Systematics and Cladistics - Vocabulary

Vocabulary flashcards covering key terms from the lecture notes on systematics and cladistics.

Systematics

The science of the interrelationships of organisms and their taxonomy.

Cladistics

A systematic approach that groups organisms by evolutionary relationships, emphasizing monophyletic groups and using the principle of parsimony.

Monophyletic

A group consisting of a common ancestor and all its descendants; the only form of grouping accepted as valid by cladistics.

Paraphyletic

A group that includes a common ancestor and some, but not all, of its descendants.

Polyphyletic

A grouping that does not include the most recent common ancestor of all members; often formed by convergent traits.

Clade

A monophyletic grouping on a phylogenetic tree; a monophyletic subset of the tree.

Ingroup

The taxonomic group under investigation in a cladistic analysis.

Outgroup

A taxon closely related to but not included in the ingroup, used to polarize character states.

Node

A branch point representing a common ancestry on a phylogenetic tree.

Branch (internode)

A line on a phylogenetic tree linking two hypothetical ancestors or an ancestor and a group.

Synapomorphy

A shared derived (apomorphic) trait that defines a clade.

Autapomorphy

A derived trait unique to a single taxon.

Apomorphy

A derived characteristic not present in the outgroup.

Plesiomorphy

A primitive (ancestral) character present in the outgroup.

Symplesiomorphy

A primitive character shared by two or more taxa.

Homologous

Structures with the same origin; not necessarily the same function.

Analogous

Structures with the same function but not from the same origin.

Character

A measurable trait used in cladistics to compare organisms.

Character state

The form a character takes in a given organism (e.g., present vs. absent).

Sister group

The closest related group or clade to a given species; also called sisters.

Taxon

Any grouping in the Linnaean hierarchy (genus, species, family, etc.).

Taxonomy

The science of naming and classifying organisms; a subset of systematics.

Phylogeny

The evolutionary history of a group of organisms.

Cladogram

A branching diagram that shows evolutionary relationships among taxa, emphasizing clades.

Amniota

Tetrapods with embryos having extraembryonic membranes (amniotic egg).

Tetrapoda

Four-legged vertebrates.

Gnathostomata

Craniates with jaws.

Agnatha

Jawless fishes.