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Dinosaur and Paleontology Dictionary

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A habitat is a space (which includes food, water and shelter) suitable for the survival and reproduction of an organism.


The Hadean Eon lasted from 4.6 to 3.9 billion years ago. This "Rockless Eon" was the time when the Earth's continental and oceanic crusts were solidifying. The name Hadean was coined by the geologist Preston E. Cloud in the 1960s.


Hadrocodium (meaning "heavy or full head") was a tiny mammalian ancestor about the size of a paperclip. It is the earliest-known animal with such mammal-like features. This shrew-like quadruped had a long tail, a long snout, delicate teeth, three middle ear bones, a powerful jaw hinge, matching upper and lower teeth, a large brain case, and five-toed feet. Hadrocodium was an insectivore (insect-eater) that may have been nocturnal (most active at night). It lived about 195 million years ago. A skull (half an inch (12 millimeters) long) was found in the Lufeng Basin in Yunnan, China, in 1985 (it was only recently determined that it was a new species). The type species is Hadrocodium wui; was named by Zhe-Xi Luo et al.


Hadrosaurids, or duck-billed dinosaurs, were the biggest ornithopods (a type of ornithischian or bird-hipped dinosaurs). They could walk on two or four legs. These plant-eaters lived during the late Cretaceous period. Hadrosaur means 'big or bulky lizard.' Hadrosaurs had a wide, flat, toothless beak, hundreds of cheek teeth and powerful jaws. Their hind legs were large and each limb had four digits. Maiasaura, Edmontosaurus, Hadrosaurus, etc. were hadrosaurs. The hadrosaurs evolved from the iguanodontids.


(pronounced HAD-roh-SAWR-us) Hadrosaurus (meaning "bulky lizard" ) was a duck-billed dinosaur, a 23 to 32 feet (7 to 10 m) long ornithischian from the late Cretaceous period. Hadrosaurus was discovered by W. P. Foulke and excavated and named by anatomist J. Leidy in 1858 from a skull-less skeleton and hundreds of teeth found in New Jersey. It was the first American dinosaur to be described and the first nearly-complete dinosaur skeleton. Although the Hadrosaurids are named for this genus, Hadrosaurus is a doubtful genus because there is so little fossil information about it (including no skull). The type species is H. foulkii; it was named by paleontologist J. Leidy in 1858.


Hainosaurus (meaning "Haine (River) lizard") was a huge mosasaur that was about 50 feet (15 m) long. The skull is about 1.5 m long. This is the largest mosasaur yet found. They had sharp teeth and ate fish, turtles, and other marine organisms. Fossils have been found in Europe. Hainosaurus was named by Dollo in 1885.


The half-life of a radioisotope is the amount of time it takes for half of the radioisotope to decay.


Hallucigenia was a strange, spiked animal that lived during the Cambrian Period, roughly 500 million years ago (found in Canada's Burgess Shale and in China). Hallucigenia as an onychophoran (a "velvet worm") that had 7 tentacles on its top side which it used to grasp food; it used 7 pairs of spines on the underside for walking. Forty fossils of Hallucigenia have been found.


A hallux, or dewclaw, is a functionless claw that doesn't hit the ground. Some dinosaurs had dewclaws.


(pronounced HALL-tik-oh-SAWR-us) Halticosaurus (meaning "leaping lizard") was a late Triassic dinosaur from about 222 million years ago. It was a very early dinosaur and its classification is unsure (it is perhaps a theropod). It was a speedy bipedal dinosaur about 17 feet (5 m) long. It had a short neck, very long feet, a long, large head with many sharp teeth. Its feet suggest that it was a theropod (a meat eater) but its hip and vertebrae are more like those of plant eaters. An incomplete skeleton was found in Wuerttemberg, Germany in 1906 and named by paleontologist von Huene.


(pronounced hap-lo-KAN-tho-SAWR-us) Haplocanthosaurus (meaning "single spine lizard") was a sauropod dinosaur from the late Jurassic period, about 156-145 million years ago. This plant-eater had a long neck, a long tail, a bulky body and a small head. It was about 70 ft (21 m) long. Partial fossils have been found in Colorado and Wyoming, USA. The type species is H. priscus. It was found by paleontologist John Bell Hatcher in 1901, and named by him in 1903.


