Cetartiodacyla

## About

   Cetartiodactyls more commonly known as cetaceans, are fully aquatic mammals that live in both freshwater and saltwater environments worldwide belonging to the clade cetacea. Cetaceans are easy to identify, having pectoral, dorsal and claudal (tail) fins, often cetaceans appear fish like to the untrained eye leading them to be commonly and incorrectly grouped with fish, cetacea even meaning 'huge fish' in Latin In reality cetaceans are mammals. Cetaceans have been recognised as mammals for hundreds of years even dating back to the Ancient Greeks, who first realised that cetaceans lack gills and breathe air, differentiating them from fish. Cetaceans are incredibly intelligent and exhibit very human like behaviour. For example a pod of dolphins will often vote on their next group decision. Cetaceans have a unique way of hunting that generally distinguishes them from other large aquatic animals known as echolocation. Echolocation is a form of hunting where the predator will use sound waves to judge the distance between them and their prey as well as other objects and creatures that are out of view. Echolocation is also used to locate members of the pod as well as communicate with them. Cetaceans are loud animals that can make a wide array of sounds, dolphins and porpoises communicate through clicks and whistles whether as whales communicate through singing their often mournful sounding songs. Cetaceans are usually social animals with even the less social species travelling in small groups. Echolocation is an ability defined by its use by cetaceans. Echolocation allows cetaceans to find prey, predators and their pods before they even see them. Cetaceans use Echolocation by making loud noises, further magnified by the melon inside of their skulls, this sound will bounce off objects and or other animals before the sound waves return to the cetaceans. Echolocation has proven itself to be quite an amazing skill in both hunting and socialising. Cetaceans are arranged into two very simple groups being toothed whales (odontocetes) and baleen whales (mysticetes). Toothed whales obviously have sharp teeth meant for slicing meats from fish to squids to penguins. Toothed whales include dolphins, porpoises and beaked whales. Baleen whales are the biggest animals to ever exist on our planet and instead of teeth, they possess bristly structures in their mouths made of keratin called baleen. Baleen is used to filter out water and to trap krill which is their main source of food, a sort of sieve.

### Historic Classification

Finding out exactly how cetacea and cetaceans fit into the rest of the mammalian lineage has proven itself to be a greatly difficult task and we have only really figured it out recently. Aside from the primitive observations claiming cetaceans are fish from long outdated sources, the first proper mammalian group biologists suspected that cetaceans were related to was mesonychia.

#### Mesonychia

Mesonychia (pronounced MESS-O-NIKE-IA) is an extinct group of mammals that shared an appearance with dog like animals such as wolves or hyenas. Mesonychids were strange mammals that despite being carnivorous and resembling dogs, were equipped with hooves in place of toes on the end of each foot. The reason for mesonychia's association with cetacea was the similarities between the teeth of mesonychids and early archaeocetes (primitive cetaceans) that lived during the early Eocene to the late Oligocene. The similarities between mesonychia and cetacea did not end there, mesonychids also lived in the exact period of time on Earth that would make them viable to be considered ancestral to cetaceans. All this being said, mesonychia and cetacea were decided to be sister groups in 1975 and were placed side by side in a clade called Cete (pronounced seat). Although mesonychia and cetacea shared an abundance of similarities, cetacea would eventually be reclassed because of numerous discoveries about the DNA of extant whale species. During the 90's, a large amount of research would be done examining the DNA and proteins present in extant whales, leading researchers to begin to realise the similarities between cetaceans and artiodactyls. This lead many researchers to believe that cetacea should be placed as a sister group to Hippopotamidae, the clade that includes hippopotamuses. Despite this discovery, many paleontologists were not convinced that cetacea was at all similar to artiodactyla, seeing as much of the morphological and fossil data still supported the similarities between cetacea and mesonychia.

#### Hippopotamidae and artiodactyla

Over time more and more evidence supporting the ties between cetacea and Hippopotamidae and artiodactyla would emerge from independant research. These researchers would time and time again, discover the same genetic indicators that whales and hippos were genetically similar. All this research into the similarities between cetacea and artiodactyla would finally culminate in 2001 when the morphological data was found that proved cetaceans possess a bone in their ankles called an Astragalus. Since all mesonychia species did not possess an Astragalus in their ankles, and cetaceans were said to be related to them caused for cetaceans to be left out of artiodactyla along with mesonychia. Seeing as cetaceans clearly do not possess the developed legs of mainly land dwelling artiodactyls, it is hard to examine their ankles at all, in order to solve to controversy. There are in fact Archaeocetes that did possess hind limbs however, much of the fossil evidence associated with them lacks much of the material of the legs, making it impossible to find any sign of an Astragalus. This is why the morphological data found in 2001 was so ground breaking, as it found that two different Archaeocetes that did have an intact Astragalus. This data is now widely accepted today as proof of cetaceans being artiodactyls closely related to hippos.

