Dinosaurs

Grizzly Bear

Text 2

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“When the grizzly is gone, we shall have lost the most sublime

specimen of wildlife that exalts the western wilderness.” Those words, coined by John McGuire, founder of Outdoor Life Magazine stand as a warning to those who have neglected the plight of this storied member of the ecosystem.

One of the largest members of the bear family, the grizzly may exceed

1,000 pounds and stretch up to eight feet tall. Grizzlies are generally brownish in

colour, and adults often have white-tipped hairs along the back, a distinction that

resulted in the common name “silvertip.”

While the silver tipped fur, the large size and a hump on the back are

all considered characteristics of the grizzly, the best way to distinguish the species is by its concave muzzle or snout. That differs from the rounded snout of the more common black bear. In addition, the grizzly’s claws on the front feet are much longer than the hind claws.

Although its name came from its grizzled coat and not its fearsome

temper, authors have depicted the grizzly as a terrifying animal that followed the herds of bison and attacked men without provocation. Even today, grizzlies fear no other animal in the wild, and they’re capable of hunting and killing most animals.

The federal government now lists the grizzly as threatened in the United States outside of Alaska, and it’s classified as endangered in Colorado. The last

documented grizzly in Colorado was killed in 1979, and two others were killed in 1951.

Conflicts with man and the civilisation of wilderness areas resulted in

the elimination of the grizzly from Colorado. There’s little chance that any grizzly

bears still exist in the state.

Text 3

A misconception commonly portrayed in popular books and media is that all the dinosaurs died out at the same time—and apparently quite suddenly—at the end of the Cretaceous Period 65 million years ago. This is not entirely correct, and not only because birds are a living branch of dinosaurian lineage. The best records, which are almost exclusively from North America, show that dinosaurs were already in decline during the latest portion of the Cretaceous. The causes of this decline, as well as the fortunes of other groups at the time, are complex and difficult to attribute to a single source. In order to understand extinction, it is necessary to understand the basic fossil record of dinosaurs.

The K–T boundary event

It was not only the dinosaurs that disappeared 65 million years ago at the Cretaceous–Tertiary, or K–T, boundary. Many other organisms became extinct or were greatly reduced in abundance and diversity, and the extinctions were quite different between, and even among, marine and terrestrial organisms. Land plants did not respond in the same way as land animals, and not all marine organisms showed the same patterns of extinction. Some groups died out well before the K–T boundary, including flying reptiles (pterosaurs) and sea reptiles (plesiosaurs, mosasaurs, and ichthyosaurs). Strangely, turtles, crocodilians, lizards, and snakes were either not affected or affected only slightly. Effects on amphibians and mammals were mild. These patterns seem odd, considering how environmentally sensitive and habitat-restricted many of these groups are today.

Whatever factors caused it, there was undeniably a major, worldwide biotic change near the end of the Cretaceous. But the extermination of the dinosaurs is the best-known change by far, and it has been a puzzle to paleontologists, geologists, and biologists for two centuries. Many hypotheses have been offered over the years to explain dinosaur extinction, but only a few have received serious consideration. Proposed causes have included everything from disease to heat waves and resulting sterility, freezing cold spells, the rise of egg-eating mammals, and X rays from a nearby exploding supernova. Since the early 1980s, attention has focused on the so-called asteroid theory put forward by the American geologist Walter Alvarez, his father, physicist Luis Alvarez, and their coworkers. This theory is consistent with the timing and magnitude of some extinctions, especially in the oceans, but it does not fully explain the patterns on land and does not eliminate the possibility that other factors were at work on land as well as in the seas

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