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The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. [2] Cetaceans are fully aquatic mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya.
The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya.
In cetaceans, evolution in the water has caused changes to the head that have modified brain shape such that the brain folds around the insula and expands more laterally than in terrestrial mammals. As a result, the cetacean prefrontal cortex (compared to that in humans) rather than frontal is laterally positioned.
They greatly affected cetacean evolution , because they spread across Earth's oceans. [7] They had long snouts, large eyes, and a nasal opening located farther up the head than in earlier archaeocetes — suggesting they could breathe with the head held horizontally, similar to modern cetaceans — a first step towards a blowhole.
The traditional theory of cetacean evolution was that cetaceans were related to the mesonychian. These animals had unusual triangular teeth very similar to those of primitive cetaceans. This is why scientists long believed that cetaceans evolved from a form of mesonychian.
The limbs of more aquatic Eocene cetaceans did not preserve very well. Ambulocetus demonstrated that cetaceans swam by flexing the spine up and down (undulation) before they had evolved the tail fluke, forelimb propulsion evolved relatively late, and that cetaceans went through an otter-like phase with spinal undulation and hindlimb propulsion ...
Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other marine mammals, such as seals and sea cows, due to convergent evolution. However, they evolved from originally terrestrial mammals.
Once cetaceans evolved from their terrestrial ancestors, the reduction in their olfactory apparatus was primarily clade-specific. Toothed whales (Odontoceti) seem to have lost their olfactory sense completely, whereas baleen whales have shown partial impairment, expressing about 58% OR pseudogenes in their cluster. Some adult tooth whales ...