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Dinosaur and Paleontology Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the dinosaur or paleontology term you are looking for is not in the dictionary, please e-mail us.

I


IBEROMESORNIS

(pronounced eye-BER-oh-mes-OR-nis) Iberomesornis (meaning "Iberian=Spanish intermediate bird") was a small, early, toothed bird that lived during the early Cretaceous period. It was capable of powered flight. It had tiny, spiky teeth in its beak and was the size of a sparrow. Its hip was primitive compared to modern birds; its ilium, ischium, and pubis were all parallel and directed backward. Iberomesornis was named by paleontologists Sanz and Bonaparte in 1992. Fossils were found in Spain. The type species is I. romeralli.

ICAROSAURUS

Icarosaurus siefkeri was an early gliding reptile (a lepidosaur) that lived during the Triassic period, roughly 175 to 200 million years ago. It was 7 inches long and had a 10 inch wingspan. [Coelurosauravus is another gliding reptiles that lived 250 million years ago, long before Icarosaurus.] A single fossil of Icarosaurus was found in Granton Quarry, North Bergen, New Jersey, USA 1960 by Alfred Siefker and Michael Bandrowski. Icarosaurus was described by Edwin Harris Colbert in 1961.

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).
    T. rex pelvis

    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.

    INDOSAURUS

    (pronounced in-doh-SAWR-us) Indosaurus (meaning "Indian lizard")was a theropod dinosaur from the late Cretaceous period, roughly 70 to 65 million years ago. This bipedal meat-eater had a thick braincase and a wide skull; it may have had two horns on its head. It is known from a partial skull found in Jabalpur, India, by Charles Matley. Indosuchus was named by paleontologists von Huene & Matley in 1933. The type species is I. matleyi.

    INDOSUCHUS

    (pronounced in-doh-SOOk-us) Indosuchus (meaning "Indian crocodile")was a theropod dinosaur from the late Cretaceous period, roughly 70 to 65 million years ago. This bipedal meat-eater had many serrated teeth and a narrow, crested skull with a flattened roof. It may have been up to 20 feet (6 m) long. It is known from a fragmentary skull found in India by Charles Matley. It was related to, but smaller and more primitive than, Allosaurus and Tyrannosaurus rex. Indosuchus was named by paleontologists von Huene and Matley in 1933. The type species is I. raptorius.


    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.

    IRIDIUM

    (pronounced irr-ID-ee-um) Iridium is a heavy metal element that is rare on the Earth's surface, but abundant on chondritic meteors and in the Earth's core.

    IRIDIUM ANOMALY

    The iridium anomaly is a layer of Earth's crust (the K-T layer, which is about 65 million years old) in which there is excess of iridium (a relatively rare element). The presence of this extra Iridium supports the Alvarez asteroid theory, since this iridium may have come from an asteroid.

    IRISH ELK

    Megaceros (=Megaloceros) giganteus (meaning "gigantic large horn"), is the prehistoric Irish elk (more closely related to the fallow deer than the elk). It was the biggest deer that ever lived; it was over 10 feet (3 m) tall and had enormous antlers 11 feet (3.3 m) across (the largest of any deer). These antlers were shed yearly. Megaceros dates from the late Pleistocene (from 1.5 million to 2,500 years ago). Large herds of these mammals lived in what is now Europe and western Asia. It was preyed upon by giant cats and wolves and it was hunted by early humans. (Class Mammalia, order Artiodactyla, family Cervidae)

    IRRITATOR

    (pronounced IRR-eh-tay-ter) Irritator was a theropod dinosaur, a spinosaurid from the early Cretaceous period. It is known from a nearly complete skull (about 80 cm long) found in Brazil. Irritator challengeri was named by paleontologists Martill, Cruikshank, Frey, Small & Clarke in 1996. The people who found the snout-less skull added plaster to it in order to make it look it more impressive. This nonsense didn't fool the paleontologists, but it did irritate them, hence the name.

    ISANOSAURUS

    (pronounced ee-sahn-o-SAWR-us) Isanosaurus (meaning "Isan lizard" - Isan is the local name for the northeastern of Thailand) was a sauropod dinosaur from the late Triassic period (it is the earliest-known sauropod). Fossils were found in the Nam Phong Formation, Thailand. Ischisaurus was named by paleontologists Buffetaut, Suteethorn, Cuny, Tong, Le Loeuff, Khansubha, and Jongautchariyakul in 2000. The type species is I. attavipachi.

    ISCHISAURUS

    (pronounced is-chee-SAWR-us) Ischisaurus (named for Ischigualasto, the valley in NW Argentina where it was found) was a small, very early theropod dinosaur from the late Triassic period, about 225 million years ago. Ischisaurus had a skull only 9.5 inches (25 cm) long with 15-16 teeth on each side of the mouth plus four longer teeth in the front. This bipedal meat-eater had short arms, and may be the same as Herrerasaurus. Fossils were found in Argentina. Ischisaurus was named by paleontologist Reig in 1963. The type species is I. cattoi.
    T. rex pelvis

    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.

    ZoomDinosaurs.com
    Dinosaur and Paleontology Dictionary
    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

    Click on an underlined word for more information on that subject.
    If the dinosaur or paleontology term you are looking for is not in the dictionary, please e-mail us.

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