Britannica Sources used in this answer

How did the extinction of dinosaurs affect the diversification of mammals?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Illustration showing examples of vertebrates: a turtle for reptiles, a songbird for birds, a bluegill fish, a salamander for amphibians, and two mammals-a whale and a groundhog. — Vertebrate The major groups of vertebrates include fishes, amphibians, reptiles, birds, and mammals.

The extinction of dinosaurs at the end of the Cretaceous Period, often referred to as the K–T extinction, played a pivotal role in the evolutionary history of mammals. Although mammals had coexisted with dinosaurs for over 100 million years, they remained relatively small during the Mesozoic Era.12

The mass extinction event eradicated dominant terrestrial dinosaurs and large marine reptiles, leaving behind numerous vacant ecological niches. In the ensuing Cenozoic Era, mammals underwent a period of rapid adaptive radiation to fill these roles.1

This diversification included:
* Placental Mammals: These radiated at a rapid rate and eventually came to comprise more than 95 percent of known mammal species.1
* Ungulates: Hoofed mammals, including both perissodactyls (odd-toed) and artiodactyls (even-toed), developed and proliferated during the Paleocene and Eocene epochs.1
* Marsupials: In regions like Australia and South America, marsupials evolved into a diverse array of forms, flourishing in the absence of competition from carnivorous placental mammals.1

Ultimately, the removal of dinosaurian dominance allowed mammals to expand into a vast range of body sizes and ecological roles, leading to the diverse mammalian fauna observed today.1