Classification!!

Classification of Organisms

Organismal diversity is the product of evolution. Evolutionary paths are branched and numerous, though most arrive at dead ends with organisms which do not survive in the face of environmental change. In this lecture we consider these evolutionary paths (called lineages), ignoring for the moment the processes that carry organisms along them.
While the lineage of any given organism may have twisted repeatedly according to the whims of chance and change, key nodes may nevertheless be tracked retrospectively. These nodes consist of times of identifiable change, particularly points of divergence between two lineages (speciation events). The delineation of these nodes in organismal lineages is accomplished through fossil reconstruction of the past as well as by comparing extant organisms, looking for similarities and differences in anatomies, physiologies, genes, behaviors, etc. From this information classification and phylogenetic reconstruction is accomplished. Classification according to similarity:
Carolus Linnaeus developed a system of classification of every (then) known organism.
This system is based on creating and differentiating groups in terms of structural (and other) similarities and differences.
Linnaeus also invented binomial nomenclature to keep track of group members.
Systematics
Systematics is the study of the diversity of organisms and their evolutionary relationships.
Science of classification:
Systematics is the science of the classification of organisms.
The main goal of systematics is the discovery and codification of phylogenetic relationships between organisms.
"The term systematics often is used for taxonomy. However, many taxonomists define it in more general terms as 'the scientific study of organisms with the ultimate object of characterizing and arranging them in an orderly manner.' Any study of the nature of organisms, when the knowledge gained is used in taxonomy, is a part of systematics. Thus (systematics) encompasses disciplines such as morphology, ecology, epidemiology, biochemistry, molecular biology, and physiology." (p. 391, Prescott et al., 1996)
Taxon [sing., taxa, pl.]
A taxon is a phylogenetic grouping of organisms.
Taxonomy
Identification and classification:
Taxonomy is the science concerned with the:
identification
classification
nomenclature
of organisms.
"Taxonomy [Greek taxis, arrangement or order, and nomos, law, or nemein, to distribute or govern] is defined as the science of biological classification. In a broader sense it consists of three separate but interrelated parts: classification, nomenclature, and identification." (p. 391, Prescott et al., 1996)
Note that the terms systematics and taxonomy can often be used semantically in a nearly indistinguishable manner.
Identification
Identification is "the practical side of taxonomy, the process of determining that a particular (organism) belongs to a recognized taxon." (p. 391, Prescott et al., 1996)
Classification
Classification is "the arrangement of organisms into groups or taxa." (p. 391, Prescott et al., 1996)
Nomenclature
Name assignment:
Nomenclature is "the branch of taxonomy concerned with the assignment of names to taxonomic groups in agreement with published rules." (p. 391, Prescott et al., 1996)
Note that ideally names have taxonimic meaning, i.e., they give clues to phylogenetic relationships.
Hierarchical classification
Hierarchy of designations:
The full description of a given organism's place among all the world's organisms does not end with its binomial designation.
There exists a hierarchy of designations only the last of which describe genera and species denomination.
"A category in any rank unites groups in the level below it based on shared properties." (p. 391, Prescott et al., 1996)
The major designations, listed in terms of increasing specificity, include:
domain (empire/super-kingdom)
kingdom
phylum
class
order
family
genus
species

Various mnemonics exist to help you remember these designations from kingdom through species
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