## Archaeocetes

Archaeocetes (pronounced ARK-E-O-SEATS) are primitive cetaceans that lived from the early Eocene to the late Oligocene (around 50-23 mya). Almost all archaeocetes are known from fossilised remains from the Indo-Pakistan region. Archaeocetes represent the earliest form of amphibious stages in cetacean evolution.

#### Pakicetidae

Pakicetidae named after pakicetus is the most basal member of Archaeociti, despite this when Icthyolestes, the first member of pakicetidae was discovered in 1958 it was placed with mesonychids, Icthyolestes was reclassified from mesonychia to cetacea in 1980. This situation once again demonstrating how the close relations between cetacea and mesonychia were unquestioned, due to the large amount of morphological data supporting the theory. Pakicetids are only known from fossil remains in North Western India and Pakistan where their remains have been found in streams supporting the idea that they were probably wading animals rather than swimming ones. Pakecetids are thought to be the most primitive whales, still living on land and not venturing into oceanic environments.

#### Ambulocetidae

In contrast to pakicetidae members of ambulocetidae named after ambulocetus lived a mainly aquatic life, attempting to fill the aquatic predator niche in its range, even being thought to have behaved in a way comparable to modern day crocodiles. Ambulocetids and ambulocetus in particular have been thought to have laid in shallow river beds preparing to ambush any terrestrial animal that ventures to close to the riverbank. This theory is supported by the position of the orbits that rest on top of the skull, a perfect position for stalking prey above water without having to emerge from the water, a strategy that all crocodilians have adapted to using.

#### Remingtonocetidae

Remingtonocetids named after remingtonocetus are the next most basal group in Archaeocetes following Ambulocetidae. Remingtonocetids gradually continued the Ambulocetus' move into aquatic environments, further evolving into the role of a 'mammalian crocodile'. Remingtonocetids probably resembled crocodiles in life, having eyes on the top of their skull, elongated bodies and large webbed feet. Judging by the coastal areas of Pakistan and India where their fossilised remains were found, we can infer that remingtonocetids lived a largely marine lifestyle.

#### Protocetidae

Protocetids named after protocetus were almost fully aquatic archaeocetes that are also known from Pakistan and India. Despite being discovered in the Indo-Pakistan region many of their fossils have been found in Europe, Africa and the Americans, supporting the idea that protocetids originated in Indo-Pakistan but spread across other ocean territories worldwide, around 49-40 mya. Although protocetids were a much more aquatic group compared to previous Archaeocetes, pelvic and hind limb material found in most protocetids supports the theory that most protocetids were still capable of moving comfortably on land. A small but none the less outstanding detail found in protocetids is the placement of their nostrils. In earlier Archaeocetes the nostrils were positioned at the front of the snout, however in protocetids the nostrils are present much further back. This small detail would eventually become the blowholes present on modern day cetaceans. Protocetid eyes were also placed on the sides of their heads rather than the crocodilian eyes of previous archaeocetes. Protocetids are thought to have lived like modern day pinnipeds (seals and sea lions) being highly equipped for aquatic life and only coming ashore to relax, mate or give birth.

#### Basilosauridae

Basilosaurids named after basilosaurus, first evolved around 41 mya during the mid Eoncene and inhabited all oceans during their time on Earth. There are three groups that basilosaurids are split into being basilosaurinae, Dorudontinae and Kekenodontidae, the last of which only has one member being Kekenodon. Kekenodon is a complicated specimen and has been previously placed in the basilosaurinae subfamily. Today the legitimacey of Kekenodontidae being its own stand alone group is questioned and is today mainly placed as a transitionary group between basilosauridae and neoceti (modern cetaceans). Basilosaurinae were enormous Archaeocetes with serpentine bodies sometimes reaching 17 metres in length. Basilosaurins would have been formidable hunters and most likely at the top of the food chain. Dorudontins were smaller and more dolphin like in size. Both groups would have been fully aquatic and it would have been impossible for either groups to live on land, marking the first time in cetacean evolution where an Archaeocete had become fully aquatic.

## Neocetes (Extant)

Neocetes are the modern day cetaceans that inhabit the Earth presently. neocetes are typically grouped into two broad classifications, which are toothed whales (odontocetes) and baleen whales (mysticetes). These groups include many different species, families and genera of modern day cetaceans that will be analysed further below.

