Camarasaurus

Camarasaurus (/ˌkæmərəˈsɔːrəs/ KAM-ər-ə-SOR-əs_) is a genus of sauropod dinosaur that lived during the Late Jurassic, between about 155 and 145 million years ago, in North America. Named by Edward Drinker Cope in 1877, it includes four species: C. supremus, C. grandis, C. lentus, and C. lewisi. The name means 'chambered lizard', referring to special hollow spaces in its neck bones.

Camarasaurus was a big, sturdy sauropod dinosaur. The largest species, C. supremus, could grow up to about 23 meters (75 feet) long and weigh as much as 42 tonnes. It had a strong skull with powerful jaws and special spoon-shaped teeth that helped it eat plants. This dinosaur lived at a time when many famous dinosaurs, such as Stegosaurus, Allosaurus, and Brachiosaurus, also roamed the Earth.

Scientists have found more than 530 fossils of Camarasaurus, making it one of the best-studied dinosaurs. Some of these fossils show that Camarasaurus could live to be about 40 years old, which is very old for a dinosaur. It likely ate plants from trees and bushes at heights between 2 and 5 meters (about 6 feet 7 inches to 16 feet 5 inches) off the ground.

History

Fossils of Camarasaurus were first found 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 them as a new genus and species, naming it Camarasaurus supremus, meaning "chambered lizard".

Between August 1877 and 1878, Lucas found many more C. supremus fossils, including various bones from several individuals. Cope used these to describe several more species, but they are now considered to be synonyms of C. supremus.

Later, more fossils were found by O. W. Lucas and his brother, Ira H. Lucas. All fossils found by I. H. Lucas were grouped together, though they came from multiple individuals. In 1877, Cope asked Dr. John A. Ryder to create a restoration of Camarasaurus using the known fossils. This was the first-ever reconstruction of a sauropod dinosaur and was made to natural size, measuring over 50 feet (15 m).

Between 1877 and 1879, paleontologists William Reed, Marshall P. Felch, and Samuel W. Williston found an incomplete skeleton of a juvenile sauropod in Como Bluff, Wyoming. Marsh described it as a new species of the genus Apatosaurus, naming it Apatosaurus grandis. In 1878, Williston sent Marsh an isolated juvenile sauropod sacrum he had found at Como Bluff. Marsh described the sacrum as belonging to a new genus and species, Morosaurus impar. M. lentus was named by Marsh in 1889 on the basis of a juvenile sauropod skeleton found at Como Bluff. Its type specimen was mounted at the Yale Peabody Museum fossil hall in 1930 and was one of the first nearly complete sauropod skeletons to be found.

After the Bone Wars, many major institutions in the eastern United States began assembling their own dinosaur fossil collections. The competition to mount the first sauropod skeleton was intense, with the American Museum of Natural History, Carnegie Museum of Natural History, and Field Museum of Natural History all sending expeditions west to find the most complete sauropod specimen. In 1899, AMNH field workers Walter Granger and Peter Kaisen uncovered a complete Camarasaurus skull, mandible, and associated cervical vertebrae in rock layers at Bone Cabin Quarry, Wyoming, the first discovery of a nearly complete Camarasaurus skull. In 1905, a plaster skull based on the Camarasaurus skull found at Bone Cabin Quarry and based on a skull later referred to Brachiosaurus was mounted on a skeleton of Brontosaurus.

In 1909, American fossil hunter Earl Douglass of the CM uncovered an extensive deposit of dinosaur fossils at what is now the 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 described by Charles W. Gilmore who supported the claim that Morosaurus is a synonym of Camarasaurus.

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. 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. 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. 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. In 2005, the northernmost specimen, an incomplete skull and postcranial skeleton, of Camarasaurus was discovered in the Little Snowy Mountains of Montana.