(pronounced HAR-pee-MIME-us) Harpymimus ("Harpy [a Greek bird-woman monster] mimic") was a theropod dinosaur, a bipedal meat-eater that lived during the Cretaceous period, about 119- 97.5 million years ago. It had a beak and 10 - 11 conical teeth in its lower jaw. Its diet is uncertain. It had tapered, three-fingered hands. This extremely fast-running dinosaur had thin, long-shinned legs and a light-weight body. It was about 6.5 feet (2 m) long and may have weighed about 275 pounds (125 kg). This bird-like dinosaur is known from a skull and a few bones found in Mongolia. Harpymimus was named by Barsbold & Perle in 1984. The type species is H. okladnikovi.


The first dinosaur models were made by Benjamin Waterhouse Hawkins of England in 1854. He made and sold plaster-cast dinosaurs through the Ward's catalogue of scientific supplies. His original models included Igauanodon, Hylaeosaurus, Megalosaurus, Plesiosaurus and Ichthyosurus. The first dinosaur used for adult amusement was a life-size model of an Iguanodon (made of concrete by Hawkins) that was used to house a dinner party for scientists (including Richard Owen, who coined the term dinosaur) at a major exhibition in London, England, in 1854. The invitations to the party were sent on fake pterodactyl wings..


Helicoprion was an ancient fish from the Late Paleozoic (it appeared during the Carboniferous period, about 345 million years ago). This predatory fish is known only from fossilized teeth; it probably had a cartilaginous body (which does not fossilized well and is possibly why a fossil skeleton from this fish has not been found). Helicoprion was probably related to sharks or was a shark itself. It had big, flattened teeth that were probably used for crushing shellfish and arthropods. These teeth grew in a series of coiled whorls; new teeth replaced broken and worn-out teeth, but the old ones went inside the jaw. These fossilized teeth have been found worldwide. Classification: Family Edestidae


Sue Hendrickson (December 2, 1949 - ) is a self-taught fossil hunter (specializing in fossil inclusions in amber), marine archaeologist, adventurer and explorer. In South Dakota in 1990, Hendrickson found the remarkable T. rex fossil that is now known as Sue. This T. rex fossil is the largest and most complete T. rex found to date. Sue (the fossil) is now displayed at the Field Museum in Chicago, Illinois, USA.

For more information on Hendrickson, click here.


(pronounced hen-o-dus) Henodus was a marine reptile about 3.25 feet (1 m) long. It was not a dinosaur, but a placodont. It had no teeth, but used its hard, horny beak to get and crush shellfish. It had a box-like head, 4 legs, a short, pointed tail, and a flat body. It was protected from predators, like Ichthyosaurs, by bony plates that formed a shell on its back and stomach. Although it resembled a turtle, it was not closely related to turtles. It lived during the late Triassic period, when it swam in the Tethys Sea. Fossils have been found in Germany. Classification: Order Placondontia, Family Henodontidae (armored placodonts).


Herbivores are animals that eat plants. Most dinosaurs were herbivores. Plant-eaters are also called primary consumers.


(pronounced huh-RARE-ah-SAWR-us) Herrerasaurus (meaning "Herrera's lizard;" Victorino Herrera was a rancher who discovered the fossil) was a late Triassic archosaur (a reptile that was almost a dinosaur) from about 230 million years ago. It used to be thought to be a very early dinosaur and a primitive prosauropod. It was a speedy bipedal carnivore about 17 feet (5 m) long, weighing roughly 440-780 pounds (200-350 kg). It had a short neck and a large head. Three partial skeletons were found in Argentina, South America. This genus was named in 1963 by O. A. Reig from a specimen found in 1958. The type species is H. ischigualastensis (the species name is from the Ischigualasto Formation of northwestern Argentina, where the fossil was found).


(pronounced HES-per-OR-nis) Hesperornis (meaning "western bird") was an early, flightless bird that lived during the late Cretaceous period. This diving bird was about 3 feet (1 m) long and had webbed feet, a long, toothed beak, and strong legs. Although it couldn't fly, it was probably a strong swimmer and likely lived near coastlines and ate fish. Fossils have been found in North America. Hesperornis was named by paleontologist O. Marsh in 1872 from fossils found near the Smoky Hill River in Kansas, USA.


(pronounced hes-PARE-uh-SAWR-us) Hesperosaurus (meaning "western lizard," and originally called Hesperisaurus) was a primitive stegosaurid dinosaur that had a single row of rounded plates running down its back; it also had four bony spikes (thagomizers) at the end of the tail. This plant-eating dinosaur lived during the late Jurassic period, roughly 150 million years ago. Fossils have been found in the Morrison Formation, Jackson County, Wyoming, USA, North America. The type species is Hesperisaurus mjosi; it was named by paleontologists K. Carpenter et al. in 2001.


