| Whippomorphs | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Clade: | Cetancodontamorpha |
| Suborder: | Whippomorpha Waddell et al. 1999 |
| Subgroups | |
| |
Whippomorpha is asuborder ofartiodactyls that contains all livingcetaceans (whales,dolphins, andporpoises) and thehippopotamids.[1][2] This makes it acrown group.[3] Whippomorpha is asuborder within the orderArtiodactyla (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 toSuidae (pigs) andTayassuidae (peccaries).[4][5] Most contemporary scientificphylogenetic andmorphological research studies link hippopotamuses with cetaceans, andgenetic evidence has overwhelmingly supported anevolutionary relationship between Hippopotamidae and Cetacea.[6] Modern whippomorphs all share a number ofbehavioural andphysiological traits, such as a dense layer ofsubcutaneous fat and largely hairless bodies. They exhibit amphibious and aquatic behaviors and possess similarauditory structures.
Whippomorpha is a subgroup ofCetancodontamorpha. Cetanconodontomorpha also includes the more basal extincthelohyids,entelodonts andAndrewsarchus.
The Latin name Whippomorpha is derived fromwhippo, a colloquial term coined in reference to the hypothesis that whales and hippopotamuses are each other's closest relatives, and the suffix-morpha (from Greekmorphē (μορφή, "form")).[3] Attempts have been made to rename the suborderCetancodonta, due to the misleading utilization of the suffix-morpha for a crown group[7] as well as the risk of confusion with the clade Hippomorpha (which consists ofequidperissodactyls).[8] However, Whippomorpha maintains precedence.[8]
Modern whippomorphs are widely distributed. Cetaceans can be found in almost all of the world's marine habitats, and some species, like theblue whale andhumpback 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.[9] 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 thenarwhal, whose range is limited to theArctic Ocean.[10]
By comparison, aside theirintroduced range,particularly in South America, modern hippopotamuses are confined entirely to theAfrican continent. Despite once being widespread acrossEurope, Africa andAsia,[11][12] hippos are now considered vulnerable and are limited to the lakes, rivers and wetlands of southern Africa.[13]
.jpg)
Both whales and hippos must surface to breathe. This can pose problems for sleeping whippomorphs. Cetaceans overcome this problem byunihemispheric sleep, meaning they rest one side of their brain at a time, allowing them to swim and surface during rest periods.[14] Hippopotamuses surface to breathe every three to five minutes, a process that is partially subconscious, allowing them to do it whilst sleeping.[15] 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.[16]
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.[17][18] 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.[15] By contrast, all cetaceans are carnivores, feeding on fish and marine invertebrates, with some species feeding on larger mammals and birds (such asseals (pinnipeds) andpenguins).[19]
All whippomorphs areplacental mammals, meaning thatembryos are fed by theplacenta, which draws nutrients from the mother's body. They arek-selected organisms, producing a limited number of offspring, but with a high rate of survival.[20]
.jpg)
Hippos reach sexual maturity when they are six years old and have agestation 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 calvessuckle on land.[citation needed]
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.[19]
Whippomorpha is a suborder located within the Order Artiodactyla, and the cladeCetancodontamorpha. It contains the clades Hippopotamoidea (ancestors of hippopotamuses) and Cetaceamorpha (ancestors of whales and dolphins). Whippomorpha is considered asister clade toRuminantia (which contains cattle, sheep and deer), as well as the extinctRaoellidae.[6][21] Hippopotamoidea was formerly included toSuiformes with Suidae (pigs) and Tayassuidae (peccaries).[22]
Most of the evidence supporting the Whippomorpha clade is based onmolecular orgenetic analysis. Early support for the existence of a Cetacea/Hippopotamidae clade originated from analysis of the molecular composition of a blood-clottingprotein γ-fibrinogen taken from whales and hippopotamuses.[23] Later studies obtained findings that indicated almost 11,000orthologous genes between cetaceans and hippopotamuses, in addition to numerous positive indicators of a shared evolutionary history between cetaceans and hippopotamuses.[6] Furthermore, some genetic sequences have been found in both whales and hippopotamuses that are not present in the genomes of other mammals.[24] This would indicate that these groups share ancestry.
