| Camarasaurus | |
|---|---|
 | |
| CM 11338, a nearly complete skeleton ofCamarasaurus lentus | |
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 | |
| Synonyms | |
List
| |
Camarasaurus (/ˌkæmərəˈsɔːrəs/KAM-ər-ə-SOR-əs) is agenus ofsauropoddinosaur that lived during theLate Jurassic in what is now the United States. Its fossils are primarily known from theMorrison Formation dating to theKimmeridgian andTithonian ages of theJurassic, between 155 and 145 million years ago (mya). It was named byEdward Drinker Cope in 1877; it definitively contains threespecies,C. supremus, thetype species,C. grandis, andC. lentus, while some researchers considerC. lewisi to be in its own genus,Cathetosaurus. The generic name means "chambered lizard", referring to the hollow chambers, known aspleurocoels, in its cervicalvertebrae (Greekκαμαρα [kamara] meaning 'vaulted chamber', or anything with an arched cover, andσαυρος [sauros] meaning 'lizard'). Hundreds of specimens have been excavated to date, including some nearly complete skeletons. It is among the best understood dinosaurs, with detailed studies of itsanatomy,paleobiology,paleoecology, and more.
A medium-large sauropod,C. supremus is estimated to have been 23 m (75 ft) long and to have weighed 42.3 tonnes whereasC. lentus was only around 15 m (49 ft) long. Like other sauropods, it wasquadrupedal, with a large body, long neck, and long tail. Itsskull was large, tall, and boxy with a hugenaris, in contrast to the low skulls of sauropods likeDiplodocus andApatosaurus.Camarasaurusteeth are distinct in their spoon-shaped teeth which bear continuous cutting edges. It had 13-14 teeth in the upper jaws and 13 teeth in thelower jaws, which were rapidly replaced.Camarasaurus was named during theBone Wars, a scientific rivalry between paleontologists Edward Drinker Cope andOthniel Charles Marsh. Marsh assigned many species to his genusMorosaurus, includingM. lentus andM. grandis which are now believed to be species ofCamarasaurus.
Camarasaurus is a member of the groupMacronaria, however its relationships with its relatives are uncertain and debated. Some paleontologists have groupedCamarasaurus with taxa likeTehuelchesaurus andLourinhasaurus in thefamilyCamarasauridae, whereas others believe it is theonly member of Camarasauridae.Camarasaurus is thought to have been a mediumbrowser, with a feeding height of 2 to 5 m (6 ft 7 in to 16 ft 5 in), and a selective feeder. The robust, large jaws of the genus indicate that it had a stronger bite than sauropods likediplodocids. This would allow forniche partitioning in the Morrison Formation where fossils ofCamarasaurus are known, which preserves a menagerie of sauropods. It is among the most common sauropods in the formation and was adapted to many environments based on its wide distribution.Camarasaurus also lived alongside dinosaurs likeStegosaurus,Allosaurus, andBrachiosaurus.
Fossils ofCamarasaurus were first discovered in the spring of 1877 by Oramel William Lucas, a school superintendent, inMorrison Formation rocks inGarden Park, Colorado. These fossils were sent toEdward Drinker Cope, apaleontologist based inPhiladelphia, who identified it as belonging to a newgenus andspecies, which he namedCamarasaurus supremus, meaning "chambered lizard, from theGreekκαμαρα (kamara) meaning "vaulted chamber", or anything with an arched cover, andσαυρος (sauros) meaning "lizard"), and from theLatinsupremus, "supreme" or "highest".[1][2] By this time, the Morrison Formation had become the main battleground of theBone Wars, a fossil-collecting competition between Cope and paleontologistOthniel Charles Marsh. Due to this, at the time many descriptions of taxa, such as that ofCamarasaurus, were rushed by Cope and Marsh.[3]Camarasaurus supremus'type specimen (AMNH 5760) consists of: onecervical vertebra, the namesake of the genus, twodorsal vertebrae, and threecaudal vertebrae. However, these elements are from differing individuals, making themcotypes.[4] The cervical vertebra has been proposed to be thelectotype ofC. supremus, though there has not been a published stance.[5]
Between August 1877 and 1878, Lucas unearthed and sent many moreC. supremus fossils, including: two cervicals, 18 dorsals, 55 caudals, 17 leftribs and several right ones, eightchevrons, one rightscapula, one rightcoracoid, twopubes, fourischia, onefemur, and onefibula. 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), andAmphicoelias latus (1877). All of these species are considered synonyms ofC. 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, includingEpanterias,Amphicoelias altus, andHypsirhophus.[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 toC. supremus includes: onebraincase, onemaxilla, onequadrate, twodentaries, several teeth, 23 cervicals, 38 dorsals, twosacra, 102 caudals, 25 chevrons, twosternal plates, 110 ribs, six scapulae, two coracoids, twohumeri, twometacarpals, fiveilia, eight ischia, six pubes, four femora, fourtibiae, two fibulae, oneastragalus, and onemetatarsal. 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 byHenry Osborn and Charles C. Mook in 1921.[4]
