C. grandis
C. lentus
C. lewisi
C. supremus (holotype)

The Camarasaurus (pronounced KAM-a-rah-SORE-us) was a genera of quadrupedal, herbivorous dinosaurs. They are the most common of the giant sauropods to be found in North America, but only average in size — about 18 metres (60 feet) in length as adults, and weighing up to 28 tonnes (31 tons). It lived in the late Jurassic period, between 155 and 145 million years ago.

Anatomy

The main feature of interest is its skull. The skull was remarkably square and the blunt snout had many holes, though it was sturdy and frequently recovered in good condition. The huge nostrils, positioned in front of the eyes, probably contained a large area of moist membrane to cool the brain in the hot weather of the Jurassic.

The 19 cm-long (7.5 inch) 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 fragile-toothed diplodocids. Like a chicken, it would probably have swallowed stones (gastroliths) to help physically digest the food in the stomach, and then regurgitated or passed them when they became too smooth. Consistent with this suggestion, the rock formation in which they are frequently found (the Morrison Formation) includes a large number of isolated piles of unusually smooth stones.

Each giant foot bore five toes, with the inner toe having a large sharpened claw for self-defence. Like most sauropods, the front legs were shorter than the hind legs, but the high position of the shoulders meant there was little slope in the back. In some sauropods there were long upward projections on each vertebra, but the absence of such structures from the spine of Camarasaurus suggests that it was not able to raise itself up on its hind legs.

The vertebrae were nevertheless specialised; as a weight-saving device seen in many later sauropods, the vertebrae were hollowed out, hence the name "chambered lizard". Like a modern elephant, Camarasaurus appears to have a wedge of spongy tissue at the base of the heel, to support the weight of such a large creature. 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. Paleontologists originally believed this to be a second brain — perhaps necessary to co-ordinate such a huge creature. Modern opinion asserts that while it was an area of large nervous activity, it was not a brain. However, this enlargement was actually larger than the remarkably small brain contained in the animals' box-like skull.

It is suggested by some paleontologists that Camarasaurus may have lived for up to a hundred years.

Behavior

There is a fossil record of adults and young that died together. This suggests that Camarasaurus travelled in herds. Also, recovered camarasaur eggs are found in lines, not in neatly arranged nests as with some other dinosaurs. Like most sauropods, it seems Camarasaurus did not care for its young.

Discovery

Our first record of Camarasaurus ("chambered lizard") comes from 1877, when a few scattered vertebrae where located in Colorado by Oramel W. Lucas. Legendary 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.

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 so many illustrations of the dinosaur from the time show it to be much smaller than we now know it 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, and there have been a number of complete skeletons recovered from Colorado, New Mexico, Utah, and Wyoming.

Classification

The scientific classification of the Camarasaurus using the Linnaean system can be seen in the box to the upper right, but among paleontologists this method of categorizing dinosaurs has been largely supplanted by cladistics. A simplified version of one possible branching evolutionary tree (cladogram), showing the relationship between Camarasaurus and the other major groups of sauropods, follows:

• Saurischia ("lizard hipped" dinosaurs)
  • Sauropoda ("lizard feet")
    • Macronaria ("large nostrils")
      • Camarasauridae
      • Titanosauriformes
        • Brachiosauridae (like the Brachiosaurus and Sauroposeidon)
        • Titanosauridae (like the Argentinosaurus)
    • Diplodocidomorpha (like the Apatosaurus and Diplodocus)

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

Cope's original Camarasaurus was the species C. supremus ("the biggest chambered lizard") in 1877. Other species since discovered include C. grandis ("grand chambered lizard") later in 1877, C. lentus in 1889, and C. lewisi (originally Cathetosaurus) in 1988.

External links

• Camarasaurus classification at the Dinosauricon. (includes a complete cladogram)
• Camarasaurus, at DinoData.