55 MYA (MILLION YEARS AGO)
The evolution of the modern whale is traced back to the fossils of dogs that lived 55 million years ago, the anatomy of the animals inner ear matches that of the modern whale. The dogs, the Indohyus and the Pakicetus prowled the basins of rivers and lakes throughout the Himalayas. They were mainly terrestrial but dipped into waterways occasionaly to supplement their diets.
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50 MYA
Fossils have also been found of the Ambulocteus, it is believed to have lived a few million years later. These fossils had the same inner ear characteristics as the Indohyus and the Pakicetus however, after an additional few million years of adaption the fossils show that the Ambulocteus was bigger than the Pakicetus and possessed a more otter like body with webbed, padded feet and a crocodile snout. With these phyisical characteristics it is likely to have spent more time in the water, possibly to better handle the changing climate, avoid predators and source more food.
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POINT OF ADAPTION
The changes seen in the early whale fossils demonstrate adaption and selection. Across the milions of years mutated and varying traits like padded and webbed feet and the crocodile snout would have been passed on, as these characteristics would have enabled survival in the changing environment, enbling those who possessed the trait to be more successful over those without. |
45 mya
The next significant whale fossil showed the Rodhochtus, which had adapted further to an aquatic lifestyle, presumably because it provided greater protection from predators and better access to food. Such conditions that would enable the survival of the animals that could adapt to them.
By this time the Rodhochtus only crawled on to land to give birth and occasionally forage for food.
By this time the Rodhochtus only crawled on to land to give birth and occasionally forage for food.
POINT OF ADAPTION
Also by this time branches of the Rodhochtus that lived near salt water had developed kidneys that could filter out salt. And, most significantly, in all fossils found from this time the Rodhochtus’s back bone had been disconnected from its hip bone. This disconnection, most likely a genetic mutation, gave the Rodhochtus much greater swimming flexibility enabling it to move its tail up and down, in the same way modern whales swim today. Such tail flexibility is one of the key reasons the Rodhochtus continued to survive in aquatic environments. |
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KEY POINTS
1. By this time the overall size of the whale was increasing as the larger whales tended to survive against their competition as they were able to retain heat through greater body mass.
2. In comparison to the earlier Indohyus, the length of the whales legs were beginning to decrease as that trait was rejected, with stronger muscly legs for swimming taking their place.
1. By this time the overall size of the whale was increasing as the larger whales tended to survive against their competition as they were able to retain heat through greater body mass.
2. In comparison to the earlier Indohyus, the length of the whales legs were beginning to decrease as that trait was rejected, with stronger muscly legs for swimming taking their place.
40 mya
The next class of whales were the Protocetus, Maiacetus and Zygorhiza. Their fossils were mainly found in and around Asia, having lived in the late Eocene Epoch. Their strength for swimming had continued to increase as they adapted strong seal like bodies with powerful legs. Their capacity to live permanently underwater had also improved as their nostrils had begun to migrate up their foreheads making resurfacing for air faster. This trait was continually passed on as those who possessed it survived with greater ease.
Around 35 million years ago fully aquatic whales, which gave birth underwater, had developed. These whales spread throughout the sea, and as their biogeography expanded the variations among species increased, eventually to such a point that they were unable to inter breed.