Description

Camarasaurus was a large dinosaur with an elephant-like body. It had a long neck ending in a small skull, and its trunk and neck bones were very light but its legs were thick and strong. It was a bit wider than other similar dinosaurs, with a big ribcage. Its neck and tail were shorter than some others, and its skull was larger. Because its front legs were longer, it stood a little taller at the shoulders than at the hips.

Camarasaurus was a medium to large dinosaur. The most common type, C. lentus, was about 15 metres long, and C. grandis and probably C. lewisi were about the same size. The weight of adult C. grandis has been estimated to be about 12.6 tonnes on average. In 2020, a scientist named John Foster said that the latest type, C. supremus, had bones about 50% longer than the smaller types. Although C. supremus is not fully known, it might have been almost 23 metres long and weighed 42.3 tonnes if it was the same shape as the smaller types. In 2024, another scientist, Gregory S. Paul, estimated it to be 18 metres long and 24 tonnes heavy.

The skull of Camarasaurus was bigger and stronger than other similar dinosaurs, with very strong upper and lower jaws. The skull varied in size between individuals, from about 46% to 58% of the length of the leg bone. Like another dinosaur called Brachiosaurus, Camarasaurus had a large opening for the nose, which made its forehead look arched. Both had a defined front part of the face, but Camarasaurus had a more rounded and shorter skull. When viewed from above, the front of the face was rounded and tapered, unlike the square front of Diplodocus. The skull was almost square when viewed from behind and taller than it was wide.

The largest openings in the skull were the nose hole, the eye hole, and a hole behind and below the eye called the infratemporal fenestra. These three openings were about the same size. The nose hole was oval-shaped, and the eye hole was shaped like a teardrop, pointing down at the end. The eye had a ring of small bones around the pupil. The infratemporal fenestra was roughly triangle-shaped and tilted backwards. There was a small, pear-shaped hole between the nose hole and the eye hole. An even smaller hole was at the back corners of the skull roof, mostly facing upwards. This hole was oval and tilted to the side.

The skull had special features not found in related dinosaurs. One of these was the bone that formed the front edge of the eye hole, which was tilted forwards. Another feature was that a bone at the back of the skull did not reach the infratemporal fenestra because its upper part was short. A bone that formed the back-bottom corner of the skull reached up to touch another bone. The side of the lower jaw had a groove running from one bone forwards and downwards.

Known samples had four teeth in the front upper jaw bone, 9 to 10 teeth in the main upper jaw bone, and 13 teeth in each lower jaw. The teeth were spoon-shaped and formed a continuous cutting edge. The teeth got longer and 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 back edges, and the teeth in the lower jaw were straighter and slightly less strong than those in the upper jaw.

The body of Camarasaurus had 12 neck bones, 12 back bones, and five hip bones. The tail had 53 tail bones in the two samples that had a complete tail. Most of the volume of the back and neck bones was made up by air sacs connected to the lungs. These air sacs filled big spaces in the bones, which gave Camarasaurus its name, meaning "chambered lizard". The neck and back bones were concave at the back and convex at the front and had big spaces on their sides. The top parts of the neck bones in the shoulder area were split, and the left and right halves formed a U-shape when viewed from the front or back. In the hip area, these top parts were not split, short, and fan-shaped when viewed from the front or back. The top parts of the second to fifth hip bones were often fused together. The neck bones had very thin and long ribs that overlapped multiple bones before them.

The left and right parts of the shoulder area were probably connected at the front of the body by certain bones. The top end of the shoulder blade was wide. In the hip, one bone was massive, while the shaft of another bone was thin, curved, and ended without widening. The area where these two bones met was long. The front leg was thin, and the upper arm bone was about 77% the length of the upper thigh bone. In contrast, the back leg was massive, and the shin bone was about 60% the length of the upper thigh bone. Camarasaurus is one of few dinosaurs that show the wrist, which in this dinosaur had only two bones. As in other similar dinosaurs, the five hand bones were long, with the middle one being one third the length of the upper arm bone. The fingers were very small, with the thumb having two finger bones, including a claw that pointed to the side. The other fingers may have had one bone each and no claws. In the ankle of the back foot, a bone was small and rounded. As in other similar dinosaurs, the back foot had five toes, with different numbers of small bones in each toe. The first three toes had claws that were flattened on the sides.

