Young Nathan M, MacLatchy Laura
Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA.
J Hum Evol. 2004 Feb;46(2):163-84. doi: 10.1016/j.jhevol.2003.11.002.
The phylogenetic relationship of the Ugandan Miocene hominoid Morotopithecus bishopi to fossil and living hominoids remains to be determined. In a cladistic approach to this question, we used three published Miocene character sets as the basis of a phylogenetic analysis: J. Hum. Evol. 29 (1995) 101; Function, Phylogeny, and Fossils: Miocene Hominoid Evolution and Adaptations, 1997, 389. Because these datasets often describe the same anatomy using different characters and states, three different datasets were created to reflect these alternatives. In addition, new postcranial characters describable in Morotopithecus were added to each of the above datasets and a fourth dataset was created using only postcranial characters. The most parsimonious tree(s) recovered in all analyses consistently placed Morotopithecus as a sister taxon to the extant great apes, with Hylobates sister to this clade. Morotopithecus was also consistently more derived than Proconsul, Afropithecus, and Kenyapithecus (as defined prior to the description of Equatorius), but less derived than Oreopithecus, Sivapithecus (only craniodentally) and Dryopithecus. These results imply that Morotopithecus is more derived than Hylobates. However, gibbons are believed to have branched off by at least 18 Ma while Morotopithecus is dated at >20.6 Ma. Possible explanations include: (1) the dating of the Morotopithecus material is too old; (2) the Hylobates divergence time has been underestimated; (3) the great ape condition, and not that of Hylobates, is primitive for hominoids; (4) the similarities of Morotopithecus and great apes are homoplasies. Given current evidence, the first possibility is unlikely, but it is not possible to choose definitively between the latter three possibilities. This conclusion is supported by the fact that despite the consistencies of the analyses, the addition of Morotopithecus and the use of different characters had a large effect on the placement of other Miocene taxa. This raises questions as to the robustness of the connections between Miocene taxa and extant hominoids since different results can be achieved by changing either a few characters, or by adding a single taxon. Many of the characters used to estimate phylogeny may need to be reassessed before a reliable assessment of the phylogenetic position of Morotopithecus can be achieved.
乌干达中新世类人猿毕氏莫罗托猿（Morotopithecus bishopi）与化石类人猿及现存类人猿之间的系统发育关系仍有待确定。在对这个问题采用分支系统学方法时，我们使用了已发表的三个中新世特征集作为系统发育分析的基础：《人类进化杂志》29卷（1995年）第101页；《功能、系统发育与化石：中新世类人猿进化与适应》，1997年，第389页。由于这些数据集常常使用不同的特征和状态来描述相同的解剖结构，因此创建了三个不同的数据集以反映这些不同情况。此外，将可在毕氏莫罗托猿中描述的新的颅后特征添加到上述每个数据集中，并仅使用颅后特征创建了第四个数据集。在所有分析中得到的最简约树一致地将毕氏莫罗托猿置于现存大型猿类的姐妹分类单元位置，长臂猿是这个类群的姐妹。毕氏莫罗托猿也始终比原康修尔猿（Proconsul）、非洲猿（Afropithecus）和肯尼亚猿（Kenyapithecus，按赤道猿（Equatorius）描述之前的定义）更为特化，但比奥氏猿（Oreopithecus）、西瓦猿（Sivapithecus，仅在颅齿方面）和森林古猿（Dryopithecus）特化程度低。这些结果表明毕氏莫罗托猿比长臂猿更为特化。然而，人们认为长臂猿至少在1800万年前就已分支出来，而毕氏莫罗托猿的年代测定为>2060万年前。可能的解释包括：（1）毕氏莫罗托猿材料的年代测定过于古老；（2）长臂猿的分化时间被低估；（3）大型猿类的状态，而非长臂猿的状态，对于类人猿来说是原始的；（4）毕氏莫罗托猿与大型猿类的相似性是趋同演化的结果。根据目前的证据，第一种可能性不大，但无法在后面三种可能性中明确做出选择。这一结论得到以下事实的支持：尽管分析结果具有一致性，但毕氏莫罗托猿的加入以及不同特征的使用对其他中新世分类单元的位置有很大影响。这就引发了关于中新世分类单元与现存类人猿之间联系的稳健性的问题，因为通过改变少数几个特征或添加一个单一分类单元就可以得到不同的结果。在能够可靠评估毕氏莫罗托猿的系统发育位置之前，许多用于估计系统发育的特征可能需要重新评估。
