Taxon (pl. taxa): a named group of organisms.

All cultures have their own set of names for local animals and plants.

Some problems, though:

• Different cultures have different names for the same animal or plant species;
• Different cultures sometimes have the same name for different animal or plant species.

A need for a universal set of names for species of animals and plants for common discourse.

Carl Linne' (Linnaeus) developed a own set of rules in the Systema Natura (“Natural System”) in 1758; later workers added and modified the system (primarily with the addition of new “ranks”).

Some of the Linnean rules:

• All names are in Latin or Greek, or are modified into Latin form;
• Each name must be unique;
• All names are fit into a nested hierarchy (species into genera, genera into families, and so forth);
• In traditional Linnean taxonomy, there is a set of official ranks (from smallest to largest, species, genus, family, order, class, phylum) (later workers added additional intermediate ranks, such as tribes, subfamilies, superfamilies, subphyla, etc.);
  • The primary unit is the species (pl. species):
    • Definition of a “species” varies from biologist to biologist; some definitions (“naturally occurring interbreeding populations”) cannot be tested for fossils!
    • Each species has a type specimen accessioned in an appropriate institution ( museum, zoological or botanical garden, or other such collection);
    • Whoever describes the type specimen of a new species has the right to name that new species (following the rules below);
  • The next higher unit, the genus (pl. genera) is composed of one or more species
    • Definition of a “genus” is problematic as well, since it is composed of one or more “species”;
    • Each genus has a type species: all other species are assigned to the genus based on their similarity to the type species;

Linnean taxonomy has its own special set of grammatical rules:

• Genera have one word names (e.g., Panthera, Homo, Ginkgo, Tyrannosaurus);
  • The genus name is always Capitalized and italicized (or underlined if you don't have access to italics);
• Species have two word names, the first part of which is the same as the genus name (e.g., Panthera leo, Homo sapiens, Ginkgo biloba, Tyrannosaurus rex)
  • The genus name is ALWAYS capitalized, the second part (“trivial nomen”) is ALWAYS in lower case, and the name is ALWAYS italicized or underlined;
  • Species names can be abbreviated by using only the first letter of the genus name, followed by a period (NEVER by a hyphen): H. sapiens and T. rex are correct; H. Sapiens or T-Rex are WRONG!! (Subtle hint: do not use the incorrect form on your homework or tests);
• Some taxon names for groups composed of multiple genera (“families” in the old sense) have special formal endings, described in the Farlow & Brett-Surman textbook. We won't be going over those details in this class;
• All taxon names other than species have one word names, which are capitalized; all taxon names other than genera and species are in roman letters (i.e., they are never italicized/underlined): Dinosauria, Tyrannosauridae, Animalia; not Dinosauria, tyrannosauridae, or animalia.

Because there is disagreement about the features used to define a particular species or genus, different biologists and paleontologists will sometimes disagree about which specimens belong in a particular species, and which species belong in a particular genus (and so forth).

Taxonomists who consider a particular set of specimens to represent many taxa are called splitters; those who consider a particular set to represent few taxa are called lumpers.

• If a taxonomist feels that some specimens of a genus belong to an as-yet unnamed species, they can split these specimens off as a new species (with a new type specimen);
• On the other hand, if a taxonomist considers that two previously named species are not distinct enough from each other to truly be distinct species (that is, the taxonomist regards the two names as synonyms), they may lump them together:
  • In these cases, the Rule of Priority is used: whichever of the names was published first, even if only by days, is the name that must be used;
  • The same case applies to genera: if two genera are thought to represent the same genus, the first named genus name is the one that is used.

See also Holtz & Brett-Surman pp. 92-99 of “The Taxonomy and Systematics of the Dinosaurs” (Chapter 8 in Farlow & Brett-Surman).

For those interested in a website concerning some unusual Linnean species names, click here.

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