Camarasaurus

Camarasaurus (meaning 'chambered lizard', referring to the holes in its vertebrae) is a genus of quadrupedal, herbivorous sauropod dinosaur. It was the most common of the giant sauropods to be found in North America but only average in size: about 18 meters (60 ft) in length as adults, and weighing up to 18 tonnes (19.8 tons). It lived in 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.

Anatomy
The arched skull of Camarasaurus may have contributed to the name 'chambered lizard'. The skull 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. Like a chicken, it may have swallowed stones (gastroliths) to help grind the food in the stomach and then regurgitated or passed them when they became too smooth.

Each giant foot bore five toes, with the inner toe having a large sharpened claw for self-defense. 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 on its hind legs.

The vertebrae were nevertheless specialized. Serving the purpose of weight-saving, as seen in many later sauropods, some of the vertebrae were hollowed out. This feature may have contributed to the name "chambered lizard". Like a modern elephant, Camarasaurus appears to have had 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. Palaeontologists originally believed this to be a second brain, perhaps necessary to co-ordinate such a huge creature. Modern opinion asserts that, while it would have been an area of large nervous, possibly reflex, (automatic) activity, it was not a brain. However, this enlargement was actually larger than the remarkably small brain contained in the animals' box-like skull.

Behavior
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.