Pakicetid
Encyclopedia
Pakicetids or Pakicetidae (meaning Pakistani whales) are a carnivorous mammal
family
of the suborder Archaeoceti
which lived during the Early Eocene to Middle Eocene (55.8 mya—40.4 mya) in Pakistan
and existed for approximately .
As Cetacea
, Pakicetidae precede the whales and dolphins in transition from land. Because their fossils were found near bodies of water, they are presumed to have spent part of their life in water.
Pakicetus
was the first discovered in 1983 by Philip Gingerich, Neil Wells, Donald Russell, and S. M. Ibrahim Shah, and all species
are known only from a few sites in Pakistan
, hence the name of the first genera and the family as a whole. The region is believed to have been coastal to the Tethys Sea when the pakicetids lived, some 53 million years ago.
The pakicetids are presumed to be ancestors of modern whales because of the three following features unique to whales: peculiarities in the positioning of the ear bones within the skull, the folding in a bone of the middle ear, and the arrangement of cusp
s on the molar teeth. The current theory is that modern whales evolved
from archaic whales such as basilosaurids
, which in turn evolved from something like the amphibious ambulocetids
, which themselves evolved from something like the land-dwelling pakicetids. Since pakicetids are the distant relatives of whales, they have similar features to the Mesonychid
.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of the suborder Archaeoceti
Archaeoceti
Archaeocetes, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to the modern cetaceans.The archaeocetes were once thought to have evolved from the mesonychids, based on dental characteristics...
which lived during the Early Eocene to Middle Eocene (55.8 mya—40.4 mya) in Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
and existed for approximately .
As Cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
, Pakicetidae precede the whales and dolphins in transition from land. Because their fossils were found near bodies of water, they are presumed to have spent part of their life in water.
Pakicetus
Pakicetus
Pakicetus is a genus of extinct terrestrial carnivorous mammal of the family Pakicetidae which was endemic to Pakistan from the Eocene .Pakicetus existed for approximately...
was the first discovered in 1983 by Philip Gingerich, Neil Wells, Donald Russell, and S. M. Ibrahim Shah, and all species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
are known only from a few sites in Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, hence the name of the first genera and the family as a whole. The region is believed to have been coastal to the Tethys Sea when the pakicetids lived, some 53 million years ago.
The pakicetids are presumed to be ancestors of modern whales because of the three following features unique to whales: peculiarities in the positioning of the ear bones within the skull, the folding in a bone of the middle ear, and the arrangement of cusp
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
s on the molar teeth. The current theory is that modern whales evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
from archaic whales such as basilosaurids
Basilosauridae
Basilosauridae is family of extinct cetaceans that lived in tropical seas during the late Eocene.-Taxonomy:*Family Basilosauridae** Subfamily Basilosaurinae*** Genus Basilosaurus*** Genus Basiloterus** Subfamily Dorudontinae...
, which in turn evolved from something like the amphibious ambulocetids
Ambulocetidae
Ambulocetidae is a family of early cetaceans from Pakistan that still were able to walk on land. The genus Ambulocetus, after which the family is named, is by far the most complete and well-known ambulocetid genus due to the discovery by Thewissen et al. of a partially complete specimen of...
, which themselves evolved from something like the land-dwelling pakicetids. Since pakicetids are the distant relatives of whales, they have similar features to the Mesonychid
Mesonychid
Mesonychia are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls and to cetaceans...
.