ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

ICE AGE An ice age is a time lasting thousands of years during which the Earth is very cold and largely covered by ice and glaciers.

ICE AGE MAMMALS Many mammals, including some very large ones, lived during the Pleistocene ice age. Saber-toothed tigers, Baluchitherium, mammoths, woolly rhinos, and others lived in the icy environment.

ICHNITES (pronounced IK-nites) Also known as trace fossils or ichnofossils, these are fossilized footprints, nests, dung, gastroliths, burrows, stomach contents, etc., but not actual body parts. Ichnofossils record the movement and behavior of animals. Ichnology is the study of ichnites.

ICHNOFOSSILS Also known as trace fossils or ichnites, these are fossilized footprints, nests, dung, gastroliths, burrows, stomach contents, coprolite, etc., but not actual body parts. Ichnofossils record the movement and behavior of animals. Ichnology is the study of ichnofossils.

ICHNOGENUS Ichnogenera (meaning "footprint groups") are groups of dinosaurs whose characteristics are surmised only from their fossilized footprints. When dinosaur trackways are found, it is nearly impossible to determine which dinosaur genus made the prints, so the prints are given a new genus name, an ichnogenus. Some ichnogenera include Theropods (bipeds with relatively long, narrow toes ending in claws): Eubrontes (early Jurassic), Grallator and Coelurosaurichnus (late Triassic), Carmelopodus (middle Jurassic), Anchisauripus (late Triassic to early Jurassic period), and Megalosauripus (late Jurassic). Prosauropods:Tetrasauropus (late Triassic), Pseudotetrasauropus (late Triassic), Otozoum. Sauropods (quadrupeds with 5-toed, elephant-like feet; the inner three or four toes had claws): Brontopodus. Ornithopods (bipeds or quadrupeds with wider tracks and hoof-like claws): Anomoepus, Amblydactylus (a hadrosaur).

ICHNOLOGY Ichnology is the study of fossilized footprints and other ichnofossils.

ICHTHYORNIS (pronounced ik-thee-ORN-is) Ichthyornis (meaning "fish bird") was an 8 inch (20 cm) long, tern-like, extinct bird that lived during the late Cretaceous period (135-70 million years ago). It had a large head, toothed jaws, and long beak. This powerful flyer is the oldest-known bird that had a keeled breastbone (sternum) similar to that of modern birds. It lived in flocks, nested on shorelines, and hunted for fish over the seas. Ichthyornis was originally found in 1872 in Kansas, USA, by a member of paleontologist Othniel C. Marsh's Yale University expedition. Ichthyornis was named by Marsh in 1872. Fossils have been found in Kansas and Texas, USA and Alberta, Canada. (Subclass Odontornithes, Order Ichthyornithiformes)

ICHTHYOSAUR (pronounced IK-thee-oh-SAWR) Ichthyosaurs were prehistoric reptiles that lived in the sea.

ICHTHYOSAURUS (pronounced IK-thee-oh-SAWR-us) Ichthyosaurus was an Ichthyosaur, a dolphin-like reptile about 6.5 feet (2 m) long. It could swim at 25 mph (40 kph). Ichthyosaurs had a tall dorsal fin, a half-moon-shaped tail, paddle-like flippers and smooth skin. The nostrils were near the eyes on the top of the head. It had massive ear bones and large eyes, probably giving it acute hearing and sight. These marine reptiles gave birth to live young. Their diet was mostly fish, but also included cephalopods (like belemnites). Hundreds of Ichthyosaurus fossils have been found in England, Germany, Greenland, and Alberta, Canada. They lived during the early Jurassic to the early Cretaceous periods. It was not a dinosaur, but another type of extinct reptile. Ichthyosaurus, which means "fish lizard," was named by Charles Koenig in 1818.

ICHTHYOSTEGA Ichthyostega were terrestrial tetrapods (having four-legs) that lived during the late Devonian period. These are the first tetrapods known to have ventrured onto land. These vertebrates were up to about 4 ft (1.5 m) long; they had a wide body, a fish-like skull, four strong, short legs, a massive ribcage, and a finned tail. Adults had no gills. Fossils have been found in East Greenland. Ichthyostega were between fish and amphibians.

IGNEOUS ROCK When molten rock cools, igneous rock is formed.

IGUANODON (pronounced ig-WAHN-oh-don) Iguanodon was a plant-eating dinosaur with thumb spikes. It was about 33 feet (10 m) long and lived during the early Cretaceous period, roughly 130 million to 110 million years ago. The type species is I. anglicum. Iguanodon was named by Holl in 1829.

