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Pakicetus: 55.8-40.4 mya
Pakicetus was a wolf like animal living in modern day Pakistan. It was driven into the waters after climate change left scarce food on land for Pakicetus. To survive, it took to the water. It was a very poor swimmer, but the water had an enormous amount of food for the animal. Larger predators took out Pakicetus, and it later disappeared from the fossil record. -
Period: to
Evolution of the Whale
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Ambulocetus: 50 to 48 mya
Ambulocetus arose after Pakicetus. It was better adpated for swimming in shallow waters, but it still wasn't the best swimmer. It's legs were still like that of land mammals (of which were widened and shortened), and it had the earbone of a whale inside its skull. It's tale had more muscle, and it was more streamlined. Ambulocetus was also able to drink freshwater, but still spent much time on land. Ambulocetus fell off the fossil record around 49 mya. -
Rodhocetus: 46 mya
After Ambulocetus came Rodhocetus, a much better animal adapted to the water than its predecessor. Rodhocetus had a shorter neck, widened legs, more muscles in the tail, and its kidneys were able to absorb salt, meaning it was the first of the whale's ancestors to live PERMANENTLY in the ocean. It had the "balance organ", which made Rodhocetus aware and able to keep its balance in the water. Although, much larger predators took out Rodhocetus, and it fell of the fossil record around 38-39 mya. -
Basilosaurus: 39 mya
Basilosaurus followed Rodhocetus. Its eyesight was improved for living in the water, as well as its hearing. It's body was very long (around 50-72 feet long), and its "legs" were merely 2 ft long, which didn't have a purpose to the creature. It could weigh up to 6, 300 kilos, and was a predominant hunter in the shallow waters. -
Dorudon: 39 mya
Dorudon was around as the same time as Basilosaurus. It was a smaller creature than Basilosaurus, and was a source of food for the large animal. It had very short forelimbs and a tale fluke. -
35 mya: Dorudon and Basilosaurus
A drop in sea levels was very bad news for Basilosaurus. The large animal wasn't built for deep waters it would have to live in. A drop in sea levels occurred due to permanent ice caps, making Basilosaurus's home of shallow costal waters dissapear. Dorudon could easily live in deep waters, as it was smaller and faster. And so Dorudon carried on the evolutionary chain for the modern day whale. -
Dorudon lives on: 30 mya
Dorudon is now carrying on the evolution of the whale. However, it was hunted by a 5m long monster shark known as Megaladon. This fierce animal had poor vision and was cold blooded, and so would die in colder waters, which is where the Dorudon migrated to. -
Modern Baleen Whales: 39-29 mya
Modern Baleen Whales are non-toothed whales. They cannot echolocate like the Modern Toothed Whales, but can produce sounds, referred to as "songs", to communicate with others. They have two blow holes, which causes them to have a v-shaped bow. Baleen whales appeared in the early Oligocene or late Eocene. -
Modern Toothed Whales
As in the name, Modern Toothed Whales have teeth rather than baleen plates to eat food. Toothed Whales have the ability to echolocate to find their food, unlike Baleen Whales. Many Toothed Whales can swim very rapidly. They have only one blowhole and has non-fused nostrils. They have rather large brains, but it has poor connection between the left and right hemispheres. Toothed Whales have a fatty organ (melon) on their heads, which helps focus their sound waves during echolocation.
