Camarasaurus

Camarasaurus (/ˌkæmərəˈsɔːrəs/ KAM-ər-ə-SOR-əs) is a genus of sauropod dinosaur that lived in North America during the Late Jurassic epoch. Its fossil remains have been found in the Morrison Formation, dating to the Kimmeridgian and Tithonian ages of the Jurassic, between 155 and 145 million years ago (mya).

Camarasaurus Temporal range: Late Jurassic, 155–143.1 Ma PreꞒ Ꞓ O S D C P T J K Pg N
CM 11338, the most complete known Camarasaurus specimen
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Clade:	†Macronaria
Family:	†Camarasauridae
Subfamily:	†Camarasaurinae Cope, 1878
Genus:	†Camarasaurus Cope, 1877a
Type species
†Camarasaurus supremus Cope, 1877a
Other species
†Camarasaurus grandis (Marsh, 1877) Gilmore, 1925 †Camarasaurus lentus (Marsh, 1889) Mook, 1914 †Camarasaurus lewisi? (Jensen, 1988) Miller, Mcintosh, Stadtman and Gillette, 1992
Synonyms
Caulodon Cope, 1877 Morosaurus Marsh, 1878 Uintasaurus Holland, 1924 Cathetosaurus? Jensen, 1988

Camarasaurus presented a distinctive cranial profile of a blunt snout and an arched skull that was remarkably square, typical of basal macronarians. The generic name means "chambered lizard", referring to the hollow chambers, known as pleurocoels, in its cervical vertebrae (Greek καμαρα [kamara] meaning 'vaulted chamber', or anything with an arched cover, and σαυρος [sauros] meaning 'lizard').

Camarasaurus contains four species that are commonly recognized as valid: C. grandis, C. lentus, C. lewisi, and C. supremus. C. supremus, the type species, is the largest and geologically youngest of the four. Camarasaurus is the type genus of Camarasauridae, which also includes its European close relative Lourinhasaurus. Camarasaurus was named in 1877 by Edward Drinker Cope, during the period of scientific rivalry between him and Othniel Charles Marsh known as the Bone Wars. Soon after, Marsh named a genus Morosaurus, but it was subsequently shown to be synonymous with Camarasaurus.

History

Multiview skeletal reconstruction of C. supremus.

Fossils of Camarasaurus were first discovered in the spring of 1877 by Oramel William Lucas, a school superintendent, in Morrison Formation rocks in Garden Park, Colorado. These fossils were sent to Edward Drinker Cope, a paleontologist based in Philadelphia, who identified it as belonging to a new genus and species, which he named Camarasaurus supremus, meaning "chambered lizard, from the Greek καμαρα (kamara) meaning "vaulted chamber", or anything with an arched cover, and σαυρος (sauros) meaning "lizard"), and from the Latin supremus, "supreme" or "highest".^[1][2] By this time, the Morrison Formation had become the main battleground of the Bone Wars, a fossil-collecting competition between Cope and paleontologist Othniel Charles Marsh. Due to this, at the time many descriptions of taxa, such as that of Camarasaurus, were rushed by Cope and Marsh.^[3] Camarasaurus supremus' type specimen (AMNH 5760) consists of: one cervical vertebra, the namesake of the genus, two dorsal vertebrae, and three caudal vertebrae. However, these elements are from differing individuals, making them cotypes.^[4] The cervical vertebra has been proposed to be the lectotype of C. supremus, though there has not been a published stance.^[5]

Between August 1877 and 1878, Lucas unearthed and sent many more C. supremus fossils, including: two cervicals, 18 dorsals, 55 caudals, 17 left ribs and several right ones, eight chevrons, one right scapula, one right coracoid, two pubes, four ischia, one femur, and one fibula. These elements came from the "Yellow Beds" of Garden Park and were also grouped with AMNH 5760, as Cope erroneously believed they belonged to the same individual.^[1][4] Based on the fossils found at Garden Park, Cope erected several more genera and species of dinosaur including; Camarasaurus leptodirus (1877), Caulodon diversidens (1877), Caulodon leptoganus (1878), and Amphicoelias latus (1877). All of these species are considered synonyms of C. supremus and were described on the basis of fragmentary or isolated fossils.^[4][6][7] Many other taxa were named by Cope based on fossils from Garden Park, including Epanterias, Amphicoelias altus, and Hypsirhophus.^[8][4]

