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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

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If the dinosaur or paleontology term you are looking for is not in the dictionary, please e-mail us.

O


OHMDENOSAURUS

(pronounced OHM-den-oh-SAWR-us) Ohmdenosaurus (meaning "Ohmden, Germany lizard") was a long-necked, plant-eating dinosaur from the early Jurassic period, about 191 million years ago. This sauropod was about 13 ft (4 m) long. Ohmdenosaurus was named by paleontologist Wild in 1978. The type species is O. liasicus. Few fossil bones (only a tibia and tarsus) have been found in Germany.
OLFACTORY BULBS
The olfactory bulbs are the parts of the brain that sense smell.
OLFACTORY CAVITY
The olfactory cavity is the part of the inside of an animal's skull that once housed the olfactory bulbs. The relative size of the olfactory cavity indicates how well the animal could sense smells. For example, the T. rex nicknamed Sue had a large olfactory cavity, suggesting that T. rex had an acute sense of smell.

OLIGOSAURUS

(pronounced OL-ig-oh-SAWR-us) Oligosaurus (meaning "small lizard") is an invalid name for Rhabdodon, a small, plant-eating dinosaur from the late Cretaceous period. Oligosaurus was named by Seeley in 1881.

OMEISAURUS

(pronounced OH-may-SAWR-us) Omeisaurus (meaning "Mount Emei (China) lizard") was a very long-necked plant-eating dinosaur from the late Jurassic period, about156-145 million years ago. This cetiosaurid sauropod was about 68 ft (20 m) long; it had a tiny head and relatively short tail. Omeisaurus was named by paleontologist Young in 1939. Many Omeisaurus fossils (perhaps a herd) were found in Sichuan, China. The type species is O. junghsienensis.

OMNIVORE

Omnivores are animals that eat both animals and plants. Some omnivores include grizzly bears, raccoons, pigs, chickens, crows, and people.
ONTOGENY BULBS
Ontogeny is the course of development of an organism.
OPHIACODON
(pronounced o-fee-ah-ko-don) Ophiacodon was a genus of pelycosaurs that did not have a sail (they were not dinosaurs - and lived before the dinosaurs appeared). Ophiacodon was a quadruped with four short, sprawling, clawed legs, a long tail, and large jaws in a narrow but large skull. It was up to about 12 feet (3.6 m) long and weighed from 65 to 110 pounds (30-50 Kg). These meat-eaters lived near water and probably ate fish and amphibians. They lived and may have been semi-aquatic. They lived during from the early Permian period (roughly 270 million years ago). Fossils have been found in Texas, USA. Classification: Synapsida (synapsids), Pelycosauria (pelycosaurs like Edaphosaurus and Dimetrodon), Suborder Eupelycosauria, Family Ophaicodontidae (very primitive pelycosaurs), Genus Ophaicodon.
OPHTHALMOSAURUS
(pronounced op-THAL-moh-SAWR-us) Ophthalmosaurus was an Ichthyosaur about 11.5 feet (3.5 m) long with a bulky body and huge eyes - the bone-lined eye sockets were 4 inches (10 cm) across. It was from the late Jurassic period in what is now England, France, Argentina, and western North America. It was not a dinosaur, but another type of extinct reptile.

OPISTHOCOELICAUDIA

(pronounced oh-PIS-tho-SEEL-ih-CAWD-ee-ah) Opisthocoelicaudia (meaning "hollow-backed tail (vertebrae)") was a sauropod dinosaur (perhaps a camarasaurid) that lived during the late Cretaceous period. This large quadruped was about 34 ft (10.5 m) long and weighed roughly 23700 kg; its femur (thigh bone) was 139.5 cm long. Fossils (almost complete, but missing the neck vertebrae) have been found in Mongolia. Opisthocoelicaudia was named by Borsuk-Bialynicka in 1977.

OPISTHOCOELUS VERTEBRAE

Opisthocoelus vertebrae are vertebrae in which the main body is convex in the front (anterior) and concave in the back (posterior). Compare with amphicoelus vertebrae.
T. rex skull

ORBIT

The orbit is the hole in the skull for the eye.
ORCOMIMUS
(pronounced or-coh-MEEM-us) Orcomimus was meat-eating, bipedal dinosaur, an advanced theropod that lived during the late Cretaceous period, roughly 84-65 million years ago. Fossils of this Ornithomimosaur, including a pelvis and a hindlimb, were found in South Dakota, USA. Orcomimus was named by Triebold in 1997.

