Whippomorpha is a suborder of artiodactyls that contains all living cetaceans (whales, dolphins, and porpoises) and the hippopotamids. This makes it a crown group. 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). 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. 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. Whippomorpha is a subgroup of Cetancodontamorpha. Cetanconodontomorpha also includes the more basal extinct helohyids, entelodonts and Andrewsarchus.
Etymology The Latin name Whippomorpha is derived from whippo, a colloquial term coined in reference to the hypothesis that whales and hippopotamuses are each other's closest relatives, and the suffix -morpha (from Greek morphē (μορφή, "form")). Attempts have been made to rename the suborder Cetancodonta, due to the misleading utilization of the suffix -morpha for a crown group as well as the risk of confusion with the clade Hippomorpha (which consists of equid perissodactyls). However, Whippomorpha maintains precedence.
Ecology
Distribution 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. 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. By comparison, aside their introduced range, particularly in South America, modern hippopotamuses are confined entirely to the African continent. Despite once being widespread across Europe, Africa and Asia, hippos are now considered vulnerable and are limited to the lakes, rivers and wetlands of southern Africa.
Behaviour
Both whales and hippos must surface to breathe. This can pose problems for sleeping whippomorphs. Cetaceans overcome this problem by unihemispheric sleep, meaning they rest one side of their brain at a time, allowing them to swim and surface during rest periods. Hippopotamuses surface to breathe every three to five minutes, a process that is partially subconscious, allowing them to do it whilst sleeping. 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. 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. 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. By contrast, all cetaceans are carnivores, feeding on fish and marine invertebrates, with some species feeding on larger mammals and birds (such as seals (pinnipeds) and penguins).
Reproduction All whippomorphs are placental mammals, meaning that embryos are fed by the placenta, which draws nutrients from the mother's body. They are k-selected organisms, producing a limited number of offspring, but with a high rate of survival.
Hippos reach sexual maturity when they are six years old and have a gestation period of approximately eight months. Mating typically occurs in the water. Female hippopotamuses isolate themselves for two weeks prior to giving birth. The birthing process also takes place underwater, meaning calves must swim to the surface in order to breathe for the first time. Hippopotamus calves suckle on land. Cetaceans generally reach sexual maturity around 10 years of age, and have a gestation period of around 12 months. Cetaceans give birth to well-developed calves, like hippopotamuses. When suckling, the mother splashes milk into the calves' mouth, as they have no lips.
Taxonomy and phylogeny Whippomorpha is a suborder located within the Order Artiodactyla, and the clade Cetancodontamorpha. It contains the clades Hippopotamoidea (ancestors of hippopotamuses) and Cetaceamorpha (ancestors of whales and dolphins). Whippomorpha is considered a sister clade to Ruminantia (which contains cattle, sheep and deer), as well as the extinct Raoellidae. Hippopotamoidea was formerly included to Suiformes with Suidae (pigs) and Tayassuidae (peccaries). Most of the evidence supporting the Whippomorpha clade is based on molecular or genetic analysis. Early support for the existence of a Cetacea/Hippopotamidae clade originated from analysis of the molecular composition of a blood-clotting protein γ-fibrinogen taken from whales and hippopotamuses. Later studies obtained findings that indicated almost 11,000 orthologous genes between cetaceans and hippopotamuses, in addition to numerous positive indicators of a shared evolutionary history between cetaceans and hippopotamuses. Furthermore, some genetic sequences have been found in both whales and hippopotamuses that are not present in the genomes of other mammals. This would indicate that these groups share ancestry. Whippomorpha's placement within Artiodactyla can be represented in the following cladogram:
Evolution
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