IGUANODONTIDS (pronounced ig-WAHN-oh-DON-tids) Iguanodontids (family Iguanodontidae, also called Iguanodonts) were large, plant-eating, ornithischian ornithopods who lived from the late Jurassic to the late Cretaceous periods. These dinosaurs had a thumb spike, a toothless beak, a long snout, long toes, and a bulky tail. Altirhinus, Iguanodon, Camptosaurus, Ouranosaurus, Probactrosaurus, Tenontosaurus (perhaps a hypsilophodontid), and Valdosaurus were iguanodontids.The Iguanodontids led to the Hadrosaurids (duckbills).

ILIUM (pronounced ILL-ee-um) The ilium (plural ilia) is a bone that is part of the hip, or pelvic girdle.

IMPACT CRATER Impact craters are the remains of collisions between an asteroid, comet, or meteorite and the Earth. Some large impact craters include the Chicxulub crater (off the Yucatan peninsula) and the Shiva crater (off the coast of India), both of which date from the K-T boundary, 65 million years ago, and were probably implicated in the K-T mass extinction.

INCERTAE SEDIS An incertae sedis is a taxonomic name that is uncertain.

INDEHISCENT Indehiscent fruit do not split open and release their seed when they mature.

INDEX FOSSILS Index fossils are commonly found fossils that are limited in time span. They help in dating other fossils. For example: trilobites were common during the Paleozoic, but not found before the Cambrian period. Ammonites were common during the Mesozoic Era, but not found after the Cretaceous period. Another example: the oldest-known ostracods are from the Cambrian period; they became widespread during the Ordovician and remain so.

INDRICOTHERIUM Indricotherium is an extinct, hornless rhinoceros with relatively long legs. (It used to be known as Baluchitherium). Adults were about 26 feet (8 m) long, 18 feet (5.5 m) tall, and weighed about 17 - 18 tons (16 tonnes). The skull was 4.25 feet (1.3 m) long. It was one of the biggest land animal ever to live on Earth (Paraceratherium was even bigger). This herbivore ate leaves and twigs from the tops of trees. It had four teeth; two tusk-like front teeth in the top jaw pointed downwards and two on the bottom pointed forwards. This extinct ungulate (hoofed mammal) had three toes on each foot. It lived from the Oligocene to the early Miocene (toughly 40-26 million years ago). Fossils have been found in Asia (Pakistan, Mongolia and China). Two of its enemies were the carnivores Hyaenodon and Dinictis. Classification: Order Perissodactyla (odd-toed ungulates), Family Hyrachyidae (odd-toed ungulates between tapirs and rhinos).

INGENIA (pronounced in-JEE-nee-ah) Ingenia was a bird-like theropod dinosaur, an oviraptorid. It was a bipedal omnivore about 4.5 feet (1.4 m) long. It lived during the late Cretaceous period, 80-70 million years ago and was named in 1981 by R. Barsbold from Mongolian fossils.

INOSTRANCEVIA Inostrancevia (named to honor the Russian geologist A. Inostrantzev) was tiger-sized therapsid (a mammal-like reptile) that lived during the Permian period, about 250 million years ago (before the time of the dinosaurs). This carnivorous quadruped had sprawling legs and a large skull with long, saber-like teeth. Fossils have been found in Russia (Arkhangelsk Region). The type species is Inostrancevia alexandri; it was named by Vladimir Prokhorovich Amalitzky in 1922.

INSECTS Insects have exoskeletons and six legs. They evolved during the Silurian Period, 438 to 408 mya, long before dinosaurs existed.

INSECTIVORE An insectivore is an organism that eats mostly insects. Some of the smaller dinosaurs (like Compsognathus) may have been insectivores.

INVERTEBRATE Invertebrates are animals without a backbone. Some invertebrates include protozoans, arthropods (insects, arachnids, crustaceans, etc.), worms, jellyfish, sponges, mollusks (like cephalopods [octopus], gastropods, bivalves [clams, oysters, scallops]), and many others.

ISCHIUM (pronounced ISH-ee-um) The ischium (plural ischia) is a rod-like bone that is part of the hip, or pelvic girdle.

ISOTOPE An isotope of an element is another form of the same element that has a different number of neutrons in the nucleus (giving it a different atomic weight).

ITEMIRUS (pronounced EYE-te-MEER-us) Itemirus (named for Itemir, the region of Mongolia where it was found) was a small, theropod dinosaur from the late Cretaceous period, about 90 million years ago. This bipedal meat-eater may have been a dromaeosaurid. A fossilized braincase (the part of the skull that contains the brain) was found in Mongolia; very little is known about this dinosaur since so little fossil material is known. Itemirus was named by paleontologist Kurzanov in 1976. The type species is I. medullaris.

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