We describe the presence of fourth molar teeth in the upper jaw of a subspecies (Macaca sinica aurifrons) of the endemic toque macaque of Sri Lanka. Compared to the first three molars, supernumerary ones were smaller by more than 50%, showed four cuspids in the crowns, and had three roots. This observation contributes to knowledge of orthodontic anomalies presence in primate populations while spotlighting the importance of osteological observation.

中文翻译：

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斯里兰卡虎牙猴（Macaca sinica aurifrons）上颌第四磨牙的存在

我们描述了斯里兰卡地方性无角猕猴亚种 ( Macaca sinica aurifrons ) 的上颌存在第四磨牙。与前三颗磨牙相比，多生磨牙小了50%以上，牙冠有4颗尖牙，有3颗牙根。这一观察有助于了解灵长类动物种群中存在的正畸异常，同时突出了骨学观察的重要性。