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Who were the ancestors of whales and dolphins?

60 million years ago the Earth was inhabited by unusual animals - mezonigie. They were ungulates, but not herbivores, and predators. Outwardly, they were like wolves or dogs with large elongated heads and large fangs.


Their teeth unusual conical shape were similar to the teeth of cetaceans. So quite a long time it was believed that mezonigie were the ancestors of cetaceans. It was assumed that mezonigie who lived by the sea, eating fish and other sea animals, and that over time they became more and more time to spend in the water. Gradually the shape of their bodies began to change, becoming more streamlined, they have powerful tails; the forelimbs were transformed into the fins, and the rear was gone.

However, when scientists appeared molecular-genetic methods of research, it turned out that the closest relatives of cetaceans on land - hippos!

The oldest known ancestor of the whale - pakicetus. Pakicetus lived about 48 million years ago on the territory of modern Pakistan. They were like dogs, but they were thin legs with tiny hooves on the fingers. They lived near the water, and way of life were amphibians, as modern seals.


The structure of the skeleton Pakicetus shows that whales are not direct descendants of mesonychid. First came the Department of cloven-hoofed animals from ancestors common to mesonychids, and after that the ancestors of whales were separated from artiodactyls and moved to an aquatic mode of life. This means that the ancestors of whales were early forms of cloven-hoofed animals, which has kept some signs of mesonychid (for example, the conical shape of the teeth), lost modern artiodactyls.

Later ancestors of whales:

Reconstruction of the form of ambulocetus Skeleton Ambulocetus natans

Ambulocetus appearance was something between a Dolphin and crocodile. Length ambulocetus - 3 meters, weight - 300 kg Hind legs of the animal are adapted for swimming than for walking on land. Believe that ambulocetus hunted like modern crocodiles: lay in wait in ambush fish and came to the watering hole.



Rodhocetus balochistanensis

Rodhocetus better adapted to water than ambulocetus. His hindquarters are ready to become a powerful fin.
Rodhocetus were found in shallow seas, and way of life were similar to seals. Between the fingers rodhocetus were probably membrane, and on the ends of the fingers were still a hoof!
Perhaps rodhocetus could only crawl out on land, as a modern seals or sea lions, but roamed the earth as awkward as they are.
The nose of rodhocetus have been moved forward, the first step to the nostrils of modern cetaceans, in which the nostrils are located on top of the snout.


Basilosaurus (zeuglodon)



Basilosaurus at first took for a dinosaur - hence the "reptilian" name. Basilosaurus lived in the Eocene, 45-36 million years ago.
Seguradora were already fully aquatic animals. They never were on land. They still had the hind limbs, but their length does not exceed half a meter. These legs could not help during the voyage. It may have been rudimentary limbs.
Seguradora were predators. They hunted almost all of the dwellers of the world, even in smaller sized whales, for example, gordonov (see below). Natural enemies they had.




Dorudon lived in the same times as basilosaurus in the Eocene, from 40 to 36 million years ago. They were approximately 5 m long and, apparently, were predators fed on small fish and mollusks. Dorudon lived in warm seas around the world: their fossilized remains found in North America and in Egypt. Shoulder gordonov was still moving, and the forearm and hand formed fins. It dorudon happened the final formation of the tail, characteristic of the whales.
It is believed that the mode of transportation they resembled dolphins, but didn't have such a complex system of social relations and were primarily solitary animals.
Body gordonov had a shape similar to the body of the Dolphin. But they, like basilosaurus, was not in the brain, adipose cushions - special authority, which gives the modern toothed whales ability to generate ultrasound and use echolocation.
Sonar, apparently first appeared in toothed whales species of Squalodon, who lived about 33-14 million years ago.



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2013-12-20 19:44:43
Very good report!
2013-04-06 18:54:20
I also love dinosaurs
2011-12-19 08:53:37
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