A 3-dimensional assessment of molar enamel thickness and distribution pattern in Gigantopithecus blacki

Reiko T. Kono, Yingqi Zhang, Changzhu Jin, Masanaru Takai, Gen Suwa

Gigantopithecus blackiの大臼歯エナメル質の厚さと分布を現生類人猿や化石人類と比較した。上顎大臼歯2点、下顎大臼歯3点をマイクロフォーカスX線CT装置で連続撮影し、このデータをもとに歯冠エナメル質の3次元形状をデジタル構築して分析したところ、G. blackiの大臼歯は非常にエナメル質が厚く、6mmを超える厚さも観察された。歯冠全体の平均厚さは、歯冠サイズで標準化すると現代人（H. sapiens）と同程度であり、頑丈型の猿人よりは薄いが、歯冠の咬合面積に対する厚さを磨り減りに対する耐性を示す指標として検討すると、G. blackiは頑丈型猿人と同程度に磨り減りへの耐性が大きいことも示された。G. blackiの大臼歯は、エナメル質が咬合面付近に厚く分布し頬舌方向の分布の偏りが見られることから、咬耗量が非常に多いが、鮮新世・更新世の人類とはまた異なる食性へと適応進化したものであることが示唆された。

Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.02.012

In order to investigate molar enamel thickness and distribution in Gigantopithecus blacki, two maxillary and three mandibular molars were micro-CT scanned, and the 3-dimensional (3D) shape of the enamel crown cap was digitally reconstructed. Results show that G. blacki molars have very thick enamel, over 6 mm in places. 3D average thickness of the entire crown relative to crown size was shown to be comparable to that of modern Homo sapiens, and thinner than in the very thick enameled robust Australopithecus condition. Durability of the tooth, calculated as the enamel volume relative to maximum horizontal area of the crown, was shown to be comparable to that of fossil hominids, including Australopithecus robustus. The thick occlusal enamel of G. blacki molars was found to be accompanied by a buccolingual gradient in which thicker enamel occurs on the cusps of the “functional” side. This is associated with higher crown height on the “functional” side of the crown, and implies an adaptation to differential buccolingual wear. These results indicate that G. blacki molars were adapted to heavy wear, but probably in a manner that was different from Pliocene and Pleistocene hominids.

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