More fossils would be found throughout the late 1870s into 1880 by O. W. Lucas and his brother, Ira H. Lucas. All fossils found by I. H. Lucas were then separated into AMNH 5761, however this specimen too included several, jumbled skeletons from multiple individuals. The total number of specimens from Garden Park referred to C. supremus includes: one braincase, one maxilla, one quadrate, two dentaries, several teeth, 23 cervicals, 38 dorsals, two sacra, 102 caudals, 25 chevrons, two sternal plates, 110 ribs, six scapulae, two coracoids, two humeri, two metacarpals, five ilia, eight ischia, six pubes, four femora, four tibiae, two fibulae, one astragalus, and one metatarsal. However, the referral of some of these fossils is questionable, as many are fragmentary or may belong to other sauropods. Intermingled are the remains of possibly six or more individuals,^[9][4] some of which were found alongside bones of theropods and ornithischians.^[10] Later, these fossils were prepared and cleaned by Jacob Geismar under Cope's direction between 1877 and the 1890s. Many additional fossils were illustrated and described by Cope in 1878, but a full review of all the Garden Park dinosaur fossils was published by Henry Osborn and Charles C. Mook in 1921.^[4]

The earliest known skeletal reconstruction of a sauropod dinosaur: C. supremus by John A. Ryder, 1877

In 1877, Cope commissioned Dr. John A. Ryder to create a restoration of Camarasaurus using the known fossils of several individuals. Due to using multiple individuals, factors like the vertebral count and proportions were inaccurate. Additionally, Camarasaurus was known only from skull fragments at the time, leading to a largely hypothetical skull which bore carnivorous teeth. This reconstruction would be the first ever made of a sauropod dinosaur and was natural size, measuring over 50 feet (15 m).^[11][4]

Morosaurus

Between 1877 and 1879, paleontologists William Reed, Marshall P. Felch, and Samuel W. Williston found an incomplete, partially articulated skeleton (YPM 1901)^[12] of a juvenile sauropod in Quarry 1 at Como Bluff, Wyoming. Marsh was sent part of the specimen which he described in 1877 as belonging to a new species of the genus Apatosaurus, naming it Apatosaurus grandis, the specific name coming from the Latin grandis meaning "great".^[12] This skeleton would be the best preserved single individual of Camarasaurus known at the time, consisting of: a basioccipital, several dorsals, a partial sacrum, the first 27 caudals, a complete left and incomplete right pectoral girdle, an incomplete left forelimb, femora, tibiae, fibulae, and ribs.^[13][9] Additionally, several paratypes were unearthed from the same locality, including: an incomplete skull and partial postcranial skeleton (YPM 1905), the holotype sacrum of the later named Morosaurus impar (YPM 1900), and a fragmentary postcranial skeleton (YPM 1903).^[14][9][13] In 1878, Williston sent Marsh an isolated juvenile sauropod sacrum (YPM 1900) he had found at Como Bluff alongside material of A. grandis. Marsh then described the sacrum as belonging to a new genus and species, Morosaurus impar, which he believed was related to Apatosaurus, Brontosaurus,^[15] and Atlantosaurus.^[16] 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").^[17] Marsh went on to refer five species of Morosaurus: M. impar, M. robustus, M. agilis, M. lentus, and M. grandis, which was previously named Apatosaurus grandis.^[18] M. lentus, the specific name coming from the Latin lentus meaning "slow", was named in 1889 by Marsh based on jaws and an incomplete skeleton that was also found at Como Bluff.^[18][19] 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.^[20]

