【進化】類人猿の進化の謎に解明の光を当てる古代の頭蓋骨

The discovery of a 13-milllion-year-old skull of an infant ape from Kenya offers new insights into ape evolution. The specimen, reported this week in Nature, is assigned to a new species in the genus Nyanzapithecus, a sister group to hominoids (gibbons, great apes and humans). Although the new species shows some similarities to gibbons, the authors suggest that it was most probably a close relative of the common ancestor of extant apes.

During the Miocene epoch (approximately 23 to 5 million years ago) hominoids diversified extensively, resulting in over 40 different species. However, only one third of these species have been identified from cranial remains. The African fossil hominoid record in particular lacks any reasonably complete crania between 17 and 7 million years ago, and no cranial specimens from between 14 and 10 million years ago have been discovered until now.

Isaiah Nengo, Fred Spoor and colleagues describe an almost complete infant ape cranium dated to 13 million years ago. The new species, Nyanzapithecus alesi, is similar to some species of gibbon in aspects of overall cranial morphology and dental development, although these features evolved independently. However, the authors note that it is distinctly different owing to the relatively small size of its semicircular canal, a feature relevant for the perception of motion. The authors suggest that N. alesi would have exhibited a slower, less agile mode of locomotion than the acrobatic swinging movements of present-day gibbon species.