A whale that swam hundreds of miles up an African river after taking a wrong turn 17 million years ago is helping shed light on a key moment in human evolution. Palaeontologists discovered the fossilised remains of the ancient ancestor to modern beaked whales in the middle of one of the harshest desert areas of Turkana, Kenya. It has allowed scientists to pinpoint when the landscape in east Africa began to change as the land around the Great Rift Valley began to rise up. This 17 million-year-old fossil shown in the photograph above is from a whale found far inland in Kenya and has shed light on when east Africa's tectonic uplift that drastically altered the climate in the area first began . This was a crucial moment in human evolution from primates as it created the dry open habitats that led our ape-like ancestors to walk upright for the first time. They say that for the whale to have travelled so far inland in a river the area must have been much wetter, far flatter and dominated by forests. It is probably one of the most peculiar aspects of human biology - that females of a certain age lose the ability to reproduce. But scientists have discovered that killer whales - a species separated from humans by almost 94 million years of evolution - also suffer from the menopause. The finding could provide clues as to why the menopause evolved in the first place. The evolution of a trait that reduces the reproductive capability of a species has long baffled biologists and there are a number of theories for why it emerged in humans. Now a team of researchers from the University of Exeter and the University of York may have unraveled the reason for the menopause - in killer whales at least. They have found that it frees up the older, more experienced females to lead their families in the search for food and so boost the ability of the entire group to survive. The findings may now also help to explain why the menopause emerged in human populations - it allowed older women to impart their knowledge and help care for the younger members. Professor Louis Jacobs, a vertebrate palaeontologist at Southern Methodist University in Dallas who led the study, said: 'The whale was stranded up river at a time when east Africa was at sea level and was covered with forest and jungle. 'As that part of the continent rose up, that caused the climate to become drier and drier. So over millions of years, forest gave way to grasslands. 'Primates evolved to adapt to grasslands and dry country. And that's when - in human evolution - the primates started to walk upright.' The whale fossil was first discovered in Loperot, west Turkana, Kenya in 1964 by palaeontologist James Mead, a curator at the Smithsonian Instution at the time. It was initially mistakenly identified as a turtle fossil but later identified as a whale in 1975. He named it Turkana ziphiid - a type of beaked whale that is related to modern marine mammals like the Baird and Cuvier's beaked whales - and estimated it had been 22ft (6.7 metres) long. Ziphiids are among the deepest diving mammals on the planet, plunging to nearly 10,000 feet (3,050 metres) in the ocean to feed on squid. The whale fossil was discovered nearly 459 miles (740km) inland and 2,000 feet (620 metres) above sea level. For it to have ended up there, the landscape at the time  must have looked very different. Palaeontologists found the remains of fish, crocodiles, turtles and mammals including primates, suggesting the area was dominated by a river and surrounded by a forest habitat. The fossil of the whale's beak (above), was found in 1964, and is thought to belong to an extinct species that became stranded in an ancient river after taking a wrong turn while swimming down the coast of east Africa . The fossil was found in an area of desert at Loperot in west Turkana, in Kenya, on the site of an ancient river . However, the whale fossil disappeared in 1979 and was only rediscovered in 2011 at Harvard University after Professor Jacobs asked curators to search for it. Professor Jacobs and his colleagues, whose work is published in the Proceedings of the National Academy of Sciences, have now re-examined the specimen and claim the whale has provided a definitive date for when the geological changes in East Africa began. Determining ancient land elevation is notoriously difficult, but the whale has provided new clues. The area of Turkana in Kenya where the fossil was found (above) is now a desert, but was a forest 17 million years ago when the whale is thought to have taken a wrong turn and swam hundreds of miles up a river . Professor Jacobs said for the whale to end up where it did, it must have swam far inland up the ancient Anza River with a low gradient ranging from 78 feet (24m) to 121 feet (37m) over 372 miles (600km) to 559 miles (900km). This suggests the landscape was very flat and close to sea level. Professor Jacobs and his colleagues believe the whale may have been migrating along the east African coast and mistakenly entered the mouth of the river. Once it began swimming up the river it could not change its course. James Mead shown above excavating the whale fossil in the 'Open Pit Turtle Mine' in Loperot, Kenya, in 1964 . The fossil was originally recorded as a large turtle in expedition log books but later it was found to be a whale. Scientists also discovered fossils of many other species including crocodiles and primates at the same site . There are some modern examples of whales making similar mistakes such as the sperm whale that swam up the Thames towards London, and other whales what have become stranded in the Sacramento River in California and the Amazon in Brazil. Professor Jacobs said: 'You don't usually find whales so far inland. Many of the known beaked whale fossils are dredged by fishermen from the bottom of the sea.' Estimates for exactly when human ancestors began walking on two feet instead of four are varied and controversial. Some claim that a six-million-year-old species called Sahelanthropus was the first to become bipedal while others point to the four-million-year-old Australopithecus anamensis. However, the latest study has now provided clues as to when the landscape in the part of Africa where these ancestors are thought to have taken their first bipedal steps began to change. Dr Henry Wichura, the lead author of the study an a palaeontologist at the University of Postdam in Germany, said: 'Surface uplift from near sea level coincides with paleoclimatic change from a humid environment to highly variable and much drier conditions, which altered biotic communities and drove evolution in east Africa, including that of primates.' The whale fossil  belongs to an ancestor of modern beaked whales like the Blainville's beaked whale pictured .
Fossil of beaked whale was discovered in desert of west Turkana in Kenya . The marine mammal's remains were unearthed 459 miles from the ocean . It is thought to have swam up the ancient Anza river after taking wrong turn . At the time East Africa would have been flatter, wet and covered in forest . Scientists say this marks a key point before the landscape began to rise . This caused the climate to dry and the habitat to become less forested . Researchers say led the primates living there to evolve bipedal walking .