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Sperm whales off Mauritius coast

Discovery of four legged whale ancestors is an evolutionary missing link

A research published in the Current Biology, reveals the discovery of a new species of ancestral whale that walked the land and sea in Peru. We may consider them as smooth, two-limbed marine mammals that even struggled to survive the Thames, but the whales originated more than 50 million years ago from land-dwelling, hooved mammals called artiodactyls. The ancestors of the whales resembled a small deer. A fossilised “missing link” discovered in India claimed that the last whale precursors took to the water when danger dawned upon them but would come onto land for reproduction and feeding.

They would generally spend a considerable amount of time slopping in shallow water, quenching for aquatic vegetation and invertebrates.

The oldest whale fossils date back 53 million years ago and were found at numerous sites located in the northern Indian Himalayas. The fossils talk of the gradual transition from simple slopping to life long living in deeper water, while retaining the ability of locomotion on land.

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42 million years ago, the freshly discovered Peregocetus pacificus started an epic journey to the other side of the world. In the Middle Eocene era (roughly 48 to 38 million years ago) when Africa and South America were far apart these animals who were smaller than 3m swam their way across, not used to marine life back then.

The hind limbs were not as small as its forelimbs, and it had really tiny hooves, suggesting that it was still quite capable of hoisting itself out of the water and then trotting about on land, that is capable of getting out of water and walking on land. However, the skeleton suggested that it was well adapted to an aquatic life that was about to become dominant. It was carnivorous, as demonstrated by its scissors- like teeth. It ate large bony fish, just as the whales do now. However, P. Pacificus had teeth which resembled that of the modern carnivores.

By using microfossils, the sediment layers where the skeleton was claimed to be positioned were precisely dated and then the details of the skeleton allowed them to conclude that the animal was capable of carrying its body both on land and in the water. However, over the millennia, their pelvic bones unattached themselves from the spine to enable more efficient swimming while increasing the time in buoyant, the gravity-easing water reduced the evolutionary resources to strong, weight-bearing legs that they possessed. Forelimbs morphed into flippers, while hind limbs shrunk and disappeared.

About the author: Kalpit Veerwal
Kalpit Veerwal is a second year Computer Science undergraduate at IIT Bombay. He is well known for being the only person to score 360/360 in JEE (Main). He is registered in the Limca Book of Records for the same. A blogger in his free time, he has also secured top ranks in various exams held in India and the world.

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