Research press release





今回、Isaiah Nengo、Fred Spoorたちの研究グループは、1300万年前と年代決定された類人猿の乳仔のほぼ完全な頭蓋骨について記述した論文を発表した。この新種Nyanzapithecus alesiは、頭蓋全体の形態と歯の成長のいろいろな側面でテナガザル科の数種と類似しているが、これらの特徴はそれぞれ独立に進化していた。これに対して、Nengoたちは、N. alesiの内耳の半規管が比較的小さいため、明らかに別種であることを指摘している。半規管は、運動の知覚にとって重要な特徴だ。また、Nengoたちは、N. alesiの移動運動には現生テナガザル種の曲芸的なぶら下がり運動ほどの素早さと機敏さがなかったと推定している。

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.

doi: 10.1038/nature23456

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