Pakicetus
Encyclopedia
Pakicetus is a genus of extinct terrestrial
carnivorous mammal
of the family
Pakicetidae which was endemic to Pakistan
from the Eocene
(55.8 ± 0.2—40 ± 0.1 Ma).
Pakicetus existed for approximately . Many paleontologists regard it as a close relative to the direct ancestors of modern day whales.
, hence their name. The strata of western Pakistan
where the fossil
s were found was then the coastal region of the Tethys Sea. The first fossil found of the creature consisted of an incomplete skull with a skull cap
and a broken mandible
with some teeth. It was thought to be from a mesonychid
, but Gingerich and Russell recognized it as an early cetacean from characteristic features of the inner ear
, found only in cetaceans: the large auditory bulla is formed from the ectotympanic
bone only. This suggests that it is a transitional species between extinct land mammals and modern cetaceans. It was restorated on the cover of Science
as a semiaquatic, somewhat crocodile
like mammal, diving after fish.
s. In 2001, J. G. M. Thewissen and colleagues wrote that "Pakicetids were terrestrial mammals, no more amphibious than a tapir."
However, in 2009 Thewissen et al argued that "the orbits ... of these cetaceans were located close together on top of the skull, as is common in aquatic animals that live in water but look at emerged objects. Just like Indohyus
, limb bones of pakicetids are osteosclerotic, also suggestive of aquatic habitat" (since heavy bones provide ballast).
called Back to the Seas, where it was portrayed as a semi-aquatic crocodilelike mammal, like it was believed to be at the time. It was also portrayed as a descendant of the mesonychids and an ancestor of Ambulocetus
.
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
carnivorous mammal
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...
of the 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...
Pakicetidae which was endemic to 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...
from the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(55.8 ± 0.2—40 ± 0.1 Ma).
Pakicetus existed for approximately . Many paleontologists regard it as a close relative to the direct ancestors of modern day whales.
Taxonomy
Pakicetus was assigned to Protocetidae by Gingerich and Russell (1981), Carroll (1988) and Benton (1993). Then to Pakicetinae by Gingerich and Russell (1990) and McKenna and Bell (1997); and to Pakicetidae by Thewissen and Hussain (1998), Thewissen et al. (2001), Thewissen et al. (2001), Geisler and Sanders (2003), McLeod and Barnes (2008) and Uhen (2010).Fossil distribution
The first fossils were uncovered in PakistanPakistan
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 their name. The strata of western 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...
where the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s were found was then the coastal region of the Tethys Sea. The first fossil found of the creature consisted of an incomplete skull with a skull cap
Calvaria (skull)
The calvaria is the upper part of the cranium and surrounds the cranial cavity containing the brain.The calvaria is made up of the frontal, occipital and right and left parietals....
and a broken mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
with some teeth. It was thought to be from a mesonychid
Mesonychid
Mesonychia are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls and to cetaceans...
, but Gingerich and Russell recognized it as an early cetacean from characteristic features of the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
, found only in cetaceans: the large auditory bulla is formed from the ectotympanic
Ectotympanic
The ectomtympanic is a bone that suspends the eardrum in mammals. It is homologus with the angular....
bone only. This suggests that it is a transitional species between extinct land mammals and modern cetaceans. It was restorated on the cover of Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
as a semiaquatic, somewhat crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
like mammal, diving after fish.
Possible semi-aquatic nature
Somewhat more complete skeletal remains were discovered in 2001, prompting the view that Pakicetus was primarily a land animal about the size of a wolf, and very similar in form to the related mesonychidMesonychid
Mesonychia are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls and to cetaceans...
s. In 2001, J. G. M. Thewissen and colleagues wrote that "Pakicetids were terrestrial mammals, no more amphibious than a tapir."
However, in 2009 Thewissen et al argued that "the orbits ... of these cetaceans were located close together on top of the skull, as is common in aquatic animals that live in water but look at emerged objects. Just like Indohyus
Indohyus
Indohyus is a genus of extinct artiodactyl known from Eocene fossils in Asia, purported to be approximately 48 million years old. A December 2007 article in Nature by Thewissen et al. used an exceptionally complete skeleton of Indohyus from Kashmir to indicate that raoellids may be the "missing...
, limb bones of pakicetids are osteosclerotic, also suggestive of aquatic habitat" (since heavy bones provide ballast).
In popular culture
The creature was featured in an episode of PaleoworldPaleoworld
Paleoworld was a documentary television series that was produced for The Learning Channel, and has had a total of 50 episodes. Some consider it to be the largest and most comprehensive paleontology series ever made. The series began in late September 1994 and, after 4 seasons, ended in 1997...
called Back to the Seas, where it was portrayed as a semi-aquatic crocodilelike mammal, like it was believed to be at the time. It was also portrayed as a descendant of the mesonychids and an ancestor of Ambulocetus
Ambulocetus
Ambulocetus was an early cetacean that could walk as well as swim. It lived during early Eocene some 50-49 million years ago. It is a transitional fossil that shows how whales evolved from land-living mammals. The Ambulocetus fossils were found in Pakistan by anthropologist Johannes Thewissen...
.