Following the Bone Wars, paleontologists also attempted to tackle the taxonomy of the many dinosaur genera named by Marsh and Cope.^[4][18] In 1898, Williston synonymized M. impar with M grandis,^[21] a suggestion supported by later authors.^[22][4][23] 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.^[24] Riggs synonymized M. impar, the type species, with M. grandis and further suggested that Morosaurus and Camarasaurus were synonyms.^[22] However, the suggestion that Morosaurus and Camarasaurus were generic synonyms was not formalized until later research.^[18] In their 1921 monograph on Camarasaurus, Osborn and Mook synonymized Morosaurus with Camarasaurus,^[4] an idea that has been accepted since.^[13][25] In 1925, American researcher Charles W. Gilmore mistakenly synonymized C. grandis with C. impar despite the former being named first.^[25] M. impar and M. robustus are now considered synonyms of C. grandis^[9][18] and M. agilis has since been moved to its own genus, Smitanosaurus.^[18]

Second dinosaur rush

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.^[23][22] In the 1890s, Osborn also suggested that Morosaurus was a synonym of Camarasaurus.^[4][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.^[9][13] This skeleton is one of the best sauropod specimens known to science, with nearly every element preserved in articulation. Sometime prior to 1922, another Camarasaurus skeleton was found at Dinosaur National Monument by Douglass however it remained in a plaster jacket for many years. In an 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][9] It too was referred to C. lentus by paleontologists.^[13][9]

Resurgent discoveries

Camarasaurus sp. SMA 0002 ("E.T.") at the Sauriermuseum Aathal.

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"), and the species name is in honor of Arnold D. Lewis, a fossil preparator and field worker.^[17][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.^[9][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).^[5][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 now resides at the Gunma Museum of Natural History in Tokyo, Japan under specimen number GMNH-PV 101.^[9][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]

Fossil record

Camarasaurus fossils are very common.^[50] Over 500 specimens are known, including many isolated bones and about 50 partial skeletons.^[51] It is found in a wide area over the western United States, from as far north as Montana to as far south as New Mexico, in rocks of the Morrison Formation.^[52] Due to this abundance, Camarasaurus is a very well-known sauropod. A juvenile specimen of Camarasaurus, CM 11338, is the most complete sauropod skeleton ever discovered. Numerous skulls are known.^[53] Even though complete necks are rarely found in sauropods, five specimens of Camarasaurus preserve all or nearly all of the cervical vertebrae.^[54] Most identifiable specimens of Camarasaurus belong to one of two species, C. grandis and C. lentus; C. lewisi and C. supremus are rarer.^[55]

Description

Scale diagram of three known species of Camarasaurus

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.^[56]: 11 Compared to other sauropods, it was relatively bulky with a wide belly. 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.^[50][57]

Camarasaurus was a medium to large-sized sauropod.^[9][50] 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.^[58][50] 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.^[50] In 2020, John Foster stated that the latest species, C. supremus, had bones about 50% longer than those of the smaller species.^[50] 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.^[50] 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.^[57]

Skull

C. supremus skull

The skull was larger and more strongly build than in other sauropods, with massive upper and lower jaws.^[59][9][50] As in the contemporary Brachiosaurus, the external naris (nostril) was enlarged, resulting in an arched forehead.^{[60][25]: 353} Both genera had a well-defined snout,^[61] but the skull of Camarasaurus was more rounded and short-faced.^{[50][62]: 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.^[25]: 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 sclerotic 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.^{[63]: 6 [25]: 364–365 [59]}

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.^[60]: 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.^[63] 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.^{[13]: 490 [25]: 365–366 [64]}

Postcranium

Restoration of a C. supremus herd

The vertebral column consisted of 12 cervical (neck), 12 dorsal (back), and five sacral (hip) vertebrae.^{[50][65]: 81} The tail was composed of 53 caudal vertebrae in the complete skeleton CM 11338, but the exact count might have varied between individuals.^[65]: 84 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').^{[66]: 14–15 [67]} 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.^{[25]: 370 [65]: 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.^{[50][63]: 37} The neural spines of the second to fifth sacral were often fused together.^[63]: 37 The cervical vertebrae had very slender and elongated cervical ribs that overlapped multiple preceding vertebrae.^{[25]: 374 [50]}

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.^{[50][63]: 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.^{[9][60]: 290} As in other macronarians, the five metacarpals were long, with the third metacarpal reaching one third of the length of the humerus.^{[63]: 37 [60]: 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.^{[25]: 379–380 [60]: 290} In the ankle of the hind foot, the calcaneum was small and rounded.^[63]: 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.^[60]: 295