ORDER

In classification, an order is a group of related or similar organisms. An order contains one or more families. A group of similar orders forms a class.

ORDOVICIAN PERIOD

(pronounced or-da-VISH-ee-en) The Ordovician Period lasted from 505 to 438 million years ago. Primitive plants appear on land, as do the first corals, primitive fishes, seaweed and fungi. Graptolites, bryozoans, gastropods, bivalves, and echinoids also appear. There were high sea levels at first, then global cooling and glaciation, and extensive volcanism. North America was under shallow seas. The Ordovician ends in >huge extinction, due to glaciation. The Ordovician was named for an ancient tribe (the Ordovices) that lived in northern Wales.


OREODONT

(pronounced OR-ee-oh-DONT) Oreodonts (meaning "mountain tooth") were the most common hoofed herbivorous (plant-eating) mammals in North America during the Oligocene (from about 35-5 million years ago). Oreodonts were quadrupedal ruminants closely related to camels, pigs, and sheep; most oreodonts were about the size of a dog or a pig. The skull was elongated and the upper canines were chisel shaped; the cheek teeth were used for grinding. Many fossils have been found in North America. Some oreodonts include Mesoreodon, Brachycrus (3.25 ft long), Promerycocherus (3.25 ft long), Sespia, and Merycoidodon (4.5 ft long, pictured above). Classification: Class Mammalia (mammals), Order Artiodactyla (even-toed ungulates), Suborder Tylopoda (padded feet - oreodonts, camels), Family Merycoidodontidae, many genera and species. Joseph Leidy coined the term oreodont in 1853.
ORNATOTHOLUS
(pronounced or-nat-oh-THO-us) Ornatotholus was plant-eating, thick-skulled bipedal dinosaur that lived during the late Cretaceous period, roughly 84-71 million years ago. It may have been about 3 m long. Skulls of this Pachycephalosaurid were found in Alberta, Canada, and Montana, USA. Ornatotholus was named by Galton and Sues in 1983. The type species is O. browni.

ORNITHISCHIAN

(pronounced or-ni-THISS-key-an ) Ornithischian (bird-hipped) dinosaurs were herbivoroud dinoaurs that had hoof-like claws. Some ornithischians include the Ornithopods (Fabrosaurs, Hadrosaurs, Hypsilophodontids, Iguanodontids, Camptosaurids), Thyreophorans (Ankylosaurids, Stegosaurids), and Marginocephalians (Ceratopsians, Pachycephalosaurs).
Ornithocheirus
ORNITHOCHEIRUS

(Pronounced or-NITH-oh-KIE-rus) Ornithocheirus (meaning "bird hand") was a large pterodactyloid pterosaur, a flying reptile that lived during the Cretaceous period. It had a long, tapering, toothed snout with a bony crest. The skull was roughly 4.8 ft (1.5 m) long; the body was 11.5 ft (3.5 m) long. Ornithocheirus had a wing span of about 38 ft (12 m) and had a very short tail. It was not a dinosaur, but was closely related to them. Fragmentary fossils of 36 different species of this flying fish-eater (including about 100 hollow, light-weight bones) have been found in England, Germany, and the Czech Republic (and perhaps Australia and South America). Ornithocheirus was named by Seeley in 1869.

ORNITHODIRA

Ornithodira (meaning "bird necks") is the clade which includes dinosaurs (including their early ancestors the lagosuchians) and pterosaurs. They have s-shaped necks.

ORNITHOLESTES

(pronounced or-NITH-oh-LES-teez) Ornitholestes (meaning "bird robber") was a fast theropod from the late Jurassic period. It had long legs, clawed hands, and a small bony crest on its snout.

ORNITHOMIMUS

(pronounced or-NITH-oh-MIME-us) Ornithomimus (meaning "bird mimic") was an ostrich-like Ornithomimidae, a theropod with a toothless beak, long legs, and hollow bones. This meat-eating dinosaur was about 15-20 feet (4.5-6 m) long and lived during the late Cretaceous period, roughly 76-65 million years ago.

