Camarasaurus
Camarasaurus is a genus of sauropod dinosaur that lived during the Late Jurassic in what is now the United States. Its fossils are primarily known from the Morrison Formation dating to the Kimmeridgian and Tithonian ages of the Jurassic, between 155 and 145 million years ago. It was named by Edward Drinker Cope in 1877; it definitively contains three species, C. supremus, the type species, C. grandis, and C. lentus, while some researchers consider C. lewisi to be in its own genus, Cathetosaurus. The generic name means "chambered lizard", referring to the hollow chambers, known as pleurocoels, in its cervical vertebrae. Hundreds of specimens have been excavated to date, including some nearly complete skeletons. It is among the best understood dinosaurs, with detailed studies of its anatomy, paleobiology, paleoecology, and more.
A medium-large sauropod, C. supremus is estimated to have been long and to have weighed 42.3 tonnes whereas C. lentus was only around long. Like other sauropods, it was quadrupedal, with a large body, long neck, and long tail. Its skull was large, tall, and boxy with a huge naris, in contrast to the low skulls of sauropods like Diplodocus and Apatosaurus. Camarasaurus teeth 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 the lower jaws, which were rapidly replaced. Camarasaurus was named during the Bone Wars, a scientific rivalry between paleontologists Edward Drinker Cope and Othniel Charles Marsh. Marsh assigned many species to his genus Morosaurus, including M. lentus and M. grandis which are now believed to be species of Camarasaurus.
Camarasaurus is a member of the group Macronaria, however its relationships with its relatives are uncertain and debated. Some paleontologists have grouped Camarasaurus with taxa like Tehuelchesaurus and Lourinhasaurus in the family Camarasauridae, whereas others believe it is the only member of Camarasauridae. Camarasaurus is thought to have been a medium browser, with a feeding height of, and a selective feeder. The robust, large jaws of the genus indicate that it had a stronger bite than sauropods like diplodocids. This would allow for niche partitioning in the Morrison Formation where fossils of Camarasaurus 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 like Stegosaurus, Allosaurus, and Brachiosaurus.
History
Initial discovery and naming
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 meaning "vaulted chamber", or anything with an arched cover, and σαυρος, and from the Latin supremus, "supreme" or "highest". 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. Camarasaurus supremusBetween 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. Based on the fossils found at Garden Park, Cope erected several more genera and species of dinosaur including; Camarasaurus leptodirus , Caulodon diversidens, Caulodon leptoganus, and Amphicoelias latus. All of these species are considered synonyms of C. supremus and were described on the basis of fragmentary or isolated fossils. Many other taxa were named by Cope based on fossils from Garden Park, including Epanterias, Amphicoelias altus, and Hypsirhophus.
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, one, one, two, 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, 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, some of which were found alongside bones of theropods and ornithischians. 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.
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.
''Morosaurus'' and the Bone Wars
Between 1877 and 1879, paleontologists William Reed, Marshall P. Felch, and Samuel W. Williston found an incomplete, partially articulated skeleton 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". This skeleton would be the best preserved single individual of Camarasaurus known at the time, consisting of: a, 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. Additionally, several paratypes were unearthed from the same locality, including: an incomplete skull and partial postcranial skeleton, the holotype sacrum of the later named Morosaurus impar, and a fragmentary postcranial skeleton.File:Lull1930-skeleton-of-camarasaurus-lentus-recently-mounted-at-yale-fig1.jpg|left|thumb|The mounted holotype specimen of C. lentus at the Yale Peabody Museum
In 1878, Williston sent Marsh an isolated juvenile sauropod sacrum 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, and Atlantosaurus. Morosaurus
During the Bone Wars, Marsh also named several other species based on material now assigned to Camarasaurus. In 1884, Marsh named a new species of Diplodocus, 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 a chimera; the skull elements come from Camarasaurus while the rest is from Apatosaurus or an indeterminate flagellicaudatan, a group containing diplodocids and rebbachisaurids.
