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Dinosaurs had long, heavy, reptilian tails. While some bipedal dinosaurs may have used their tails as braces for standing upright, it seems that the main purpose of tails in these dinosaurs was to counterbalance their bodies when walking or running. Quadrupedal dinosaurs with long tails needed them to counterbalance their long necks; such is the case of the sauropodomorphs. The ankylosaurs and stegosaurs, however, had tails which may have served as weapons. Deinonychus, Tenontosaurus, Ankylosaurus, and Stegosaurus.

Teeth are a useful tool for identifying dinosaur remains, since every dinosaur tooth is distinctive. Scientists can tell whether the animal was a plant-eater or a meat-eater, and sometimes they can use the teeth to gauge its size. Carnivorous dinosaurs had sharp, pointed, blade-like teeth. Herbivorous dinosaurs typically had leaf-shaped molars, although the shape of their teeth shows greater variety than those of the meat-eaters. Dinosaurs with both blade-shaped and leaf-shaped teeth may have eaten both plants and meat, while dinosaurs with no molars or grinding teeth, such as the sauropods, probably swallowed their food whole, depending upon gastroliths to grind it for digestion. The worn teeth of some dinosaurs were continuously re-grown throughout their lives. See Carnosaurs and Sauropods

Tertiary Period
Translation: Third Period
The Tertiary Period is the first of the two periods of the Cenozoic Era. It immediately followed the Cretaceous Period (the last period of the Mesozoic Era) and lasted from 66 million years ago to 2 million years ago. No dinosaur fossils have been found in rocks of this age, and during this time mammals became the dominant life form.

The Tetanurae (teh-tuh-NOOR-ree) are one of three infraorders of theropods. This large group of theropods covers a great diversity of dinosaurs, including the micro-orders Carnosauria (to which Tyrannosauridae belonged), and Coelurosauria (to which several bird-like families belonged).

Tethys Sea
Named after the daughter of Oceanus in Greek mythology, Tethys was the sea separating the two super continents Laurasia and Gondwanaland during the Mesozoic Era.

Translation: Four-footed
Tetrapodite (TEH-tra-poh-dight) is the name given to rare dinosaur footprints found in British Columbia and Alberta, Canada. Scientists believe that they were made by a ceratopsian, which had rather massive, four-toed hind feet and five-toed forefeet.

Thecodontia (Thecodonts)
Translation: Socket-toothed
Thecodontia (thee-koh-DON-tee-ah) is an order of Triassic reptiles from which dinosaurs, crocodilians, and pterosaurs, and possibly birds arose. There were four suborders of thecodonts: Aetosauria, Phytosauria, Proterosuchia, and Pseudosuchia.

Thecodontosauridae (Thecodontosaurids)
Translation: Socket-toothed
Thecodontosauridae (thee-koh-DON-toh-saw-ree-day) is a family of small, primitive prosauropods. Whereas prosauropods as a whole were quadrupedal some of the time and bipedal at others, thecondontosaurids were fully bipedal. Thecodontosaurus

Theropoda (Theropods)
Translation: Beast Footed
Theropoda (thair-uh-PODE-ah) is one two suborders of saurischia. Theropods were the carnivores of Dinosauria. They walked on strong hind legs, their bodies parallel to the ground, tails outstretched to counterbalance the weight of their bodies and heads. They lived during the Middle Triassic through the Cretaceous Periods, and their sizes ranged from 7 inches (17 cm) to 50 feet (15 meters) in length. Infraorders of Theropoda are: Ceratosauria, Tetanurae and Segnosauria.

Thyreophora (thye-REE-oh-FOR-ah) is one of three suborders of Ornithischia. The size of these ornithischians ranged from small-to-large. They were mostly quadrupedal (with the exception of more primitive species) and all possessed body armor.

Titanosauridae (Titanosaurids)
Translation: Large Lizards
The Titanosauridae (tye-tan-uh-SAWR-ih-day) was a family of sauropods. Like most herbivores, they were equipped with stump-shaped teeth. Characteristically, they had long hind legs and shorter front legs. They grew from 15 to 90 feet (27 meters) in length. Some titanosaurid remains show their backs to be covered with embedded armor plates, and it is speculated that all titanosaurids may have been similarly armored. These sauropods lived during the Middle Jurassic through Late Cretaceous Periods.

Trackways are sites where fossilized dinosaur footprints have been found. As dinosaurs walked or ran in sand or soft earth they left tracks which were covered slowly by minerals and buried deep within the Mesozoic mud. Fossilized footprints reveal to scientists many characteristics about dinosaurs. For example, scientists can determine whether dinosaurs went into water, if they were bipedal or quadrupedal, and how fast they were able to travel. If footprints are discovered alone, it is difficult to conclude exactly which dinosaur made them. However, if bones are discovered along with the footprints, scientists can make several conclusions about the tracks. For example, a trackway in Glen Rose, Texas, seems to indicate that dinosaurs traveled in herds and that those herds were subject to predation by carnosaurs. Dinosaur tracks must be carefully evaluated. For example, one set of tracks was interpreted as those of a dinosaur hopping along like a kangaroo. Later, it was demonstrated that the tracks were made by a dinosaur which was swimming in water and occasionally touching the bottom. It is also not unusual to discover the tracks of dinosaurs running up the faces of cliffs. These tracks do not illustrate dinosaur mountain-climbing ability. They show, rather, how the surface of the Earth has changed over the ages -- what was once a seashore or a riverbed has been thrust from horizontal to vertical.

Triassic Period
The Triassic (try-ASS-ik) Period is the first of the divisions of the Mesozoic Era. (The other two periods are the Jurassic and the Cretaceous.) The Triassic Period began 245 million years ago and ended 208 million years ago, and it was toward the middle of the period that dinosaurs appeared. Evidence suggests that at the beginning of the Triassic Period, before the appearance of dinosaurs, the global temperature averaged around 50º to 60º F (10º to 15º C). Toward the end of period, however, the global climate began to become drier and hotter; deserts began to appear on much of Pangaea's surface area. In the northern hemisphere, gingko and tree fern forests flourished, while near the equator were forests of conifers and cycads. Horsetails grew near bodies of water.

Troödontidae (Troödontids)
Translation: Gnaw Tooth
The Troödontidae (troh-uh-DON-tih-day) is a branch of small theropods (falling into the Maniraptora branch) who possessed the largest brains of any dinosaur yet discovered. Their heads were narrow and long, with slender jaws bearing small, densely-spaced teeth. The hind limbs were also slender and very long, with large, clawed second toes.

Tyrannosauridae (Tyrannosaurids)
Translation: Tyrant Lizard
The Tyrannosauridae (tye-ran-uh-SAWR-ih-day) were a family of carnosaurs that lived during the Late Cretaceous Period. Like all theropods, tyrannosaurs were bipedal; that is, they strode on two legs with their bodies held close to horizontal and their tails outstretched for balance. They had very short but powerful arms and powerfully built legs. Heavier than earlier carnosaurs, tyrannosaurs reached weights of up to 14,000 lbs (6350 kg) and grew to lengths of 50 feet (15 meters) and more. They were equipped with huge, strong jaws and sharp, serrated teeth. They may have hunted in packs, and it is thought that they were relatively fleet of foot. One recently expressed opinon would make tyrannosaurs mere scavengers, but this idea is debatable. Tyrannosaurids have been discovered in North America, Mongolia, India, and Japan.

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