CLASSIFICATION: The process and practice of describing, defining and ranking taxa within a hierarchical series of groups; permits organizing and ordering knowledge about organisms, and creates a simplified language for conveying information about order in the diversity of life. In biology, we use the Linnean classification hierarchy (Kingdom, Phylum, Class, Order, Family, Genus, Species).

Kingdom MetazoaPhylum ChordataClass MammaliaOrder PrimatesFamily HominidaeGenus Homospecies sapiens

Binomen(scientific name) in“binomial” or“binominal”nomenclature

Class MammaliaSubclass

InfraclassCohort

SuperorderOrder Primates

Suborder AnthropoideaInfraorder

Superfamily HominoideaFamily Hominidae

SubfamilyTribe

SubtribeGenus Homo

Subgenusspecies sapiens

subspecies

G.G. Simpson, 1945

Systematics: The field of biology that deals with the diversity of living organisms, usually divided into the two subdisciplines of taxonomy and phylogenetics.

Taxonomy: The science of describing, naming, and classifying (grouping) organisms.

Taxon (plural: taxa): Any named group of organisms (not necessarily a clade). A subspecies respresents a "taxon," as does every hierarchical level up to Kingdom.

Phylogenetics: The field of biology that deals with the relationships between organisms, including the discovery of these relationships and the study of the causes behind these patterns.

Phylogeny: The evolutionary relationships among organisms; the patterns of lineage branching produced by the evolutionary history of organisms.

time

Terminal node

(terminal)

(=interior branch)

Outgroups

Most Recent CommonAncestor of B+C

MRCA of A+B+C

MRCA of N+A+B+C

“basal” to the ingroup

A B C DA

B

C

D

AA

B

B

C

C

D

D

A B C D A B C D

A B C D A BC D

Types of “trees”DENDROGRAM: A branching diagram with nodes and branches.

PHYLOGENETIC TREE or CLADOGRAM: A dendrogram representingthe genealogic relationships between taxa with ancestry and relative time implied.

A B C D

Types of “trees”DENDROGRAM: A branching diagram with nodes and branches.

PHYLOGENETIC TREE or CLADOGRAM: A dendrogram representingthe genealogic relationships between taxa with ancestry and relative time implied.

EVOLUTIONARY TREE: A phylogenetic tree that includes a time axis and (generally) all members, living and extinct.

Types of “trees”

PHYLOGRAM: A tree with branch lengths drawn to represent the degree of genetic (or other) divergence.

A B

CD

scale=10%

Monophyly(monophyletic)

monophyletic group (monophyly): A group of organisms/taxa that includes ALL known descendants of that group's common ancestor (including the common ancestor). Monophyletic groups (clades) are grouped by shared derived characters (synapomorphies) not present in earlier ancestors or other groups. Monophyletic groups are also called "natural" groups. Mammalia is an example of a monophyletic group.

Monophyly(monophyletic)

clade: A monophyletic or “natural” group.

subclade: A clade nested within a larger, more inclusive clade.

clade clade clade subclade

Monophyly(monophyletic)

paraphyletic group (paraphyly): An artificial group of organisms/taxa that includes some, but NOT ALL, of the descendants of a common ancestor. Paraphyletic groups are typically recognized by the sharing of primitive (plesiomorphic) characters. Reptiles are an example of a paraphyletic group. A "grade" is also, by definition, paraphyletic.

Paraphyly(paraphyletic)

Monophyly(monophyletic)

grade: An artifical (non-monophyletic) taxon, frequently paraphyletic and sometimes polyphyletic. Grades are supposed to represent some level of evolutionary progress.

Paraphyly(paraphyletic)

grade

Monophyly(monophyletic)

Paraphyly(paraphyletic)

Polyphyly(polyphyletic)

polyphyletic group (polyphyly): An artificial group of organisms/taxa derived from two or more independent, distinct ancestral taxa. The common ancestor, and many closely related taxa, are excluded from the group. Polyphyletic groups are generally recognized by superficial similarities resulting from convergence that do not reflect close evolutionary relationships.

Monophyly(monophyletic)

Paraphyly(paraphyletic)

Polyphyly(polyphyletic)

Anapsida Diapsida

SynapsidaSaurapsida

Turtles

Lizards & snakesCrocodilesDinosaurs & birds

Mammals &reptile-like mammals

Amniota -evolution of cleidoic (shelled) egg; ca. 350 mya

Amphibians

-ca. 320 mya

Why do we care?

1. Meaningful classifications.

2. Need pattern (=phylogeny) to study process (evolution, biogeography, etc.).

3. The “comparative method”

4. Predict properties of organisms