Following the Bone Wars, paleontologists also attempted to tackle the taxonomy of the many dinosaur genera named by Marsh and Cope. In 1898, Williston synonymized M. impar with M grandis, a suggestion supported by later authors. 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. Riggs synonymized M. impar, the type species, with M. grandis and further suggested that Morosaurus and Camarasaurus were synonyms. However, the suggestion that Morosaurus and Camarasaurus were generic synonyms was not formalized until later research. In their 1921 monograph on Camarasaurus, Osborn and Mook synonymized Morosaurus with Camarasaurus, an idea that has been accepted since. In 1925, American researcher Charles W. Gilmore mistakenly synonymized C. grandis with C. impar despite the former being named first. M. impar and M. robustus are now considered synonyms of C. grandis and M. agilis has since been moved to its own genus, Smitanosaurus.
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. The competition to mount the first sauropod skeleton specifically was the most intense, with the American Museum of Natural History, Carnegie Museum of Natural History, and Field Museum of Natural History all sending expeditions to the west to find the most complete sauropod specimen, bring it back to the home institution, and mount it in their fossil halls. 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. This material, mostly consisting of limb bones, was referred to Morosaurus and led to new reconstructions of sauropod manus and pes structure. In the 1890s, Osborn also suggested that Morosaurus was a synonym of Camarasaurus. In 1899, AMNH field workers Walter Granger and Peter Kaisen unearthed a complete Camarasaurus skull, mandible, and associated cervical vertebrae in rock layers at Bone Cabin Quarry, Wyoming, the first discovery of a nearly complete Camarasaurus skull. In 1905, a plaster skull based on the Camarasaurus skull found at Bone Cabin Quarry and based on a skull later referred to Brachiosaurus was mounted on a skeleton of Brontosaurus, leading to a trend of mistakenly mounting Camarasaurus-like skulls on apatosaurine bodies. This was the first-ever mounted skeleton of a sauropod.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. In 1909, American fossil hunter Earl Douglass of the CM uncovered an extensive deposit of dinosaur fossils at what is now the iconic Dinosaur National Monument near Jensen, Utah. In 1914 during excavations at the Monument, Douglass unearthed a nearly complete skull and skeleton of a juvenile C. lentus still preserved in articulation. In 1925, this skeleton was then described by Charles W. Gilmore who supported the claim that Morosaurus is a synonym of Camarasaurus, a position supported by other authors. This skeleton is one of the best sauropod specimens known to science, with nearly every element preserved in articulation. Sometime prior to 1922, Douglass found another Camarasaurus skeleton at Dinosaur National Monument, however it remained in a plaster jacket for many years. In exchange for several fossils, money, and time to work with Gilmore, the National Museum of Natural History acquired the skeleton and several other fossils. This specimen was then prepared publicly at the Texas Centennial Exposition of 1936 before it was mounted in a death pose in the museum's fossil hall in 1947. This skeleton would turn out to be the second most complete skeleton of Camarasaurus known. It too was referred to C. lentus by paleontologists.
Resurgent interest
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. 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. The generic name Cathetosaurus lewisi comes from the Greek κάθετος, in reference to its supposed ability to stand upright, and σαυρος, and the species name is in honor of Arnold D. Lewis, a fossil preparator and field worker. This original 1988 description was brief, but John McIntosh and colleagues extensively described BYU 9740 in 1996 where they determined that Cathetosaurus lewisi was a species of Camarasaurus, an opinion supported by many other authors. In 2013, paleontologists Octavio Mateus and Emanuel Tschopp argued in a conference abstract that Cathetosaurus is a distinct genus, but this was not supported by later research and phylogenetic analyses.In 1992, a nearly complete and articulated skeleton of C. grandis was collected by fossil hunter Jeffrie Parker and colleagues from a site near the Bone Cabin Quarry. This specimen now resides at the Gunma Museum of Natural History in Gunma, Japan. 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. The specimen, SMA 002, has not yet gotten a full identification, but has been suggested to be a specimen of C. lewisi. In 1996, several fragmentary remains of Camarasaurus were described from western South Dakota and New Mexico, extending the northeastern and southern range of the genus. The New Mexican remains were found in the Summerville Formation, indicating Camarasaurus lived outside of the Morrison Formation. In 2005, the northernmost specimen, an incomplete skull and postcranial skeleton, of Camarasaurus was discovered in the Little Snowy Mountains of Montana.