In 1877, Cope commissioned Dr. John A. Ryder to create a restoration ofCamarasaurus 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 fromskull 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]
Between 1877 and 1879, paleontologistsWilliam Reed, Marshall P. Felch, andSamuel W. Williston found an incomplete, partially articulated skeleton (YPM 1901)[12] of a juvenile sauropod in Quarry 1 atComo Bluff, Wyoming. Marsh was sent part of the specimen which he described in 1877 as belonging to a new species of the genusApatosaurus, naming itApatosaurus grandis, the specific name coming from the Latingrandis meaning "great".[12] This skeleton would be the best preserved single individual ofCamarasaurus known at the time, consisting of: abasioccipital, several dorsals, a partial sacrum, the first 27 caudals, a complete left and incomplete rightpectoral girdle, an incomplete left forelimb, femora, tibiae, fibulae, and ribs.[13][9] Additionally, severalparatypes were unearthed from the same locality, including: an incomplete skull and partial postcranial skeleton (YPM 1905), the holotype sacrum of the later namedMorosaurus 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 ofA. grandis. Marsh then described the sacrum as belonging to a new genus and species,Morosaurus impar, which he believed was related toApatosaurus,Brontosaurus,[15] andAtlantosaurus.[16]Morosaurus' name comes from the Greek Μόρος (moros meaning "stupid"), in reference to its small brain size compared to its body size, andσαυρος (sauros meaning "lizard").[17] Marsh went on to refer five species toMorosaurus:M. impar, M. robustus, M. agilis, M. lentus, andM. grandis, which was previously namedApatosaurus grandis.[18]M. lentus, the specific name coming from the Latinlentus meaning "slow", was named by Marsh in 1889 on the basis of a juvenile sauropod skeleton that was found at Como Bluff.[18][19] Its type specimen, YPM 1910, was mounted at theYale Peabody Museum fossil hall in 1930 and was one of the first nearly complete sauropod skeletons to be found,[20] consisting of: thevertebral 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.[13][20]
During the Bone Wars, Marsh also named several other species based on material now assigned toCamarasaurus. In 1884, Marsh named a new species ofDiplodocus, D. lacustris, on the basis of several teeth and fragments from the upper and lower jaws, from Morrison Formation outcrops in Morrison, Colorado. This species has since been considered achimera; the skull elements come fromCamarasaurus while the rest is fromApatosaurus[21] or an indeterminateflagellicaudatan, a group containingdiplodocids andrebbachisaurids.[22]
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 synonymizedM. impar withM grandis,[23] a suggestion supported by later authors.[24][4][25] In 1901, American researcherElmer Riggs concluded that of the fiveMorosaurus species named at the time, only three were valid:M. grandis, M. lentus, andM. agilis.[26] Riggs synonymizedM. impar, the type species, withM. grandis and further suggested thatMorosaurus andCamarasaurus were synonyms.[24] However, the suggestion thatMorosaurus andCamarasaurus were generic synonyms was not formalized until later research.[18] In their 1921monograph onCamarasaurus, Osborn and Mook synonymizedMorosaurus withCamarasaurus,[4] an idea that has been accepted since.[13][27] In 1925, American researcherCharles W. Gilmore mistakenly synonymizedC. grandis withC. impar despite the former being named first.[27]M. impar andM. robustus are now considered synonyms ofC. grandis[9][18] andM. agilis has since been moved to its own genus,Smitanosaurus.[18]
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.[28]: 64–65, 105 The competition to mount the first sauropod skeleton specifically was the most intense, with theAmerican Museum of Natural History (AMNH),Carnegie Museum of Natural History (CM), andField Museum of Natural History (FMNH) all sending expeditions to the west to find the most complete sauropod specimen,[28]: 1, 5 bring it back to the home institution, and mount it in their fossil halls.[28]: 1, 5, 247 In the mid-late 1890s, the AMNH and FMNH were the first to mount expeditions, finding sauropod material at Como Bluff andFruita, Colorado respectively.[28]: 38–39, 117–118 This material, mostly consisting of limb bones, was referred toMorosaurus and led to new reconstructions of sauropodmanus andpes structure.[25][24] In the 1890s, Osborn also suggested thatMorosaurus was a synonym ofCamarasaurus.[4][29] In 1899, AMNH field workersWalter Granger and Peter Kaisen unearthed a completeCamarasaurus skull, mandible, and associated cervical vertebrae in rock layers atBone Cabin Quarry, Wyoming, the first discovery of a nearly completeCamarasaurus skull.[30][31] In 1905, a plaster skull based on theCamarasaurus skull found at Bone Cabin Quarry and based on a skull later referred toBrachiosaurus[32][33] was mounted on a skeleton ofBrontosaurus,[34][31] leading to a trend of mistakenly mountingCamarasaurus-like skulls on apatosaurine bodies. This was the first-ever mounted skeleton of a sauropod.[31]
