Taylor Andrea B
Departments of Community and Family Medicine and Biological Anthropology and Anatomy, Duke University Medical Center, Box 3907, Durham, NC 27710, USA.
J Hum Evol. 2006 Apr;50(4):377-93. doi: 10.1016/j.jhevol.2005.10.006. Epub 2006 Jan 18.
Orangutans are amongst the most craniometrically variable of the extant great apes, yet there has been no attempt to explicitly link this morphological variation with observed differences in behavioral ecology. This study explores the relationship between feeding behavior, diet, and mandibular morphology in orangutans. All orangutans prefer ripe, pulpy fruit when available. However, some populations of Bornean orangutans (Pongo pygmaeus morio and P. p. wurmbii) rely more heavily on bark and relatively tough vegetation during periods of low fruit yield than do Sumatran orangutans (Pongo abelii). I tested the hypothesis that Bornean orangutans exhibit structural features of the mandible that provide greater load resistance abilities to masticatory and incisal forces. Compared to P. abelii, P. p. morio exhibits greater load resistance abilities as reflected in a relatively deeper mandibular corpus, deeper and wider mandibular symphysis, and relatively greater condylar area. P. p. wurmbii exhibits most of these same morphologies, and in all comparisons is either comparable in jaw proportions to P. p. morio, or intermediate between P. p. morio and P. abelii. These data indicate that P. p. morio and P. p. wurmbii are better suited to resisting large and/or frequent jaw loads than P. abelii. Using these results, I evaluated mandibular morphology in P. p. pygmaeus, a Bornean orangutan population whose behavioral ecology is poorly known. Pongo p. pygmaeus generally exhibits relatively greater load resistance capabilities than P. abelii, but less than P. p. morio. These results suggest that P. p. pygmaeus may consume greater amounts of tougher and/or more obdurate foods than P. abelii, and that consumption of such foods may intensify amongst Bornean orangutan populations. Finally, data from this study are used to evaluate variation in craniomandibular morphology in Khoratpithecus piriyai, possibly the earliest relative of Pongo from the late Miocene of Thailand, and the late Pleistocene Hoa Binh subfossil orangutan recovered from Vietnam. With the exception of a relatively thicker M(3) mandibular corpus, K. piriyai has jaw proportions that would be expected for an extant orangutan of comparable jaw size. Likewise, the Hoa Binh subfossil does not differ in skull proportions from extant Pongo, independent of the effects of increase in jaw size. These results indicate that differences in skull and mandibular proportions between these fossil and subfossil orangutans and extant Pongo are allometric. Furthermore, the ability of K. piriyai to resist jaw loads appears to have been comparable to that of extant orangutans. However, the similarity in jaw proportions between P. abelii and K. piriyai suggest the latter may have been dietarily more similar to Sumatran orangutans.
红毛猩猩是现存颅骨测量变异最大的大型猿类之一，但尚未有人尝试将这种形态变异与行为生态学中观察到的差异明确联系起来。本研究探讨了红毛猩猩的摄食行为、饮食与下颌形态之间的关系。所有红毛猩猩在有成熟多汁果实的时候都更喜欢食用。然而，与苏门答腊红毛猩猩（Pongo abelii）相比，一些婆罗洲红毛猩猩种群（Pongo pygmaeus morio和P. p. wurmbii）在果实产量低的时期更依赖树皮和相对坚韧的植被。我检验了这样一个假设：婆罗洲红毛猩猩的下颌具有结构特征，能为咀嚼和切割力提供更大的抗负荷能力。与P. abelii相比，P. p. morio表现出更强的抗负荷能力，如下颌体相对更深、下颌联合部更深更宽以及髁突面积相对更大。P. p. wurmbii也表现出这些相同的形态特征，并且在所有比较中，其颌部比例要么与P. p. morio相当，要么介于P. p. morio和P. abelii之间。这些数据表明，与P. abelii相比，P. p. morio和P. p. wurmbii更适合抵抗较大和/或频繁的颌部负荷。利用这些结果，我评估了P. p. pygmaeus（一种行为生态学鲜为人知的婆罗洲红毛猩猩种群）的下颌形态。Pongo p. pygmaeus通常表现出比P. abelii相对更强的抗负荷能力，但比P. p. morio弱。这些结果表明，P. p. pygmaeus可能比P. abelii食用更多更坚韧和/或更坚硬的食物，并且在婆罗洲红毛猩猩种群中，这类食物的消耗量可能会增加。最后，本研究的数据被用于评估Khoratpithecus piriyai（可能是来自泰国晚中新世的最早的红毛猩猩亲属）以及从越南发现的更新世晚期和平亚化石红毛猩猩的颅下颌形态变异。除了下颌体的M(3)相对较厚外，K. piriyai的颌部比例与同等颌部大小的现存红毛猩猩预期的比例相同。同样，和平亚化石在头骨比例上与现存的红毛猩猩没有差异，不受颌部大小增加的影响。这些结果表明，这些化石和亚化石红毛猩猩与现存红毛猩猩在头骨和下颌比例上的差异属于异速生长。此外，K. piriyai抵抗颌部负荷的能力似乎与现存红毛猩猩相当。然而，P. abelii和K. piriyai在颌部比例上的相似性表明，后者在饮食上可能与苏门答腊红毛猩猩更相似。
