geological time scale

a division of Earth's history into eons, eras, periods, and epochs defined by major geological or biological events

paleontology

the study of fossil remains or other clues to past life

fossil

any evidence of an organism from more than 10,000 years ago

radiometric dating

a type of absolute dating that uses known rates of radioactive decay to date fossils

half-life

the time it takes for half the atoms in a sample of a radioactive substance to decay

homologous

similar in structure or position because of common ancestry

analogous

similar in function but not in structure because of convergent evolution, not common ancestry.

convergent evolution

the evolution of similar adaptations in organisms that do not share the same evolutionary lineage

vestigial

having no apparent function in one organism, but homologous to a functional structure in another species

homeotic

describes any gene that, when mutated, leads to organisms with structures in the wrong places

molecular clock

application of the rate at which DNA mutates to estimate when two types of organisms diverged from a shared ancestor

systematics

field of study that includes taxonomy and phylogenetics

phylogenetics

field of study that attempts to explain the evolutionary relationships among species

ancestral character

characteristic already present in the ancestor of a group being studied

derived character

characteristic not found in the ancestor of a group being studied

cladistics

a phylogenetic system that defines groups by shared derived characters 

clade (aka monophyletic)

- a group of organisms consisting of a common ancestor and all of its decendants.

- a group of species united by a single evolutionary pathway

cladogram

a tree like diagram built using shared derived characteristics.

parsimonious

a tree that requires the fewest steps to construct 

paraphyletic 

describes a group of organisms that contains a common ancestor and some, but not all, of its descendants

polyphyletic

describes a group of organisms that excludes the most recent common ancestor of all members of the group