Classification and species

Camarasauridae

Camarasaurus is the type genus of the family Camarasauridae, a clade that is typically regarded as only including Camarasaurus itself. However, phylogenetic analyses have recovered genera like Bellusaurus, Tehuelchesaurus, and Lourinhasaurus as members of the family.^[68][69][24] Cope recognized that Camarasaurus was a relative of Cetiosaurus, Bothriospondylus, Ornithopsis, and Anchisaurus (Megadactylus) in his description, but failed to name a family for these taxa.^[70] In 1878 with the description of Amphicoelias, Cope named the families Camarasauridae and Amphicoelidae based on differences in vertebral anatomy, however he did not specify what other taxa were members of these groups.^[71]

In 1970, Rodney Steel took an expansive concept of Camarasauridae, encompassing all sauropods then known except diplodocoids and titanosaurs.^[72] In 1990, John S. McIntosh regarded Camarasauridae as made up of two subfamilies: Camarasaurinae, containing Camarasaurus, Aragosaurus, Euhelopus, and Tienshanosaurus, and Opisthocoelicaudiinae, containing Opisthocoelicaudia and Chondrosteosaurus.^[11] Dashanpusaurus, from the Middle Jurassic of China, was originally described as a camarasaurid, but was subsequently found to be a basal macronarian by phylogenetic analysis.^[73] Many of these taxa were referred to Camarasauridae in the 20th century on the basis of their teeth anatomy, such as Euhelopus, Asiatosaurus, and Chiayusaurus, or vertebral anatomy, like Opisthocoelicaudia, but are now thought to be in different groups. Camarasauridae is often seen as monophyletic, but a wider group known as Camarasauromorpha has been recovered in phylogenetic analyses.^[24][74] This group was initially defined as applying to the clade including the most recent common ancestor of Camarasauridae and Titanosauriformes and all of its descendants.^[75]

Several sauropods have been suggested to be in Camarasauridae, or in a wider group known as Camarasauromorpha, including Lourinhasaurus, Bellusaurus, and Oplosaurus, however this has come under critiscism.^[76][69][5] Bellusaurus was recovered as a Camarasaurid in a 2014 paper, but has been considered a member of Turiasauria,^[77] Mamenchisauridae,^[78] or basal Macronaria.^[69] Lourinhasaurus was classified as a camarasaurid and a species of Camarasaurus itself, but some studies have found it to be a basal neosauropod,^[79] basal macronarian^[68] or eusauropod,^[80][81] or laurasiform instead.^[82][83] However, in a 2019 study, Mannion and colleagues found Lourinhasaurus as a sister taxon of Camarasaurus.^[77] The dubious British genus Oplosaurus has been suggested to be a camarasaurid,^[84] however other studies have placed it in Turiasauria^[85][86] or Macronaria in general.^[87]

A simplified cladogram of basal Macronaria after Tan et al (2021) is shown below:^[88]

Eusauropoda	Turiasauria Jobaria Neosauropoda Diplodocoidea Macronaria Camarasaurus Bellusaurus Europasaurus Tehuelchesaurus Galvesaurus Euhelopus Titanosauriformes

Species

Camarasaurus is regarded as containing four valid species by most researchers: C. grandis, C. lentus, C. lewisi, and C. supremus.^[42] C. supremus, the species named by Cope in 1877, is the type species. C. grandis was named in 1877 and C. lentus in 1889. The fourth species, C. lewisi, is of uncertain affinities. It was originally described as a distinct genus, Cathetosaurus, in 1988, but reclassified as a species of Camarasaurus in 1996.^[89][90] Some researchers have suggested that Cathetosaurus should be reinstated as a distinct genus,^[39][91][42] whereas others have suggested that C. lewisi may be synonymous with another Camarasaurus species.^[9][92]

