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Dinosaur Discussion List Dictionary

Here are a few potential definitions for the Dinosaur Discussion
List Dictionary. Comments, additions--especially additions--and
corrections are welcomed. This may help you get going on this little

APOMORPHY--n. A character state present throughout a clade but
not present in any close outgroup of the clade.

AUTAPOMORPHY--n. An apomorphy that distinguishes a single clade.

CHARACTER--n. Any well-defined feature, whether anatomical,
behavioral, biochemical, or genomic, of an organism.

CHARACTER STATE--n. A changeable attribute of a character. The
most basic character state is absent/present.

CLADE--n. A monophyletic taxon.

CLADISTICS--n. A method of classifying organisms by analyzing the
distribution of their characters and character states, determining which
characters are synapomorphies, plesiomorphies, or homoplasies, and
then grouping the organisms into clades using the synapomorphies.

CLADOGRAM--n. A diagram (usually a graph) depicting the results
of a cladistic analysis and displaying the clades into which the
analyzed organisms have been classified.

COMMON ANCESTOR--n. In the context of evolution, a species that
evolves into a clade.

DERIVED--adj. Describing a character or group of characters as
changed from its primitive state. For example, the anatomy of a
bird's wing is derived relative to the anatomy of a reptilian

DESCENDANT--adj. In the context of evolution, describing a
species or taxon that has evolved from another species or from
within a taxon.

EVOLUTION--n. The changes in the character states of organisms,
species, and clades through time.

HOMOPLASY--n. A character present in at least two clades that is
absent in the common ancestor of the two clades.

MONOPHYLETIC--adj. Describing a taxon that contains all the
descendant organisms or taxa of its common ancestor.

OUTGROUP--n. A clade considered primitive to a group of organisms
in a cladistic analysis of that group.

ORGANISM--n. An individual member of a species. A single
biological entity.

PARAPHYLETIC--adj. Describing a taxon that does not contain all
the descendant organisms or taxa of its common ancestor.

PLESIOMORPHY--n. A character present throughout a taxon because
it is present in an outgroup of the taxon.

POLYPHYLETIC--adj. Describing a group of organisms that does not
include its common ancestor.

PRIMITIVE--adj. Describing a character state in the common
ancestor of a clade. For example, a five-digit forefoot is the
primitive forefoot state in amniotes.

SPECIES--n. A freely interbreeding population of organisms. The
organisms in a species usually share a large number of
characters. The species is generally the lowest level in a
taxonomy; a species that is a common ancestor to a clade is by
definition paraphyletic and is not itself a clade.

SYNAPOMORPHY--n. An apomorphy that occurs in two related clades
and thereby supports grouping of the two clades into a single
larger clade. Also called a shared derived character.

TAXON--n. (pl.: taxa) A group of organisms or other taxa sharing
a single common ancestor.

TAXONOMY--n. The method of classifying things into groups. In
biology, taxonomy refers to the classification of living
organisms into taxa. A biological taxonomy is cladistic if all
the taxa are clades.