Description
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. 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.Camarasaurus was a medium to large-sized sauropod. The most common species, C. lentus, was about in length, and C. grandis and probably C. lewisi were comparable in size. 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. In 2020, John Foster stated that the latest species, C. supremus, had bones about 50% longer than those of the smaller species. Although C. supremus is too incompletely known to allow for precise size estimates, it would have reached almost in length and 42.3 tonnes in weight if its body proportions were identical to those of the smaller species. American paleontologist Gregory S. Paul, in 2024, instead gave a length estimate of and a weight estimate of 24 tonnes for this species.
Skull
The skull was larger and more strongly build than in other sauropods, with massive upper and lower jaws. Skull length varied between individuals, ranging from about 46% to 58% of the length of the femur. As in the contemporary Brachiosaurus, the was enlarged, resulting in an arched forehead. Both genera had a well-defined snout, but the skull of Camarasaurus was more rounded and short-faced. When viewed from above, the snout was rounded and slightly tapering, different to the rectangular snout of Diplodocus. The skull was almost rectangular when viewed from the back and higher than wide.The largest openings that penetrated the skull were the external naris, the , and the, 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 was present between the external naris and the orbit. Even smaller was the, which was present in the rear corners of the skull roof and mostly facing upwards. This opening was oval in shape and obliquely oriented.
The skull showed several autapomorphies. According to a 2004 review, these include the , 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, which formed the rear-bottom corner of the skull, reached upwards to make contact with the. 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.
Known specimens had four teeth in each , 9 to 10 teeth in each maxilla, and 13 teeth in each lower jaw. 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.
Postcranium
The vertebral column consisted of 12 cervical, 12 dorsal, and five sacral vertebrae. The tail was composed of 53 caudal vertebrae the two specimens that preserve a complete tail. Most of the volume of the dorsal and cervical vertebrae was made up by air sacs which were connected to the lungs. These air sacs filled extensive excavations in the vertebrae that gave Camarasaurus its name. The cervical and dorsal vertebrae were and had large excavations on their sides called. The 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. The neural spines of the second to fifth sacral were often fused together. The cervical vertebrae had very slender and elongated that overlapped multiple preceding vertebrae.The left and right halves of the shoulder girdle were probably connected at the front of the trunk by the. 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. The forelimb was slender, and the was about 77% the length of the . In contrast, the hindlimb was massive, and the 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 and the. As in other macronarians, the five metacarpals were long, with the third metacarpal reaching one third of the length of the humerus. 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 , including a claw that was slanted sidewards. The remaining digits possibly consisted of one phalanx, and lacked claws. In the ankle of the hind foot, the was small and rounded. 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.
Soft tissue and footprints
show that the hind feet of sauropods were supported by a large, fleshy pad akin to that of elephants. Such a fleshy pad was absent in the forefoot, as shown by skin skin impressions preserved close to the palmar surface of the metacarpals of the Camarasaurus specimen SMA 0002. The skin impressions also indicate that the second to fourth fingers of the forefoot were together wrapped in tissue. Patches of skin impressions are also preserved on the hind limbs of "E.T.", where they mostly show hexagonal scales that were between in diameter. In 2015, Tschopp and colleagues created models of the fore- and hind feet based on "E.T." to produce hypothetical footprints, showing that the prints of the hind feet were almost four times larger than those of the forefeet. Fossil trackways of sauropods can be "narrow-gauged" or "wide-gauged", depending on how close the tracks are to the trackway midline; Camarasaurus might have had an intermediate gauge. So far, tracks have not been confidently assigned to Camarasaurus.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. Cope recognized that Camarasaurus was a relative of Cetiosaurus, Bothriospondylus, Ornithopsis, and Anchisaurus in his description, but failed to name a family for these taxa. 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. Marsh proposed his own family of sauropods, Morosauridae, which he thought included Morosaurus and possibly Camarasaurus, with Amphicoelias considered a synonym of the latter. However, Morosauridae has since been synonymized with Camarasauridae.In 1970, Rodney Steel took an expansive concept of Camarasauridae, encompassing all sauropods then known except diplodocoids and titanosaurs. 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. 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. 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. 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. 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. In 1995, Paul Upchurch defined Camarasauridae as consisting of Camarasaurus and Haplocanthosaurus, 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. However, Haplocanthosaurus has since been reclassified as a basal diplodocoid.
