Rocks tell tales. They are nature's chronicles, encasing in stone the narratives of the millennia. That's how Ashok Sahni, a geologist, found a missing chapter to a whale of a tale.Three years ago he discovered an inch long bit of tooth embedded in a rock at the foot of the Himalayas. The tooth, as new tests show, is about 50 million years old - and it came from a whale that walked.The tooth Sahni found on the banks of a mountain stream in Subathu in Himachal Pradesh is one of the pieces of a complex evolutionary jigsaw. Put together, the jigsaw should explain how fierce meat eaters roaming a prehistoric land could become today's gentle giants, spending their lives swallowing tonnes of plankton under the seas. "This is exciting," says Philip Gingerich, a palaeontologist at the University of Michigan, who first described Pakicetus, believed to be the first walking whale, from fossils in Pakistan. The Subathu tooth might predate Pakicetus, notes Gingerich, who, like Sahni, says more data will establish "whether the first whale walked into the sea from India or Pakistan". These findings could push back the beginnings of whale evolution.The nearly complete skeleton of the walking whale ambulocetusIt's generally agreed that whales originated from a group of prehistoric meat-eaters called Mesonychians, ancient ancestors of both modern carnivores like the lion and grass-eaters like the horse. "But the modern whale did not emerge in a flash," says Sahni, chairman of the Centre of Advanced Studies in Geology of the Panjab University. Actually it took some 13 million years, six times the length of man's entire stay on earth. The chain of evolution that led to this drastic transformation from a dog like ancestor, the size of a bear, to a crocodile like creature to the first sea-going whale - had many missing links. Only now is the story coming together.Many bits of bones are emerging at the foot of the Himalayas. In the hills and river banks across India and Pakistan, scientists are finding more evidence of the missing links in the whale's evolution. In a new study released in the noted German journal CFS, a team of American and Pakistani geologists led by J.G.M. Thewissen described the discovery in the Kuldana hills of Pakistan of an unusually complete fossil of a walking whale called Ambulocetus natan. The half tooth found in SubathuIt looked like a giant seal or otter, but lived the life of a crocodile, hunting in shallow coastal seas and on land. Another missing link emerging through various fossil finds is Himalayacetus, a dog like whale, from Himachal Pradesh. Two decades ago Sahni and geologist V.P Mishra had described Indocetus, a developed whale that swam in the seas near Kutch, Gujarat.Sahni had then predicted that the lower Himalayas would throw up fossils of previous evolutionary changes, which explained how the walking whale began to swim. He was right. Some of the richest fossil finds are turning up at Subathu, near an Indian Army firing range. If there be a palaeontology heaven, it could be this. "Oysters, fish and crocodiles have been fossilised in almost every rock here," says palaeontologist Raminder Singh of the Panjab University. This was once the edge of a sea called Tethysa yawning chasm that separated India before it crashed into the underbelly of Asia, throwing up the Himalayas. There's no better place to unlock the secrets of India's incredibly distant past, a time when human beings were nowhere on the scene.Evolution on a large scale unfolds as the famed naturalist Edward Wilson put it like much of human history, as a succession of dynasties. It all began with the Mesonychians hunting like today's wolves and hyenas, on the beaches of Tethys. Some were as small as the weasel; others were the size of bears. They survived whatever killed the dinosaurs from the plains of central India 65 million years ago. As competition with other carnivores began, evolution began to change them, giving them organs to match sharks in diving, swimming and hunting at sea. That's a big evolutionary jump. And the remains of a progression of creatures that lived in Subathu and other areas of lower Himalayas, will hopefully explain how that happened. The dog like Himalayacetus, whose bones are emerging now, could provide that link.What's clear is that the whale's ancestors gradually become crocodile like, adapting to life on sea and land. This has been confirmed by the team of Pakistani and American geologists. In the same study, they describe an unusually complete 49 million-year-old fossil of Ambulocetus natans, "the walking whale that swam". These fossils, found in Baluchistan, share remarkable similarities with bones found in Himachal Pradesh.The primitive whales were clumsy walkers. They lurched forward on land, chest and abdomen bumping the ground, just fast enough to ambush prey in shallow waters, like crocodiles. While resting on land, they had a pad of fat in the ear, which helped them pick up sounds travelling through the earth. In the sea, the fat pad evolved to let them hear in water as well. It could gradually withstand more and more water pressure, which would have busted the ears of predecessors like Pakicetus.Over another couple of million years, the limbs became shorter and robust tails evolved. Their body weight became too heavy to move on land; they were on the cusp of a complete move into the sea. The whales adapted to increased salt loads and dispersed quickly into the oceans. Just in time too. Tethys narrowed and finally disappeared as India slammed into Asia. The Himalayas rose skyward, finishing life for millions of sea dwellers.Click here to EnlargeThe early whales were no gentle giants. The legacy of their violent quest for food continued for another era. They were fierce marine carnivores and ceaseless hunting made them bulkier and longer. Eventually, Gingerich says, they probably became the direct ancestors of modern whales. On land, the carnivorous Mesonychians survived and struggled for existence as their now distant cousins ruled the seas. But about 37 million years ago, 10 million years after whales became fully aquatic, the creatures that began it all finally became extinct.Meanwhile, the search for the story of evolution continues in the foothills of the Himalayas. There is still much about the long march of the whales that Sahni, Gingerich and others like them aren't as yet clear about. The rocks of Subathu, they hope, will reveal more of their secrets.Published By: AtMigration Published On: Aug 25, 1997 00:00 IST--- ENDS ---
