Uplift associated with the East Africa’s Great Rift Valley has puzzled scientists for many years because the timing and starting elevation have been poorly constrained. Now a team of paleontologists from Southern Methodist University in Dallas, TX, the University of Potsdam in Germany, and the National Museums of Kenya, has tapped a fossil from the world’s most precisely dated beaked whale to pinpoint for the first time a date when East Africa’s mysterious elevation began.
The 17 million-year-old beaked whale fossil. Image credit: Southern Methodist University.
The fossil of the beaked whale (family Ziphiidae), dating from 17 million years ago, was found about 740 km inland at an elevation of 620 m at Loperot in West Turkana, Kenya.
At the time the whale was alive, it would have been swimming far inland up a river with a low gradient ranging from 24 to 37 m over more than 600-900 km.
“The whale was stranded up river at a time when east Africa was at sea level and was covered with forest and jungle,” said Prof Louis Jacobs of Southern Methodist University, a co-author of the paper published in the Proceedings of the National Academy of Sciences.
“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 Turkana whale would have lived in the open ocean, like its modern beaked cousins. In contrast to most whale fossils, which have been discovered in marine rocks, it was found in river deposits, known as fluvial sediments.
The ancient large Anza River flowed in a southeastward direction to the Indian Ocean. The whale, probably disoriented, swam into the river and could not change its course, continuing well inland.
“The specimen is approximately 17 million years old and represents the oldest derived beaked whale known, consistent with molecular estimates of the emergence of modern straptoothed whales (Mesoplodon),” the scientists wrote in the PNAS paper.
“The whale traveled from the Indian Ocean inland along an eastward-directed drainage system controlled by the Cretaceous Anza Graben and was stranded slightly above sea level.”
“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.”
“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,” Prof Jacobs said.
“Determining ancient land elevation is very difficult, but the whale provides one near sea level.”
Source: sci.news