Whippomorpha's placement withinArtiodactyla can be represented in the followingcladogram:[4][25][26][27][28]
| Artiodactyla |
| ||||||||||||||||||||||||
It is unknown whether the last common ancestor of whales and hippos led anaquatic,semiaquatic/amphibious, orterrestrial lifestyle. Therefore, it is a matter of contention whether the aquatic traits of both hippopotamuses and cetaceans are linked or the product ofconvergent evolution. Recent findings seem to indicate that the latter is more likely.[6]
Whippomorpha diverged from othercetartiodactyls approximately 59 Mya, whilst whales diverged from hippos approximately 55 Mya.[6] The first branch contained ancestors of Cetacea; semi-aquaticprotowhales such asPakicetus in the groupArchaeoceti, which developed into the exclusively aquatic ancestors of modern cetaceans.[29]
One evolutionarily significant whale ancestor was theraoellidIndohyus, which was aHimalayas-dwelling,digitgradeomnivore roughly the size of araccoon. It was not an adept swimmer, although it was thought to have spent considerable periods of time wading in shallow water. This would have been assisted by its heavy bones, providing stability.Indohyus was likely to have a diet at least partially based on aquaticforaging. Evidence for this includes the fact that the toothenamel ofIndohyus was considerably less worn than would be expected for an animal with an exclusively terrestrial diet.[21] One of the most crucial facets of the discovery ofIndohyus was the presence of a thickened auditorybulla, otherwise known as aninvolucrum. This discovery was significant as the involucrum was a morphology thought previously to be exclusive to cetaceans, asynapomorphy. This feature irrefutably linked cetaceans to raoellids.[21]
It is thought that early whales such asNalacetus andPakicetus were restricted tofreshwater environments, as modern hippopotamuses are.[29] The laterAmbulocetus, was likely to have lived a much more aquatic lifestyle, with shorter legs and paddle-like hands and feet. It also likely represented a transitional organism from freshwater toseawater, as theisotopic analysis of the bones and teeth ofAmbulocetus indicate that it inhabitedestuaries.[30]
The second branch of Whippomorpha is thought to have developed into the familyAnthracotheriidae, who were the putative ancestors of modern hippopotamuses. The sediments in which anthracotheriid fossils have been fossilized indicate that they were at least partially amphibious, whilst the jaw structure of fossils of select species, particularlyAnthracotherium, seem to indicate that it was an ancestral form of modern hippopotamuses.[21]
These findings somewhat explain the once confusing paleontological age gap that existed as a major piece of evidence against an evolutionary link between Hippopotamidae and Cetacea. Previously, the oldest known cetacean fossils were approximately 50 Myr, while the earliest known hippopotamus fossils were around 15 Myr.[31] The sum of the fossil knowledge indicates that whales and hippopotamuses developed amphibious and aquatic traits independently from one another, but that the features developed by their shared ancestors created pathways to the development of said adaptations.[32] Thus the large difference in time between the discovery of cetacean and hippopotamid fossils is explained by the fact that hippos simply developed their semi-aquatic adaptations at a much later time than their cetacean cousins.[6]
All members of the suborder Whippomorpha share some anatomical similarities. Hippopotamusstomachs are multi-chambered as with allruminants; however, they do notregurgitate food. Instead, the hippopotamus stomach contains two preliminary chambers, which acts similarly to a compost bin, allowing foodstuffs toferment before entering the animal's main stomach. All whale species possess similar stomach structures. Additionally, both animals bear single-lobedlungs (similar to other aquatic mammals), which allow to be filled with air more rapidly. This is a criticaladaptation for both amphibious and aquatic organisms, as it reduces the frequency of dangerous trips to the water surface, where such organisms are more vulnerable topredation.[33]
