Science  17 May 2013:
Vol. 340, Issue 6134, pp. 794
  1. New Fossils Provide Earliest Glimpse of Ape Origins


    When did apes, the group that today includes gorillas, chimpanzees, and humans, splinter off from Old World monkeys, such as baboons and macaques, and go their own evolutionary way? The answer is critical to understanding primate evolution and the origins of our own species. Molecular evidence from living primates suggests that this split occurred between 25 million and 30 million years ago, but no one has found fossils that old from either group—until now. This week in Nature, a team led by scientists at Ohio University in Athens reports finding teeth and partial jaws of an ape ancestor and an Old World monkey ancestor, both dated to 25 million years ago, in the Rukwa Rift in Tanzania. The new species, named Rukwapithecus fleaglei (left) and Nsungwepithecus gunnelli (right), respectively, arose at a time when East Africa was undergoing tumultuous climatic, environmental, and tectonic upheavals.

  2. U.S. East Coast Not So Passive

    A geological tenet holds that so-called "passive" continental margins—coastlines not shaped by earthquakes or volcanoes but instead by the slow accumulation of sediments from rivers and the oceans—tell a relatively straightforward geological history. Those margins, some scientists have suggested, can therefore be used to trace the rise and fall of global sea level over millions of years—and perhaps to assess past melting of the Greenland and Antarctic ice sheets.

    But a new study, published online this week in Science, notes that these passive margins have a dynamic side ( The slow circulation of hot mantle deep beneath the surface warps the topography over time. In particular, a ridge that runs along much of the U.S. East Coast called the Orangeburg Scarp, previously a centerpiece of past sea-level assessments, has been warped in several places by this mantle flow, the authors note. River incisions and ongoing post-glacial rebound following the retreat of heavy ice sheets further complicate the story. Global models of mantle convection will be needed to make real headway in interpreting past sea-level changes and ice sheet melting, researchers say.

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