ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

TRACE FOSSILS Also known as ichnofossils, these are fossilized footprints, nests, dung, gastroliths, etc., but not actual body parts. They record the movement and behavior of animals.

TRACHODON (pronounced TRACK-oh-don) Trachodon (meaning "rough tooth") is a plant-eating dinosaur that is known only from a few teeth and parts of the jaw that were found in Montana, USA. It dates from the late Cretaceous period, about 77-73 million years ago. From the teeth, it has been surmised that it was probably a duck-billed dinosaur (a lambeosaurine hadrosaur). Trachodon was named in 1856 by Joseph Leidy; the type species is T. mirabilis. This is a dubious genus due to the sparsity of fossils.

TRACKWAYS Many animal track fossils (fossilized footprints) have been found. They can indicate the animal's speed, weight, and herding behavior. Determining which animal made the tracks can be difficult.

TRANSGRESSION Transgression is the flooding of a continent as the sea level increases, usually caused by melting polar ice. Another cause is sea floor spreading and underwater volcanism, in which large amounts of underwater lava cause water to be displaced onto land.

TREE FERN Tree ferns are tall vascular plants that live in warm climates. These ferns have a clump of fronds on top of a fibrous trunk.

T. rex (pronounced TEE recks) Tyrannosaurus rex (meaning "tyrant lizard king") was a huge, meat-eating theropod dinosaur from the late Cretaceous period.

TRIADOBATRACHUS Triadobatrachus massinoti is the earliest-known salientian, a proto-frog. Morphologically, it is between a salamander and a frog. This 4 inch (10 cm) long amphibian lived during the early Triassic period, about 250 million years ago. A single fossils was found in Madagascar. Triadobatrachus had long jumping hind legs and a well-developed eardrum. It had a short body, a short tail, and 14 back vertebrae (compared to 5 to 9 vertebrae in modern frogs). Classification: Order Proanura.

TRIASSIC PERIOD (pronounced tri-ASS-ik PEER-ee-ud) Dinosaurs and mammals evolved during the Triassic period, 248 - 208 million years ago.

TRICERATOPS (pronounced tri-SER-uh-tops) Triceratops was a frilled dinosaur, a ceratopsian, from the late Cretaceous period that had three horns on its head. This plant-eater was about 25 feet (8 m) long.

TRICONODONT Triconodonts (meaning "three-coned teeth") were small, early mammals that lived from the Triassic period until the Cretaceous period (from about 200-100 million years ago). These long-tailed, quadrupedal mammals had three-cusped teeth (hence their name) and ranged from a just a few inches long to the size of a cat. They had relatively advanced, grasping hands, but a primitive pelvis and hind limbs. These insectivores may have had large eyes, and may have been nocturnal (most active at night). The most complete triconodont, the 5 inch long, 125 million-year-old Jeholodens jenkinsi, was recently found in Lianong, China.

TRIGONIAS (pronounced tri-GO-nee-us) Trigonias was one of the earliest rhinoceroses. It lived during the early Oligocene Epoch, about 35 million years ago. This large, plant-eating mammal was about 8 ft (2.5 m) long, had five-toed front feet, and had more teeth than modern-day rhinos. It did not have a snout "horn," as modern-day rhinos do. Fossils have been found in Europe (France) and western North America (Montana). The type species is Trigonias osborni. Classification: Order Perissodactyla (odd-toed ungulates), Suborder Ceratomorpha (tapirs, rhinos), Family Rhinocerotidae, Genus Trigonas. Photo courtesy of Jim Puckett.

TRILOBITE (pronounced TRI-low-bite) Trilobites were early invertebrates with a segmented body and an exoskeleton. Trilobites dominated the environment during the Cambrian Period (540 to 500 mya).

TRIMUCRODON Trimucrodon (meaning "triply-pointed tooth"), Trimucrodon was a small plant-eating dinosaur that lived during the late Jurassic period, roughly 150 million years ago. A fossilized tooth of this ornithischian dinosaur have been found in Provincia do Estremadura, Portugal. The type species of this genus is T. cuneatus, named by Thulborn in 1973. Due to the lack of fossil information, this genus is a nomen dubium.

TRIOLOPHODON Trilophodon (meaning "three crested tooth") was an ancient mammal that lived during the Miocene - it is sometimes called Tetrabelodon. This large Gomphothere was an ancestor of mastodons. Trilophodon was about 5 m long and 2.5 m high. It was a heavy, plant-eating animal that walked on four column-like legs. It had a large skull, and elephant-like proboscis, four parallel tusks (two on the top jaw, two smaller ones on the bottom jaw), high-ridged grinding teeth, and a short tail. Fossils have been found in Europe (France), Africa (Kenya), Asia (Pakistan), and North America (Nebraska, South Dakota). Classification: Kingdom Animalia, Phylum Chordata, Class Mammalia (mammals), Order Proboscidea, Suborder Elephantiodea (elephants, mastodonts, mammoths), Family Gomphotheriidae, Genus Gomphothere.

TRIONYX (pronounced triI-ON-iks) Trionyx is a genus of soft-shelled turtles that first appeared during the Jurassic period.

TRIOPS (pronounced TRI-ops) Triops (Triops longicaudatus) are small, freshwater crustaceans (often found in rice fields) that look a little like trilobites. Also called tadpole shrimp, they are branchiopods with a hard exoskeleton, and sturdy mandibles (jaws). They eat animals and plants, and are sometimes cannibalistic. Their life span is about 20 to 40 days. Triops evolved during the Devonian period, about 350 million years ago (long before the dinosaurs appeared).

TROCHANTER The trochanter is a bony bump on the femur (the thigh bone) to which large muscles are attached.

TROÖDON (pronounced TROH-oh-don) Troodon was a very smart, human-sized, meat-eating theropod dinosaur from the late Cretaceous period, about 76 to 70 million years ago. Fossils of Troodon have been found in Montana, Wyoming (USA) and Alberta (Canada). The type species is T. formosus.

TROPEOGNATHUS Tropeognathus (meaning "keel jaw") was a pterosaur that lived during the middle Cretaceous period, about 122 to 112 million years ago. This flying reptile ate fish and lived near the sea. A Pterodactyloid, it had a wingspan of about 20 feet (6.2 m) and a short tail. The skull was 2.2 feet (67 cm) long. Tropeognathus had a large beak that was enlarged at the tip; it had many sharp teeth. Fossils have been found in the Santana Formation in norteastern Brazil. Tropeognathus was named by Wellnhofer in 1987. The type species is T. mesembrinus.

TROPHIC LEVEL A trophic level is a level of the grazing food chain. For example, plant-eaters are primary consumers; they occupy the second trophic level in the grazing food chain.

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