Stratigraphic evidence suggests that chronological sequence aligned with the physical differences between the three species, and it describes an evolutionary progression within the Morrison Formation. C. grandis is the oldest species and occurred in the lowest rock layers of the Morrison. C. lewisi only briefly coexisted with C. grandis in the lowest strata of the upper Morrison until going extinct,^[9] but it is possible this is because of a lack of specimens from C. lewisi.^[9] C. lentus appeared later, co-existing with C. grandis for several million years, possibly due to different ecological niches as suggested by differences in the spinal anatomy of the two species. At a later stage, C. grandis disappeared from the rock record, leaving only C. lentus.^[9] Then C. lentus, too, disappeared; at the same time, C. supremus appeared in the uppermost layers. This immediate succession of species, as well as the very close similarity between the two, suggests that C. supremus may have evolved directly from C. lentus, representing a larger, later-surviving population of animals.^[93]

Synonyms

• Amphicoelias latus was named in 1877 by Cope in the same paper that described A. altus. It was described on the basis of a right femur and four caudal vertebrae that had been found at Garden Park alongside fossils of C. supremus. However, it is now considered a synonym of C. supremus or C. grandis.^[10][9]
• Caulodon diversidens was named in 1877 by Cope on the basis of several teeth. These teeth however are undiagnostic and have been considered either indeterminate macronarian or synonym of C. supremus.^[9][4]
• Caulodon leptoganus was named in 1878 by Cope on the basis of two incomplete teeth. These teeth are undiagnostic and have been considered either indeterminate macronarian or synonym of C. supremus.^[9][4]
• Morosaurus impar was named in 1878 by Marsh as the type species of his genus Morosaurus. This species was named on the basis of a sacrum that had been found at Como Bluff. However, it is now considered a synonym of C. grandis.^[9]

• Morosaurus robustus was named in 1878 by Marsh on the basis of an ilium that had been collected at Como Bluff. It is now considered a synonym of C. grandis.^[9]
• Camarasaurus leptodirus was in 1879 by Cope on the basis 3 partial cervical vertebrae. It has been suggested to be a synonym of C. supremus.^[9]
• Diplodocus lacustris was named in 1884 by Marsh on the basis of several teeth, a premaxilla, and a maxilla. These fossils were collected by American fossil hunters Arthur Lakes and Benjamin Mudge in 1877 from an outcrop in Morrison, Colorado.^[94] However, this species has been considered a chimera. Although the teeth and dentary of D. lacustris are flagellicaudatan, the skull material is likely from a Camarasaurus.^[94]
• Pleurocoelus montanus was named in 1896 by Marsh as a new species of Pleurocoelus on the basis of several vertebral centra and assorted bones of a juvenile sauropod found at Como Bluff. It is generally regarded as a synonym of C. grandis.^[9][95]
• Uintasaurus douglassi was named in 1919 by American paleontologist W. J. Holland for 5 anterior cervical vertebrae unearthed from Dinosaur National Monument.^[96] The species was later regarded as a synonym of C. lentus.^[9][13]
• Camarasaurus annae was named in 1950 by American zoologist Tage Ellinger on the basis of an isolated dorsal vertebra that had been found at Dinosaur National Monument.^[97] This species is generally considered a synonym of C.lentus.^[9]

  

  Teeth from the Caulodon diversidens holotype.

Reassigned species/specimen

• Morosaurus agilis was named in 1889 by Marsh on the basis on a partial skull and 3 vertebrae unearthed in Garden Park, Colorado.^[98] The species remained in taxonomic uncertainty until 2020, when it was placed in a new genus, Smitanosaurus, and reclassified as a dicraeosaurid.^[18]
• Camarasaurus becklesiii was initially described as Pelorosaurus becklesii in 1842 by British scientist Gideon Mantell based on a partial forelimb that had been found in the Cretaceous-aged Hastings Beds of Sussex, United Kingdom. It was placed in Morosaurus by Marsh in 1889^[99] and Camarasaurus by von Huene in 1932^[100] until in 2015, it was placed in its own genus, Haestasaurus.^[101]
• Morosaurus marchei was named in 1898 by French scientist Henri Sauvage on the basis of an incomplete distal caudal vertebra and tooth found in the Upper Jurassic-aged Alcobaca Formation of Lisbon, Portugal.^[102] He selected the caudal vertebra to be the holotype. Later, French paleontologists Albert de Lapparent & Georges Zbyszewski referred the holotype^[103] vertebra to Megalosaurus insignis, whereas American paleontologist James Henry Madsen and colleagues assigned it to indeterminate Megalosauria.^[63] The tooth was identified as belonging to an indeterminate turiasaurian in 2017.^[104]
• Camarasaurus alenquerensis was named as a species of Apatosaurus in 1957 by Lapparent and Zbyweski on the basis of a partial postcranial skeleton from the Upper Jurassic-aged rocks of the Lourinha Formation in Lourinha, Portugal.^[105] It was placed in Camarasaurus by American researcher John McIntosh in 1990,^[11] but was granted a new genus in 1998, Lourinhasaurus.^[68]