(pronounced HET-er-oh-CROW-knee) heterochrony (meaning "differeny time") is a evolutionary (genetically determined) change in the timing of developmental events or a change in the growth rate, as compared to the same events in ancestors. For example, the time it takes to grow to adulthood may change over time.


(pronounced HET-er-oh-DON-toh-SAWR-us) Heterodontosaurus (meaning "different-tooth lizard") was an early ornithischian dinosaur. It was an herbivore with three different types of teeth. This lightly-built plant-eater was up to 4 ft (1.2 m) long and weighed perhaps 10 kg. It lived during the early Jurassic period, about 208-200 million years ago. The type species is H. tucki. Heterodontosaurus was named by Crompton and Charis in 1962.


(pronounced HET-er-oh-TROFE) A heterotroph (or consumer) is a living thing that eats other living things to survive. It cannot make its own food (unlike plants, which are autotrophs). Animals are heterotrophs.


The hindlimbs are the back legs of an animal. The hindlimbs of most dinosaur were larger than the forelimbs. Diplodocid dinosaurs (like Diplodocus) are an exception.


The hip or pelvis of dinosaurs is composed of three bones, the Pubis, Ilium, and Ischium. Based on hip structure, the British paleontologist H. G. Seeley divided the dinosaurs into the orders Saurischia (or "Lizard-hipped") and Ornithischia (or "Bird-Hipped").


(pronounced hi-RON-oh-SAWR-us) Hironosaurus was large, duck-billed dinosaur from the late Cretaceous period, about 97.5-65 million years ago. Very little is known about this hadrosaur since only fragmentary fossils have been found. This plant-eater was found in Japan. Hironosaurus is an unofficial name due to a sparsity of fossils.


Histology is the study of tissue structure. A histologist is a scientist who studies histology.

(pronounced HIS-tree-ah-SAWR-us) Histriasaurus (meaning "Istrian lizard," for the Istrian peninsula of northwest Croatia, on the Adriatic Coast) was a large plant-eating dinosaur that lived during the early Cretaceous period (from the late Hauterivian to early Barremian, about 126-125 million years ago). Histriasaurus was a diplodocimorpha, a long-necked, whip-tailed giant that walked on four columnar legs. It had peg-like teeth and high vertebral spines. It may have had a sail on its back. Fossils of this sauropod were found in Croatia. The type species is H. boscarollii, named for Dario Boscarolli, who discovered the fossil site. Histriasaurus was named by Dalla Vecchia in 1998. It is probably closely related to, but more primitive than Rebbachisaurus.


Edward B. Hitchcock (1793-1864) was a US clergyman and geologist who found the first large dinosaur trackways (in Connecticut, USA). He collected over 20,000 fossil footprints. Hitchcock collected over 20,000 dinosaur fossil footprints; he thought that the trackways had been made by huge, extinct birds (and was essentially correct).
Arthur Holmes (1890 - 1965) was a British geologist who first proposed the idea of a geologic time scale in 1913. This was soon after the discovery of radioactivity, and using radio-isotope dating, Holmes estimated that the Earth was about 4 billion years old - this was much greater than previously believed.



The Holocene (meaning "entirely recent" in Greek) is the most recent epoch in geologic time, lasting from about 11,000 years ago until the present day (the time since the last Ice Age).


A holotype is a specimen of an organisn that serves as the standard for a species or a subspecies; it is often the first of its kind to be scientifically reported and described.
Thomas R. Holtz, Jr. (1965- ) is an American vertebrate paleontologist and author. Holtz is a lecturer at the Department of Geology, University of Maryland, College Park. He was born in Los Angeles and spent his early childhood near Houston, Texas. He was an undergraduate at the Johns Hopkins University, and received his Ph. D. at Yale University. Holtz's main research is on the evolution, anatomy, and ecology of theropod dinosaurs (especially tyrannosaurids). Holtz is the coauthor of The World of Dinosaurs (with Michael Brett-Surman, illus. by James Gurney - Greenwich Workshop Books, 1998), contributor to The Complete Dinosaur [Dinosaur hunters of the Southern Continents and other sections] (ed. James O. Farlow and Michael Brett-Surman - Indiana University Press, 1997), coauthor of the Dinosaur Field Guide (with Michael Brett-Surman - Random House, 2001), author of the Little Giant Book of Dinosaurs (2001, Sterling Press), author of the Tyrannosaur sections of the Univ. of Arizona's Tree of Life classification project on the Web (2000), and has many other publications.


