Classifying Plants And Animals

In what is known as the Linnaean system, each organism — animal or plant, living or fossil —is identified by two names. The first is the generic or general name (the name of the genus), which is written with a capital letter; the second is the trivial name, which is not capitalized. Latin and Greek words are adapted to the purpose of naming organisms so that the names will be identical in all countries and all languages. Thus man is Homo sapiens; the common cat is Felis domestica; and the common oyster Ostrea virginica. The two words, which together form the species or specific name, are printed in italics. The generic name can be thought of as similar to the surname, such as Smith or Doe, and the trivial name to the baptismal or personal name, such as Marcia or John.

The generic name can be used only once within a related group of organisms, but the trivial name can be used with other generic names. For instance, the trivial name "robustus," of obvious meaning, is applied to some two dozen genera (the plural of "genus") of invertebrate fossils. At least four of the genera — Scaphiocrinus, Zeacrinus, Protaxicrinus, and Synbathocrinus—are crinoids. But a generic name such as Zeacrinus could not be used for any other animal. In practice, generic names are not duplicated. They must not be duplicated within a kingdom —that is, they cannot be used for two animals or two plants.

An organism retains its trivial name even though reassignment to a different genus is necessary if the fossil classification is reorganized when better information about relationships becomes available. For a full description, the name of the person who originally described and named the fossil and occasionally the date when he did so are added to the generic and trivial names. A common Pennsylvanian-period snail from the Mississippi Valley, for example, is called Worthenia tabulata (Conrad). Conrad named it Turbo tabulatus, but research later showed that it belonged to the genus Worthenia. The trivial name was retained, though changed in grammatical gender to agree with the generic name, and Conrad's name was put in parentheses to show that the species has been assigned to a different genus.

A third name, that of a subspecies or variety, may be added to the two terms forming the specific name. A subspecies or variety is a form that is not sufficiently different, in the classifier's judgment, to stand as a distinct species, yet is morphologically distinct within the character range of the species.

A next largest unit above the genus is the family. Under generally accepted rules, names of families are now formed by adding -idae to the stem of the name of the genus chosen as the type for the family. Man, for example, belongs to the family Hominidae, and the cat to the family Felidae. Subfamilies (smaller groups) have names ending in -inae, and superfamilies (larger groups) have names ending in -acea. Larger groupings, in ascending order of size, are the orders, the class, and the phylum. Names in these three largest classifications are capitalized but not italicized. Detailed description of the phyla of interest to the fossil collector has been postponed until the last chapter of this book, a place more convenient for reference in identifying and classifying a puzzling specimen.

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