Department of Anthropology, University of Arkansas, Fayetteville, AR, 72701, USA.
Department of Pathology and Anatomical Sciences, M263 Medical Sciences Building, University of Missouri, Columbia, MO, 65212, USA.
J Hum Evol. 2019 Oct;135:102623. doi: 10.1016/j.jhevol.2019.05.011. Epub 2019 Jul 15.
Although modern guenons are diverse and abundant in Africa, the fossil record of this group is surprisingly sparse. In 2012 the West Turkana Paleo Project team recovered two associated molar teeth of a small primate from the Pliocene site of Kanapoi, West Turkana, Kenya. The teeth are bilophodont and the third molar lacks a hypoconulid, which is diagnostic for Cercopithecini. The teeth are the same size as those of extant Miopithecus, which is thought to be a dwarfed guenon, as well as a partial mandible preserving two worn teeth, previously recovered from Koobi Fora, Kenya, which was also tentatively identified as a guenon possibly allied with Miopithecus. Tooth size and proportions, as well as analysis of relative cusp size and shearing crest development clearly separate the fossil from all known guenons. Based on the Kanapoi material, we erect a new genus and species, Nanopithecus browni gen. et sp. nov. The small size of the specimen suggests either that dwarfing occurred early in the lineage, or at least twice independently, depending on the relationship of the new species with extant Miopithecus. Further, the distinctive habitat and geographic separation from Miopithecus suggests that the origin of small body size is not uniquely linked to the current habitat of Miopithecus, and possibly that relatives of extant Miopithecus were much more widely distributed in the past. This in turn argues caution in using extant biogeography in models of the origins of at least some guenons.
尽管现代疣猴在非洲种类繁多且数量丰富，但该类群的化石记录却出奇地稀少。2012 年，西图尔卡纳古生物研究团队在肯尼亚图尔卡纳湖西岸的卡纳波伊遗址发掘出两颗小型灵长类动物的相关臼齿。这两颗臼齿呈双尖齿型，第三臼齿缺少下尖突，这是长尾猴亚科的特征。这些牙齿与现存的矮猕猴的牙齿大小相同，而矮猕猴被认为是一种体型缩小了的疣猴。此外，研究团队还发现了部分保存完好的下颌骨，其中包含两颗磨损的牙齿，这些牙齿之前在肯尼亚的科比福拉遗址被发现，当时也被暂时鉴定为一种可能与矮猕猴有关联的疣猴。牙齿大小和比例，以及相对牙尖大小和剪切嵴发育的分析，都清楚地将化石与所有已知的疣猴区分开来。基于卡纳波伊遗址的材料，我们建立了一个新的属种，布朗氏小猿（Nanopithecus browni）。该标本的体型较小，这表明体型缩小可能发生在该物种的早期，或者至少独立发生了两次，这取决于新物种与现存矮猕猴的关系。此外，这种独特的栖息地和与矮猕猴的地理隔离表明，小型体型的起源不一定与矮猕猴目前的栖息地有关，现存矮猕猴的亲缘种可能在过去分布得更为广泛。这反过来又表明，在某些疣猴起源的模型中，使用现存的生物地理学来进行推断需要谨慎。