(pronounced HOMM-ah-low-SEF-ah-lee) Homalocephale (meaning "Level head") was a pachycephalosaurid, a thick-skulled dinosaur. Its skull was relatively flat and had bony knobs along the edges. It was an herbivore (a plant-eater) about 5 feet (1.5 m) long and weighed about 43 kg. It walked on two legs and lived during the late Cretaceous period (80-70 million years ago). An almost complete skeleton was found in Mongolia in 1901 and named by paleontologists Maryánska & Osmólska in 1974.


Homeosaurus is a genus of sphenodontian, a type of lizard (a reptile similar to the Tuatara, but not a dinosaur). The earliest-known Homeosaurus dates from the Triassic period, about 230 million years ago. This quadruped has long legs and a very long tail. There is still one living species of Homeosaurus inhabiting New Zealand and some nearby islands.


Homeothermic animals maintain a constant body temperature. Birds and mammals are homeothermic.
Ardipithecus ramidus 4.4 million years ago
Australopithecus afarensis 4 to 2.7 million years ago
Australopithecus africanus 3.0 to 2.0 million years ago
Australopithecus robustus 2.2 to 1.0 million years ago
Homo habilis 2.2 to 1.6 million years ago
Homo erectus 2 to 0.4 million years ago
Homo sapiens neandertalensis 200,000 to 30,000 years ago
Homo sapiens sapiens 30,000 years ago to the present


Hominids (family Hominidae) are the group that includes people and our close ancestors and relatives.


The Superfamily Hominoidea includes the apes and humans. It includes the Family Hominidae (people and our close ancestors and relatives), Family Pongidae (orangutans, chimpanzees, and gorillas), and Family Hylobatidae (gibbons and siamangs).


Homology is the similarity of characters found in different species that are due to common descent. Examples include the flippers of whales and our arms.


Homoplasy is the similarity of characters found in different species that are NOT from common descent. Examples include the wings of insects and the wings of pterosaurs. These characters derive from convergent evolution, parallel evolution, or character reversal.


(pronounced huh-PLEE-toh-SAWR-us) Hoplitosaurus (meaning "Hoplite lizard;" a hoplite was an armed soldier) was an ankylosaur, an armored dinosaur. It had rows of flattened horny plates running along its back. Hoplitosaurus was an herbivore (a plant-eater) that walked on four legs and lived during the early Cretaceous period (135-119 million years ago). An incomplete fossil was found in South Dakota, USA in 1901 and named in 1902 by F. A. Lucas.


(pronounced hop-loh-PHONE-ee-us) Hoplophoneus was a relatively small saber-toothed cat (about 1 1/2 to 2 times the size of a housecat) that lived during the Oligocene period (from about 40 million to 20 milion years ago). Fossils have been found in Wyoming, USA. This cat's skull was 6 inches (15 cm) long. This predator had long, saber-like upper canine teeth that fit into a socket in its lower jaw. Hoplophoneus was plantigrade (flat-footed, unlike modern-day cats, which are digitigrade). Its large jaws could open about 90 degrees, allowing it to stab its victims with its incisors. Classification: Superfamily Feloidea (cats, mongooses), Family Felidae, Subfamily Machairodontinae, Genus Hoplophoneus


(pronounced hop-loh-SOOK-us) Hoplosuchus (meaning "armored crocodile") was a small, primitive crocodilian from the Jurassic period. This marsh dweller was an evolutionary dead-end. This carnivorous reptile was found in 1909 by paleontologist Earl Douglass, in what is now Dinosaur National Monument, Utah, USA.


Horn is an organic substance made mostly of the fibrous protein called keratin (our nails, hair, bull's horns, feather quills, and horse hoofs are also made of keratin). Some dinosaurs, like Triceratops, had bone-like "horns" that may have been covered by a layer of keratin (horn) when they were alive. Since keratin does not fossilize well, we do not know if horn covered the bone and if so, how much it was.


