Having spent at least 20 million years acquiring the machinery to survive on dry land and hundreds of millions more diversifying and exploiting every conceivable niche, a number of landlubbers made their way back to the sea.
Among these were pond snails, water spiders, water beetles, crocodiles, otters, sea snakes, water shrews, Galapagos flightless cormorants, marine iguanas, penguins and turtles. Of course the most impressive example of all are the whales and their little cousins the dolphins. These have gone all the way back to an aquatic existence as have dugongs and their close cousins the manatees jointly known as the sirenians, they don’t even come ashore to breed. They do however still breath air, having never developed anything resembling the gills of their ancestors. Seals and sea lions on the other hand have only gone part-way back and are a living example of what intermediate species must have been like.
In recent years the evidence from genetics and from the fossil record provides us with a rich record of the history of aquatic mammals.
Their genome shows that the closest living relative of whales are hippos. Molecular evidence shows that hippos are more closely related to whales than they are to cloven-hoofed animals like pigs and the ruminants. If anybody has seen hippos in deep water you cannot have failed to be impressed with how graceful these giants are. But as they have stayed at least partly on land, they still resemble their more distant cousins the ruminants, while their close cousins the whales took to the water and changed so drastically that their close affinity was only discovered by the molecular geneticists.
In recent years the evidence from genetics and from the fossil record provides us with a rich record of the history of aquatic mammals.
Their genome shows that the closest living relative of whales are hippos. Molecular evidence shows that hippos are more closely related to whales than they are to cloven-hoofed animals like pigs and the ruminants. If anybody has seen hippos in deep water you cannot have failed to be impressed with how graceful these giants are. But as they have stayed at least partly on land, they still resemble their more distant cousins the ruminants, while their close cousins the whales took to the water and changed so drastically that their close affinity was only discovered by the molecular geneticists.
While geneticists were busy in the lab the paleontologists were getting their hands dirty in the field. In Pakistan a rich seam of fossils has been discovered that sheds light on the evolution of the whale. A whole series of specimens beautifully demonstrates the gradual disappearance of the hind legs, the transformation of the front legs from walking limbs to swimming fins and the movement of the nostrils back to the top of the skull to become the blowhole.
It is one of the very best examples of a series of transitional fossils.
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The following image shows the vestigial pelvis and leg bones that still exist in four species of modern whales.
| Part 1 - Protein Functional Redundancy - - - - - - - | Part 2 - DNA Functional Redundancy |
| Part 3 - ERVs | Part 4 - Smelly Genes |
| Part 5 - Vitamin C | Part 6 - Human Chromosome 2 |
| Part 7 - Human Egg Yolk Gene | Part 8 - Jumping Genes |
| Part 9 - Less Chewing More Thinking | Part 10 - Non-Coding DNA |
| Part 11 - Tiktaalik | Part 12 - Lenski's E.coli Experiment |
| Part 13 - Morris Minor Bonnets | Part 14 - Joey Goes to Oz |
| Part 15 - Robinson Crusoe |