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. Bellusaurus was recovered as a camarasaurid in a 2014 paper, but has been considered a member of Turiasauria, Mamenchisauridae, or basal Macronaria. Lourinhasaurus was classified as a camarasaurid and a species of Camarasaurus itself, but some studies have found it to be a basal neosauropod, basal macronarian or eusauropod, or laurasiform instead. However, in a 2019 study, Mannion and colleagues found Lourinhasaurus as a sister taxon of Camarasaurus. The dubious British genus Oplosaurus has been suggested to be a camarasaurid, however other studies have placed it in Turiasauria or Macronaria in general. Upchurch suggested that Chondrosteosaurus, 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. Camarasaurus is now often considered a basal macronarian outside of any clades of sauropods, similar to Yuzhoulong. Below is a simplified cladogram from Mocho and colleagues, which recovered Camarasauridae as including Camarasaurus, Tehuelchesaurus, and Lourinhasaurus, three genera of Late Jurassic sauropods.
File:Edward Cope with Camarasaurus.jpg|thumb|260x260px|Photo of Edward Drinker Cope, the describer of Camarasaurus, to the right of a C. supremus cervical vertebra
A simplified cladogram of basal Macronaria, which finds Camarasaurus in polytomy with Bellusaurus at the base of Macronaria, after Tan and colleagues is shown below:
Species
Camarasaurus is regarded as containing four valid species by most researchers: C. grandis, C. lentus, C. lewisi, and C. supremus. 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. Some researchers have suggested that Cathetosaurus should be reinstated as a distinct genus, whereas others have suggested that C. lewisi may be synonymous with another Camarasaurus species.The diagnostic traits of each Camarasaurus species are uncertain, with all being poorly defined and most specimens assigned simply as Camarasaurus sp. rather than a species. Additionally, the holotype of C. supremus is a composite of several adult individuals and the type of C. grandis is from a juvenile individual, making them difficult to compare based on morphological features due to a lack of understanding of Camarasaurus ontogeny. In 2005, Japanese paleontologist Takehito Ikejiri defined each Camarasaurus 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, and C. 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 of Camarasaurus, was diagnosed by its deep, narrow neural spine bifurcation on presacral vertebrae, starting at cervical 3 and ending in dorsal 11.
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, but it is possible this is because of a lack of specimens from C. lewisi. 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. 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.
Synonyms
- Amphicoelias latus was named by Cope in 1877 on the basis of a right femur and four caudal vertebrae that were found in layers of the Morrison Formation at Garden Park alongside fossils of C. supremus. However, it is now considered a synonym of C. supremus or C. grandis.
- Caulodon diversidens was named by Cope in 1877 on the basis of several teeth that were found in layers of the Morrison Formation at Garden Park. However, this species has been considered a nomen dubium or a synonym of C. supremus.
- Caulodon leptoganus was named by Cope in 1878 on the basis of two incomplete teeth that were found in layers of the Morrison Formation at Garden Park. However, this species has been considered a nomen dubium or a synonym of C. supremus.
- Morosaurus impar was named in by Marsh in 1878 on the basis of a sacrum that had been found in strata of the Morrison Formation at Como Bluff. It was described as the type species of Morosaurus, a genus that would grow to include several species now considered to be species of Camarasaurus or synonyms of them, however it is now considered a synonym of C. grandis.
- Morosaurus robustus was named by Marsh in 1878 on the basis of an ilium that had been collected from strata of the Morrison Formation at Como Bluff. It is now considered a synonym of C. grandis.
- Camarasaurus leptodirus was by Cope in 1879 on the basis of three partial cervical vertebrae that were found in layers of the Morrison Formation at Garden Park. It is now thought to be a synonym of C. supremus.
- Diplodocus lacustris is a nomen dubium named by Marsh in 1884 based on specimen YPM 1922 found by Benjamin Mudge and Arthur Lakes, consisting of the upper jaws, lower jaws, and teeth of a small sauropod from Morrison, Colorado. The remains are now believed to have been from an immature animal, rather than from a separate species of Diplodocus. Mossbrucker et al., 2013 surmised that the lower jaws and teeth of D. lacustris come from Apatosaurus ajax. Later in 2015, it was concluded that the upper jaws of the specimen actually belonged to Camarasaurus, while the teeth and lower jaws come from an indeterminate flagellicaudatan.