Horn coral is a type of large, horn-shaped coral (order Rugosa) that lived as a solitary individual or as a colony. This invertebrate evolved during the Ordovician Period, roughly 500 million years ago. Horn corals are important index fossils. Their fossils are also sometimes used to determine the length of the day (and the year) in the distant past due to the manner in which they grew.
John R. (Jack) Horner is a US paleontologist (born on June 15, 1946 in Shelby, Montana) who named: Maiasaura (with Makela, 1979), and Orodromeus (with D.B. Weishampel, 1988). He discovered the first egg clutches (from Maiasaura) in the Americas and the first evidence of parental care from dinosaurs. Horner is the Curator of Paleontology at the Museum of the Rockies in Bozeman, Montana, USA. Horner attended the University of Montana, majoring in geology and zoology. Horner is the author of: "Digging Dinosaurs" (Workman Pub., 1988), "Complete T-rex" (with D, Lessem, Simon and Schuster,1993), "Maia, A Dinosaur Grows Up" (Museum of the Rockies, Montana State University, 1985), "Digging Up Tyrannosaurus rex" (with D, Lessem, 1992), "Dinosaur Eggs and Babies" (Cambridge University Press, 1994), and "Dinosaur Lives" (HarperCollins, 1997). Horner was a technical advisor for the movies Jurassic Park and The Lost World.


The modern horse (genus Equus, which also includes zebras, asses, etc.) evolved about 4 million years ago in North America. It spread to Asia, Europe and Africa. North American horses went extinct about 8,000 years ago, probably due to disease.
Horsetail is a primitive, spore-bearing plant (a sphenopsid) with rhizomes that was common during the Mesozoic Era. Its side branches are arranges in rings along the hollow stem. Horsetails date from the Devonian period 408-360 million years ago, but are still around today and are invasive weeds. Classification: Pteridophyte, Sphenopsid.


(pronounced hwah-YANG-oh-SAWR-us) Huayangosaurus was a stegosaurid, a dinosaur with a double row of spiky triangular plates and spikes running along its back. It was an quadrupedal herbivore (a plant-eater) 13 feet (4 m) long that lived during the mid-Jurassic period (about 170 million years ago). It was found in China and was named in 1982 by Zhiming Dong.


Friedrich von Huene was a German paleontologist who named: Altispinax (1922), Avipes (1932), Antarctosaurus (1929), Betasuchus (1932), Cetiosauriscus (1927), Coeluroides (1932), Compsosucus (1932), the family Dicraeosauridae (1956), Dolichosuchus (1932), Dryptosauroides (1932), Erectopus (1922), Fulgurotherium (1932), the family Halticosauridae (1956), Halticosaurus (1908), Iliosuchus (1932), Indocuchus (1933), Jubbulpuria (1932), Laevisuchus (1932), the family Lambeosauridae (1948), Laplatasaurus (1927), Loricosaurus (1929), Magyarosaurus (1932), the family Melanorosauridae (1929), Ornithomimoides (1932), the family Podokesauridae (1914), the infraorder Prosauropoda (1920), Proceratosaurus (1926), the family Procompsognathidae (1929), Rapator (1932), Saltopus (1910), the suborder Sauropodomorpha (1932), Sellosaurus (1908), Thecocoelurus (1923), Velocipes (1932), and Walgettosuchus (1932).


The humerus is the bone in the upper part of the arm.


Thomas H. Huxley (1825-1895) was a British scientist and friend of Charles Darwin. He was the first scientist to notice the similarity between birds and dinosaurs. He named: Acanthopholis (1865), the family Archaeopteryglidae (1871), Euskelosaurus (1866), Hypsilophodon (1869), and the family Megalosauridae (1869).


Hybodus is a genus of extinct sharks from the Carboniferous period, that lived from the Triassic period until it went extinct during the huge K-T mass extinction 65 million years ago, when the dinosaurs died. This hybodont had fin spines, an anal fin, a blunt snout, and a long body. It had sharp teeth at the front of the jaws (for catching fish) and blunt teeth towards the back (for crushing shellfish). Hybodus was about 7.5 feet (2.5 m) long. Hybodus tooth fossils are found worldwide.


Hydrotherosaurus (meaning "water beast lizard") was an elasmosaurid plesiosaur (not a dinosaur, but an extinct marine reptile from the late Cretaceous period (roughly 65 million years ago) that lived in the open oceans and breathed air). It had a long neck (with 60 vertebrae), a long snout, long, sharp teeth, a short, pointed tail, a streamlined body, and four flippers. This reptile was about 42 feet (12.75 m) long; its skull was about 12 inches (33 cm) long. It was found with fish and gastroliths (indicating that it ate fish and used stomach stones to aid digestion). Fossils have been found in California, USA, North America. The type species, Hydrotherosaurus alexandrae (named by Welles in 1943 to honor Annie Montague Alexander (1867-1950), a fossil collector). Hydrotherosaurus is known from a complete skeleton (with the skull).