Paleobiology

Feeding

Camarasaurus was a herbivore that probably fed at moderate heights of 2 to 5 m (6 ft 7 in to 16 ft 5 in).^[50]: 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.^[106] 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.^[107] 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.^[108][106] The diet of adult Camarasaurus might have consisted of the leaves of conifers, such as those of the extinct Cheirolepidiaceae, and ginkgos.^[106] In 2016, Mark Hallett and Matt Wedel suggested that female cones of araucarians as well as resins could have supplemented its diet.^[106]

Jaw adductor musculature (muscles responsible for closing the mouth) of Camarasaurus lentus. Origin and insertion surfaces for the muscles (left) and reconstructed muscles (right)

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).^[59] 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.^{[109]: 900 [110]: 182} The sturdy construction of the skull also suggests that it was able to resist greater stresses during feeding than other sauropods.^[59][109] 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.^[59] 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.^[111][59]

Cross-sections of the teeth of Camarasaurus (left) and Diplodocus (right), with white arrows showing daily growth lines

As 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.^[112] 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.^[64] Alternatively, these blood vessels could have supported "lips" like those found in today's lizards.^[110]: 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.^{[113][56]: 13}

Tail function

Early paleontologists assumed that sauropods dragged their tail, but trackway evidence confirms that the tail was held high-up and rarely touched the ground. The tail counter-balanced the neck and might have been used for defence against predators.^{[56]: 11 [114]} 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, suggesting that it was 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.^[114]

Ontogeny

In a 1994 paper, a premaxilla fragment of an embryonic sauropod was assigned to Camarasaurus sp. This fragment was unearthed in the Dry Mesa Quarry, an area that may have been a sauropod nesting site similar to those in France and South Africa.^[115][116] The premaxilla fragment itself is 37 millimetres (1.5 in) in length, suggesting a skull length of about 70 millimetres (2.8 in) and body length of about 1,090 millimetres (43 in). Based on these measurements, the authors of the paper created a full-scale model of a hypothetical egg. This egg had a volume of 7.5 liters (2.0 U.S. gal), one smaller than those of large birds like ostriches.^[117] This suggests that sauropod embryos were small enough to fit in eggs and provided evidence against proponents of sauropod viviparity.^[118]

Growth

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.^[119] A 2024 study estimated the maximum age at death for Camarasaurus sp. GPDM 220 to be around 35 years.^[120]

Metabolism

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.^[121] Camarasaurus grew in size quickly to limit the time it would be vulnerable to predation. This would imply it had a relatively high metabolic rate as a juvenile.^[122]

Paleopathology

Main article: Paleopathology

A Camarasaurus pelvis recovered from Dinosaur National Monument in Utah shows gouging attributed to Allosaurus^[123] and on the ilium of the C. lewisi type there are large Theropod bite marks.^[124]

