Camarasaurus

Camarasaurus Temporal range: Late Jurassic,
Mounted skeletal cast, Jurassic Museum of Asturias
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	†Sauropodomorpha
Infraorder:	†Sauropoda
Family:	†Camarasauridae Cope, 1877
Genus:	†Camarasaurus Cope, 1877
Species
C. supremus Cope, 1877 (type) C. grandis (Marsh, 1887 [originally Apatosaurus]) C. lentus (Marsh, 1889 [originally Morosaurus]) C. lewisi (Jensen, 1988 [originally Cathetosaurus])
Synonyms
Cathetosaurus Jensen, 1988 Caulodon Cope, 1877 Morosaurus Marsh, 1878 Uintasaurus Holland, 1919

Camarasaurus (Template:PronEng KAM-uh-ruh-SAWR-us) meaning 'chambered lizard', referring to the hollow chambers in its vertebrae (Greek καμαρα/kamara meaning 'vaulted chamber', or anything with an arched cover, and σαυρος/sauros meaning 'lizard') was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America. Its fossil remains have been found in the Morrison Formation of Colorado and Utah, dating to the late Jurassic Period (late Oxfordian to Tithonian stages), between 155 and 145 million years ago. A Camarasaurus pelvis recovered from Dinosaur National Monument in Utah shows gouging attributed to Allosaurus.

Description

C. lentus skull

Camarasaurus is among the most common and frequently well-preserved sauropod dinosaurs. The maximum size of the most common species, C. lentus, was about 15 meters (50 ft) in length. The largest species, C. supremus, reached a maximum length of 23 meters (75 ft) and maximum estimated weight of 47 tonnes (51.8 tons).

The arched skull of Camarasaurus was remarkably square and the blunt snout had many fenestrae, though it was sturdy and is frequently recovered in good condition by paleontologists. The 19 centimeter long (7.5 in) teeth were shaped like chisels (spatulate) and arranged evenly along the jaw. The strength of the teeth indicates that Camarasaurus probably ate coarser plant material than the slender-toothed diplodocids.

Each front limb bore five toes, with the inner toe having a large sharpened claw. Like most sauropods, the front limbs were shorter than the hind legs, but the high position of the shoulders meant there was little slope in the back.

Serving the purpose of weight-saving, as seen in other sauropods, many of the vertebrae were hollowed out or pneumatic, riddled with passages and cavities for an intricate system of air sacs connected to the lungs. This feature was relatively unknown at the time Camarasaurus was discovered, and was the inspiration for its name, meaning "chambered lizard". The neck and counter-balancing tail were shorter than usual for a sauropod of this size. Camarasaurus, again like certain other sauropods, had an enlargement of the spinal cord near the hips. Palaeontologists originally believed this to be a second brain, perhaps necessary to co-ordinate such a huge creature. However, while it would have been an area of large nervous, probably reflex (automatic) activity, it was not a brain, and such enlargements are actually found to some degree in all vertebrate animals.

History of study

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

The first record of Camarasaurus comes from 1877, when a few scattered vertebrae were located in Colorado, by Oramel W. Lucas. The paleontologist Edward Drinker Cope paid for the bones, as part of his long-running and acrimonious competition with Othniel Charles Marsh (known as the Bone Wars) and named them in the same year. Marsh later named some of his sauropod findings Morosaurus grandis but most paleontologists today consider this to be a species of Camarasaurus [1]. Such naming conflicts were common between the two rival dinosaur hunters, the most famous being Brontosaurus/Apatosaurus.

The first known complete skeleton, C. lentus

It was not until 1925 that a complete skeleton of Camarasaurus was recovered, by Charles W. Gilmore. However, it was the skeleton from a young Camarasaurus, which is why so many illustrations of the dinosaur from the time show it to be much smaller than it is now known to be.

The Morrison Formation, along the eastern flank of the Rocky Mountains, is home to a rich stretch of Late Jurassic rock. A large number of dinosaur species can be found here, including relatives of the Camarasaurus such as Diplodocus, Apatosaurus and Brachiosaurus. However, camarasaurs are the most abundant of all the dinosaurs in the Formation. There have been a number of complete skeletons recovered from Colorado, New Mexico, Utah, and Wyoming. Present in stratigraphic zones 2-6.

Paleobiology

Inferred range of head motion by Erwin Christman

Herding

There is a fossil record of two adults and a 12.2 meter (40 ft) long juvenile that died together in the Late Jurassic Period, approximately 150 million years ago (in north east Wyoming, USA, excavated by the Division of Vertebrate Paleontology of the University of Kansas Natural History Museum and Biodiversity Center, during the 1997 and 1998 'field seasons'). It is assumed that their bodies were washed to their final resting place, in alluvial mud, by a river in spate. This suggests that Camarasaurus traveled in herds or, at least, 'family' groups. Also, recovered camarasaur eggs have been found in lines, rather than in neatly arranged nests as with some other dinosaurs, which appears to suggest that, like most sauropods, Camarasaurus did not tend its young.

Digestion

Previously, some scientists had suggested that Camarasaurus and other sauropods may have swallowed stones (gastroliths) to help grind the food in the stomach and then regurgitated or passed them when they became too smooth. However, more recent analysis of the evidence for stomach stones has suggested that this was not the case. Furthermore, the strong, robust teeth of Camarasaurus in particular were more developed than those of most sauropods, indicating that it may have processed food in its mouth to some degree before swallowing.

Classification

The scientific classification of Camarasaurus, using the Linnaean system, is given in the box to the upper right but, among palaeontologists, this method of taxonomic classification of dinosaurs is being supplanted by the cladistics inspired phylogenetic taxonomy. A simplified version of one possible branching evolutionary tree, showing the relationship between Camarasaurus and the other major groups of sauropods, follows:

Saurischia ("lizard hipped" dinosaurs)
 `--Sauropoda ("lizard feet")
    |--Macronaria ("large nostrils")
    |   |--Camarasaurus
    |   `--Titanosauriformes
    |        |--Brachiosauridae (which includes Brachiosaurus and Sauroposeidon)
    |        `--Titanosauria (including Argentinosaurus)
    `--Diplodocoidea (including Apatosaurus, Diplodocus) 

Camarasaurus is considered to be a basal macronarian, more closely related to the common ancestor of all macronarians than to more derived forms like Brachiosaurus.

Species

Artist's impression of a C. supremus herd

The type species of Camarasaurus is Cope's original species, C. supremus (meaning "the biggest chambered lizard"), named in 1877. Other species since discovered include C. grandis ("grand chambered lizard") in 1877, C. lentus in 1889, and C. lewisi (originally described as a the new genus Cathetosaurus) in 1988.

C. supremus, as its name suggests, is the largest known species of Camarasaurus and one of the most massive sauropods known from the late Jurassic Morrison Formation. Besides its huge size, it was nearly indistinguishable from C. lentus. C. supremus was not typical of the genus as a whole, and is only known from the latest, uppermost parts of the formation. C. grandis and C. lentus were both smaller and present in the earlier stages of the Morrison. Research published in 2005 suggested that the chronological sequence of the Camarasaurus species aligned with their physical differences and suggests an evolutionary progression within the Morrison Formation. C. grandis is the oldest known species, present in the lowest rock layers of the Morrison. C. lentus appeared later, and co-existed with C. grandis for several million years, possibly due to different ecological niches suggested by differences in the spinal anatomy of the two species. At a later stage, C. grandis disappears from the rock record, leaving only C. lentus, which then also disappeared at the same time C. supremus appears 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 simply a larger, later-surviving population of animals.

External links

• Camarasaurus from Palaeos.com
• Camarasauridae from DinoData.org