Around the same time as the AMNH, the CM was conducting its own fossil expeditions to quarries in Wyoming where it recovered severalCamarasaurus specimens. However, paleontologists of the time assigned these fossils toMorosaurus instead ofCamarasaurus.[35][36] In 1909, American fossil hunterEarl Douglass of the CM uncovered an extensive deposit of dinosaur fossils at what is now the iconicDinosaur National Monument nearJensen, Utah.[37] In 1914 during excavations at the Monument, Douglass unearthed a nearly complete skull and skeleton of a juvenileC. lentus still preserved in articulation. In 1925, this skeleton was then described by Charles W. Gilmore who supported the claim thatMorosaurus is a synonym ofCamarasaurus, 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, Douglass found anotherCamarasaurus 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, theNational Museum of Natural History acquired the skeleton and several other fossils. This specimen was then prepared publicly at theTexas Centennial Exposition of 1936 before it was mounted in adeath pose in the museum's fossil hall in 1947. This skeleton would turn out to be the second most complete skeleton ofCamarasaurus known.[38][9] It too was referred toC. lentus by paleontologists.[13][9]
In 1967, American researcherJames Jensen collected a well preserved and articulated postcranial skeleton ofCamarasaurus fromUncompahgre Hill inwestern Colorado which was then deposited atBrigham Young University under specimen number BYU 9740.[39][40] 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.[40][39][41] The generic nameCathetosaurus lewisi comes from the Greek κάθετος (kathetos meaning "vertical"), in reference to its supposed ability to stand upright, andσαυρος (sauros meaning "lizard"), and the species name is in honor of Arnold D. Lewis, a fossil preparator and field worker.[17][40] This original 1988 description was brief,[40] but John McIntosh and colleagues extensively described BYU 9740 in 1996 where they determined thatCathetosaurus lewisi was a species ofCamarasaurus,[39] an opinion supported by many other authors.[9][42][5] In 2013, paleontologists Octavio Mateus and Emanuel Tschopp argued in aconference abstract thatCathetosaurus is a distinct genus,[41] but this was not supported by later research andphylogenetic analyses (studies of the interrelationships of organisms).[5][43][42]
In 1992, a nearly complete and articulated skeleton ofC. grandis[44] was collected by fossil hunter Jeffrie Parker and colleagues from a site near the Bone Cabin Quarry.[45] This specimen (GMNH-PV 101) now resides at theGunma Museum of Natural History inGunma, Japan.[9][46] Another well-preservedCamarasaurus specimen was found in 1992 at theHowe Quarry in Wyoming by Swiss field workers working for theSauriermuseum Aathal inZurich, Switzerland. The skeleton is one of the best known, with nearly every element articulated and skin impressions from the skull and hindlimb.[47][42] The specimen, SMA 002, has not yet gotten a full identification, but has been suggested to be a specimen ofC. lewisi.[42] In 1996, several fragmentary remains ofCamarasaurus were described from westernSouth Dakota[48] andNew Mexico,[49] extending the northeastern and southern range of the genus. The New Mexican remains were found in theSummerville Formation, indicatingCamarasaurus lived outside of the Morrison Formation.[49] In 2005, the northernmost specimen, an incomplete skull and postcranial skeleton, ofCamarasaurus was discovered in theLittle Snowy Mountains ofMontana.[50]
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.[51]: 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.[52][53]
Camarasaurus was a medium to large-sized sauropod.[9][52] The most common species,C. lentus, was about 15 m (49 ft) in length, andC. grandis and probablyC. lewisi were comparable in size.[54][52] The body weight of adultC. 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.[52] In 2020, John Foster stated that the latest species,C. supremus, had bones about 50% longer than those of the smaller species.[52] AlthoughC. 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.[52] American paleontologistGregory S. Paul, in 2024, instead gave a length estimate of 18 m (59 ft) and a weight estimate of 24 tonnes for this species.[53]
