrae, which are wider in C. lentus, and the tips of the neural spines of the frontmost caudal vertebrae, which are broader in C. grandis. C. supremus shows wide neural arches as C. lentus but broad neural spine tips as C. grandis; this species is also substantially larger. In C. lewisi, the bifurcation of the neural spines was not restricted to the shoulder region but occurred from the third cervical to the twelfth dorsal vertebra.^[25][77]

In 2005, Takehito Ikejiri argued that the four established species are separated in time.^[25] The oldest species, C. grandis, would have occurred during the Kimmeridgian and was followed by C. lentus in the late Kimmeridgian. C. supremus would have primarily occurred during the Tithonian, at the very top of the Morrison Formation.^[25] In 2017, Cary Woodruff and Foster cautioned that the relative dating of the different localities within the Morrison Formation is still uncertain, which could undermine this proposed succession of species.^[78] There may also be some geographical separation between species, and C. supremus appears to have been restricted to the eastern part of the Morrison Formation in southern Colorado and western Oklahoma.^[25][78] However, Foster noted in 2020 that there is no clear distribution pattern of the different species.^[51]: 274

Fossils of Camarasaurus leptodirus, Amphicoelias latus, and Caulodon diversidens; synonyms of C. supremus

Four other species named by Cope between 1877 and 1879 are now considered to be synonyms of Camarasaurus supremus: Amphicoelias latus, Caulodon diversidens, Caulodon leptoganus, and Camarasaurus leptodirus.^[25][79][6] Likewise, two species named by Marsh in 1878 and 1896 are considered synonyms of Camarasaurus grandis: Morosaurus impar and Pleurocoelus montanus.^{[25][80]: 275} Two species described from vertebrae found at Dinosaur National Monument, Uintasaurus douglassi and Camarasaurus annae, are now considered synonyms of Camarasaurus lentus.^[81][25][82]

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,^[83] but was described as a new genus of dicraeosaurid under the name Smitanosaurus in 2020.^[16] 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.^[84] The vertebra was later found to be of a theropod, while the tooth is from an indeterminate macronarian sauropod.^{[85]: 259–260} 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.^[86] It was tentatively placed in Camarasaurus by McIntosh in 1990,^[7] but was granted a new genus in 1998, Lourinhasaurus.^[74]

Camarasaurus was a herbivore that probably fed at moderate heights of 2 to 5 m (6 ft 7 in to 16 ft 5 in).^[51]: 274 It might have been able to rear on its hind legs to reach higher vegetation, as indicated by anatomical features such as the short neural spines of its caudal vertebrae.^[87] 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.^[88] 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.^[89][87] The diet of adult Camarasaurus might have consisted of the leaves of conifers, such as those of the extinct Cheirolepidiaceae, and ginkgos.^[87] In 2016, Mark Hallett and Matt Wedel suggested that female cones of araucarians as well as resins could have supplemented its diet.^[87]

Camarasaurus probably had a more powerful bite than other sauropods due to the very large coronoid process (an upwards facing projection of the mandible) and the supratemporal fenestra that provided extensive attachement surfaces for large masticatory muscles (the external mandibular adductor muscles).^[54] A 2016 study by David Button and colleagues estimated that the bite force of Camarasaurus was almost four times higher than that of Diplodocus. The bite force was highest in the posterior portion of the tooth row, where it is estimated to have reached up to 1978 newton.^{[90]: 900 [91]: 182} The sturdy construction of the skull also suggests that it was able to resist greater stresses during feeding than other sauropods.^[54][90] Per Christiansen, in a 2000 paper, suggested that Camarasaurus was adapted to biting off vegetation, but did not rake leaves as Diplodocus or Brachiosaurus did.^[54] The upper and lower teeth appeared to have fit into each other. In a 1994 study, Jorge Calvo suggested that Camarasaurus could crush food items against its teeth by moving its jaws back and forth, allowing some degree of food processing before shallowing.^[92][54]

As with other dinosaurs, Camarasaurus continuously replaced its teeth, and underneath each erupted tooth there were up to three replacement teeth. A tooth was replaced after 62 days on average, as indicated by daily growth rings called von Ebner lines that are visible in cross-section of the teeth. This was slower than in Diplodocus, where a tooth only lasted for about 35 days, but as fast or faster than in ornithischian dinosaurs.^[93] 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.^[40] Alternatively, these blood vessels could have supported “lips” like those found in today’s lizards.^[91]: 157

A juvenile and heavily scavenged Camarasaurus specimen from Wyoming was found with 14 polished quartz stones that are between 1 and 13 cm (0.39 and 5.12 in) in diameter and have been identified as gastroliths (stomach stones). Sauropods were once assumed to have swallowed such stones to help grind food in the stomach, but the rarity of skeletons preserving gastroliths and their low numbers suggest that they were instead swallowed accidentally or for mineral intake.^{[94][50]: 13}

