Anklebone kicks up primate debate

An anklebone excavated last year in southern Asia may put a controversial theory of primate evolution on firmer footing. The nearly 40-million-year-old fossil adds to evidence that anthropoids, a primate group that includes monkeys, apes, and humans, originated in Asia, according to a team led by Laurent Marivaux of Université Montpellier II in France.

The identity of comparably ancient primate remains, unearthed near the site of the new find in Myanmar, has inspired plenty of debate (SN: 10/16/99, p. 244: https://www.sciencenews.org/sn_arc99/10_16_99/fob1.htm). Some researchers classify these finds as remains of anthropoids, while others regard them as fossils of adapiforms, a group that includes extinct species related to lemurs and lorises.

On close inspection, the Myanmar anklebone resembles the bones of living and extinct anthropoids more than those of adapiforms, Marivaux and his coworkers report in the Nov. 11 Proceedings of the National Academy of Sciences. The ankle fossil’s anatomy indicates that it supported a roughly 15-pound creature capable of moving deftly through trees using its arms and legs, the researchers say.

However, the new fossil also contains similarities to the ankles of lemurs and lorises and could just as easily have belonged to adapiforms, contends Gregg F. Gunnell of the University of Michigan in Ann Arbor. On the basis of fossil teeth found earlier in Myanmar and Thailand, Gunnell theorizes that all of the region’s ancient large-bodied primates, which weighed between 13 and 20 pounds, were adapiforms. He supports the traditional view that anthropoids originated in Africa.

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