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The skull was larger and more strongly build than in other sauropods, with massive upper and lower jaws.[55][9][52] Skull length varied between individuals, ranging from about 46% to 58% of the length of the femur.[56] As in the contemporaryBrachiosaurus, theexternal naris (nostril) was enlarged, resulting in an arched forehead.[57][27]: 353 Both genera had a well-defined snout,[58] but the skull ofCamarasaurus was more rounded and short-faced.[52][59]: 194 When viewed from above, the snout was rounded and slightly tapering, different to the rectangular snout ofDiplodocus. The skull was almost rectangular when viewed from the back and higher than wide.[27]: 354
The largest openings that penetrated the skull were the external naris, theorbit (eye opening), and theinfratemporal 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 asclerotic ring, a ring of small plate-like bones around thepupil of the eye. The infratemporal fenestra was roughly triangular and tilted backwards at an angle of 30°. A small and pear-shapedantorbital fenestra was present between the external naris and the orbit. Even smaller was thesupratemporal 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.[60]: 6 [27]: 364–365 [55]
The skull showed severalautapomorphies (features not found in related genera). According to a 2004 review, these include thelacrimal (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. Thequadratojugal bone, which formed the rear-bottom corner of the skull, reached upwards to make contact with thesquamosal 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 thedentary bone.[57]: 306
Known specimens had four teeth in eachpremaxilla (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.[60] 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 [27]: 365–366 [42]
The vertebral column consisted of 12 cervical (neck), 12 dorsal (back), and five sacral (hip) vertebrae.[52][61]: 81 The tail was composed of 53 caudal vertebrae the two specimens that preserve a complete tail (CM 11338 and GMNH 101).[62]: 5 Most of the volume of the dorsal and cervical vertebrae was made up byair sacs which were connected to the lungs. These air sacs filled extensive excavations in the vertebrae that gaveCamarasaurus its name ('chambered lizard').[63]: 14–15 [64] The cervical and dorsal vertebrae wereopisthocoelous (concave at the rear andconvex at the front) and had large excavations on their sides calledpleurocoels.[27]: 370 [61]: 76 Theneural 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.[52][60]: 37 The neural spines of the second to fifth sacral were often fused together.[60]: 37 The cervical vertebrae had very slender and elongatedcervical ribs that overlapped multiple preceding vertebrae.[27]: 374 [52]
The left and right halves of the shoulder girdle were probably connected at the front of the trunk by thecoracoids.[65]: 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.[52][60]: 37 The forelimb was slender, and thehumerus was about 77% the length of thefemur (upper thigh bone). In contrast, the hindlimb was massive, and thetibia (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, theulnare and theradiale.[9][57]: 290 As in other macronarians, the fivemetacarpals were long, with the third metacarpal reaching one third of the length of the humerus.[60]: 37 [57]: 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 twophalanges (finger bones), including a claw that was slanted sidewards. The remaining digits possibly consisted of one phalanx, and lacked claws.[27]: 379–380 [57]: 290 In the ankle of the hind foot, thecalcaneum was small and rounded.[60]: 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.[57]: 295
Footprints show that the hind feet of sauropods were supported by a large, fleshy pad akin to that of elephants.[66]: 146 Such a fleshy pad was absent in the forefoot, as shown by skin skin impressions preserved close to thepalmar (rear) surface of the metacarpals of theCamarasaurus 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.[47]: 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 toCamarasaurus.[47]: 54–55
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Camarasaurus is the type genus of the familyCamarasauridae, a clade that is typically regarded as only includingCamarasaurus itself. However, phylogenetic analyses have recovered genera likeBellusaurus,Tehuelchesaurus, andLourinhasaurus as members of the family.[67][68][26] Cope recognized thatCamarasaurus was a relative ofCetiosaurus,Bothriospondylus,Ornithopsis, andAnchisaurus (Megadactylus) in his description, but failed to name a family for these taxa.[69] In 1878 with the description ofAmphicoelias, 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.[70] Marsh proposed his own family of sauropods, Morosauridae, which he thought includedMorosaurus and possiblyCamarasaurus, withAmphicoelias considered a synonym of the latter.[71]: 241 However, Morosauridae has since been synonymized with Camarasauridae.
