SECTION 1 — Systematics & Phylogeny

Taxon

Any named biological group (species, family, order, clade).

Taxa

Plural of taxon.

Phylogeny

Evolutionary hypothesis showing relationships among organisms.

Node

Branching point in a phylogeny representing a common ancestor.

Monophyletic group

A group containing a common ancestor and ALL descendants.

Synapomorphy

Shared, derived trait defining a monophyletic group.

Symplesiomorphy

Shared ancestral trait that does NOT define modern groups.

Homoplasy

Similar trait evolved independently through convergence.

Sister taxa

Two lineages that share the most recent common ancestor.

Clade

A monophyletic group united by synapomorphies.

Character state

The form a character takes (e.g., presence/absence of bone).

Outgroup

Taxon used to determine ancestral vs derived states.

Parsimony

The simplest tree (fewest evolutionary changes) is preferred.

Crown group

A clade including all living members and their ancestors.

Stem group

Extinct taxa more closely related to a crown group than others but not part of crown group.