ORNITHOPOD

(pronounced or-NITH-oh-pod) Ornithopods (Suborder Ornithopoda) are a suborder of ornithischian dinosaurs that have no hole in the outer, lower jaw and a long pubis that extends farther forwards than than the ilium (Paul Sereno, 1986). Ornithopods were beaked, mostly bipedal, herbivorous (plant-eating) dinosaurs that lived from the late Triassic to the late Cretaceous. Ornithopod means "Bird feet." Ornithopods are divided into the groups: Hadrosaurs, Hypsilophodontids, Iguanodontids, and Fabrosauria. Drinker, Iguanodon, Hypsilophodon, Muttaburrasaurus, Leaellynasaura, and Othnielia are examples of ornithopods.

ORNITHOSUCHUS

(pronounced or-nith-oh-SOOK-us) Ornithosuchus (meaning "bird crocodile") was a mid to late Triassic period thecodont, (the group of reptiles from which the arcosaurs, including the dinosaurs, evolved). It was not a dinosaur, but was closely related to dinosaurs and pterosaurs. It was a bipedal (walked on two legs) carnivore (meat-eater) that had long legs, short arms, five-fingered hands, a long snout, a long tail and sharp teeth. It was about 6 feet long and weighed about 100+ pounds. Fossil have been found in England (and a few other locations). Ornithosuchus was named by Huxley in 1877. Ornithosuchus used to be thought to be a dinosaur.

ORNITHURA

(pronounced or-nith-EUR-an) Ornithurans are a clade that includes modern birds (neornitheans) and their close ancestors (which included hesperornithiformes, patagopterygiforms, and ambiortimorphs, toothed bird groups from the Mesozoic Era).

ORODROMEUS

(pronounced OR-oh-DROHM-ee-us) Orodromeus (meaning "mountain runner") was a small, lightly-built, fast-running, plant-eating dinosaur about 8 feet (2.5 m) long. This Ornithischian ornithopod lived during the late Cretaceous period about 77 to 73 million years ago. Fossils have been found at Egg Mountain, Montana, USA. (Eggs were also found at the site, but they belong to Tröodon) It was named by paleontologists Horner & Weishampel in 1988. The type species is O. makelai.
Orthoceras
ORTHOCERAS

(pronounced ORTH-oh-SEER-us) Orthoceras (meaning "straight horn") were primtive types of nautiloids that looked like squid with a long, straight (or slightly curved), conical, chambered, and furrowed shell. The shell ranged from a few centimeters to over 9 feet long. The Orthoceras lived in the largest chamber in the shell. These invertebrates swam in shallow seas using jet-propulsion and breathed with gills. Orthoceras lived from the middle Ordovician Period to the Devonian Period, from about 470 to 360 million years ago. Fossils are common and have been found on many continents including the Americas, Africa, Europe, and Asia. Classification: Phylum Mollusca, Class Cephalopoda (Nautiloidea), Order Orthocerida, genus Orthoceras, many species.

ORYCTODROMEUS

(pronounced oh-RIC-to-DRO-ee-us) Oryctodromeus cubicularis (meaning "digging runner of the lair") was a burrowing, herbivorous ornithopod dinosaur (a Hypsilophodontid) that lived about 95 million years ago, during the mid-Cretaceous period. This small, fast-running, bipedal dinosaur was about 4.3 ft (1.2 m) long; it would stand about knee-high to an adult human. Three partial fossils (an adult and two juveniles) were in found an ancient burrow in southwestern Montana in 2004 by Yoshihiro Katsura. Oryctodromeus was named by David J. Varricchio in 2007.


OSBORN, HENRY
Henry F. Osborn (1857-1935) was a US paleontologist who found and named many dinosaurs in Mongolia and the US in the early 1900's. He was the curator of the American Museum of Natural History starting in 1891. He did extensive research on brontotheres ( early, rhino-like mammals). Osborn also named and described the following dinosaurs: Albertosaurus (1905), Asiatosaurus (1924), Ornitholestes (1903), Oviraptor (1924), Pentaceratops (1923), Prodeinodon (1924), Psittacosaurus (1923), Saurornithoides (1924), Struthiomimus (1916), Tyrannosaurus (1905), and Velociraptor (1924).

OSHANOSAURUS

(pronounced oh-san-oh-SAWR-us) Oshanosaurus was a sauropod dinosaur from the early Jurassic period in what is now China. The type species is O. youngi. It was named by paleontologist Zhao in 1983.