Hippos' bodies contain a layer of densefat, reminiscent of a whales'blubber, and situated betweenskin and muscle. Hippos and whales both possess thickbones, which aid in rapid descent into water, have minimal hair (to aid inhydrodynamics)[32] and a lack ofsweat glands.[34] Webbing is also present between the toes of hippopotamuses; a more land-suitable version of a whale's flippers.[32] Hippos possess unique hind-limbmusculature that provides them with powerful propulsion capabilities, rather than fine-tuned control. These features are characteristic of other ungulates.[35]
There is strong resemblance between thedentition of primitive cetaceans and primitive ungulates, which seemingly cements the position of Cetacea within Artiodactyla.[23] In addition, both cetaceans and artiodactyls possess two distinct components in their ears, theinvolucrum andsigmoid process. Similar features are considered responsible for the ability of cetaceans tohear underwater. The skeletons of prehistoric whales also contain uniquely shapedankle bones, including a double-pulley system found only in even-toed ungulates and crucially not present inodd-toed ungulates.[24]
Both hippos and whales have an unusually large and strangely shapedlarynx, which enables the boomingcalls of whales underwater and the unique noises produced by hippos to communicate while submerged.[33]
 | This sectionneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources in this section. Unsourced material may be challenged and removed.(December 2025) (Learn how and when to remove this message) |
Whippomorphs have always had complexcultural andsocial relationships with humans. Hippopotamuses have a reputation for extremeaggression towards humans. Hippos are incredibly territorial and protective of their young, and are the deadliest mammal in Africa, killing between two and three thousand people each year.[13] Despite this, hippos remain popularzoo animals and a recognizable species in popular culture. Hippos were hunted by ancient humans for food and sport. InAncient Egypt, hippos were recognized as dangerous inhabitants of the riverNile, and a red hippo was the symbol of the godSet.[citation needed] ThebiblicalBehemoth is thought to be based on or inspired by the hippo.[citation needed]
Hippopotamuses face a number of threats from humans.Common hippopotamuses are classed asvulnerable, and are subject to habitat destruction as a result ofagriculture,water management,climate change and development of housing and urban areas.[36]Pygmy hippopotamuses are consideredendangered, with less than three thousand individuals in the wild. The few surviving pygmy hippopotamuses occupy a much smaller habitat area inLiberia,Sierra Leone, and theIvory Coast. They face threats frommining andquarrying,hunting,poaching, andlogging.[37]
Cetaceans have also had an extensive history with humans. The primary threats to cetaceans are direct danger (fromwhaling), and indirect damage to whale habitats (throughpollution andoverfishing).[citation needed] Commercial shipping,petroleum drilling and coastal development can disrupt cetacean habitats. Thousands of cetaceans are affected bybycatching every year.[38] Some evidence also exists that human-generated sound may account for increases in the rate ofcetacean strandings.[39]
Whales were inspirations for many mythical creatures, including theLeviathan, which was associated with the Behemoth.[citation needed] Dolphins are mentioned in historical literature far more frequently than whales.[citation needed] Stories of dolphins typically include them playing a role in helping shipwrecked sailors or guiding lost ships.[citation needed] In the 20th century, perceptions of whales changed, and now tourism for the purposes ofwhale-watching has become very popular.[citation needed] Cetaceans are revered for their immense size, intelligent and playful dispositions, displays of speed in water, and contributions to scientific research.[citation needed]
Whales have been kept in captivity by humans for research and entertainment for centuries.[citation needed] Particularly popular arekiller whales.[citation needed]Conservation andanimal rights organizations have been vehemently opposed to the captivity of these cetaceans.[citation needed] It is common for captive killer whales to display aggression towards other whales and their trainers.[citation needed]Bottlenose dolphins are also popular, due to their friendly behavior.[citation needed] They also fare better in captivity than other cetaceans.[citation needed]
.png)
_(white_background).jpg)
.jpg)
.jpg)
{{cite journal}}: CS1 maint: multiple names: authors list (link)