In 1970, Rodney Steel took an expansive concept of Camarasauridae, encompassing all sauropods then known exceptdiplodocoids andtitanosaurs.[72] In 1990, John S. McIntosh regarded Camarasauridae as made up of two subfamilies: Camarasaurinae, containingCamarasaurus,Aragosaurus,Euhelopus, andTienshanosaurus, andOpisthocoelicaudiinae, containingOpisthocoelicaudia andChondrosteosaurus.[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 asEuhelopus,Asiatosaurus, andChiayusaurus, or vertebral anatomy, likeOpisthocoelicaudia, 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.[26][74] This group was initially defined as applying to the clade including the most recent common ancestor of Camarasauridae andTitanosauriformes and all of its descendants.[75] This group was initially defined as applying to the clade including the most recent common ancestor of Camarasauridae andTitanosauriformes and all of its descendants.[76] In 1995, Paul Upchurch defined Camarasauridae as consisting ofCamarasaurus andHaplocanthosaurus, which were united by: cervicals with large, flat ventral surfaces, deeply excavated sections on the posterior faces of proximal dorsal ribs, and strongly twisted shafts at the distal ends of ischia.[77] However,Haplocanthosaurus has since been reclassified as a basal diplodocoid.[22][78]
Several sauropods have been suggested to be in Camarasauridae, or in a wider group known as Camarasauromorpha, includingLourinhasaurus, Bellusaurus, andOplosaurus, however this has come under criticism.[79][68][5]Bellusaurus was recovered as a camarasaurid in a 2014 paper, but has been considered a member ofTuriasauria,[80]Mamenchisauridae,[81] or basal Macronaria.[68]Lourinhasaurus was classified as a camarasaurid and a species ofCamarasaurus itself, but some studies have found it to be a basal neosauropod,[82] basal macronarian[67] or eusauropod,[83][57] orlaurasiform instead.[84][85] However, in a 2019 study, Mannion and colleagues foundLourinhasaurus as a sister taxon ofCamarasaurus.[80] Thedubious British genusOplosaurus has been suggested to be a camarasaurid,[86] however other studies have placed it in Turiasauria[87] or Macronaria in general.[88] Upchurch (1995) suggested thatChondrosteosaurus, a dubious sauropod from the Cretaceous of the United Kingdom, was a camarasaurid, however he noted the fragmentary nature of the only known specimen, two incomplete cervical vertebrae.[77]Camarasaurus is now often considered a basal macronarian outside of any clades of sauropods, similar toYuzhoulong.[89] Below is a simplified cladogram from Mocho and colleagues (2014), which recovered Camarasauridae as includingCamarasaurus, Tehuelchesaurus, andLourinhasaurus, three genera of Late Jurassic sauropods.[67]
A simplified cladogram of basal Macronaria, which findsCamarasaurus in polytomy withBellusaurus at the base of Macronaria, after Tan and colleagues (2021) is shown below:[90]
Camarasaurus is regarded as containing four valid species by most researchers:C. grandis,C. lentus,C. lewisi, andC. supremus.[43]C. supremus, the species named by Cope in 1877, is the type species.C. grandis was named in 1877 andC. 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 ofCamarasaurus in 1996.[40][61] Some researchers have suggested thatCathetosaurus should be reinstated as a distinct genus,[41][91][43] whereas others have suggested thatC. lewisi may be synonymous with anotherCamarasaurus species.[9][92]
Thediagnostic (distinguishing) traits of eachCamarasaurus species are uncertain, with all being poorly defined and most specimens assigned simply asCamarasaurus sp. rather than a species.[41][5][43][9] Additionally, the holotype ofC. supremus is a composite of several adult individuals[4] and the type ofC. grandis is from a juvenile individual,[12][14] making them difficult to compare based on morphological features due to a lack of understanding ofCamarasaurus ontogeny. In 2005, Japanese paleontologist Takehito Ikejiri defined eachCamarasaurus species by differences in their size and vertebrae:C. supremus was defined as having a larger body with T-shaped neural spines in some caudal vertebrae and relatively shorter neural arches in dorsals 3-8,C. grandis was defined as having T-shaped neural spines in anterior view in some caudal vertebrae and tall neural arches in dorsals 3-8, andC. lentus was defined as bearing short, massive neural arches in dorsals 3-8 and anterior caudal neural spines with gradually expanded. However,C. lewisi, which Takejiri believed was a species ofCamarasaurus, was diagnosed by its deep, narrow neural spine bifurcation on presacral vertebrae, starting at cervical 3 and ending in dorsal 11.[9]
