Ambulocetidae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of early

cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

ns from

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...

. The genus ''

Ambulocetus ''Ambulocetus'' (Latin ''ambulare'' "to walk" + ''cetus'' "whale") is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, ' ...

'', after which the family is named, is by far the most complete and well-known ambulocetid genus due to the excavation of an 80% complete specimen of ''Ambulocetus natans''. The other two genera in the family, ''

Gandakasia ''Gandakasia'' is an extinct genus of ambulocetid from Pakistan, that lived in the Eocene epoch. It probably caught its prey near rivers or streams. Just like ''Himalayacetus'', ''Gandakasia'' is only known from a single jaw fragment, making c ...

'' and ''

Himalayacetus ''Himalayacetus'' is an extinct genus of carnivorous aquatic mammal of the family Ambulocetidae. The holotype was found in Himachal Pradesh, India, (: paleocoordinates ) in what was the remnants of the ancient Tethys Ocean during the Early Eoc ...

'', are known only from teeth and mandibular fragments. Retaining large hindlimbs, it was once thought that they could walk on land—indeed, their name means "walking whales"—, but recent research suggests they may have been fully aquatic like modern cetaceans.

Description

The most basal of marine cetaceans, ambulocetids lived in shallow near-shore environments such as estuaries and bays, but were still dependent on

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

during some stage of their life. Some of the characteristics related to sound transmission found in the lower jaws of modern whales that were absent in pakicetids are present in ambulocetids. They probably swam by paddling their large feet, which is not a very efficient mode of locomotion, suggesting they ambushed rather than chased prey. Ambulocetids had a narrow head with eyes facing laterally. Another lineage of fully aquatic freshwater predators, the neochoristoderes such as ''

Champsosaurus ''Champsosaurus'' is an extinct genus of crocodile-like choristodere reptile, known from the Late Cretaceous and early Paleogene periods of North America and Europe (Campanian-Paleocene). The name ''Champsosaurus'' is thought to come from , () ...

'', also have forward-faced eyes, as opposed to the dorsally positioned eyes of crocodilians and other amphibious predators. John Acorn, Deep Alberta: Fossil Facts and Dinosaur Digs, University of Alberta, 07/02/2007 ''Ambulocetus'' and ''Gandakasia'' primarily ate terrestrial prey, while a combination of low-

oxygen isotope There are three known stable isotopes of oxygen (8O): , , and . Radioactive isotopes ranging from to have also been characterized, all short-lived. The longest-lived radioisotope is with a half-life of , while the shortest-lived isotope is ...

and high-

carbon isotope Carbon (6C) has 15 known isotopes, from to , of which and are stable. The longest-lived radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenically by t ...

values suggests that ''Himalayacetus'' consumed fresh water but ate marine prey, thus that it foraged in a marine environment but drank fresh water.

Phylogeny

Ambulocetid fossils have been found in

along the former coastline of Cimmeria. The sedimentary facies in which these fossils were found indicates that ambulocetids inhabited a shallow, swampy near-shore marine environment. They may have occupied a similar ecological niche to

river dolphin River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...

s. The family is believed to have diverged from the more terrestrial

Pakicetidae Pakicetidae ("Pakistani whales") is an extinct family of Archaeoceti (early whales) that lived during the Early Eocene in Pakistan. Description described the first pakicetid, ''Ichthyolestes'', but at the time they did not recognize it as a cet ...

. The families

Protocetidae Protocetidae, the protocetids, form a diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America. Description There were many genera, and some of these are very well known (e.g., ''Ro ...

and possibly

Remingtonocetidae Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg. Description Remingtonocetids have long and narrow skulls with the external nare openings located ...

, are believed to have arisen from a common ancestor with ambulocetids. Together with

Basilosauridae Basilosauridae is a family of extinct cetaceans. They lived during the middle to the early late Eocene and are known from all continents, including Antarctica. They were probably the first fully aquatic cetaceans.Buono M, Fordyce R.E., Marx F.G. ...

, the five families are classified under the suborder

Archaeoceti Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initia ...

Notes

References

* * * * * * * * {{Taxonbar, from=Q134967 Eocene first appearances Eocene extinctions Prehistoric mammal families

Description

Phylogeny

See also

Notes

References