Cetartiodactyla

The Cetartiodactyla are the clade in which whales (including dolphins) and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls. Under this definition, their closest living land relative is thought to be the hippopotamus. The clade formed by uniting whales and hippos is called Whippomorpha. Alternatively, the term 'Cetartiodactyla' is used to denote a clade where Cetacea evolved alongside Artiodactyla and not within it. Under this definition, all artiodactyls, including hippos, are more closely related to one another than any are to the whales.

This group has been proposed as a new order, but evidence of the exact relationship between the two current orders is not sufficient to efficiently merge them.

Whales evolved from land mammals and appear to form a monophyletic group. It is well accepted that all whales evolved from a single ancestor. The most widely accepted hypothesis before the 1990s was the closest relatives to whales were the fossil group Mesonychia. These were hooved, predominantly carnivorous mammals known only from fossils. But, today, few authorities still consider mesonychids to be more closely related to whales than artiodactyls. Instead, they are usually considered to be the closest relative of the Cetartiodactyla as a whole.