Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans (whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives, i.e. Entelodonts and Andrewsarchus.[1] All Whippomorphs are descendants of the last common ancestor of Hippopotamus amphibius and Tursiops truncatus. This makes it a crown group.[2] Whippomorpha is a suborder within the order Artiodactyla (even-toed ungulates). The placement of Whippomorpha within Artiodactyla is a matter of some contention, as hippopotamuses were previously considered to be more closely related to Suidae (pigs) and Tayassuidae (peccaries).[3][4] Most contemporary scientific phylogenetic and morphological research studies link hippopotamuses with cetaceans, and genetic evidence has overwhelmingly supported an evolutionary relationship between Hippopotamidae and Cetacea.[5] Modern Whippomorphs all share a number of behavioural and physiological traits; such as a dense layer of subcutaneous fat and largely hairless bodies. They exhibit amphibious and aquatic behaviors and possess similar auditory structures.
The name Whippomorpha is a combination of English (wh[ale] + hippo[potamus]) and Greek (μορφή, morphē = form).[2] Some attempts have made to rename the suborder Cetancodonta, due to the misleading utilization of the suffix -morpha for a crown group,[6] as well as the risk of confusion with the clade Hippomorpha (which consists of equid perissodactyls);[7] however Whippomorpha maintains precedence.[7]
Modern Whippomorphs are widely distributed. Cetaceans can be found in almost all of the world's marine habitats, and some species, like the blue whale and humpback whale, have migratory ranges that comprise nearly the entire ocean. These whales typically migrate on a seasonal basis, moving to warmer waters to give birth and raise young before travelling to cooler waters with more optimal feeding grounds.[8] Other cetacean species have smaller ranges that are concentrated around either tropical or subtropical waters. Some cetaceans live exclusively within a single marine body, such as the narwhal, whose range is limited to the Arctic Ocean.[9]
By comparison, modern hippopotamuses are confined entirely to the African continent. Despite once being widespread across Europe and North Africa, hippos are now considered vulnerable and are limited to the lakes, rivers and wetlands of southern Africa.[10]
Both whales and hippos must surface in order to breathe. This can pose problems for sleeping Whippomorphs. Cetaceans overcome this problem by exhibiting unihemispheric sleep, meaning they rest one side of their brain at a time, allowing them to swim and surface during rest periods.[11] Hippopotamuses surface to breathe every three to five minutes. This process is partially subconscious, allowing hippopotamuses to surface and breathe whilst sleeping.[12] Both whales and hippos exhibit symbiotic relationships with smaller fish, which they use as cleaning stations, allowing the smaller organisms to feed on parasites that enter the creature's mouth.[13]
Hippos are herbivores, normally their diet consists entirely of short grasses that they graze on. Some hippos have been observed consuming animals such as zebra and even other hippo carcasses.[14][15] A hippo normally spends up to five hours a day grazing. They normally feed only on land, though occasional consumption of aquatic vegetation has been observed.[12] By contrast, cetaceans are all carnivores, feeding on fish and marine invertebrates, with some individual species feeding on larger mammals and birds (such as seals and penguins).[16]