by Mary Caperton Morton Tuesday, June 16, 2015
About 17 million years ago, a 7-meter-long beaked whale took a wrong turn off Africa’s east coast and swam hundreds of kilometers up the Anza River before stranding. In 1964, the fossilized remains of the wayward whale were discovered at high elevation in West Turkana, Kenya, and then transported to the U.S., where they were subsequently lost in storage for more than 30 years before being rediscovered at Harvard in 2011. The whale’s incredible journey is now providing crucial clues about the timing of uplift in East Africa.
When the whale made its fateful journey, much of East Africa was near sea level and covered with dense forests — a very different place from the rugged, arid landscape that exists today. Around the same time, a mantle plume rose through the lithosphere under the region, creating the East African Rift system and causing extensive uplift, changes that many anthropologists suggest coincided with the evolution of the first hominins.
Pinpointing when this uplift began has proved difficult, however, as the evidence typically used to determine paleoelevations has mostly been erased by the rifting process itself, says Henry Wichura, a geologist at the University of Potsdam in Germany and lead author of a study detailing new insights offered by the Kenyan whale.
Extensive lava flows produced during rifting have covered or destroyed older land surfaces. “It’s the old surfaces that can tell us when the uplift process started, but those are hard to find,” he says. “So we need to get creative and find other approaches to determine paleoelevations for East Africa.” That’s where the whale came in.
“This whale has an amazing story to tell,” Wichura says. Identified as a specimen of Turkana ziphiid — whose modern relatives include bottlenose whales and Cuvier’s beaked whales — it was found 740 kilometers inland, preserved in river sediments at an elevation of 620 meters in the desert region on the northern periphery of the East African Plateau.
The Anza River is now extinct, but the team retraced its ancient course and determined that the whale swam inland between 600 and 900 kilometers, depending on paleo-sea level and the location of the mouth of the river.
For a whale to swim that far up a river, the waterway must have been large, with a relatively gentle slope, and no steep rapids or waterfalls, Wichura says. Based on modern cases of whale strandings far up rivers — such as in the Thames River in London and in the Columbia River in Washington state — the team estimated the gradient for the former Anza River at 4 centimeters of rise per kilometer.
Given the distance it swam and the river’s estimated gradient, Wichura and colleagues calculated a paleoelevation for the whale’s resting place at the time it died of between 24 and 37 meters. Because the fossil was found at a modern elevation of 620 meters, the find implies that the region must have been uplifted by at least 590 meters over the last 17 million years.
The only other clear evidence of uplift found in East Africa is from the 13.5-million-year-old Yatta lava flow located 500 kilometers south of the whale’s location, which revealed that the region had been uplifted at least 1,400 meters by then. “So the Turkana ziphiid helps to constrain the onset of uplift of the East African Plateau to between 17 million and 13.5 million years ago,” Wichura and colleagues wrote in Proceedings of the National Academy of Sciences.
The story told by the whale is “an important one,” says Pierre Sepulchre, a paleoclimatologist at the University of Versailles in France. “We have so little evidence left from this time period, and it’s such an important phase of East Africa’s evolution to understand,” particularly in terms of early human evolution.
After its rediscovery, the whale fossil was returned to Kenya, where it resides in the National Museum in Nairobi.
© 2008-2021. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the expressed written permission of the American Geosciences Institute is expressly prohibited. Click here for all copyright requests.