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 withC. 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 fromC. lewisi.[9]C. lentus appeared later, co-existing withC. 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 onlyC. lentus.[9] ThenC. 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 thatC. supremus may have evolved directly fromC. lentus, representing a larger, later-surviving population of animals.[93]
Camarasaurus was aherbivore that probably fed at moderate heights of 2 to 5 m (6 ft 7 in to 16 ft 5 in).[52]: 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.[109] In 1998,Anthony Fiorillo analysedmicroscopic pits and scratches on the tooth surfaces and concluded that adultCamarasaurus consumed coarser foods than the contemporaryDiplodocus. JuvenileCamarasaurus, in contrast, appeared to have consumed the same soft foods as adultDiplodocus.[110] 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-snoutedCamarasaurus andBrachiosaurus were selective feeders while the square-snouted diplodocids andrebbachisaurids were bulk feeders.[111][109] The diet of adultCamarasaurus might have consisted of the leaves of conifers, such as those of the extinctCheirolepidiaceae, andginkgos.[109] In 2016, Mark Hallett and Matt Wedel suggested that female cones ofaraucarians as well asresins could have supplemented its diet.[109]
Camarasaurus probably had a more powerful bite than other sauropods due to the very largecoronoid 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).[55] A 2016 study by David Button and colleagues estimated that the bite force ofCamarasaurus was almost four times higher than that ofDiplodocus. The bite force was highest in the posterior portion of the tooth row, where it is estimated to have reached up to 1978newton.[112]: 900 [113]: 182 The sturdy construction of the skull also suggests that it was able to resist greater stresses during feeding than other sauropods.[55][112] Per Christiansen, in a 2000 paper, suggested thatCamarasaurus was adapted to biting off vegetation, but did not rake leaves asDiplodocus orBrachiosaurus did.[55] The upper and lower teeth appeared to have fit into each other. In a 1994 study,Jorge Calvo suggested thatCamarasaurus could crush food items against its teeth by moving its jaws back and forth, allowing some degree of food processing before shallowing.[114][55]
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 calledvon Ebner lines that are visible in cross-section of the teeth. This was slower than inDiplodocus, where a tooth only lasted for about 35 days, but as fast or faster than in ornithischian dinosaurs.[115] In a 2017 study, Kayleigh Wiersma and Martin Sander described a patch of soft tissue covering parts of the lower jaw and teeth of aCamarasaurus 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 ahornybeak, 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.[42] Alternatively, these blood vessels could have supported "lips" like those found in today's lizards.[113]: 157
A juvenile and heavily scavengedCamarasaurus 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 asgastroliths (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.[116][51]: 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.[51]: 25 The probable neck posture has been the subject of controversy.[51]: 12 A 1921 skeletal reconstruction ofCamarasaurus by Osborn and Mook shows a rather straight and horizontal neck,[117]: 219 while some later authors assumed a nearly vertical,swan-like neck.[117][51]: 12 Some complete skeletons, such as the juvenileC. lentus specimen CM 11338, also show a vertical neck, but these representopisthotonic death poses that do not necessarily reflect the original neck posture.[117] 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 ofCamarasaurus would have been powerful and inflexible, and that the elongated cervical ribs would have braced it along its underside.[118] 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 ofCamarasaurus and other sauropods were typically held straight with a slight downwards slope.[119][117]: 228
The idea of a more-or-less horizontal neck was questioned by several subsequent studies.[51]: 12 In 2005, David Berman and Bruce Rothschild usedComputed 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.[120] 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 ofCamarasaurus was habitually inclined downwards by about 15°, based on the orientation of thesemicircular canals in theinner ear, which housed thesense 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.[121][122]
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.[65]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 ofCamarasaurus based on thoseGreater Rhea, in which the neural spines are similarly bifurcated. Thenuchal ligament would have run along the top with branches connecting to either side of the bifurcated neural spines, while a second ligament, theLigamentum elasticum interspinale, would have run in-between the two prongs of the bifurcated neural spines.[123][113]: 184–185
