animal diversification

Phylogenetic relationships

The evolutionary connections between different species or groups of organisms.

Cambrian Explosion

A period of rapid diversification of life on Earth that occurred approximately 540 million years ago.

Punctuated equilibrium

A theory suggesting that evolution occurs in rapid bursts followed by long periods of stability.

Choanoflagellates

Single-celled organisms considered the closest living relatives of animals.

Diversification

The process by which a species evolves into a variety of forms to adapt to different environments.

Hox genes

A group of regulatory genes that control the body plan of an embryo along the head-tail axis.

Sarcopterygian ancestor

A common ancestor of lobe-finned fishes and terrestrial vertebrates.

Extinction events

Periods in Earth's history where a significant percentage of species go extinct.

Cephalization

The concentration of sensory and neural organs at one end of an organism, leading to the formation of a head.

Amniotes

A clade of tetrapod vertebrates that lay eggs on land or retain the fertilized egg within the mother.

Synapsids

A group of animals that includes mammals and their ancestors, characterized by having a single temporal fenestra.

Echinoderms

A diverse group of marine organisms including sea stars and sea urchins.

Lobe-finned fishes

Fishes that possess fleshy, lobed fins, which are precursors to limbs in tetrapods.

Ordovician Period

A period in the Paleozoic era, known for the first appearance of many fish and the colonization of land by plants.

K-Pg boundary incident

A mass extinction event around 65 million years ago that wiped out non-avian dinosaurs and allowed mammals to diversify.

Tetrapods

Four-limbed vertebrates that evolved from lobe-finned fishes.