OSTRACOD

(pronounced OS-tra-KOD) Ostracod (meaning "shell like") are also called seed shrimp or mussel shrimp. These tiny freshwater and marine crustaceans belong to the subclass Ostracoda. They are scavenger that have a shrimp-like body plus two hard shells connected by a hinge; they have one or two appendages. Ostracods range in size from micoscopic to about an inch (2.5 cm) long. There are about 20,000 species of living ostracods and many more extinct species. These very common animals are used as index fossils, helping to date rock layers. The oldest-known ostracods are from the Cambrian period; they became widespread during the Ordovician and remain so.

OSTRACODERM

Ostracoderms (also called Agnaths) are extinct, primitive, armored, jawless fish that lived during from the Ordovician period to the Devonian period. These vertebrates had bodies that were protected by bony plates and scales. Fossils have been found in North America and Europe. Some ostracoderms include the Pteraspids.
OSTROM, JOHN H.
John H. Ostrom is a US paleontologist and author who found (1964) and named (1969) Deinonychus with Grant E. Meyer et alia. He named Microvenator (1970), Sauropelta (1970), and Tenontosaurus (1970). Ostrom has championed the theory that birds arose from theropod dinosaurs. Ostrom also argued that the dinosaur's must have high body temperatures given their erect posture (1969). Ostrom's books include "The Strange World of Dinosaurs" (Putnam, 1964), "Dinosaurs" (Carolina Biological Supply Co., 1984), "Marsh's Dinosaurs : The Collections from Como Bluff" (with McIntosh and Dodson, Yale Univ Press, 2000), and others. The Cretaceous period bird/dinosaur Rahonavis ostromi was named to honor Ostrom.


OTHNIELIA

(pronounced OTH-ni-EE-lee-ah) Othnielia was a ornithopod dinosaur from the late Jurassic period, about 156 to 145 million years ago. It was a bipedal plant-eater with a horny beak and strong jaws. It had long legs with very long shins; this made it a very fast runner. It had short arms, a long, stiff tail, and was about 4.6 feet (1.4 m) long. It had five-fingered hands and four-toed feet, all clawed. Its fossils (two partial skeletons and teeth) were found in Colorado, Utah, and Colorado in the western USA. It was named by Galton in 1977 in honor of Othniel Marsh, the fossil hunter.

OTOGORNIS

Otogornis was an early, toothless bird from the early Cretaceous period. Otogornis, belonging to the group Enantiornithes (toothless birds), was found in China and named by Hou in 1994.


OURANOSAURUS

(pronounced oo-RAHN-oh-SAWR-us) Ouranosaurus (meaning "brave monitor lizard") was a sail-backed, plant-eating, Ornithischian dinosaur. It was an iguanodontid from the early Cretaceous period, about 115 million years ago.

OUTCROPPING

An outcropping is a place where the bedrock (the underlying rock) is exposed on the Earth's surface.

OVERBURDEN

The overburden is the rock that lies on top of a fossil.


OVIPAROUS

Oviparous animals hatch from eggs. Fossilized eggs from some prehistoric animals have been found.

OVIRAPTOR

(pronounced OH-vi-RAP-tor) Oviraptor was a theropod dinosaur with a parrot-like head, toothless beak, long fingers, and long legs.



OWEN, RICHARD

Sir Richard Owen (1804-1892) was a British comparative anatomist who coined the term dinosauria (meaning "fearfully great lizard") as a suborder of large, extinct reptiles in 1841. He also named and described the following dinosaurs: Bothriospondylus (1875), Cetiosaurus (1841), Chondrosteosaurus (1876), Dacentrurus (1875), Dinodocus (1884), Echinodon (1861), Massospondylus (1854), Nuthetes (1854), Polacanthus (1867), and Scelidosaurus (1859).

OZRAPTOR

(pronounced oz-RAP-tor) Ozraptor (meaning "Australian plunderer") was a 6.5 to 10 feet (2-3 m) long bipedal carnivore (meat-eater) from the mid-Jurassic period. It was a Tetanurine (advanced theropod dinosaurs that had three-fingered hands, maxillary fenestra, long legs, and a stiff tail). Ozraptor was named by Long & Molnar in 1998 and is known from a part of a tibia (shin bone) found in Australia.

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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