Smith Tanya M
Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, United States.
J Hum Evol. 2016 May;94:92-105. doi: 10.1016/j.jhevol.2016.02.008. Epub 2016 Apr 14.
Numerous studies have investigated molar development in extant and fossil hominoids, yet relatively little is known about orangutans, the only great ape with an extensive fossil record. This study characterizes aspects of dental development, including cuspal enamel daily secretion rate, long-period line periodicities, cusp-specific molar crown formation times and extension rates, and initiation and completion ages in living and fossil orangutan postcanine teeth. Daily secretion rate and periodicities in living orangutans are similar to previous reports, while crown formation times often exceed published values, although direct comparisons are limited. One wild Bornean individual died at 4.5 years of age with fully erupted first molars (M1s), while a captive individual and a wild Sumatran individual likely erupted their M1s around five or six years of age. These data underscore the need for additional samples of orangutans of known sex, species, and developmental environment to explore potential sources of variation in molar emergence and their relationship to life history variables. Fossil orangutans possess larger crowns than living orangutans, show similarities in periodicities, and have faster daily secretion rate, longer crown formation times, and slower extension rates. Molar crown formation times exceed reported values for other fossil apes, including Gigantopithecus blacki. When compared to African apes, both living and fossil orangutans show greater cuspal enamel thickness values and periodicities, resulting in longer crown formation times and slower extension rates. Several of these variables are similar to modern humans, representing examples of convergent evolution. Molar crown formation does not appear to be equivalent among extant great apes or consistent within living and fossil members of Pongo or Homo.
众多研究已对现存和化石类人猿的臼齿发育进行了调查，但对于猩猩（唯一具有丰富化石记录的大型猿类），我们所知相对较少。本研究描述了牙齿发育的各个方面，包括牙尖釉质每日分泌率、长期线周期、特定牙尖的臼齿冠形成时间和扩展率，以及现存和化石猩猩犬齿后牙齿的起始和完成年龄。现存猩猩的每日分泌率和周期与先前的报告相似，而冠形成时间通常超过已发表的值，尽管直接比较有限。一只野生婆罗洲猩猩在4.5岁时死亡，其第一臼齿（M1）已完全萌出，而一只圈养猩猩和一只野生苏门答腊猩猩的M1可能在五六岁左右萌出。这些数据强调需要更多已知性别、物种和发育环境的猩猩样本，以探索臼齿萌出变异的潜在来源及其与生活史变量的关系。化石猩猩的牙冠比现存猩猩的更大，在周期上表现出相似性，并且每日分泌率更快，冠形成时间更长，扩展率更慢。臼齿冠形成时间超过了其他化石猿类（包括巨猿）的报告值。与非洲猿类相比，现存和化石猩猩的牙尖釉质厚度值和周期都更大，导致冠形成时间更长，扩展率更慢。其中几个变量与现代人类相似，代表了趋同进化的例子。现存大型猿类的臼齿冠形成似乎并不等同，在猩猩属或人属的现存和化石成员中也不一致。