### Odontocetes

Odontocetes or toothed whales are a group of cetaceans that are classified by their possession of teeth. Odontocetes include porpoises, dolphins and some whales such as beaked whales and sperm whales.

#### Physeteridae

Physeteridae is a family of odontocetes that in the present day has only one extant member remaining, this species being the sperm whale ***(Physeter macrocephalus)***. Sperm whales are known for being by far the largest odontocetes and also the largest toothed predator today. physeteridae, much like kogiidae is also made up of many species of extinct members, the most prominent of which probably being Livyatan Melvillei. Phyceteroid fossil evidence dates furthest back to the Oligocene, some of this evidence proposes that there were at one point in Earth's history, many different species of physeteroids coexisted in the same environments. Physeteroids and sperm whales in particular are known for the spermaceti organ that fill up a portion of their large heads. The spermaceti organ's exact purpose has been debated with some plausible theories being that it magnifies sounds the sperm whales create similar to the melon, whilst others propose that it contains a wax like liquid that can harden allowing these whales to dive to unusual depths. Sperm whales only have teeth present on their lower jaw which fit perfectly into sockets on the inside of their upper jaw. This is an unusual trait that is only exhibited in physeteroids and kogiids.

#### Kogiidae

Kogiidae (pronounced KOJI-E-DAY) is a small family of odontocete whales only having two extant members with the rest of the known members being extinct. The dwarf and pygmy sperm whales ***(Kogia sima)*** and ***(Kogia breviceps)*** are the remaining extant species in kogiidae, which is placed in the larger physeteroid super-family along with the family physeteroidae which includes Sperm whales. This placement is supported by mitochodrial DNA which represents a close relation between the two groups however, some other studies propose that kogiidae fits closer to other odontocete families. Kogiids are known for their square heads reminiscent of physeteroids as well as their prominent dorsal fins, and needle like teeth.

#### Ziphiidae

Ziphiidae (pronounced ZIF-EYE-E-DAY) is a family of cetaceans that is comprised of twenty-three known members, commonly known as beaked whales. Ziphiids are often characterised by their long narrow bodies and slim snouts known as beaks as well as some more minute details include their lack of a notch in their flukes along with the throat groves located on the undersides of their heads. Ziphiids are extremely elusive and secretive cetaceans and not much is known about them, with some species being only discovered in the last century, whilst others are only known from skeletal evidence. Ziphiids are deep diving cetaceans that have only one pair of functional teeth with only some members being an exception. Ziphiids are Sexually Dimorphic, the males possess more prominent teeth that grow out of the sides of their mouths like tusks. Ziphiids are thought to be most closely related to physeteroids and delphinids however, these relations are not fully documented and will probably change as new information is discovered about ziphiids.

#### Delphinidae

Delphinidae is a the biggest family of all cetaceans, delphinidae includes all thirty-eight species of known oceanic dolphins. Delphinids are a gigantic group that contains many diverse species of cetaceans from the tiny Hector's dolphin ***(Cephalorhynchus hectori)*** to the ginormous killer whale ***(Orcinus orca)***. Delphinids can be identified by their long beaks and prominent melons. Despite all Odonticetes possessing a melon, delphinids seem to have much more noticeable ones that give their heads a bulbous appearance. The melon is a clump of tissue in a cetacean's head that acts like a sound lens/magnifier, directing the noises that cetaceans produce. Delphinids can also be recognised by their small, sharp teeth perfectly adapted for their diet of fish and squid. Killer whales being the largest and most brolic cetaceans, feed upon sea birds, penguins and even other marine Mammals such as Pinnipeds and other cetaceans. Including monodontids and phocoenids and many other extinct families, delphinidae makes up the super-family of delphinoids.

#### Monodontidae

The delphinoid family monodontidae is made up of two separate genera each containing only one species, known as the narwhal and beluga whale, these animals share a characteristic of living in icy arctic and sub-arctic waters. Both species are very iconic and easy to identify, beluga whales being completely white in colour, having a bulbous melon and lacking a dorsal fin. Narwhals on the other hand are splotched black, grey and white, and also exhibit extreme sexual dimorphism, males having a highly specialised tusk like tooth that protrudes from their forehead. The exact purpose of the narwhal's tusk was debated for a very long time until recently researchers have discovered that the narwhal's tusk has nerve endings that connect to the brain, allowing them to take in information about their surroundings. Monodontids first appear in the fossil record during the Miocene epoch (11 mya). Monodontids comprise the delphinoid super-family along with delphinids and phocoenids.