- Pleurocoelus montanus was named in by Marsh in 1896 as a species of Pleurocoelus, a sauropod from the Cretaceous of Maryland, on the basis of several vertebral centra and assorted bones of a juvenile sauropod that were found in layers of the Morrison Formation at Como Bluff. It is generally regarded as a synonym of C. grandis.
- Uintasaurus douglassi was named in W. J. Holland in 1919 for 5 anterior cervical vertebrae that were unearthed from Dinosaur National Monument, an outcrop of the Morrison Formation. The species is now considered a synonym of C. lentus.
- Camarasaurus annae was named by Tage Ellinger in 1950 on the basis of an isolated dorsal vertebra that had been unearthed from Dinosaur National Monument, an outcrop of the Morrison Formation. This species is generally considered a synonym of C.lentus.File:Smitanosaurus agilis skull and neck.jpg|thumb|The holotype posterior skull and cervical vertebrae of Smitanosaurus ''agilis''
Reassigned species/specimen
- Morosaurus agilis was named in 1889 by Marsh on the basis on a partial skull and 3 vertebrae unearthed in Morrison Formation strata in Garden Park, Colorado. The species remained in taxonomic uncertainty until 2020, when it was placed in a new genus, Smitanosaurus, and reclassified as a dicraeosaurid.
- 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. He selected the caudal vertebra to be the holotype. Later, French paleontologists Albert de Lapparent & Georges Zbyszewski referred the holotype vertebra to Megalosaurus insignis, whereas American paleontologist James Henry Madsen and colleagues assigned it to indeterminate Megalosauria. The tooth was identified as belonging to an indeterminate turiasaurian in 2017.
- Apatosaurus alenquerensis was named 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. It was tentatively placed in Camarasaurus by American researcher John McIntosh in 1990, but was granted a new genus in 1998, Lourinhasaurus.
- In 1987, Michael Raath and John McIntosh described an assortment of sauropod fossils that had been found in the Late Jurassic-aged Kadzi Formation of the Zambezi Valley, northern Zimbabwe. These fossils were first reported in studies in 1965 and 1971, however Raath and McIntosh analyzed the material in detail. Among the fossils was a femur and a coracoid they tentatively assigned to Camarasaurus, however Mark Goodwin and colleagues stated that this conclusion is unreliable and that taxonomic revision of the Zimbabwe sauropod material is needed.
- A manual ungual and trackways from Kimmeridgian-aged sandstones in Lübbecke, northwestern Germany were suggested to belong to Camarasaurus by Cajus Diedrich in a 2011 paper. However, this was very tentative, with the manual ungual also proposed to be from Brachiosaurus and the trackways, named Elephantopoides, were also suggested to be from Brachiosaurus, Diplodocus, and Apatosaurus.
Paleobiology
Feeding
Camarasaurus was a herbivore that probably fed at moderate heights of. 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. In 1998, Anthony Fiorillo analysed microscopic pits and scratches on the tooth surfaces and concluded that adult Camarasaurus consumed coarser foods than the contemporary Diplodocus. Juvenile Camarasaurus, in contrast, appeared to have consumed the same soft foods as adult Diplodocus. Modern herbivorous mammals with rounded snouts are often selective feeders that feed on particular plants that are less abundant but nutritious, while wide-snouted species are non-selective feeders that feed on less nutritious but abundant food in bulk. Based on this observation, John Whitlock argued in 2011 that the round-snouted Camarasaurus and Brachiosaurus were selective feeders while the square-snouted diplodocids and rebbachisaurids were bulk feeders. The diet of adult Camarasaurus might have consisted of the leaves of conifers, such as those of the extinct Cheirolepidiaceae, and ginkgos. In 2016, Mark Hallett and Matt Wedel suggested that female cones of araucarians as well as resins could have supplemented its diet.Camarasaurus probably had a more powerful bite than other sauropods due to the very large and the supratemporal fenestra that provided extensive attachement surfaces for large masticatory muscles. 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. The sturdy construction of the skull also suggests that it was able to resist greater stresses during feeding than other sauropods. 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. 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.
As with other dinosaurs, Camarasaurus continuously replaced its teeth, and underneath each erupted tooth there were up to three replacement teeth. A tooth was replaced after 62 days on average, as indicated by daily growth rings called von Ebner lines that are visible in cross-section of the teeth. This was slower than in Diplodocus, where a tooth only lasted for about 35 days, but as fast or faster than in ornithischian dinosaurs. 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 and grooves on the outer surfaces of the jaws that would have contained blood vessels in life. Alternatively, these blood vessels could have supported "lips" like those found in today's lizards.
