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Dinosaurs Habitats. J.B. Hatcher discovered
and collected dozens of horned Dinosaur remains for Marsh and Yale College, among them the first specimens of
Triceratops and Torosaurus. Marsh was aided in his work at these and other localities by the skills and efforts
of many other collaborators like Hatcher, William Reed, Benjamin Mudge, Arthur Lakes, William Phelps, and
Samuel Wendell Williston, to name a few. Marsh's specimens now form the core of the Mesozoic collections at the
National Museum of Natural History of the Smithsonian Institution and the Peabody Museum of Natural History at
Yale University.
Dinosaurian habitats must have been as diverse as the animals themselves. One can infer something about the habitats of particular Dinosaur from a variety of clues, such as the kind of sedimentary rock in which the remains are preserved, other animal or plant fossils associated with them, and certain anatomic features like claws or hoofs. The kind of rock, its mineral composition, and sedimentary structures such as scour marks are especially important clues. The presence of ripple marks, for example, indicates a shallow-water environment. Fossil plants indicate something about climate. Associated animal remains like turtle, crocodile, or fish scales point to a nearby aquatic environment. Whatever habitat is inferred from clues like these, however, one must keep in mind that it is only an inference and does not necessarily reflect the actual living conditions of the Dinosaur in question. Rather, such clues reflect the animal's death environment or burial situation. The condition of the skeleton and its bones and their degree of disarticulation help to reveal the extent of preburial transport. Anatomic features indicate that all Dinosaur were basically terrestrial animals. All had well-developed legs and feet; none had fins or flippers; most had long tails, but only those of the duckbills and their near relatives were deep and flat-sided as might be expected in swimmers. In general, it can be concluded that none were primarily aquatic animals. Of course, that does not preclude aquatic activity; most animals can swim if necessary, but the ability cannot always be predicted from their anatomy. The earliest Dinosaur known are from South America, found in Argentina and Brazil in rocks of the Middle and Late Triassic epochs. The oldest are carnivorous varieties named Eoraptor, Staurikosaurus , and Herrerasaurus . Until 1989, the only known specimens were far from complete, but they suggested that all three kinds occupied distinctly terrestrial habitats with sufficiently large prey communities (not yet discovered) to support their predaceous habits. The encompassing sedimentary rocks the Santa Maria Formation of Brazil and the Ischigualasto Formation of Argentina, respectively indicate lowland, coastal plain environments and lowland streams and lakes. It is not clear which of these predators came first (stratigraphic correlations between Argentina and Brazil are still under study). Associated with Herrerasaurus remains are fragments of another predator, Ischisaurus, and a smaller herbivore, Pisanosaurus . All four predators in question are considered to have been exceedingly primitive theropods (two-legged carnivorous dinosaurs). Eoraptor is the most primitive Dinosaur yet discovered, closely resembling the łoriginal˛ dinosaur. Presumably, they preyed on small herbivores like Pisanosaurus and on the rhynchosaurs and mammallike reptiles that were abundant at the time. These few specimens represent a meagre beginning (probably because of a highly incomplete early record) of the dinosaurian reign. Before that time, all the continents of the world had joined together to form one very large supercontinent called Pangaea. But movements of the Earth's great crustal plates were changing its geography. By Early Triassic time (245 to 240 million years ago), as Dinosaur were beginning to gain a foothold, Pangaea had started to split apart at a rate averaging a few centimetres a year. The initial separation was an east-west breach called Tethys‹the precursor of the Mediterranean Sea which divided Pangaea into a northern and a southern landmass. The northern landmass, known as Laurasia, consisted of the North American and Eurasian continental plates; the southern landmass, called Gondwanaland, was composed of the African, South American, Indian, Australian, and Antarctic plates. These landmasses continued to break up to form separate continents. In short, it appears that, just as the Dinosaur line arose and experienced its initial diversification during the last half of the Triassic Period, the land areas of the world were in motion, splintering and drifting apart. Their respective inhabitants, Dinosaur and others, were consequently isolated from each other. Throughout the Mesozoic Era the ocean barriers grew wider and the separate faunas became increasingly different. As the continents drifted apart, successive assemblages arose on each landmass, diversified, waned, and disappeared, to be replaced by a new fauna. By Late Cretaceous time each continent occupied its own unique geographic position and climatic zone, and its fauna reflected that separation. Food and feeding During the passage of time from the Triassic through the Jurassic and into the Cretaceous, the Earth's vegetation
changed slowly from forests rich in gymnosperms (cycadeoids, cycads, and conifers) to
angiosperm-dominated forests of palms and hardwoods. Although conifers continued to flourish at high
latitudes, palms were increasingly confined to subtropical and tropical regions. These forms of plant life, the vast
majority of them high in hard-to-digest cellulose and low in calories and proteins, were the foodstuffs of the
changing Dinosaur communities.
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