Temporal range: Early Eocene
|A restoration of Pakicetus inachus|
Gingerich & Russell 1981
| †Pakicetus inachus|
Gingerich & Russell 1981
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 million years ago). Pakicetus existed for approximately 15.8 . Many paleontologists regard it as a close relative to the direct ancestors of modern day whales.
The first fossils were uncovered in Pakistan, hence their name. The strata of western Pakistan where the fossils 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 as a crocodile-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 mesonychids. 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).
More about Pakicetus
Pakicetus was an extinct carnivorous mammal, related to Ambulocetus. It was one of the oldest known precursors of modern China, which lived about 48 million years ago and adapted to finding food in the water that lived in what is now Pakistan.This primitive "whale" was still amphibious like a modern otter. The ear has already begun to adapt to hear under water, but still could not withstand much pressure. It had powerful jaws, posing it a predator, close-set eyes and a muscular tail.
Sharp teeth were adapted to grabbing slippery fish. It resembles a dog, but with their hooves on the fingers and with a long thin tail, and had a skeleton that is adapted to life on land and that is no worse than any ungulate. It probably had webbed fingers. The main feature is that its ankle bone is most similar to the bones of pigs, sheep and hippos. The cranial bone is very similar to the bones of whales. The earliest ancestors of all hoofed mammals were probably partly carnivorous or "scavengers". The ancestors of whales were separated from cloven-hoofed animals and went to an aquatic life has after themselves artiodactyls separated from common ancestors with mezonihidami.