A juvenile and heavily scavenged Camarasaurus specimen from Wyoming was found with 14 polished quartz stones that are between in diameter and have been identified as gastroliths. 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.
Neck posture and function
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. The probable neck posture has been the subject of controversy. A 1921 skeletal reconstruction of Camarasaurus by Osborn and Mook shows a rather straight and horizontal neck, while some later authors assumed a nearly vertical, swan-like neck. Some complete skeletons, such as the juvenile C. lentus specimen CM 11338, also show a vertical neck, but these represent opisthotonic death poses that do not necessarily reflect the original neck posture. In 1998, John Martin and colleagues instead argued that the necks of sauropods were held approximately horizontal, like a beam. They stated that the neck of Camarasaurus would have been powerful and inflexible, and that the elongated cervical ribs would have braced it along its underside. In 1999 and 2005, Kent Stevens and Michael Parrish analyzed how the neck vertebrae connected to each other in neutral pose, and concluded that the necks of Camarasaurus and other sauropods were typically held straight with a slight downwards slope.The idea of a more-or-less horizontal neck was questioned by several subsequent studies. In 2005, David Berman and Bruce Rothschild used Computed tomography 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. In 2009, Mike Taylor and colleagues showed that in modern animals, necks are usually extended and therefore curved upwards, suggesting that the same was true for sauropods. In a 2007 study, Paul Sereno and colleagues suggested that the head of Camarasaurus was habitually inclined downwards by about 15°, based on the orientation of the semicircular canals in the inner ear, which housed the sense of balance. Taylor and colleagues argued that in this posture, the occipital condyle would have faced downwards, requiring that the front part of the neck was steep, and possibly close to vertical.
The right shoulder blade of the specimen CM 11338 is inclined by approximately 45° with respect to the horizontal. Gilmore, in his 1925 monograph, argued that this specimen reflected the original orientation of the bone, and consequently, his skeletal reconstruction was slightly taller at the hips than at the shoulders. This finding contradicted the 1921 reconstruction of Osborn and Mook, which showed a much steeper shoulder blade, resulting in an animal that was taller at the shoulders than at the hips and with the base of the neck higher above the ground. Gilmore's interpretation of a low-angled shoulder blade subsequently became widely accepted for sauropods in general. In a 2007 study, Daniela Schwarz and colleagues compared the anatomy of the shoulder girdle with that of modern animals and concluded that Osborn and Mook's original interpretation of a steeply inclined shoulder blade and a consequently higher shoulder was correct. Ligaments would have run along the top of the neck, which would have been taut when the neck was sloping downwards or sidewards, helping with holding it. In a 2004 study, Takanobu Tsuihiji reconstructed the ligaments of Camarasaurus based on those Greater Rhea, in which the neural spines are similarly bifurcated. The nuchal ligament would have run along the top with branches connecting to either side of the bifurcated neural spines, while a second ligament, the Ligamentum elasticum interspinale, would have run in-between the two prongs of the bifurcated neural spines.
