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period, in grammar

(Encyclopedia)period: see punctuation.

period, in physics

(Encyclopedia)period, in physics: see harmonic motion; wave. ...

(Encyclopedia)period, unit of time on the geologic timescale. Periods are shorter than an era and longer than an epoch. Periods are of variable length, generally lasting tens of millions of years, with characterist...

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...

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...

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...