Early whales’ front arms gradually evolved into fins over millions of years Stocktrek Images, Inc. / Alamy Stock Photo

Some early whales may have swum using their arms as well as their legs, a bit like a dog paddling in water. Despite this primitive swimming style, they seem to have managed to spread long distances across the ocean, from India to the western tip of Africa at a minimum.

“Even if they are not very good swimmers, they could cross at least one ocean,” says Quentin Vautrin at the University of Montpellier in France.

Whales are descended from hoofed land animals similar to modern deer, so the first proto-whales to venture into the water presumably used all four limbs for propulsion, as four-legged animals do today. More modern whales swim by undulating their entire bodies and only use their front limbs – their flippers – for steering. This crucial evolutionary transition took place between 50 and 35 million years ago.


We do not fully understand what happened to early whales’ arms during this time because we don’t have many fossils. “We only know the forelimbs for a few species,” says Vautrin.

His team has now found a new one. Vautrin and his colleagues unearthed a partial skeleton of an early whale called a protocetid in Senegal. The fossil includes two vertebrae, two ribs, fragments of the feet and tail – and most of an arm.

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Dated at between 43 and 41 million years old, it sits in the middle of whales’ transition to marine life. “We are far from the earliest whale, but we are a few million years before the real whales,” says Vautrin.

Even at this relatively late stage in the evolution of early whales, it seems the animal was using its arms to propel itself. The bones show the protocetid’s arm had powerful muscles and the ability to bend at the elbow.

This suggests the animal used it arms — and presumably legs too — to swim, in a way that could have resembled a modern dog. In truth, it is not clear exactly what ‘stroke’ the animal used. The shoulder bones have not been found, so we can’t tell whether the arm could move sideways or just forwards and backwards. “We don’t know if it’s just crawl or more like butterfly,” says Vautrin.

These forms of swimming are not as efficient as that used by modern whales, but it does not seem to have stopped the protocetids travelling great distances. The first whale-like animals are only known from the vicinity of India, but the new fossil shows that the protocetids reached the west coast of Africa.

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Early whales probably tried many different ways of swimming, says Vautrin. He suggests that the first group to evolve the modern undulating mechanism may have out-competed the others.

Journal reference: Palaeontology, DOI: 10.1111/pala.12442