Sexual dimorphism
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 rather than direct fusion of the vertebral bodies, and was identified as diffuse idiopathic skeletal hyperostosis. Therefore, this fusion is not pathological but might be an adaptation for stiffening the tail. Rothschild and Berman argued that the fusion was a sexually dimorphic feature that occurred only in the males or only in the females. In males, it could have supported whip-lash motions with the tip of the tail during fights with other males. In females, the stiffening could have helped with arching the tail to allow for copulation. In a 2008 study, Takehito Ikejiri suggested that Camarasaurus specimens can be classified either as robust or as gracile. 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. In another 2008 study, Nicole Klein and Martin Sander found that individuals of similar age tend to fall into two size classes that might represent different species or sexual dimorphism.Life history
In 1883, Marsh reported the fragmentary skeleton of a very small sauropod discovered at Como Bluff, which he estimated at about in body length. Based on the small size and the incomplete ossification of the bones, Marsh argued that it must have belonged to an embryo. In 1896, Marsh assigned the specimen to a new species, Pleurocoelus montanus, without further comment, but probably because of the very large pleurocoels in the vertebrae. In 1994, Carpenter and McIntosh assigned this specimen to Camarasaurus grandis, and interpreted the large pleurocoels as a juvenile feature. Although a small juvenile, there is no evidence that this specimen is indeed an embryo as proposed by Marsh. In 1994, Brooks Britt and Bruce Naylor described a minute premaxilla of Camarasaurus discovered in Dry Mesa Quarry. The teeth of this bone have not yet erupted, suggesting that the individual did not yet hatch and was therefore an embryo. The bone is in length, suggesting a skull length of about, a body length of just over, and a body weight of. Based on these estimates, the diameter of an hypothesized spherical egg would have been about, smaller than the largest known bird eggs. The small size of the embryo provided evidence that sauropods were oviparous, questioning a hypothesis proposed by Robert T. Bakker in 1980 that sauropods were viviparous and gave birth to relatively large young. The first definitive sauropod embryos and eggs were described from the Argentinian locality Auca Mahuevo in 1998.Juveniles had shorter necks and tails than adults. As the individual matured, the neural arches of the vertebrae fused with the vertebral bodies; in Camarasaurus, the vertebrae of the mid and rear portion of the tail fused before those of the sacrum. Other age-related changes found in adults include the rugose articular surfaces in the limbs, the ossification of entheses of the vertebral column, and the fusion of the individual sacral vertebrae into a single structure. Changes during growth are particularly pronounced in the sternum, which is circular in the juvenile CM 11338 but grew long and narrow in adults. In contrast, the proportions of the limb bones did not change during growth.
Growth rings and other features visible in thin sections of bones allow for reconstructing life history. As other sauropods, Camarasaurus grew as fast as modern birds and mammals, and reached sexual maturity well before reaching maximum body size. In 2013, Eva Maria Griebeler and colleagues examined thin sections of limb bones of a large Camarasaurus individual 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. 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. The specimen "E.T." was even older. In a 2014 study, Katja Waskow and Sander estimated that this specimen reached sexual maturity at an age of 18 or 19 years and its full size at 40 years. As of 2024, GPDM 220 and "E.T." are amongst the oldest dinosaur individuals identified, even though representing relatively small individuals. Dinosaurs might have grown throughout most of their lives. In 2021, Bruce Rothschild and Florian Witzmann determined that of 13 analyzed Camarasaurus specimens, 2 had probably reached full size, as indicated by the closure of vascular openings on the articular surfaces of long bones that provided nutrients for bone growth.
Metabolism
Dinosaurs have traditionally been assumed to be cold-blooded ectotherms that depend on environmental temperatures. Since the 1960s, evidence has been presented that dinosaurs instead were homoiotherm or even endotherm. 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. Body temperatures can be directly estimated based on isotope compositions of bones and teeth. In a 2002 study, William Showers and colleagues used oxygen [isotope thermometry] to analyse bone apatite. They found that, in their studied Camarasaurus specimen, temperatures were variable in the trunk, but decreased in the legs and hips and increased in the neck and tail, compared to a specimen of the theropod Giganotosaurus. These differences between body parts might have resulted from countercurrent exchange of heat, when excess heat was pumped from the trunk into the peripheral body parts as a cooling mechanism. In 2011, Robert Eagle and colleagues analyzed tooth enamel of two sauropods, Camarasaurus and Giraffatitan, using clumped isotope thermometry. This analysis indicated body temperatures of, comparable to those of modern mammals.Pathologies
Multiple instances of pathologies have been recorded in Camarasaurus specimens. In 1996, McIntosh and colleagues described pathologies in thirteen vertebrae of the complete tail of the C. grandis specimen GMNH-PV 101. In two of these vertebrae, the neural arch failed to completely develop, a developmental defect known as spina bifida – the first reported example of this condition in dinosaurs. In the 40th tail vertebra, only half of the neural arch had formed, leaving the spinal cord partly unprotected. At least five vertebrae show bone outgrowths around the joints of the vertebral centra, indicating osteoarthritis. Five consecutive tail vertebrae are pathologically fused into a single structure.A specimen from Bone Cabin Quarry showed erosions in the in four out of twenty tail vertebrae. In 2002, Rothschild and colleagues identified these pathologies the oldest fossil evidence for inflammatory arthritis. In 2001, Lorrie McWhinney and colleagues described a periostitis, an injury of the periosteum, in a humerus assigned to C. grandis. This injury involved parts of the bone to be fractured or torn off, possibly due to stress or repeated excessive exertion of muscles. The subsequent healing process caused a tumor-like mass protruding from the bone surface. The injury would have been long-term and may have impaired the movement of the forelimb and caused a limp. In 2016, Emanuel Tschopp and colleagues described five different types of pathologies in the bones of the fore- and hind feet of SMA 0002. Such co-occurrence of different pathologies in a single individual is rare and might be due to the advanced age of the individual. The pathologies include a deep pit interpreted as osteochondrosis as well as various types of bony overgrowths, one of which was interpreted as osteoarthritis. Bony shelves extending above the front articular surfaces of the phalanges of the hind feet and were interpreted as enthesophytes caused by the insertion of tendons. These may have formed due to excessive use of the claws during life, possibly due to scratch-digging.