#### Phocoenidae

Phocoenidae (pronounced FO-SCENE-E-DAY) is made up of three seperate genera with each having a total that adds up to seven species between them. Phocoenidae is a family that includes only true porpoises. Porpoises are small cetaceans that are differentiated from other delphinoids by their stout bodies, short beaks and spade shaped teeth. In contrast to monodontids, phocoenids inhabit warmer coastal waters worldwide. Similar to the monodontids, phocoenids first appeared during the Miocene (11 mya) and were also much more diverse in species than they are now, having many extinct species listed as part of phocoenidae. Phocoenids are often preyed upon by pinnipeds and even other cetaceans which make easy meals out of the small animals. Phonoecids are also threatened by human encroachment on their habitat whuch has devistated the populations of some species and in particular the tiny Vaquita ***(Phocoena sinus)***.

#### Iniidae

Iniidae (pronounced IN-E-DAY is a family of freshwater dolphins that may include three separate species and many extinct species. Iniids are a complicated group as two of the three species are unrecognised by the Society for Marine-Mammalogy. One being the Araguaian river dolphin ***(Inia araguaiaensis)*** which is a freshwater dolphin species that lives in the Araguaian river basin in Brazil. These unrecognised dolphins were officially described first in 2014, with their proposition to be recognised as a seperate species being the difference in mitochondrial DNA from the amazon river dolphin ***(Inia geoffriensis)***. The other unrecognised species, the Bolivian river dolphin ***(Inia boliviensis)*** is larger than its Amazon counterpart however, it is possible the animal is just amazon river dolphins that live in the Amazon river area in Bolivia. All river dolphins are identified by their shortened dorsal fin, to avoid getting it entangled in foliage, as well as their elongated beaks used for catching freshwater fish and crustaceans. It is widely believed that iniids got to the inland rivers of South America because of floods that rose the sea level, causing a brackish environment of which the marine dolphins could inhabit. Once the water levels returned to normal, these dolphins were trapped and through evolution became adapted to freshwater environments.

#### Pontoporiidae

Pontoporiidae is a tiny family which only has one extant member. The La Plata dolphin ***(Pontoporia blainvillei)*** is a species of estuarine dolphin that after years of debating the family it fits into, has been placed separate from iniids in its own family. Pontoporiidae, together with iniidae makes up the greater iniioid super-family. Pontoporrids can be easily identified by their prominent beaks, small stature and unfused cervical bones which allow greater neck flexibility, a feature that all iniioids possess.

#### Platanistidae

Plantanistidae is another small family, being only comprised of one species and two subspecies being, the Ganges river dolphin ***(Platanista gangetica)*** and the Indus river dolphin ***(Platanista minor)***. Platanistids can be identified by their needle-like teeth that protrude from their mouthed even when closed, and their unique way of swimming on their sides. platanistids have extremely poor eyesight, as a result of living in naturally murky waters, this in turn makes them almost completely reliant on Echolocation in order to hunt.

#### Lipotodae

Lipotodae is small group that has only two members, of which one is extinct, whilst the other has not been seen for twenty years. The baiji ***(Lipotes vexillifer)*** or Yangtze river dolphin was a once plentiful dolphin that lived in the Yangtze river in China. Due to the industrialisation of the river, the baiji faced a mass population decline and would eventually be declared functionally extinct in 2006. With the baiji's extinction the entire family of lipotodae has been lost and no extant members remain, making the extinction of the Baiji at the time the first extinction of a megafaunal mammal in fifty years. Many Extinct cetaceans have been placed in lipotodae in the past, as researchers suspected they were closely related to Lipotids. Parapontaporia, for example is a genus of extinct cetaceans presently thought to be Lipotids. Lipotids have also before been placed with Inioids as well platanistids however, they are now considered a different family altogether.

### Mysticetes

Mysticetes or baleen whales is a group of neocetes that can be easily identified by their lack of teeth, as well as the large bristly plates in their mouths known as baleen. Baleen allows mysticetes to swallow mass amounts of food and discard the sea water caught along with it. Mysticetes are typically much bigger than odontocetes and only eat small fish and krill as opposed to larger prey. Mysticetes are slow moving cetaceans and the biggest animals to ever exist on our planet.

#### Balanopteridae

Balanopterids also commonly known as Rorquals (pronounced ROAR-KELS), comprise the largest family in mysticeti. Balanopteridae includes four species of whales including the enormous blue whale ***(balaenoptera musculus)***. Balanopteridae has a fluctuating number of species depending on the research you believe, one Rorqual Omura's whale ***(Balanoptera omurai)***, was only officially described in 2003 after it was thought to just a be miniature variant of the Bryde's whale ***(Balanoptera brydei)***. Rorquals can be identified by the noticable pleated ventral groves that help the cetaceans open their mouths as wide as possible. Rorquals are also typically slender cetaceans though some sizes and appearances vary between species. The grey whale ***(eschrichtius robustus)*** is a member of eschrichtiidae, and together with balanopteridae it makes up the balanopteroid super-family. However, new morphological data shows that the grey whale may also be a Rorqual despite lacking some characteristics.

