Artiocetus

Artiocetus Temporal range: early Lutetian
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Cetacea
Suborder:	Archaeoceti
Family:	Protocetidae
Subfamily:	Indocetinae
Genus:	Artiocetus P. D. Gingerich
Species
Artiocetus clavis P. D. Gingerich et al. 2001 (type species)

Artiocetus clavis is an extinct genus of early whales belonging to the family Protocedidae. Their name arises from a combination of Cetacean and Artiodactyl, as this fossil was the first to show that early whales possessed artiodactyl-like ankles.

Artiocetus belongs to the order Cetacea, which includes whales, dolphins and porpoises. Cetus is Latin, its literal meaning being "large sea mammal" and is used in biological names to mean "whale". It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster".

Artiodactyla refers to the mammal order of even-toed ungulates the group containing cattle, deer, camels, giraffes, antelope, goats, sheep, pigs and hippopotamuses. If the animal has more than two toes, the weight is borne equally by the third and fourth toe. The shape of the astragalus is another key feature which has a double-pulley structure in artiodactyls, giving the foot greater flexibility.

Description

Artiocetus clavis existed in the early Lutetian age (47 million years ago) and is one of the oldest known protocetid archaeocetes. Though the whale may have been primarily aquatic, the discovery of ankle bones lends to the idea that this fossil may have been a transition between sea-based and land-based mammals. While whales eventually returned to the sea, a cousin of the whales, the hippopotamus is thought to have descended from an ancestor shared with the whale.

Though it likely spent the majority of its time in the water, the well-developed fore and hind limbs suggest that this species may have been a wader - capable of movement in more shallow water and possibly able to propel itself on land as well.

Protocetidae were the first group of whales to develop tail flukes, which suggests they were quick, agile predators. Though Protocetidae as a family possessed tail flukes, it has been suggested that Artiocetus did not. Thewissen et al. states that "Artiocetus had a long tail and thus probably lacked a tail fluke".

Fossil finds

Fossils located in 2001 in the Balochistan Province of Pakistan showed that Artiocetus had both an astragalus and cuboid bone in the ankle (a diagnostic traits of artiodactyls), suggesting that early whales had fore and hind limbs. The distribution of fossils in Indo-Pakistan, Africa, Europe, and North America suggests that this species preferred a warmer sea climate, preferably in the tropics.

There is no commonly agreed ancestry of the whale, but they are thought to have evolved from an early group of carnivorous artiodactyla (even-toed ungulates).

DNA studies have suggested that the hippopotamus is the closest land relative to the whale. Artiocetus fossils represent intermediate forms between land-living ungulates and whales, lending support to the theory that whales and hippopotomi descended from a common ancestor.

The discovery of this fossil is important as it helped solidify the theory that whales shared a common ancestor with Artiodactyl. In 2005, an international team of scientists suggested that whales and hippopotami share a common water and terrestrial dwelling ancestor, which lived 50 to 60 million years ago. Two groups emerged from this common ancestor: early cetaceans, which in time returned to the sea permanently, and a large group of pig-like land-based mammals called anthracotheres. The only surviving descendant of anthracotheres is the hippopotamus.

References

• Rose, Kenneth D. (2006). The Beginning of the Age of Mammals
• Kemp, T.S. (Oxford Biology).The Origin and Evolution of Mammals
• Archaeocetes:Archaic Whales, Dolphins and Porpoises, by Candice "Orca" Mottet
• Dolphins: The Oracles of the Sea
• Thewissen, JGM (1997). "Even toed fingerprints on whale ancestry", faculty.virginia.edu

External links

• WikiAnswers: questions and answers about whales
• Whale Evolution
• Research on the Origin and Early Evolution of Whales (Cetacea)
• Origin of Whales from Early Artiodactyls: Hands and Feet of Eocene Protocetidae from Pakistan
• Distinctive characteristics of artiodactyl ankle bones