We classify our keychains & figures according to Biological Classification / Scientific Taxonomy:

http://en.wikipedia.org/wiki/Biological_classification 

Carolus Linnaeus 

Linnaean taxonomy

Carolus Linnaeus' great work, the Systema Naturæ (1st ed. 1735), ran through twelve editions during his lifetime. In this work, nature was divided into three kingdoms: mineral, vegetable and animal. Linnaeus used five ranks: class, order, genus, species, and variety.

He abandoned long descriptive names of classes and orders still used by his immediate predecessors (Rivinus and Pitton de Tournefort) and replaced them with single-word names, provided genera with detailed diagnoses (characteres naturales), and combined numerous varieties into their species, thus saving botany from the chaos of new forms produced by horticulturalists.

Linnaeus is best known for his introduction of the method still used to formulate the scientific name of every species. Before Linnaeus, long many-worded names (composed of a generic name and a differentia specifica) had been used, but as these names gave a description of the species, they were not fixed. In his Philosophia Botanica (1751) Linnaeus took every effort to improve the composition and reduce the length of the many-worded names by abolishing unnecessary rhetorics, introducing new descriptive terms and defining their meaning with an unprecedented precision. In the late 1740s Linnaeus began to use a parallel system of naming species with nomina trivialia. Nomen triviale, a trivial name, was a single- or two-word epithet placed on the margin of the page next to the many-worded "scientific" name. The only rules Linnaeus applied to them was that the trivial names should be short, unique within a given genus, and that they should not be changed. Linnaeus consistently applied nomina trivialia to the species of plants in Species Plantarum (1st edn. 1753) and to the species of animals in the 10th edition of Systema Naturæ (1758).

By consistently using these specific epithets, Linnaeus separated nomenclature from description. Even though the parallel use of nomina trivialia and many-worded descriptive names continued until late in the eighteenth century, it was gradually replaced by the practice of using shorter proper names consisting of the generic name and the trivial name of the species. In the nineteenth century, this new practice was codified in the first Rules and Laws of Nomenclature, and the 1st edn. of Species Plantarum and the 10th edn. of Systema Naturae were chosen as starting points for the Botanical and Zoological Nomenclature respectively. This convention for naming species is referred to as binomial nomenclature.

Today, nomenclature is regulated by Nomenclature Codes, which allows names divided into taxonomic ranks.

Read more on Wikipedia (you can donate to Wiki, too):  http://en.wikipedia.org/wiki/Biological_classification