#### Eschrichtiidae

Eschrichtiidae (pronounced ESH-RICK-TEE-A-DAY) is a small family that only has one extant member. The grey whale is the only member of eschrichtiidae and is being considered for being placed in the balanopteridae family despite grey whales lacking key characteristics of Rorquals. Grey whales have shorter baleen plates as well as lack any dorsal fins, instead having a series of humps on their backs comprising a dorsal ridge, on top of this do not have nearly as many pleated groves, at most possessing four. Balanopteridae and eschrichtidae would have split away from each other during the late Miocene epoch. grey whales do have genetic similarities to Rorquals and for this reason they may be placed in the balanopteridae family in the near future.

#### Balaenidae

Balaenidae is a family of mysticetes that includes four extant genera, with a collective total of four species. the genus balaena contains one species whilst the genus eubalaena contains three. Balaenidae was once thought to include only Right whales however, one species that was once known as the Greenland right whale, was discovered to be part of a different genus than other balaenids. For this reasoning the cetacean is now known as the bowhead whale ***(Balaena mysticetus) .*** Until recently, there was only thought to be one species of Right whale, until during the early 2000's it was discovered that there are actually three different species being; the North Atlantic right whale ***(Eubalaena glacialis)***, the North Pacific right whale ***(Eubalaena japonica)*** and the Southern right whale ***(Eubalaena australis)***. Right whales can be identified by their arched mouths, angular heads and stocky bodies. Balaenids possess highly arched mouths in order to house their huge baleen plates, perfectly adapt for catching copepods. Most striking of all right whales possess callosities that grow around the whale's face. Callosities are patches of roughened skin that exhibit a yellowish white colour due to the whale lice that inhabit them. These callosities are a great way to distinguish right whales from bowhead whales.

#### Cetotheriidae

Cetotheriids are a strange group of cetaceans that only has one extant member. The pygmy right whale ***(Caperea marginata)*** is the only remaining member of this group, but until recently cetotheriids were thought to completely extinct. This reasoning was because prior to 2012 pygmy right whales were thought to be part of neobalaenidae, which was thought to be one of the four mysticeti groups. During the 2012 study, Pygmy right whales were found to have been similar in many ways to cetotheriids, after the details in the skeletal remains of the animal had been noticed. Due to the cetacean being placed in cetotheriidae, the family had gained an extant member and is no longer considered an extinct family.

## Sources

* Society for Marine Mammalogy - https://marinemammalscience.org/
* Baleen Whale | Wikipedia - https://en.wikipedia.org/wiki/Baleen\_whale
* Toothed Whale | Wikipedia - https://en.wikipedia.org/wiki/Toothed\_whale
* Cetacea | Wikipedia - https://en.wikipedia.org/wiki/cetacea
* Oceanic Dolphin | Wikipedia - https://en.wikipedia.org/wiki/Oceanic\_dolphin
* Porpoise | Wikipedia - https://en.wikipedia.org/wiki/Porpoise
* monodontidae | Wikipedia - https://en.wikipedia.org/wiki/monodontidae
* La Plata Dolphin | Wikipedia - https://en.wikipedia.org/wiki/La\_Plata\_dolphin
* Lipotidae | Wikipedia - https://en.wikipedia.org/wiki/Lipotidae
* iniidae | Wikipedia - https://en.wikipedia.org/wiki/iniidae
* Beaked Whale | Wikipedia - https://en.wikipedia.org/wiki/Beaked\_whale
* platanistidae | Wikipedia - https://en.wikipedia.org/wiki/platanistidae
* platanistidae | Animal Diversity Web, University of Michigan Museum of Zoology - https://animaldiversity.org/accounts/platanistidae/
* physeteridae | Science Direct - https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/physeteridae
* kogiidae | Wikipedia - https://en.wikipedia.org/wiki/kogiidae
* Rorqual | Wikipedia - https://en.wikipedia.org/wiki/Rorqual
* eschrichtiidae | Wikipedia - https://en.wikipedia.org/wiki/eschrichtiidae
* Neobalaenidae | Wikipedia - https://en.wikipedia.org/wiki/Neobalaenidae
* balaenidae | Wikipedia - https://en.wikipedia.org/wiki/balaenidae
* Cetortheriidae | Wikipedia - https://en.wikipedia.org/wiki/Cetotheriidae