Ambulocetidae is a

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

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 th ...

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'', 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 ...

'' and '' Himalayacetus'', 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 incl ...

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 , () s ...

'', also have forward-faced eyes, as opposed to the dorsally positioned eyes of crocodilians and other amphibious predators.

John Acorn John Acorn is a Canadian naturalist. He is a lecturer at the University of Alberta, a research associate at the Royal Tyrrell Museum of Paleontology, and a research associate at the E.H. Strickland Entomology Museum. He is also a local Edmonto ...

, 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 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 dolphins. The family is believed to have diverged from the more terrestrial Pakicetidae. The families Protocetidae and possibly Remingtonocetidae, are believed to have arisen from a common ancestor with ambulocetids. Together with Basilosauridae, the five families are classified under the

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

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 initial ...

Notes

References

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

Description

Phylogeny

See also

Notes

References