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Dinosaurs Studies. The flesh-eating Dinosaur must have eaten anything they could catch, since predation is a highly opportunistic
lifestyle. In several instances the prey victim of a particular carnivore has been established beyond much doubt.
Remains of the small predator Compsognathus were found containing a tiny skeleton of the lizard Bavarisaurus
in its stomach region. In Mongolia two different Dinosaur skeletons were found together, a nearly adult-size
Protoceratops in the clutches of its predator Velociraptor.
Much attention has been devoted to Dinosaur as once-living animals as moving, eating, growing, and reproducing biological machines. But how fast did they grow? How long did they live? How did they reproduce? The evidence concerning growth and life expectancy is sparse. Histological studies by Armand de Ricqlès in Paris and R.E.H. Reid in Ireland show that plexiform perichondral bone in Dinosaur skeletons grew quite rapidly. The time required for full growth has not been quantified, but the life span of most Dinosaur would seem to have been short and probably did not exceed five or six decades. The largest varieties probably lived longer than the smaller ones, but no precise age has been determined for any kind. Reproduction As for reproduction, considerable evidence is now available. The idea that dinosaurs, like most living reptiles and birds, built nests and laid eggs had been widely debated before the 1920s, when a team of scientists from the American Museum of Natural History made an expedition to Mongolia. Their discovery of Dinosaur eggs in the Gobi proved conclusively that at least one kind of dinosaur, Protoceratops, had been an egg layer and nest builder. These findings were substantiated in 1978 when John R. Horner discovered Dinosaur nests in western Montana. A few other finds, mostly of eggshell fragments from a number of sites, established oviparity as the dinosaurian mode of reproduction. The almost complete absence of juvenile Dinosaur remains, however, was puzzling. Horner, first of Princeton University and later of Montana State University, demonstrated that most paleontologists simply had not been exploring the right territory. After a series of intensive searches for immature Dinosaur material, he succeeded beyond all expectations. He unearthed the first such bones near Choteau, Mont., U.S., and during the 1980s he and his field crews discovered hundreds of nests, eggs, and newly hatched dinosaurs, mostly of the duck-billed variety. Horner observed that previous explorations had usually concentrated on geologically old lowland areas, where sediments were commonly deposited and most fossil remains were preserved. He recognized that those regions were not likely to produce Dinosaur nests and young because they would have been hazardous places for nesting and raising hatchlings. Upland regions would have been safer, but they were subject to erosion rather than deposition and therefore less likely to preserve nests and eggs. It was exactly in such ancient upland areas, though, close to the rising young Rocky Mountains, that Horner made his discoveries. Egg Mountain, as the area was named, produced some of the most important clues to dinosaurian habits yet found. For example, the sites show that a number of different Dinosaur species made annual treks to this same nesting ground (perhaps not all at the same time). Because of the stratigraphic succession of like nests and eggs one on top of the other, it is thought that particular species returned to the same site year after year to lay their clutches. As Horner concluded, site fidelity was an instinctive part of dinosaurian reproductive strategy. If site fidelity was a universal instinct among dinosaurs, that strategy could help to explain their success for some 150 million years. As mountain building increased toward the end of the Mesozoic era, geologic processes might have reduced appropriate nesting grounds and contributed to the decline and eventual extinction of dinosaur communities. Body temperature There is no doubt about the dinosaurs' success. Their worldwide domination of the land during the Mesozoic and what brought it about is every bit as important as what caused their extermination, or more so. Understanding their success requires further consideration of them as living animals. Beyond eating, digestion, assimilation, reproduction, and nesting, there are many other processes and activities that go into making a successful biological machine. Breathing, fluid balance, temperature regulation, and other such capabilities are also required. Dinosaurian body temperature regulation, or lack thereof, has been a hotly debated topic among students of Dinosaur life. Body temperature Ectothermy and endothermy All land animals possess some degree of thermoregulation. Much of the terrestrial environment is highly variable and beyond the control of most organisms. The internal environment of the body is under the influence of both external and internal conditions. When the outside world is hotter than preferred, organisms usually respond by moving to a cooler spot. Some perspire or pant to increase cooling. When it is dangerously cold, organisms may move to warmer climates (migrate), generate heat (shiver), or conserve body heat and energy by lowering their metabolism (hibernate), and the human species, of course, can further adjust body temperature by artificial means. The so-called warm-blooded animals today are the mammals and birds; reptiles, amphibians, and most fish are labeled as cold-blooded. These two terms are imprecise and misleading. Some cold-blooded lizards have higher normal body temperatures than do some mammals, for instance. More precise terms for these conditions are ³ectothermy² and ³endothermy.² Ectothermy is that state in which thermoregulation depends on the behaviorally and autonomically regulated uptake of heat from the external environment. Endothermy, on the other hand, depends on a high (tachymetabolic) and controlled rate of internal heat production. Mammals and birds have a high metabolism, which produces body heat internally. They possess temperature sensors that control heat production and switch on heat-loss mechanisms such as perspiration. Reptiles and amphibians are ectotherms that must gain heat energy from sunlight, a heated rock surface, or some other external source. The endothermic state is effective but expensive; the metabolic ³furnaces² must produce heat continuously, and that requires correspondingly high quantities of fuel (i.e., food). On the other hand, endotherms can be active and can survive quite low external temperatures. Ectotherms do not require as much fuel, but most cannot deal as well with cold surroundings. What, then, about the dinosaurs? From the time of the earliest discoveries in the 19th century, experts like
Owen, Leidy, Marsh, and Cope classified all then-known Dinosaur remains as reptilian because they exhibited a
set of anatomic features that were typical of living reptiles like turtles, crocodiles, and lizards. Dinosaur all had
lower jaws constructed of several bones, featured a reptilian jaw joint, and possessed a number of other
nonmammalian characteristics. Consequently, it was assumed that living Dinosaur were like living reptiles‹scaly,
cold-blooded ectotherms and not furry, warm-blooded creatures that gave live birth. A chauvinistic attitude
seems to prevail that the warm-bloodedness of mammals is better than the cold-blooded reptilian state. Turtles,
snakes, and other reptiles, however, do very well by regulating their body temperature in a different way.
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