The East African Plateau is at least 1,000 meters (3,280 ft) above sea level, but millions of years ago, the area was underwater. Now, according to researchers examining a prehistoric whale fossil unearthed at these high elevations, the East African Plateau began to rise above sea level about 17 million years ago—around the same time highly variable climate and drier conditions began to drive primate (including human) evolution. These findings are published in Proceedings of the National Academy of Sciences this week.
In 1964, the fossilized skull of a deep-diving, open-ocean-living whale was discovered 740 kilometers (460 miles) inland from the Indian Ocean coastline and at an elevation of 620 meters (2,000 ft) in the Open Pit Turtle Mine of Williams’ Flat Loperot in West Turkana, Kenya. These days, the area is a pretty harsh desert; a photo of the excavation is pictured below to the right. The 17-million-year-old fossil belonged to the oldest beaked whale known (family Ziphiidae), and the only stranded whale found so far inland on the African continent. But it went missing years later from the National Museums of Kenya and resurfaced three decades later in 2011 at Harvard.
Now, an international team led by Henry Wichura from University of Potsdam examined the newly rediscovered whale using decades’ old field notes and phylogenetic analyses, as well as 3D and CT scans. The 7-meter-long (23 ft) beaked whale likely swam eastward from the Indian Ocean along an ancient drainage system called the Anza River, and it probably couldn’t change its course, so it kept heading inland for 600 to 900 kilometers (370-560 miles). It ultimately became stranded at an elevation slightly above sea level, likely around 24 to 37 meters (80-120 ft).
"The whale was stranded up river at a time when East Africa was at sea level and was covered with forest and jungle," study co-author Louis Jacobs of Southern Methodist University says in a news release. East Africa 17 million years ago had a low elevation, high rainfall and humidity, and was densely vegetated—until activity in Earth’s mantle pushed the area (together with the whale’s fossils) several hundred meters up. Previous work with mantle plumes indicated that the uplift of the East African Plateau had already happened by 13.5 million years ago, so now researchers have finally bookended the onset of uplift.
These tectonics resulted in increasingly arid and open habitats. "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,” Jacobs adds. “Primates evolved to adapt to grasslands and dry country. And that's when—in human evolution—the primates started to walk upright."
Wichura tells Live Science: "It's more or less the story about the bipedalism.”
Images: Southern Methodist University (top), James G. Mead (middle), H. Wichura et al., PNAS 2015 (bottom)
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