Footprints show that the back feet of these dinosaurs were supported by a large, fleshy pad like that of elephants. This fleshy pad was not present on the front feet, as shown by skin impressions close to certain bones of a Camarasaurus sample. The skin impressions also show that the second to fourth fingers of the front foot were wrapped together in tissue. Patches of skin impressions are also preserved on the back legs, where they show scales that were between 6 and 18 millimetres in diameter. In 2015, scientists made models of the front and back feet to create hypothetical footprints, showing that the prints of the back feet were almost four times larger than those of the front feet. Tracks of sauropods can be "narrow-gauged" or "wide-gauged", depending on how close the tracks are to the middle line of the trackway; Camarasaurus might have had an intermediate gauge. So far, tracks have not been confidently identified as Camarasaurus.

Classification and species

Main article: Camarasauridae

In 1877, Edward Drinker Cope described Camarasaurus and suggested it was related to other dinosaurs like Cetiosaurus. Later, scientists used different groups to classify these dinosaurs.

Camarasaurus has four recognized species: C. supremus, C. grandis, C. lentus, and C. lewisi. C. supremus was the first species named by Cope in 1877. The species differ mainly in size and shape of their vertebrae. Some scientists think C. supremus may have evolved from C. lentus.

A simplified family tree of these dinosaurs shows Camarasaurus close to other sauropods.

Species

Most researchers agree that Camarasaurus has four species: C. grandis, C. lentus, C. lewisi, and C. supremus. These species are mainly distinguished by their size and the shape of their vertebrae. The species appeared in a specific order over millions of years, suggesting an evolutionary progression.

Synonyms and reassigned species

Fossils once named as different species like Camarasaurus leptodirus are now considered part of C. supremus. Other species once placed in Camarasaurus have been moved to different genera, such as Smitanosaurus and Lourinhasaurus.

Paleobiology

Feeding

Camarasaurus was a plant-eater that likely fed at moderate heights of 2 to 5 meters (about 6 feet 7 inches to 16 feet 5 inches). It might have been able to stand on its back legs to reach higher plants, as shown by features in its tail bones. In 1998, a scientist named Anthony Fiorillo studied the tiny marks and pits on the teeth of Camarasaurus and found that adult Camarasaurus ate tougher plants than another dinosaur called Diplodocus. Young Camarasaurus seemed to eat the same soft plants as young Diplodocus. Some scientists think that Camarasaurus had a stronger bite than other long-necked dinosaurs because of special bones in its jaw that gave it strong chewing muscles. A study in 2016 estimated that Camarasaurus could bite almost four times harder than Diplodocus. The shape of its skull also suggests it could chew food better than other long-necked dinosaurs.

Camarasaurus continuously replaced its teeth, and each new tooth grew in about 62 days. In 2017, scientists found a patch of soft tissue on the jaw of a Camarasaurus specimen nicknamed "E.T." that might have been its gums. This could explain why their teeth are often found in good shape even when separated from the jaw. Some scientists think this tissue might have been covered by a beak that helped cut plants and protect the teeth. There were also small holes and grooves on the jaw that might have held blood vessels, possibly supporting lips like those in lizards today.

A young Camarasaurus specimen from Wyoming was found with 14 small, polished stones in its stomach. These stones, called stomach stones, were once thought to help grind food, but scientists now think they might have been swallowed by accident or for minerals.

