Some 17 million years ago, a beaked whale took a wrong turn up an African river, something which ultimately turned out to be its demise. But now, geologists studying the whale’s fossils believe the whale’s unfortunate end might shed a new light on early human evolution, putting a timestamp on when the environment started to change in East Africa, enabling humans to evolve.
The Cradle of Humanity
17 million years ago, we’re in the Neogene, in a period called the Burdigalian; back then, Africa looked entirely different, with the East African Plateau being substantially lower and covered by rich, dense forests. Because it was so low lying and close to the ocean, there was enough water to go around and the forest was properly nourished. But as the plateau started to rise, the land started to dry up, and East Africa slowly turned into the savannah we see today.
Geologists have wondered for quite a while when that uplift actually happened, especially because those areas of eastern Africa are the cradle of humanity – where our species developed and slowly started to walk on two feet. It was this uplift that caused the climate to change, that in turn caused the vegetation and environment to shift, ultimately allowing us to develop as a species. This whale fossil is actually very important, because it tells a part of the story.
“The whale is telling us all kinds of things,” said study co-author Louis Jacobs, a paleontologist at Southern Methodist University in Dallas. “It tells us the starting point for all that uplift that changed the climate that led to humans. It’s amazing.”
“It’s more or less the story about the bipedalism,” said study researcher Henry Wichura, a postdoctoral candidate in geoscience at University of Potsdam in Germany.
The fossil was actually found 50 years ago, in 1964, but a study on it wasn’t published until 1975. Then, they misplaced the skull until 2011. Jacobs read the 1975 paper and had been looking for this skull since the 1980s, when he was head of paleontology at the National Museums of Kenya. Every time Jacobs visited Harvard, Washington or Nairobi, he would try to find it and study it, but every time he came back empty handed.
“It was protected by a plaster jacket, so you couldn’t really see it,” he said. “I suspect nobody knew what it was. It was just kept in the collections there.”
Ultimately, in 2011, he managed to locate it and remove the plaster coating. He then contacted Wichura, who is a structural geologist studying the uplift of the East African plateau and found that rivers and lava had flowed east from high points on the plateau at least 13 million years ago.
“What was missing was geological evidence of the onset” of uplift, Wichura said. “That doesn’t exist in this area, not in the normal geological sense.”
The fact that no indicative fossils were found can mostly be owed to the volatile environment that is East Africa – a hot spot in the mantle has been pushing magma upwards, thinning and spreading up a wide area, while rifts from tectonic forces have been breaking the crust apart. This doesn’t bode well for fossils, whose formations requires a relatively quiet and peaceful setting. This is where our whale steps in.
The fossil is the oldest known fossil of a beaked whale, and it surprised researchers at first. Beaked whales are divers that live in the oceans, but the fossil was found 460 miles (740 kilometers) inland from the present-day East African coast, and, to top it off, at an elevation of 2,100 feet (640 meters). How did the whale get all the way there? The most likely response seems to be that while it did live in the Indian Ocean, it ventured up a river in Africa.
“We came to the idea that it used a large river system, because the whale had been found in lake sediments which are [mixed with] river sediments,” Wichura said. “So we can say that it died in a kind of river-lake environment.”
But the fact that the whale traveled so much, not only in distance but also in elevation seems shocking. There is no recorded case of a whale swimming across such an elevation. Even the Antarctic minke, known for its very long travels of up to 600 miles (900 km) , only reached an elevation of little more than 3 feet above the Atlantic Ocean. A humpback whale, dubbed Humphrey, twice swam a more modest 82 miles (130 km) up the Sacramento River in California. Freshwater dolphins have been found at elevations of more than 300 feet (90 meters) in Peru. So it seems safe to say that this whale also couldn’t have swam so much uphill – so the uplift started after this whale’s adventure. This was the evidence Wichura and Jacobs were looking for.
It was time for a little math: today, the plateau is about 2,034 feet (620 m) tall. Considering the grade of the steepest river from case reports, the river couldn’t have rose by more than 2.5 inches a mile (4 centimeters per km) from the coast – this means that the East African plateau was between 79 feet and 121 feet high (24 m and 37 m) when the whale was there, so over the past 17 million years, the uplift amounted to about 1,925 feet (590 m). Everything seems to have started with the whale. Scientists know for sure the fossil was about 17 million years ago, because they found it in an undisturbed area just under a lava flow dated to 17 million years old. Around it were mammal fossils that date to a period when Africa and Eurasia were joined.
Without the whale, and without the collaborative study which involved structural geology, paleontology, biology and geography, scientists wouldn’t have been able to date the uplift.
“We knew it had to be after the big exchange between Eurasia and Africa, when elephants left Africa, and when carnivores and various kinds of hoofed animals came in,” 23 million years ago, Jacobs said.
The study reminds both professional and amateur paleontologists to study the location and age of each fossil they find, said Frank Brown, a professor of geology at the University of Utah, who was not involved in the study.
“Even single specimens of organisms tell us a great deal about the history of the Earth, and they sometimes appear in surprising cases,” Brown said. “This is one such case.”
Journal Reference: Henry Wichura, Louis L. Jacobs, Andrew Lin, Michael J. Polcyn, Fredrick K. Manthi, Dale A. Winkler, Manfred R. Strecker, and Matthew Clemens. A 17-My-old whale constrains onset of uplift and climate change in east Africa. doi: 10.1073/pnas.1421502112
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