In a 1991 study, Bruce Rothschild and David Berman noted that in 25% ofCamarasaurus specimens, some of the foremost tail vertebrae were fused together. InApatosaurus andDiplodocus, such fusion even occurred in 50% of the individuals. The fusion is caused byossified tendons rather than direct fusion of the vertebral bodies, and was identified asdiffuse idiopathic skeletal hyperostosis (DISH).[a] Therefore, this fusion is notpathological but might be an adaptation for stiffening the tail. Rothschild and Berman argued that the fusion was asexually 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.[125] In a 2008 study, Takehito Ikejiri suggested thatCamarasaurus 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.[126] 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.[127]
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 incompleteossification of the bones, Marsh argued that it must have belonged to anembryo.[128][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.[71][129] In 1994, Carpenter and McIntosh assigned this specimen toCamarasaurus grandis, and interpreted the large pleurocoels as a juvenile feature.[129] Although a small juvenile, there is no evidence that this specimen is indeed an embryo as proposed by Marsh.[130] In 1994, Brooks Britt and Bruce Naylor described a minute premaxilla ofCamarasaurus discovered inDry Mesa Quarry. The teeth of this bone have not yeterupted, 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 wereoviparous (egg-laying), questioning a hypothesis proposed byRobert T. Bakker in 1980 that sauropods wereviviparous and gave birth to relatively large young.[130][131] The first definitive sauropod embryos and eggs were described from the Argentinian localityAuca Mahuevo in 1998.[132]
Juveniles had shorter necks and tails than adults.[130][51]: 11 As the individual matured, the neural arches of the vertebrae fused with the vertebral bodies; inCamarasaurus, the vertebrae of the mid and rear portion of the tail fused before those of the sacrum.[9] Other age-related changes found in adults include the rugose articular surfaces in the limbs, the ossification ofentheses of the vertebral column, and the fusion of the individual sacral vertebrae into a single structure.[133][61]: 81 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 bonesdid not change during growth.[134]
Growth rings and other features visible inthin sections of bones allow for reconstructing life history. As other sauropods,Camarasaurus grew as fast as modern birds and mammals, and reachedsexual maturity well before reaching maximum body size.[127][135]: 865 In 2013, Eva Maria Griebeler and colleagues examined thin sections of limb bones of a largeCamarasaurus 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.[136]: 3 A 2017 study by Cary Woodruff and Foster estimated the specimen GPDM 220 was probably about 30 years old, and maximally 35 years old, at the age of death.[137] 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.[135]: 866 As of 2024, GPDM 220 and "E.T." are amongst theoldest dinosaur individuals identified, even though representing relatively small individuals.[138]: 684 Dinosaurs might have grown throughout most of their lives. In 2021, Bruce Rothschild and Florian Witzmann determined that of 13 analyzedCamarasaurus 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.[139]: 263, 267
Dinosaurs have traditionally been assumed to be cold-bloodedectotherms that depend on environmental temperatures. Since the 1960s, evidence has been presented that dinosaurs instead werehomoiotherm (capable of maintaining constant body temperatures) or evenendotherm (having an increased metabolism capable of maintaining elevated constant temperatures).[51]: 15 [140] 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.[51]: 17 Body temperatures can be directly estimated based onisotope compositions of bones and teeth.[140][141] In a 2002 study, William Showers and colleagues usedoxygen isotope thermometry to analyse boneapatite. They found that, in their studiedCamarasaurus 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 theropodGiganotosaurus. These differences between body parts might have resulted fromcountercurrent exchange of heat, when excess heat was pumped from the trunk into the peripheral body parts as acooling mechanism.[140] In 2011, Robert Eagle and colleagues analyzedtooth enamel of two sauropods,Camarasaurus andGiraffatitan, usingclumped isotope thermometry. This analysis indicated body temperatures of 36–38 °C (97–100 °F), comparable to those of modern mammals.[141]
