Phylogeny

Fossil

Preserved remains or traces of organisms in rock.

Transitional forms

Linking ancestors and descendants found in the fossil record.

Speciation

The process by which new species arise.

Vestigial structures

Reduced, nonfunctional remnants that provide evidence of ancestry.

Homologous structures

Structures that have the same origin but different functions, indicating common ancestry.

Analogous structures

Structures that serve similar functions but have different origins, a result of convergent evolution.

Molecular clock

A method that uses DNA and protein comparisons to estimate the time of evolutionary divergence between species.

Adaptive radiation

The rapid diversification of a species into a wide variety of forms to adapt to different environments.

Derived trait

A new trait that was not present in the ancestor of a lineage.

Synapomorphy

A shared derived trait used to determine evolutionary relationships in cladistics.

Cladistics

A method of classification that groups organisms based on evolutionary relationships and shared derived traits.

Phylogeny

The study of evolutionary relationships among biological entities, often depicted as phylogenetic trees.

Mass extinction

A rapid loss of many species in a short period, often followed by adaptive radiation.