Jurassic

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of or belonging to the geologic time, rock series, or sedimentary deposits of the second period of the Mesozoic Era, in which dinosaurs continued to be the dominant land fauna and the earliest birds appeared. See Table at geologic time.
2. n. The Jurassic Period or its system of deposits.

Century Dictionary and Cyclopedia

1. Pertaining or relating to the Jura mountains, and specifically, in geology, to the Jurassic series.
2. n. In geology, that part of the geological series which includes all the groups and subgroups older than the Cretaceous and newer than the Triassic: so called from the predominance of rocks of this age in the Jura mountains. The Triassic, Jurassic, and Cretaceous together form the Mesozoic series. The flora of the Jurassic is distinguished by a predominance of cycadaceous forms, ferns being also plentiful. Its fauna is rich and varied. The most highly developed animals in this geological position are certain small marsupials. The oldest known bird, possessing also some marked reptilian characters, is found in the Upper Jurassic. The Jurassic series covers a wide area in Europe, and is also of great interest and importance in the Cordilleran region of the United States. The name Oölite was originally applied to the rocks of Jurassic age in England by William Smith, by whom the order of succession of this part of the series was first worked out and published. The Jurassic of England includes the Lias as its lower member, and above this the Lower, Middle, and Upper Oölites. In northwestern Germany the Jurassic is divided into the lower or Black Jura, the Middle or Brown, and the Upper or White. Of these divisions the lower corresponds to the English Lias. The fossil remains of the Jurassic series in the United States are of great interest. Among them is the Atlantosaurus, a dinosaur, supposed to have been a hundred feet in length and thirty or more in height. The auriferous rocks of the western edge of the North American continent are, at least in large part, of Jurassic age.

Wiktionary

1. adj. geology Of or pertaining to the second period of the Mesozoic era, a time still dominated by dinosaurs.
2. adj. Of or pertaining to the people or region near the Jura Mountain Range of Europe.
3. n. The period from 200 to 146 million years ago, after the Triassic and before the Cretaceous; the geologic formations of this period.

GNU Webster's 1913

1. adj. (Geol.) Of the age of the middle Mesozoic, about 190 to 140 million years ago, including, as divided in England and Europe, the Lias, Oölite, and Wealden; -- named from certain rocks of the Jura mountains. It was noted for the predominance of dinosaurs on land, and the development of the first birds and mammals.

WordNet 3.0

1. adj. of or relating to or denoting the second period of the Mesozoic era
2. n. from 190 million to 135 million years ago; dinosaurs; conifers.