external nares) opened well above and in front of the eyes in this blunt-faced sauropod.
of the camarasaurids were less splayed than those of the diplodocids, as the elongated foot bones were arranged in an arc rising from the base of the toes toward the “wrist” and ankle. The tails of cama- rasaurids were relatively short and thick, consisting of about fifty or so vertebrae below which simple, bladelike chevron bones were suspended.
The family Camarasauridae seems to be a less diverse assemblage of sauropods than the Diplodo- cidae. Only two or three North American genera can be confidently placed in the Camarasauridae. Several other camarasaurids are known from other continents. Though they may be less diverse than the diplodocids, the camarasaurids, particularly the namesake genus Camarasaurus, are by far the most common dinosaur found in the Morrison Forma- tion. Russell (1989) has estimated that about one of every five dinosaur bones ever recovered from the Morrison sediments belongs to Camarasaurus.
Camarasaurus
Camarasaurus was a medium-sized sauropod, about 50 feet (about 15 meters) long, that stood some 12 feet (4 meters) high at the hips and prob- ably weighed between 25 and 30 tons as a mature adult. The remains of Camarasaurus are remark- ably abundant in the Morrison Formation of Utah and adjacent states. Consequently Camarasau- rus is perhaps the best-known sauropod dinosaur in the world. As our knowledge of its anatomy has developed over the past century, some of the earli- est sauropod remains described from the Morrison Formation, such as Morosaurus and Uintasaurus, are now known to be specimens of Camarasaurus. The number of Camarasaurus fossils known to sci- ence is large, probably in the thousands, allowing paleontologists to make some very detailed recon- structions of this dinosaur. At least three different species of Camarasaurus have been identified from the Morrison Formation, differing slightly from each other in body proportions and minor anatom- ical details. Nearly all Utah specimens have been identified as Camarasaurus lentus, and the following discussion is based on this species.
The skull of Camarasaurus is large and massive but not very long. The lower jaw is particularly heavy and expands toward the front. The snout and lower jaw are both strongly curved, giving Camarasau- rus its unique brusque snout (fig. 4.14). The nostrils of Camarasaurus are very large in comparison to those of the diplodocids, are located high above the eyes and well in front of them, and open outward to either side of the skull. The spoonlike teeth of Cama- rasaurus are comparatively large and are positioned along the entire margin of the jaws. The large teeth commonly exhibit prominent wear surfaces pro- duced when the upper and lower teeth contacted each other during chewing. The teeth are firmly set into sockets along a deep groove in the jaws.
The skeleton of Camarsaurus (fig. 4.15) is of typi- cal sauropod form but is proportioned much differ- ently than in the diplodocids. The neck, consisting of only a dozen or so vertebrae, is shorter and more corpulent than the slender neck of Diplodocus. The cervical vertebrae of the neck, as well as the bones elsewhere in the spinal column, have deep side pockets known as pleurocoels. Many dinosaurs have these weight-saving cavities, but they are particu- larly well developed in Camarasaurus. The tail is also short and relatively blunt. In some specimens of Camarasaurus the caudal vertebrae in the for- ward portion of the tail are fused together into a solid mass of bone (Rothschild and Berman 1991; fig. 4.16). This condition would have resulted in a pronounced stiffening of the tail just behind the rump. That suggests that the relatively short tail of Camarasaurus was carried high above the ground, at least for those individuals that exhibit the fusion of caudal vertebrae. A similar fusion of caudal ver- tebrae is sometimes seen in Diplodocus (Rothschild and Berman 1991). Contrary to some popular depic- tions, no strong evidence indicates that either of these sauropods habitually dragged its tail behind it like a dead snake. Because the caudal vertebrae are fused in only some specimens, this feature might be linked to the sex of the dinosaur. It seems plau- sible that males might have possessed the stiffened
tail for defense against predators and competition for mates, while the more flexible tails of females might have been better suited for reproductive pos- turing and egg-laying. The chevron bones in the tail of Camarasaurus, as is the case in all cama- rasaurids, are bladelike and divided at the upper end where they join the caudal vertebrae (fig. 4.17). Camarasaurus forelimbs are longer in relation to the hind limbs than are those of the diplodocids. This difference in forelimb/hind limb proportions is reflected in the nearly level positioning of the back of Camarasaurus, as opposed to the slight for- ward slope along the backs of most diplodocids. The hind foot of Camarasaurus had five widely splayed toes; the innermost toe was the largest and bore a large curved claw. The bones of the middle feet (the
metacarpals and metatarsals, fore and aft), however, were more elongated than in the diplodocids and were arranged in an arcuate pattern between the toes and the ankles (or “wrists”).
One of the most complete dinosaur skeletons ever discovered was excavated in the early 1900s at Dinosaur National Monument. This famous find is the skeleton of a juvenile Camarasaurus and is one of the most notable dinosaur treasures collected in Utah. The young Camarasaurus was only about 17 feet (about 5 meters) long, less than half the normal adult length of this genus. Remarkably, 90 percent