Experts believe that the dolphin’s ancestor was a dog-like creature which roamed the earth many millions of years ago. And now the extraordinary discovery of a bottlenosed dolphin with an extra set of flippers has provided living proof of the theory.
At first glance it looks like any other of its kind. But closer inspection reveals a rogue set of rear fins.
Each the size of a human hand, the fins are thought to be the remains of a pair of hind legs, adding to evidence that dolphins once walked on all fours.
While dolphins with odd-shaped lumps jutting out near the tail have been caught before, this five-year-old bottlenose is thought to the first with a full second set of fins.
Scientists have so far been unable to tell whether the four-finned dolphin, caught in fishermen’s nets off Japan’s Wakayama province a week ago, uses its extra set of fins when swimming.
The creature, 9ft from nose to tail, is now in a tank at a whaling museum where it will undergo both X-ray and DNA testing.
Seiji Osumi, of the Institute of Cetacean Research in Tokyo, said: “I believe the fins may be remains from the time when the dolphin’s ancestors lived on land. This is an unprecedented discovery.”
Recent fossil finds support the belief that, 50million years ago, forerunners of the present deep-sea mammals had limbs and were quick on their feet.
The creatures, which belonged to a group called Pakicetids, looked like a cross between a wolf and a tapir and had large heads, long powerful tails, spindly legs and ankle bones well adapted for running.
They also had bones in their ears which are unique to cetaceans, the sea family to which whales and dolphins belong.
It is thought the dolphin’s land-loving ancestors first crawled into the sea to escape predators or seek food between 50million and 35million years ago.
Their hind legs became smaller and smaller before eventually disappearing altogether. The new aerodynamic shape reduced drag in the water, speeding their swimming.
Mark Simmonds, of the Whale and Dolphin Conservation Society, said: “They became more and more streamlined, lost their hair and developed a layer of fat for insulation.”
Evidence of the long-lost rear legs can still be seen in the dolphin foetus, which contains leg ‘buds’ which disappear before birth.
Now, it seems a freak mutation, perhaps caused by pollution of the oceans, has caused the long-lost trait to reassert itself in a modern-day dolphin.
Further evidence of the dolphin’s past as a land-dweller comes from its inability to breathe under water, and the bones of its fins, which are very similarly jointed those in the human hand. By FIONA MACRAE, Daily Mail, UK