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Dinosaurs Bones. A large number of skeletons of Plateosaurus were recovered in the 1920s from a site in Germany. The occurrence there of multiple remains, together with the nature of the enclosing sediments, led to the thought that this assemblage had been overcome by drought and sandstorm while migrating to more suitable environs. Whether migrating or not, the abundance of Plateosaurus individuals in one location lends support to the herding instinct that has been attributed to several kinds of dinosaurs.. Prosauropod forelimbs were stout and heavily built, with five complete digits. The hind limbs were about 50 percent longer than the forelimbs and even more heavily built. The foot was of primitive design, and its five-toed configuration could be interpreted as a forerunner of the sauropod foot. Walking apparently was semidigitigrade (partly on the toes), with the metatarsus held well off the ground. The vertebral column was unspecialized and bore little indication of the cavernous excavations that were to come in later sauropod vertebrae or of the processes and projections that were to buttress the sauropod vertebral column. The long tail probably served as a counterweight or stabilizer whenever the animal assumed a bipedal position. The more widely known sauropods - the huge 'brontosaurs' - varied in length from 6 or 7 metres (about 20 feet) in the primitive ancestral sauropods Riojasaurus of South America and Vulcanodon of Africa up to 28 to 30 metres (90 to 100 feet) or more in advanced Jurassic North American forms like Apatosaurus (formerly known as Brontosaurus), Diplodocus, and Seismosaurus. Weights ranged from about 20 tons or less in the smaller kinds like Barapasaurus of India to 80 tons or more for the gigantic Brachiosaurus of Africa and North America. Sauropods were worldwide in distribution but have not as yet been found in Antarctica. In geologic time they ranged from the Late Triassic Riojasaurus to the Late Cretaceous Alamosaurus of North America and Laplatasaurus of South America. Their greatest diversity and abundance took place during the Late Jurassic (163 to 144 million years ago). Sauropods are notable for their body form as well as their enormous size. Their large bodies were almost barrel-shaped, with long (sometimes very long) necks and tails. They had columnar legs, like those of elephants, with little freedom to bend at the knee and elbow. The legs were maintained in a nearly vertical position beneath the shoulder and hip sockets. Because of their great bulk, sauropods unquestionably were obligatory quadrupeds, and the largest forms could not have assumed a bipedal stance even momentarily. The sauropod limb bones were heavy and solid. The feet were broad, close to plantigrade (adapted for walking on the soles), and graviportal (adapted for bearing great weight). The five toes were generally short, blunt, and broad, but some kinds featured a large straight claw on the first digit of the forefoot and the first and second toes of the hind foot. These claws probably improved traction. Movement for these animals must have been relatively slow, with short steps necessary because of the comparative inflexibility of the limbs. Running must have been stiff-legged and no better than an elephantine pace of 16 kilometres (10 miles) per hour, if that. Their tremendous bulk placed them out of the reach of predators and eliminated any need for speed. The vertebrae of the backbone were highly modified, with numerous excavations and struts to reduce bone weight. Complex spines and projections for muscle and ligament attachment compensated for any loss of skeletal strength that resulted from reductions in bone density and mass. The long and sometimes massive tails, characteristic of so many sauropods, would appear to have been carried well off the ground. Tail drag marks associated with sauropod trackways are not known, and damaged (stepped-on) tails are also not known, even though these animals apparently traveled in herds (albeit of undetermined density). The sauropod tail may have served as a modest whiplike weapon, but there is no evidence to that effect. Another possible use of the tail may have been thermal regulation‹improved heat loss through its large surface area. A more likely explanation of its function is that the massive muscular base of the tail was the critical anchor site of the large, powerful hind leg muscles that produced most of the walking force required to move the many tons of sauropod weight. The muscle arrangement of the tail was precisely that of modern alligators and lizards. The most important part of any skeleton is the skull, because it provides the most information about an animal, its mode of life, and its general biology. Sauropod skulls were of several main types; the high, boxy Camarasaurus type (often incorrectly associated with Apatosaurus) and the low, narrow, streamlined Diplodocus type. The former had broad, spatulate teeth, while the latter had narrow, pencil-shaped teeth. Both kinds of teeth seem weak and totally ill-designed to crop or chew the volumes of plant food necessary to sustain such large animals. Correspondingly, the jaws were relatively weakly developed, and there is no special evidence indicating powerful jaw muscles to activate the feeding system. Until recently, sauropods were visualized as swamp or lake dwellers because their legs were thought to be incapable of supporting their great weights or because such huge creatures would naturally prefer the buoyancy of watery surroundings. Not only is that thinking incompatible with their food requirements (food would seem to have been most plentiful on land), but research has refuted it. Experiments with fresh bone samples have shown that bone of the type which composed the sauropods' limb bones could easily have supported their estimated weights. Moreover, there is no feature in their skeletons that suggests an aquatic, or even amphibious, existence. In addition, numerous trackway sites clearly prove that sauropods could navigate on land, or at least where the water was too shallow to buoy up their weight. Accordingly, newer interpretations see these animals as forest inhabitants. Still another blow has been dealt to the old swamp image by the physical laws of hydrostatic pressure, which prohibit the explanation that the long neck enabled a submerged animal to raise its head to the surface for a breath of fresh air. The depth at which the lungs were submerged would not allow them to be expanded by normal atmospheric pressure, the only force that fills the lungs. Consequently, the long necks of sauropods must be explained in terms of terrestrial functions such as elevating the feeding apparatus or the eyes. On all counts, sauropods are best seen as successful giraffelike browsers and only occasional waders. Staurikosauria Very little is known about the animals grouped in this suborder because so few specimens have been found, and all of those are fragmentary. The remains of Staurikosaurus, from the Middle Triassic of Brazil, the specimen for which the suborder was established, consist only of the vertebral column and pelvis, the hind legs lacking the feet, and the lower jaw. The skull and forelimbs, like the feet, are not known. Those parts that are known, however, are similar to those of the later theropods, and a flesh-eating habit is suggested by the piercing teeth of the lower jaw. The skeleton indicates a moderate-size animal of about two metres (seven feet) in length, possibly having a bipedal posture and gait. Appearing as it does in Middle Triassic rocks, it may be the oldest kind of Dinosaur known‹if in fact it proves to be a dinosaur. Several other fragmentary remains from South America may be of related types. Specimens of Herrerasaurus
and Ischisaurus from Middle to Late Triassic rocks of Argentina are those of carnivores about the same size as
Staurikosaurus or slightly heavier. But again, the material is so incomplete that relationships are still uncertain.
What is preserved suggests a theropod identity.
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