NEW DISCOVERIES
The team combined many different lines of evidence — from geology , fossil soils , isotopes , and phytoliths ( plant silica microfossils )— to reach their conclusions .
“ The history of grassland ecosystems in Africa prior to 10 million years had remained a mystery , in part because there were so few plant fossils , so it was exciting when it became clear that we had phytolith assemblages to add to the other lines of evidence ,” said coauthor
Caroline Strömberg at the University of Washington .
Figure 2 . Today , the Songhor fossil site in western Kenya is covered by a mixture of grass and trees adjacent to a modern river . Evidence from this site indicates that it was likely a relatively closed tropical seasonal forest environment between 19 and 20 million years ago . ( Image credit : John Kingston )
“ What we found was thrilling , and very different from what was the accepted
story . We used to think tropical , C4- dominated grasslands only appeared in the last 8 million years or so , depending on the continent . Instead , both phytolith data and isotopic data showed that
C4-dominated grassy environments appeared over 10 million years earlier , in the early Miocene in eastern Africa .”
This much earlier occurrence of C4 grasses and open habitats found at the same sites as early apes also allowed the researchers to assess the kinds of environments in which the early apes were living . One of the most advanced early apes , Morotopithecus , was found to inhabit open woodland environments with abundant grasses and to rely on leaves as an important component of its diet . This contradicts long-standing predictions that the unique features of apes , such as an upright torso , originated in forested environments to enable access to fruit resources . These findings are transformative , said Robin Bernstein , program director for biological anthropology at the U . S . National Science Foundation .
“ For the first time , by combining diverse lines of evidence , this collaborative research team tied specific aspects of early ape anatomy to nuanced environmental changes in their habitat in eastern Africa , now revealed as more open and less forested than previously thought . The effort outlines a new framework for future studies regarding ape evolutionary origins ,” Bernstein said .
Figure 3 . Artistic rendering of the open woodland habitat reconstruction at Moroto II with the early ape Morotopithecus bishopi climbing with an infant on its back and a juvenile below . ( Artist credit : Corbin Rainbolt )
The research team includes Daniel J . Peppe , Susanne M . Cote , Alan L . Deino , David L . Fox , John D . Kingston , Rahab N . Kinyanjui , William E . Lukens , Laura M . MacLatchy , Alice Novello , Caroline A . E . Strömberg , Steven G . Driese , Nicole D . Garrett , Kayla R . Hillis , Bonnie F . Jacobs , Kirsten E . H . Jenkins , Robert Kityo , Thomas Lehmann , Fredrick K . Manthi , Emma N . Mbua , Lauren A . Michel , Ellen R . Miller , Amon A . T . Mugume , Samuel N . Muteti , Isaiah O . Nengo , Kennedy O . Oginga , Samuel R . Phelps , Pratigya Polissar , James B . Rossie , Nancy J . Stevens , Kevin T . Uno , and Kieran P . McNulty .
This work was funded by the National Science Foundation ( USA ).
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