Paleozoic

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of, belonging to, or designating the era of geologic time that includes the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods and is characterized by the appearance of marine invertebrates, primitive fishes, land plants, and primitive reptiles. See Table at geologic time.
2. n. The Paleozoic Era.

Century Dictionary and Cyclopedia

1. In geology, belonging to or constituting a geological formation characterized by the presence of ancient forms of life: applied to the oldest division of the geological series, beginning with the lowest stratified fossiliferous group, and extending upward to the base of the Triassic, or to the top of the Permian. The grand divisions of the Paleozoic are, proceeding upward or to groups later in age, the Silurian, Devonian, Carboniferous, and Permian. (See these words.) Of these the Permian is much the least important. The other divisions have been designated respectively as the “age of mollusks,” the “age of fishes”, and the “age of coal or of land-plants.” The Paleozoic series may, from a paleontological point of view, be properly separated into two great divisions, a newer and an older. The former embraces the Silurian; the latter, the Devonian, Carboniferous, and Permian. The older Paleozoic is distinguished by the great predominance of graptolites, trilobites, and brachiopods, and by the absence of vertebrates; the newer Paleozoic, by the number and variety of the fishes and amphibia, by the disappearance of graptolites and trilobites, and by an extraordinarily developed flora, largely cryptogamic in character, from which a very considerable part of the coal of the globe has been formed. Rocks of Paleozoic age are spread over wide areas. They are especially important in the eastern and northeastern United States and in the Upper Mississippi valley, in which regions they usually form the surface-rock, being covered only with detrital formations of the most recent age. Almost the whole of the bed-rock in New York and Pennsylvania is of Paleozoic age, and here the various groups of this series were studied out by the Geological Surveys of those States from 1834 on. To the labors of Sedgwick and Murchison in Wales and western England, carried on at about the same time with the beginnings of the New York and Pennsylvania Surveys, is due the larger share of the credit of disentangling the complicated structure of a region where the Paleozoic rocks are extensively developed, and it is there that the materials were obtained for the establishment by Murchison of the Silurian and Devonian systems, which, with the Carboniferous and Permian, form the Paleozoic epoch.

Wiktionary

1. adj. geology Of a geologic era within the Phanerozoic eon that comprises the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods from about 542 to 250 million years ago, from the age of trilobites to that of reptiles.
2. n. geology The Paleozoic era.

GNU Webster's 1913

1. adj. (Geol.) Of or pertaining to, or designating, the older division of geological time during which life is known to have existed, including the Silurian, Devonian, and Carboniferous ages, and also to the life or rocks of those ages. See Chart of geology.
2. n. (Geol.) The Paleozoic time or strata.

WordNet 3.0

1. n. from 544 million to about 230 million years ago
2. adj. of or relating to or denoting the Paleozoic era