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Cretaceous period
(Encyclopedia)Cretaceous period krĭtāˈshəs [key], third and last period of the Mesozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table), lasting from approximately 144 to 65 millio...mass extinction
(Encyclopedia)mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were thos...Jurassic period
(Encyclopedia)Jurassic period jərăsˈĭk [key] [from the Jura Mts.], second period of the Mesozoic era of geologic time, lasting from 213 to 144 million years ago. At the start of the Jurassic most of the contine...chalk
(Encyclopedia)chalk, mineral of calcium carbonate, similar in composition to limestone, but softer. It is characteristically a marine formation and sometimes occurs in great thickness; the chief constituents of the...Triceratops
(Encyclopedia)Triceratops trīsĕrˈətŏps [key] [Gr., = three-horn face], genus of ornithischian quadruped dinosaurs of the late Cretaceous period. Because of some variations in sample fossils, it was thought...Iguanodon
(Encyclopedia)Iguanodon ĭgwănˈədŏn [key] [Gr., = iguana tooth], herbivorous ornithiscian dinosaur, characterized by teeth similar to those of the iguana, a horny beak, spikelike thumbs, and a powerful tail...Deinonychus
(Encyclopedia)Deinonychus dīˌnənīˈkəs [key] [Gr.,=terrible claw], swift bipedal carnivorous dinosaur of the early Cretaceous period, approximately 119–93 million years ago. Fossil specimens have been discov...Velociraptor
(Encyclopedia)Velociraptor vəlŏsˈĭrăpˌtər [key] [Gr.,=swift robber], swift bipedal carnivorous dinosaur of the late Cretaceous period. It was relatively small, being approximately 6 ft (1.8 m) long. It was s...Paleocene epoch
(Encyclopedia)Paleocene epoch pāˈlēəsēnˌ [key], first epoch of the Tertiary period in the Cenozoic era of geologic time (see geologic timescale) between 60 to 66 million years ago. In W North America, the upl...pterosaur
(Encyclopedia)pterosaur tĕrˈəsôrˌ [key] [Gr., = winged lizard], extinct flying reptile (commonly called pterodactyl [Gr., = wing finger]) of the order Pterosauria, common in the late Triassic and Creta...Browse by Subject
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