| allosaur | (noun) late Jurassic carnivorous dinosaur; similar to but somewhat smaller than tyrannosaurus | Synonyms: allosaurus |
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| ankylosaur | (noun) having the back covered with thick bony plates; thought to have walked with a sprawling gait resembling a lizard's | Synonyms: ankylosaurus |
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| apatosaur | (noun) huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic | Synonyms: apatosaurus, Apatosaurus excelsus, brontosaur, brontosaurus, thunder lizard |
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| archosaur | (noun) extinct reptiles including: dinosaurs, plesiosaurs, pterosaurs, ichthyosaurs, thecodonts | Synonyms: archosaurian, archosaurian reptile |
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| argentinosaur | (noun) huge herbivorous dinosaur of Cretaceous found in Argentina | - |
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| barosaur | (noun) a dinosaur that could grow to be as tall as a building five stories tall | Synonyms: barosaurus |
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| brontosaur | (noun) huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic | Synonyms: apatosaur, apatosaurus, Apatosaurus excelsus, brontosaurus, thunder lizard |
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| carnosaur | (noun) large carnivorous bipedal dinosaur having huge claws | - |
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| ceratosaur | (noun) primitive medium-sized theropod; swift-running bipedal carnivorous dinosaur having grasping hands with sharp claws and a short horn between the nostrils; Jurassic in North America | Synonyms: ceratosaurus |
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| corythosaur | (noun) duck-billed dinosaur with nasal passages that expand into a crest like a hollow helmet | Synonyms: corythosaurus |
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| dinosaur | (noun) any of numerous extinct terrestrial reptiles of the Mesozoic era | - |
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| dromaeosaur | (noun) a kind of maniraptor | - |
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| hadrosaur | (noun) any of numerous large bipedal ornithischian dinosaurs having a horny duck-like bill and webbed feet; may have been partly aquatic | Synonyms: duck-billed dinosaur, hadrosaurus |
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| herrerasaur | (noun) a kind of theropod dinosaur found in Argentina | Synonyms: herrerasaurus |
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| ichthyosaur | (noun) any of several marine reptiles of the Mesozoic having a body like a porpoise with dorsal and tail fins and paddle-shaped limbs | - |
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| ictodosaur | (noun) intermediate in form between the therapsids and most primitive true mammals | - |
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| megalosaur | (noun) gigantic carnivorous bipedal dinosaur of the Jurassic or early Cretaceous in Europe | Synonyms: megalosaurus |
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| nothosaur | (noun) extinct marine reptile with longer more slender limbs than plesiosaurs and less completely modified for swimming | - |
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| pachycephalosaur | (noun) bipedal herbivore having 10 inches of bone atop its head; largest boneheaded dinosaur ever found | Synonyms: pachycephalosaurus |
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| pelycosaur | (noun) large primitive reptile having a tall spinal sail; of the Permian or late Paleozoic in Europe and North America | - |
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| pisanosaur | (noun) primitive dinosaur found in Argentina | Synonyms: pisanosaurus |
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| plesiosaur | (noun) extinct marine reptile with a small head on a long neck and a short tail and four paddle-shaped limbs; of the Jurassic and Cretaceous | Synonyms: plesiosaurus |
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| psittacosaur | (noun) primitive dinosaur actually lacking horns and having only the beginning of a frill; long hind limbs and short forelimbs; may have been bipedal | Synonyms: psittacosaurus |
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| pterosaur | (noun) an extinct reptile of the Jurassic and Cretaceous having a bird-like beak and membranous wings supported by the very long fourth digit of each forelimb | Synonyms: flying reptile |
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| seismosaur | (noun) huge herbivorous dinosaur of the Cretaceous found in western North America | Synonyms: ground-shaker |
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| staurikosaur | (noun) primitive dinosaur found in Brazil | Synonyms: staurikosaurus |
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| stegosaur | (noun) herbivorous ornithischian dinosaur with a row of bony plates along its back and a spiked tail probably used as a weapon | Synonyms: Stegosaur stenops, stegosaurus |
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| styracosaur | (noun) an unusual ceratopsian dinosaur having many large spikes around the edge of its bony frill and a long nose horn; late Cretaceous | Synonyms: styracosaurus |
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| titanosaur | (noun) amphibious quadrupedal herbivorous dinosaur with a long thin neck and whiplike tail; of the Cretaceous mostly in the Southern Hemisphere | Synonyms: titanosaurian |
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| tyrannosaur | (noun) large carnivorous bipedal dinosaur having enormous teeth with knifelike serrations; may have been a scavenger rather than an active predator; later Cretaceous period in North America | Synonyms: tyrannosaurus, Tyrannosaurus rex |
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