Multiple instances of pathologies (injuries or diseases) have been recorded inCamarasaurus specimens. In 1996, McIntosh and colleagues described pathologies in thirteen vertebrae of the complete tail of theC. grandis specimen GMNH-PV 101. In two of these vertebrae, theneural arch failed to completely develop, a developmental defect known asspina bifida – the first reported example of this condition in dinosaurs. In the 40th tail vertebra, only half of the neural arch had formed, leaving thespinal cord partly unprotected. At least five vertebrae show bone outgrowths around the joints of the vertebral centra, indicatingosteoarthritis (degenerative joint disease). Five consecutive tail vertebrae (49 through 53) are pathologically fused into a single structure.[62]: 17–18 [142]
A specimen from Bone Cabin Quarry showed erosions in thezygapophyses (joints between vertebrae) in four out of twenty tail vertebrae. In 2002, Rothschild and colleagues identified these pathologies the oldest fossil evidence forinflammatory arthritis.[143][c] In 2001, Lorrie McWhinney and colleagues described aperiostitis, an injury of theperiosteum (the outer layer of bones), in a humerus assigned toC. grandis. This injury involved parts of the bone to be fractured ortorn off, possibly due tostress or repeated excessiveexertion 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 alimp.[145] 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 asosteochondrosis 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 asenthesophytes caused by the insertion of tendons. These may have formed due to excessive use of the claws during life, possibly due to scratch-digging.[5]
_(Morrison_Formation%2c_Upper_Jurassic%3b_Carnegie_Quarry%2c_Dinosaur_National_Monument%2c_Utah%2c_USA)_4_(48696432982).jpg)
Camarasaurus is known fromsedimentary rocks of the Morrison Formation dating to theKimmeridgian andTithonian ages (155 to 143 million years ago).[57]: 266 A single tail vertebra from theSummerville Formation of New Mexico has been assigned to the genus by Adrian Hunt andSpencer G. Lucas in 1993, but this occurrence was not recognized in a subsequent review.[146][49][57]: 266 The Morrison Formation covers about 1.2 million km² of western North America, andCamarasaurus is found across this range, from more than 100 localities as far north as Montana to as far south as New Mexico.[147][148]
Camarasaurus is known from over 530 specimens, including isolated bones and about 50 partial skeletons.[149] It is the most common dinosaur of the Morrison Formation and, due to its abundance, one of the best-understood sauropods.[52]: 240, 272 In a 2003 survey of more than two hundred fossil localities, John Foster reported 179 specimens of the genus, comparable toApatosaurus (112) andDiplodocus (98), but far greater thanBrachiosaurus (12),Haplocanthosaurus (12) andBarosaurus (13).[150] Most identifiable specimens ofCamarasaurus belong to one of two species,C. grandis andC. lentus;C. lewisi andC. supremus are rarer.[151] Even though complete necks are rarely found in sauropods, five specimens ofCamarasaurus preserve all or nearly all of the cervical vertebrae.[152] 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 fromCamarasaurus.[153]
The Morrison Formation is interpreted as asemiarid environment with distinctwet anddry seasons.[154][155] In 2011, Henry Fricke and colleagues analyzed the relative abundance of oxygen isotopes (δ18O values) of bothCamarasaurus teeth andcarbonate rocks across the Morrisonbasin. 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 theCamarasaurus must havemigrated 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).[156]
As of 2024, a total of 25 sauropod species are recognized from the Morrison Formation.[148] The most common genera are thediplodocidsApatosaurus,Diplodocus,Supersaurus,Barosaurus,Brontosaurus, andGaleamopus; themacronarianBrachiosaurus, andHaplocanthosaurus. Dicraeosaurids such asSmitanosaurus,Dyslocosaurus, andSuuwassea were rarer components of the fauna.[148] Other dinosaurs known from the Morrison Formation include the predatorytheropodsKoparion,Stokesosaurus,Ornitholestes,Ceratosaurus,Allosaurus andTorvosaurus, as well as the herbivorousornithischiansCamptosaurus,Dryosaurus,Gargoyleosaurus andStegosaurus.[157]Allosaurus accounted for 70 to 75 percent of theropod specimens and was at the toptrophic level of the Morrisonfood web.[158] Other vertebrates that shared this paleoenvironment includedray-finned fish,frogs,salamanders,turtles likeDorsetochelys,sphenodonts,lizards, terrestrial and aquaticcrocodylomorphs such asHoplosuchus, and several species ofpterosaur likeHarpactognathus andMesadactylus. Shells ofbivalves and aquaticsnails are also common. The flora of the period has been revealed by fossils ofgreen algae,fungi,mosses,horsetails,cycads,ginkgoes, and several families ofconifers. Vegetation varied from river-lining forests in otherwise treeless settings (gallery forests) withtree ferns, andferns, to fernsavannas with occasional trees such as theAraucaria-like coniferBrachyphyllum.[159]
