Phylogenetic tree terms

(Plesiomorphy):

trait that was
present in the ancestor of a group (Ancestral trait )

Apomorphy

trait in a descendent that differs from the ancestral trait (Derived trait)

Synapomorphy

a derived trait or shared
among taxa that has evolved from an
ancestral form (e.g., vertebral column, four
limbs)

Autapomorphy

an apomorphy unique to a single taxon (e.g., feathers in birds)

Symplesiomorphy

a shared ancestral trait between
two taxa

Analogous traits

functionally similar structures that have independent evolutionary origins

Homoplasy

representing similarities NOT inherited directly from a common ancestor

Parsimony principle

The simplest explanation of observed data is the preferred explanation

Cladistic Approach

based on creating monophyletic groups through phylogenetic trees

Linnaean Taxonomy

based on similarity of morphology but does not consider evolutionary relationship

Monophyletic

a group containing the most recent common ancestor AND all its descendants [a.k.a. a monophyly]

Polyphyletic

a group that does not include the common ancestor of the group [a.k.a. a polyphyly]. E.g., pachyderms grouped by skin characteristics

Paraphyletic

a group containing the most recent common ancestor, but NOT all the descendants [a.k.a. a paraphyly]; E.g., dinosaurs without birds