Camarasaurus

Camarasaurus, 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 inNorth 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.

Description
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 counterbalancing 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.

Camarasaurus lewisi and C. grandis both had more robust radii than fellow sauropod Venenosaurus.

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.

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 or Dreadnoughtus.

Species
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 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. Stratigraphic evidence suggests that the chronological sequence of the Camarasaurus species aligned with their physical differences and describe an evolutionary progression within the Morrison Formation.[5] C. grandis is the oldest known species, present in the lowest rock layers of the Morrison.[5] 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.[5] At a later stage, C. grandisdisappears from the rock record, leaving only C. lentus, which then also disappeared at the same time C. supremus appears in the uppermost layers.[5] 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.[5]

Cathetosaurus lewisi species was originally named as Cathetosaurus lewisi and later synonymized with Camarasaurus. A 2013 analysis split the two genera again.

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. Camarasaurus' teeth according to the findings of Michael D'Emic et all, were replaced on average every 62 days. These findings also indicate that it preferred to eat different vegetation than other sauropods like Diplodocus, allowing them to share the same environment without competition.