Neck posture and function

Main article: Sauropod neck posture

The long necks of these dinosaurs might have evolved to reach high plants or to eat more without moving their bodies, saving energy. Scientists have debated how these necks were held. Some early reconstructions showed a straight, horizontal neck, while others suggested a more vertical, swan-like curve. Some complete skeletons show a vertical neck, but these might be special poses that happened when the dinosaur died, not how it normally held its neck. In 1998, some scientists argued that the necks were held horizontally, like a beam. Later studies suggested different postures, with some supporting a more vertical neck and others a downward slope. The shoulder blade’s angle also varied in different reconstructions, affecting how tall the dinosaur appeared at different parts of its body.

Sexual dimorphism

In a 1991 study, scientists noticed that in some Camarasaurus specimens, certain tail bones were fused together. This fusion was not a disease but might have helped stiffen the tail. Some scientists suggested this feature might have been used differently by male and female dinosaurs — males possibly using it in fights, and females possibly using it during mating. In later studies, scientists found that Camarasaurus specimens could be classified as either robust (strongly built) or gracile (slender). These differences might reflect variations between males and females, though it is not fully certain which was which.

Life history

In 1883, a scientist named Marsh described a very small, incomplete dinosaur skeleton from Como Bluff, estimating it to be about 2.1 meters (7 feet) long. Based on its small size and incomplete bone development, Marsh thought it might have been an embryo. In 1994, this specimen was assigned to Camarasaurus grandis, and although it was small, there was no clear evidence it was an embryo. In 1994, another tiny bone piece of Camarasaurus was found in Dry Mesa Quarry, suggesting it belonged to an embryo that had not yet hatched. This small embryo provided evidence that sauropods laid eggs, challenging an older idea that they might have given birth to large young live.

As dinosaurs grew, they developed in several ways: juveniles had larger heads, shorter necks and tails, and shorter limbs compared to adults. As they matured, the bones of the spine fused together, and other changes occurred, like the spine branches becoming more forked and the shoulder bones changing shape. Growth rings in the bones show that Camarasaurus grew quickly, like modern birds and mammals, and reached maturity before they were fully grown. Studies estimate that some Camarasaurus individuals lived to be about 26 to 40 years old, making them some of the oldest known dinosaurs.

Metabolism

For a long time, dinosaurs were thought to have cold blood, depending on the environment to control their temperature. But since the 1960s, evidence has suggested that dinosaurs might have been able to keep a constant body temperature, similar to modern birds and mammals. Young sauropods might have had higher metabolism, allowing them to grow quickly, while fully grown individuals might have kept their temperature up simply because of their large size. Studies of bone and tooth chemistry in Camarasaurus suggest their body temperatures were about 36–38 °C (97–100 °F), similar to modern mammals.

Pathologies

Scientists have found several injuries and diseases in Camarasaurus fossils. In one specimen, some tail bones did not fully develop, a condition known as spina bifida, which was the first time this had been seen in dinosaurs. Other tail bones showed signs of arthritis, with extra bone growth around the joints. One specimen had damaged joints between its tail bones, showing signs of inflammatory arthritis — the oldest known evidence of this condition in fossils. Another Camarasaurus had an injury on its upper arm bone, where a piece of bone appeared to have broken off or been torn, possibly from stress or heavy use. This injury healed but may have affected the dinosaur’s ability to move its arm. Another specimen showed several different bone abnormalities, possibly due to its advanced age, including deep pits and extra bone growth on its foot bones.

Paleoecology

Distribution and abundance

Camarasaurus lived in what is now western North America during the Late Jurassic period, about 155 to 143 million years ago. Its fossils have been found in many places, from Montana in the north to New Mexico in the south. This dinosaur is one of the most common fossils found in these rock layers, called the Morrison Formation.

Paleoenvironment and migration

The Morrison Formation was a dry area with wet and dry seasons. Scientists think Camarasaurus may have traveled between this area and higher places to the west during the dry season. This travel was probably seasonal and covered a distance of about 300 kilometers or 190 miles. Many different kinds of dinosaurs and other animals lived in this ancient environment, including other large plant-eating dinosaurs and meat-eating predators.