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Phylogeny

The study of the evolutionary history and relationships among individuals or groups of organisms.

Chordata

A phylum that includes all animals with a notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and endostyle.

Cranium

The bony or cartilaginous case that encloses the brain in vertebrates.

Notochord

A flexible rod-shaped body found in embryos of all chordates, providing structural support.

Dorsal Hollow Nerve Cord

A tube above the notochord that develops into the central nervous system in vertebrates.

Pharyngeal Slits

Structures that connect the pharynx to the outside, present at some stage in all chordates.

Post-anal Tail

An extension of the body past the anus, characteristic of all chordates at some stage of development.

Endostyle

A mucous-secreting groove in the throat that is homologous to the thyroid gland in vertebrates.

Deuterostomes

A group of animals characterized by their embryonic development, including chordates and echinoderms.

Agnatha

Jawless vertebrates such as lampreys and hagfish.

Gnathostomata

Jawed vertebrates that include fish and tetrapods.

Amniotes

Tetrapods that produce an amnion during development, including reptiles, birds, and mammals.

Anamniotes

Tetrapods that do not produce an amnion, such as amphibians.

Echinodermata

A phylum of marine animals such as sea stars and sea cucumbers, characterized by a water vascular system.

Metamorphosis

A developmental process in which organisms undergo a transformation from larval to adult stages.

Teleostomi

A taxon that includes bony fish and tetrapods.

Lissamphibia

The clade that includes all living amphibians.

Synapsid

Amniotes characterized by having a single temporal fenestra.

Diapsid

Amniotes characterized by having two temporal fenestrae.

Parareptilia

An extinct group of amniotes that includes the early ancestors of turtles.

Eureptilia

The group that includes modern reptiles and birds.

Mammalia

The class of vertebrates characterized by hair and mammary glands.

Monotremata

An order of egg-laying mammals such as the platypus and echidna.

Metatheria

The group of mammals that includes marsupials.

Eutheria

The group of mammals that have a complex placenta and give birth to live young.

Sarcopterygii

The class that includes lobe-finned fish and the ancestors of tetrapods.

Actinopterygii

The class that includes ray-finned fishes.