Dinosaurs have a 175 million-year history beginning
in the Permian period and extending
through the Triassic and Jurassic periods to the
Cretaceous, the last period in the Mesozoic era,
which lasted 160 million years and ended 65 million
years ago. Tyrannosaurus dates to the latter
part of the Cretaceous period, which ceased when
a great deal of life on earth disappeared for reasons
that are not fully known, although it is speculated
that a huge meteor crashed into earth, causing
a heavy cloud to hang over the planet long
enough to kill most vegetation.
No land animal weighing over about fifty-five
pounds survived whatever catastrophe caused the
sudden end of an era when huge animals roved the
earth. Tyrannosaurus, the largest terrestrial carnivore,
was almost forty feet long. Tyrannosaurus had
a huge head, a large mouth, and menacing teeth.
Physical Characteristics and Habitat
An adult Tyrannosaurus standing upright would have been as tall as a four-story building, but Tyrannosaurus did not stand erect. Its hind legs provided sturdy underpinnings, whereas its arms were short and weaker than its legs. They could be used defensively when necessary. Fossil footprint evidence substantiates that Tyrannosaurus has feet over three feet long. This dinosaur depended on its hind legs for most of its locomotion, although it used its arms minimally when it walked. Bulky in the midsection, its long tail aided its balance. Its long neck supported a huge head with a large mouth and seven-inch-long serrated teeth. Adults weighed about seven tons. Most of the extant remains of Tyrannosaurus have been found in the United States, mostly in the South Dakota, Montana, and Wyoming Badlands. The first three Tyrannosaurus rex remains were found in Montana andWyoming in the early 1900's. This area was also inhabited by duckbilled dinosaurs, much smaller animals than Tyrannosaurus, who were often eaten by their larger counterparts. During the late Cretaceous period, the area in which Tyrannosaurus remains were found was warmer than it currently is. It is known fromfossil remains that its climate resembled the current climate of the southern states. The area was rich in such plant life as ferns, palm trees, redwoods, and flowering plants, which contributed to the diet of dinosaurs. The preserved contents of Tyrannosaurus stomachs reveal that they ate many of these plants. Most of the animals that coexisted with dinosaurs were small, seldom exceeding the size of a domestic cat. Birds were abundant, as were such insects as spiders and beetles. Opossums existed in large numbers, and the waterways of the ancient landscape were filled with fish and turtles, all of which became part of the Tyrannosaurus diet. One thing is clear: For a period of 150 million years, dinosaurs ruled the earth. They were the largest, most complex organisms in existence, and Tyrannosaurus was preeminentamongdinosaurs. Tyrannosaurus rex lived closer to the beginnings of human existence than it did to the time when the earliest dinosaurs roved the earth. Some paleontologists believe that it was descended from a species of carnivores in Mongolia that migrated from Asia to North America over a formation that once bridged the Bering Straits, but has since disappeared. The Badlands are the richest depository in the United States discovered to date of dinosaur remains.
The Largest Tyrannosaurus rex Ever Found
Peter Larson, an independent collector of fossils who knew a great deal about paleontology, unearthed the skeleton of Sue, the largest and most perfect Tyrannosaurus skeleton ever found. Painstakingly cleaned and reassembled, it is dramatically displayed in Chicago's Field Museum. Sue was discovered by Sue Hendrickson in August of 1990, when she noticed three large dinosaur vertebrae and a femur protruding from a cliff in the Badlands of South Dakota. These items obviously belonged to Tyrannosaurus because the vertebrae were concave from the disk, unlike the straight vertebrae of duck-billed dinosaurs. With Larson's help, Hendrickson determined that because part of its skull was damaged, Sue died in some sort of conflict. Sue had suffered a fractured fibula that healed but that must have left her defenseless for some time. Contents of its stomach indicated that Sue's last meal was a duckbilled dinosaur.
Suborders: Theropoda (four-toed bipeds), Sauropodomorpha (lizard-footed, five toes), Carnosaurus (large predators)
Geographical location: Every continent except Antarctica
Gestational period: Unknown; presumably two to three years
Life span: Unknown; presumably over fifty years
Special anatomy: Strong hind legs, with arms weaker than the legs; two fingers on each hand; large head; sharp, serrated teeth
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