Ambulocetus natans

Ambulocetus natans, Photo: Michael Lahanas

Cladus: Eukaryota
Supergroup: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Placentalia
Superordo: Cetartiodactyla
Ordo: Cetacea
Subordo: †Archaeoceti
Familiae: Ambulocetidae
Genus: Ambulocetus
Species: Ambulocetus natans

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Ambulocetus (or the "'walking whale'") 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. Having the appearance of a 3 meter long mammalian crocodile, it was clearly amphibious, as its back legs are better adapted for swimming than for walking on land, and it probably swam by undulating its back vertically, as otters and whales do. It has been speculated that Ambulocetids hunted like crocodiles, lurking in the shallows to snatch unsuspecting prey. Chemical analysis of its teeth shows that it was able to move between salt and fresh water.

Ambulocetus did not have external ears. To detect prey on land, they may have lowered their heads to the ground and felt for vibrations.

Scientists consider Ambulocetus to be an early whale because it shares underwater adaptations with them: it had an adaptation in the nose that enabled it to swallow underwater, and its periotic bones had a structure like those of whales, enabling it to hear well underwater. In addition, its teeth are similar to those of cetaceans.

The Ambulocetus fossils were found in Pakistan by anthropologist Johannes Thewissen. When the animal was alive, eastern Pakistan formed the coastal region of the ancient Tethys Sea.
In Popular Culture

Ambulocetus can be seen in Walking with Beasts. During chapter 1 it is said to have swum upstream from the coast, explaining why it is seen in Germany, rather than its native Pakistan.

In the novel "Ice Hunt" by James Rollins, live Ambulocetus (called "grendels") are found inside an artic iceberg.
It makes an appearance in the two shows called National Geographic Evolutions: The Walking Whale and Prehistoric Park.
References

* J. G. M. Thewissen, S. I. Madar, and S. T. Hussain (1996). "Ambulocetus natans, an Eocene cetacean (Mammalia) from Pakistan". Courier Forschungsinstitut Senckenberg 191: 1–86.

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