In 1992, a partial C. grandis skeleton was discovered at the Bryan Small Stegosaurus Quarry of the Morrison Formation near Cañon City, Colorado.^[125] This specimen preserved a partial right humerus cataloged as DMNH 2908 and associated vertebrae from the back and tail.^[125] In 2001, Lorie McWhinney, Kenneth Carpenter, and Bruce Rothschild published a description of a pathology observed on the humerus.^[126] They noted a juxtacortical lesion 25 by 18 cm wide made of bone that resembled woven fibers.^[127] Although woven bone forms in accessory dental bone, in other locations, it is a sign of injury or illness.^[127] The woven bone's "undulating fibrous bundles" were observed oriented in the direction of the m. brachialis.^[127] The lesion's fusion and lack of porosity at its near and far ends indicate the periostitis was inactive or healed.^[127] McWhinney and the other researchers argued that this injury would have been a continuous source of hardship for the animal.^[128] It would have exerted pressure on the muscles.^[126] 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.^[126] This effect would have hindered the M. brachialis, m. brachoradialis, and to a lesser degree the m. biceps brachii to the lesion's position on the humerus.^[126] 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.^[129] The lesion would also have caused long-term fasciitis and myosistis.^[126] 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."^[128] To help determine the cause of the pathology, McWhinney and the other researchers performed a CT scan in 3-mm increments.^[130] The CT scan found that the mass had a consistent radiodensity and was separated from the cortex of the bone by a radiolucent line.^[131] No evidence was found of stress fracture or infectious processes like osteomyelitis or infectious periostitis.^[130] They also ruled out osteochondroma because the axis of the spur is 25° relative to the vertical axis of the humerus, whereas an osteochondroma would have formed at 90° to the axis of the humerus.^[127] Other candidates identified by the scientists for the origin of the spur-bearing lesion included:

1. Hypertrophic osteoarthropathy – although this was ruled out by the presence of the spur-like process.^[132]
2. Osteoid osteoma – but this would not explain the spur or osteoblastic reaction.^[133]
3. Shin splints or tibial stress syndrome – a possible origin, as many symptoms would be held in common, but shin splints would not explain the spur.^[134]
4. Myositis ossificans traumatica (circumscripta) – possible, but unlikely source.^[135]
5. Avulsion injury – McWhinney and the other researchers considered an avulsion injury caused by "repetitive overexertion of the muscles" to be the most likely source for the lesion on the humerus.^[126] The researchers believed the lesion to have originated with the avulsion of the m. brachialis causing the formation of "a downward-sloping elliptical mass".^[128] The bone spur was caused by an osteoblastic response following a tear at the base of the m. brachioradialis caused by its flexor motion.^[128]

Paleoecology

Habitat

Skull and neck in mudstone matrix, Dinosaur National Monument

The Morrison Formation, situated along the eastern flank of the Rocky Mountains, is home to a fossil-rich stretch of Late Jurassic rock. A large number of dinosaur species can be found here, including relatives of Camarasaurus such as Diplodocus, Apatosaurus, and Brachiosaurus, but camarasaurs are the most abundant of the dinosaurs in the formation.^[136] Camarasaurus fossils have been found in almost every major locality and have one of the greatest known distributions of Morrison dinosaurs, with fossils found in localities from New Mexico to Montana and Utah to Oklahoma.^[9] According to radiometric dating, the Morrison sedimentary layers range between 156.3 million years ago (Mya) at the base, to 146.8 Mya at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period.^[137][138] Its environment is interpreted as semiarid with distinct wet and dry seasons.

Dinosaur and trace fossils are found particularly in the Morrison Basin, which stretches from New Mexico to Alberta and Saskatchewan and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. Eroded material from their east-facing drainage basins was carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains.^[139] The formation is similar in age to the Lourinha Formation in Portugal and the Cañadón Calcáreo Formation in Argentina, Camarasaurid fossils have been found at the 2 formations.^[105][24] In 1877, it became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope, with Camarasaurus itself being discovered and named by the latter Paleontologist during the conflict.

Paleofauna

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as Maraapunisaurus, Amphicoelias, Barosaurus, Diplodocus, Apatosaurus, Brontosaurus, and Brachiosaurus. Dinosaurs living alongside Camarasaurus included the herbivorous ornithischians Camptosaurus, Gargoyleosaurus, Dryosaurus, Stegosaurus, and Nanosaurus. Predators in this paleoenvironment included the theropods Torvosaurus, Ceratosaurus, Marshosaurus, Stokesosaurus, Ornitholestes,^[140] and Allosaurus, which accounted for up to 75% of theropod specimens, and was at the top trophic level of the Morrison food web.^[141][142] Camarasaurus is commonly found at the same sites as Allosaurus, Apatosaurus, Stegosaurus, and Diplodocus.^[143]

Other organisms in this region included bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, 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.^[144]