The long necks of sauropods might have evolved for feeding on plants that were high above the ground or otherwise difficult to access, or to maximize the amount of food they could access without moving the body, thus saving energy.^[50]: 25 The probable neck posture has been the subject of controversy.^[50]: 12 A 1921 skeletal reconstruction of Camarasaurus by Osborn and Mook shows a rather straight and horizontal neck,^[95]: 219 while some later authors assumed a nearly vertical, swan-like neck.^{[95][50]: 12} Some complete skeletons, such as the juvenile C. lentus specimen CM 11338, also show a vertical neck, but these represent opisthotonic death poses that do not necessarily reflect the original neck posture.^[95] In 1998, John Martin and colleagues instead argued that the necks of sauropods were held approximately horizontal, like a beam. They stated that the neck of Camarasaurus would have been powerful and inflexible, and that the elongated cervical ribs would have braced it along its underside.^[96] 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.^{[97][95]: 228}

The idea of a more-or-less horizontal neck was questioned by several subsequent studies.^[50]: 12 In 2005, David Berman and Bruce Rothschild used Computed tomography (CT) data to propose that there were two types of sauropod neck vertebrae, a robust type and a slender type. Camarasaurus had the robust type, indicating that its neck was held vertical or almost vertical, while the slender type suggests a horizontal neck posture.^[98] 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.^[99][100]

Historical reconstructions by Osborn and Mook, 1921 (top) and Gilmore, 1924 (bottom), showing differences in the orientation of the shoulder blade and the sloping of the back

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.^[63] Ligaments would have run along the top of the neck, which would have been taut when the neck was sloping downwards or sidewards, helping with holding it. In a 2004 study, Takanobu Tsuihiji reconstructed the ligaments of Camarasaurus based on those Greater Rhea, in which the neural spines are similarly bifurcated. The nuchal ligament would have run along the top with branches connecting to either side of the bifurcated neural spines, while a second ligament, the Ligamentum elasticum interspinale, would have run in-between the two prongs of the bifurcated neural spines.^{[101][91]: 184–185}

Historically, sauropods have been reconstructed with their tails dragged over the ground.^[50]: 11 In the 1921 Camarasaurus reconstruction of Osborn and Mook, the tail begins to slope downwards immediately behind the hips. While discussing his own Camarasaurus reconstruction in 1925, Gilmore argued that the first few tail vertebrae must have been horizontal, and that the tail sloped down only after this section.^{[24]: 383–384} Sauropods are now thought to have had held their entire tails clear off the ground, as indicated by anatomy and trackway evidence.^[50]: 11

In a 1991 study, Bruce Rothschild and David Berman noted that in 25% of Camarasaurus specimens, some of the foremost tail vertebrae were fused together. In Apatosaurus and Diplodocus, such fusion even occurred in 50% of the individuals. The fusion is caused by ossified tendons rather than direct fusion of the vertebral bodies, and was identified as diffuse idiopathic skeletal hyperostosis (DISH).^[a] 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.^[103] In a 2008 study, Takehito Ikejiri suggested that Camarasaurus specimens can be classified either as robust (strongly built) or as gracile (slender). These robust and gracile morphs also subtly differ in size and are apparent in the three most common species. Ikejiri argued that the two morphs reflect differences between the sexes, although it is unclear which morph represents male and which represents female individuals.^[104] 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.^[105]

In 1883, Marsh reported the fragmentary skeleton of a very small sauropod discovered at Como Bluff, which he estimated at about 2.1 m (7 ft) 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.^[67][b] 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.^[106][80] In 1994, Carpenter and McIntosh assigned this specimen to Camarasaurus grandis, and interpreted the large pleurocoels as a juvenile feature.^[80] Although a small juvenile, there is no evidence that this specimen is indeed an embryo as proposed by Marsh.^[107] In 1994, Brooks Britt and Bruce Naylor described a minute premaxilla of Camarasaurus discovered in Dry Mesa Quarry. The teeth of this bone have not yet erupted, suggesting that the individual did not yet hatch and was therefore an embryo. The bone is 37 mm (1.5 in) in length, suggesting a skull length of about 70 mm (2.8 in), a body length of just over 1 m (39 in), and a body weight of 7.5 kg (17 lb). Based on these estimates, the diameter of a hypothesized spherical egg would have been about 24 cm (9.4 in), smaller than the largest known bird eggs. The small size of the embryo provided evidence that sauropods were oviparous (egg-laying), questioning a hypothesis proposed by Robert T. Bakker in 1980 that sauropods were viviparous and gave birth to relatively large young.^[107][108] The first definitive sauropod embryos and eggs were described from the Argentinian locality Auca Mahuevo in 1998.^[109]

