It may seem that mostly land-dwelling even-toed ungulates such as giraffes and deer have little in common with exclusively aquatic whales and dolphins. However, recent scientific evidence suggests that cetaceans may have evolved from even-toed ungulate ancestors. Shared origins can now be seen within the fossil record, with early cetaceans possessing a specialised ankle bone that brings together Cetacea and Artiodactyla into a mammalian superorder, Cetartiodactyla. This groups the largest animal ever to have lived (the blue whale) together with the tiny, 2kg mouse deer.
Scientific name: Cetartiodactyla
An evolutionary tree for the group of mammals known as Cetartiodactyla. When the evolution of mammals is analysed, some surprises emerge - such as the fact that hippos and deer share a common ancestor with whales.
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Additional data source: Animal Diversity Web
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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.