(pronounced hie-LEE-oh-SAWR-us) Hylaeosaurus (meaning "Wealden lizard") was an armored, quadrupedal, plant-eating dinosaur, an ankylosaur. It lived during the early Cretaceous period in what is now Europe. Hylaeosaurus was named by paleontologist Gideon Mantell in 1833.


(pronounced high-LON-oh-mus) Hylonomus is one of the earliest-known reptiles; it was NOT a dinosaur. Hylonomus was about 8-12 inches (20-30 cm) long and looked much like a modern-day lizard. It had a long tail, a short neck, and a deep skull with conical teeth (the front teeth were longer than the back teeth). It has a typical reptilian sprawling leg stance; each of the four legs went out to the side instead of under the body (unlike dinosaur legs which went directly under the body). Hylonomus had five long toes on each of its four feet. Hylonomus ate insects and other small invertebrates. Hylonomus evolved from amphibians, which layed their egg and lived part of their lives in the water - Hylonomus lived entirely on land and laid its eggs on land. Hylonomus was the ancestor of lizards, crocodiles, turtles, and birds. It may have been preyed upon by pelycosaurs like Archaeothyris. It lived during the late Carboniferous period, about 300 million years ago. Fossils of Hylonomus were found in Nova Scotia, Canada. Classification: Subclass Anapsida, Order Captorhinida, Family Protorothyrididae, Genus Hylonomus.


(pronounced hi-PACK-roh-SAWR-us) Hypacrosaurus (meaning "under the top lizard") was a large, plant-eating, hollow-crested duck-billed dinosaur (a hadrosaur) similar to Corythosaurus. It was about 30 feet (9 m) long, had almost 40 rows of cheek teeth, a short toothless beak, and a row of short spines coming out of its vertebrae, forming a small fin along its back. It lived in humid forests during the late Cretaceous period, about 72 to 70 million years ago. Fossils (mostly skulls) have been found in Alberta, Canada and Montana, USA. It was found and named by fossil hunter Barnum Brown.


(pronounced HIP-sel-oh-SAWR-us) Hypselosaurus (meaning "high ridge lizard") was a long-tailed, long-necked plant-eater from the late Cretaceous period, about 73 to 65 million years ago. This titanosaurid was about 27 feet (8 m) long, weighing about 10 tons, small for a sauropod. Its fossils, including bones from 10 individuals and many eggs have been found in France and Spain. The eggs were the first dinosaur eggs found. Many of these eggs have been found in France; they are half-gallon (2-liter) in volume and about 1 foot (30 cm) long. Some eggs were found in groups of 5. Hypselosaurus was named by Matheron in 1869. The type species is H. priscus.


(pronounced HIP-seh-BEE-muh) Hypsibema (meaning "high platform," referring to its feet) is a doubtful genus of plant-eating dinosaur; it may be a duck-billed dinosaur (hadrosaur). It is only known from a few bones, some tail vertebrae, a humerus (upper arm bone), a tibia (a lower leg bone), and a metatarsal (ankle bone). Hypsibema was found in North Carolina, USA. This ornithopod lived during the late Cretaceous period, about 83-73 million years ago. Hypsibema was named by paleontologist E.D. Cope in 1869. The type species is H. crassicauda. Hypsibema may be the same as Parrosaurus.


(pronounced hip-seh-LOFF-oh-don ) Hypsilophodon was a small, bipedal, plant-eating dinosaur from the early Cretaceous period, about 125 to 115 million years ago. It was an ornithischian dinosaur about 7. 5 feet (2.3 m) long. It was one of the first dinosaur fossils found. The type species is H. foxii. Hypsilophodon was named by Thomas Huxley in 1869.


Hypsilophodontids were small, fast, plant-eating dinosaurs that lived from the late Triassic to the Cretaceous period.


Hyracotherium is the genus of the earliest-known horse. Another name for this genus is Eohippus (meaning "dawn horse"). This tiny horse dates from the early Eocene Epoch and lived in the Northern hemisphere. It was about 2 feet (60 cm) long and perhaps 12-14 inches high at the shoulder (the size of a small dog!). It had 4 hoofed toes on each front foot and 3 hoofed toes on each hind foot.
Dinosaur and Paleontology Dictionary

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