Lecture 4 - Phylogenies and the History of Life

Phylogeny

The evolutionary history of a group of organisms

Phylogenetic tree

A graphical summary of the evolutionary history of a group of organisms

Branch

Represents a population through time

Node

Represents a point where a branch splits

Tip

Represents the endpoint of a branch

Root

The most ancestral branch in the tree

Outgroup

A taxon that diverged before the taxa that are the focus of the phylogeny and helps to root the tree and a sister group that shares a recent common ancestor with taxa being studied, but is not part of the study group

Polytomy

A node that divides into 3 or more branches

Sister groups

Closely related taxa that share a recent common ancestor

Ancestral trait

A character that existed in an ancestor

Derived trait

Trait that is a modified form of the ancestral trait, found in a descendant

Synapomorphy

Trait found in two or more taxa that are present in their most recent common ancestor but missing in more distant ancestors

Monophyletic group

An evolutionary unit that includes an ancestral population and all of its descendants

Parsimony

Used to identify most likely trees

Homology

When traits are similar due to shared ancestry

Homoplasy

When traits are similar for reasons other than common ancestry

Limitations of Fossil Records

• Habitat bias

• Taxonomic and tissue bias

• Temporal bias

• Abundance bias

Precambrain era

Era where life was exclusively unicellular

Adaptive radiation

The rapid production, from a single lineage, of many descendant species

Cambrian explosion

When the first animals appeared