As in other dinosaurs, juveniles had proportionally larger heads, shorter necks and tails, and shorter limbs than adults.^[110]: 264 As the individual matured, the neural arches of the vertebrae fused with the vertebral bodies; in Camarasaurus, the vertebrae of the mid and rear portion of the tail fused before those of the sacrum.^[25] The bifurcation (forking) of the neural spines became more pronounced as the individuals aged. Other age-related changes found in adults include the rugose articular surfaces in the limbs, the closure of the coracoid foramen (opening), the ossification of entheses of the vertebral column, and the fusion of the individual sacral vertebrae into a single structure.^{[111][59]: 81 [110]: 264} Changes during growth are particularly pronounced in the sternum, which is circular in the juvenile CM 11338 but grew long and narrow in adults. In contrast, the proportions of the limb bones did not change during growth,^[112] although the limbs were overall more robust in adults.^[110]: 264

Growth rings and other features visible in thin sections of bones allow for reconstructing life history. As other sauropods, Camarasaurus grew as fast as modern birds and mammals, and reached sexual maturity well before reaching maximum body size.^{[105][113]: 865} In 2013, Eva Maria Griebeler and colleagues examined thin sections of limb bones of a large Camarasaurus individual (CM 36664) with an estimated weight of 14.3 tonnes. This individual was estimated to have reached a maximum growth rate of 1.5 tonnes per year, sexual maturity at about 21 years, and an age at death of around 26 years.^[114]: 3 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.^[115] 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.^[113]: 866 As of 2024, GPDM 220 and “E.T.” are amongst the oldest dinosaur individuals identified, even though representing relatively small individuals.^[116]: 684 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.^{[117]: 263, 267}

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).^{[50]: 15 [118]} 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.^[50]: 17 Body temperatures can be directly estimated based on isotope compositions of bones and teeth.^[118][119] In a 2002 study, William Showers and colleagues used oxygen isotope thermometry to analyse bone apatite. They found that, in their studied Camarasaurus specimen, temperatures were variable in the trunk, but decreased in the legs and hips and increased in the neck and tail, compared to a specimen of the theropod Giganotosaurus. These differences between body parts might have resulted from countercurrent exchange of heat, when excess heat was pumped from the trunk into the peripheral body parts as a cooling mechanism.^[118] In 2011, Robert Eagle and colleagues analyzed tooth enamel of two sauropods, Camarasaurus and Giraffatitan, using clumped isotope thermometry. This analysis indicated body temperatures of 36–38 °C (97–100 °F), comparable to those of modern mammals.^[119]

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.^{[60]: 17–18 [120]}

A specimen from Bone Cabin Quarry showed erosions in the zygapophyses (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.^[121][c] 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.^[123] 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.^[41]

Camarasaurus is known from sedimentary rocks of the Morrison Formation dating to the Kimmeridgian and Tithonian ages (155 to 143 million years ago).^[56]: 266 The Morrison Formation covers about 1.2 million km² of western North America, and Camarasaurus is found across this range, from more than 100 localities as far north as Montana to as far south as New Mexico.^[124][125] 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.^{[126][48][56]: 266} Remains from Zimbabwe and Germany have been assigned to Camarasaurus,^[127][128] which was questioned by subsequent studies.^{[129][130]: 26–27}

Camarasaurus is known from over 530 specimens, including isolated bones and about 50 partial skeletons.^[131] It is the most common dinosaur of the Morrison Formation and, due to its abundance, one of the best-understood sauropods.^{[51]: 240, 272} In a 2003 survey of more than two hundred fossil localities, John Foster reported 179 specimens of the genus, comparable to Apatosaurus (112) and Diplodocus (98), but far greater than Brachiosaurus (12), Haplocanthosaurus (12) and Barosaurus (13).^[132] As of 2022, 27% of sauropod specimens from the Morrison that could be assigned to a genus were Camarasaurus specimens.^[110] 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.^[77] Even though complete necks are rarely found in sauropods, five specimens of Camarasaurus preserve all or nearly all of the cervical vertebrae.^[133] 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.^[134]

The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons.^[135][136] In 2011, Henry Fricke and colleagues analyzed the relative abundance of oxygen isotopes (δ¹⁸O values) of both Camarasaurus teeth and carbonate rocks across the Morrison basin. δ¹⁸O 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 300 km (190 mi).^[137]

As of 2024, a total of 25 sauropod species are recognized from the Morrison Formation.^[125] The most common genera are the diplodocids Apatosaurus, Diplodocus, Supersaurus, Barosaurus, Brontosaurus, and Galeamopus; the macronarian Brachiosaurus, and Haplocanthosaurus. Dicraeosaurids such as Smitanosaurus, Dyslocosaurus, and Suuwassea were rarer components of the fauna.^[125] Other dinosaurs known from the Morrison Formation include the predatory theropods Koparion, Stokesosaurus, Ornitholestes, Ceratosaurus, Allosaurus and Torvosaurus, as well as the herbivorous ornithischians Camptosaurus, Dryosaurus, Gargoyleosaurus and Stegosaurus.^[138] Allosaurus accounted for 70 to 75 percent of theropod specimens and was at the top trophic level of the Morrison food web.^[139] 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.^[140]