Paleoecology
Distribution and abundance
Camarasaurus is known from sedimentary rocks of the Morrison Formation dating to the Kimmeridgian and Tithonian ages. A single tail vertebra from the Summerville Formation of New Mexico has been assigned to the genus by Adrian Hunt and Spencer G. Lucas in 1993, but this occurrence was not recognized in a subsequent review. The Morrison Formation covers about 1.2 million km² of western North America, and Camarasaurus is found across this range, from more than 100 localities as far north as Montana to as far south as New Mexico.Camarasaurus is known from over 530 specimens, including isolated bones and about 50 partial skeletons. It is the most common dinosaur of the Morrison Formation and, due to its abundance, one of the best-understood sauropods. In a 2003 survey of more than two hundred fossil localities, John Foster reported 179 specimens of the genus, comparable to Apatosaurus and Diplodocus, but far greater than Brachiosaurus, Haplocanthosaurus and Barosaurus. Most identifiable specimens of Camarasaurus belong to one of two species, C. grandis and C. lentus; C. lewisi and C. supremus are rarer. Even though complete necks are rarely found in sauropods, five specimens of Camarasaurus preserve all or nearly all of the cervical vertebrae. Juvenile sauropod specimens are generally uncommon as their smaller size reduces their preservation potential. As of 2005, 44% of the sauropod specimens found in the Morrison Formation that are smaller than 50% of adult size are from Camarasaurus.
Paleoenvironment and migration
The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons. In 2011, Henry Fricke and colleagues analyzed the relative abundance of oxygen isotopes of both Camarasaurus teeth and carbonate rocks across the Morrison basin. δ18O values vary geographically depending on factors such as aridity and altitude. Because the values obtained from the teeth differ from those obtained from the rocks they were found in, Fricke and colleagues concluded that the Camarasaurus must have migrated between the Morrison basin and the high-altitude areas in the west to avoid the basin's dry season. This migration would probably have been seasonal and over a distance of.As of 2024, a total of 25 sauropod species are recognized from the Morrison Formation. The most common genera are the diplodocids Apatosaurus, Diplodocus, Supersaurus, Barosaurus, Brontosaurus, and Galeamopus; the macronarian Brachiosaurus, and Haplocanthosaurus. Dicraeosaurids such as Smitanosaurus, Dyslocosaurus, and Suuwassea were rarer components of the fauna. Other dinosaurs known from the Morrison Formation include the predatory theropods Koparion, Stokesosaurus, Ornitholestes, Ceratosaurus, Allosaurus and Torvosaurus, as well as the herbivorous ornithischians Camptosaurus, Dryosaurus, Gargoyleosaurus and Stegosaurus. Allosaurus accounted for 70 to 75 percent of theropod specimens and was at the top trophic level of the Morrison food web. Other vertebrates that shared this paleoenvironment included ray-finned fish, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs such as Hoplosuchus, and several species of pterosaur like Harpactognathus and Mesadactylus. Shells of bivalves and aquatic snails are also common. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests in otherwise treeless settings with tree ferns, and ferns, to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.
Works cited
Category:Dinosaur genera
Category:Kimmeridgian dinosaurs
Category:Tithonian dinosaurs
Category:Morrison Formation
Category:Fossil taxa described in 1877
Category:Taxa named by Edward Drinker Cope
Category:Dinosaurs of the United States