Taxonomy and Systematics

Taxonomy

The science that identifies, names, and classifies new species.

Carolus Linnaeus

The first modern practitioner of taxonomy (1707-1778).

Binomial Nomenclature

A system introduced by Linnaeus where species are given a unique two-part name consisting of the genus and specific epithet.

Specific epithet

The second part of a species' binomial name, which follows the genus (e.g., canadensis in Castor canadensis).

Taxonomic hierarchy

The classification system that organizes species into successive levels: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Systematics

The study of biological diversity and evolutionary relationships, both extinct and modern.

Taxon

Each group at any level of the taxonomic hierarchy.

Monophyletic taxa

Groups that include one ancestral species and all of its descendants.

Homologous Characters

Traits that result from common ancestry and indicate evolutionary relationships.

Analogous Characters (Homoplasies)

Traits that are phenotypically similar but do not result from common ancestry; they evolved independently.

Convergent Evolution

The evolution of similar adaptations in distantly related organisms that occupy similar environments.

Synapomorphies

Shared derived characters that are useful for determining evolutionary relationships.

Outgroup comparison

A method used to identify derived characters by comparing with a less related group.

Molecular Clocks

Estimates of evolutionary time based on mutations in noncoding regions of DNA.

Principal of Parsimony

The preferred hypothesis is the simplest explanation for all characters and their states.

Cladistics

The study and classification of species based on evolutionary relationships.

Branch Point

The point in a cladogram where two species diverge based on shared derived characters.

Phylogenetic Trees

Diagrams that depict the evolutionary history of a group of organisms.

Characters States

Distinct features of organisms that can be ancestral or derived.

Polarity of Characters

Determined by examining fossil evidence or outgroup comparisons.

Paraphyletic Taxa

Taxa that contain an ancestor and some, but not all, descendants.

Polyphyletic Taxa

Taxa that include species from separate lineages and are not used in systematics.

Homoplasies

Phenotypic similarities that evolved independently in different lineages.

Cladogram

A phylogenetic tree that represents the evolutionary pathways among species.