Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan; Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, C/ Columnes S/n, Campus de La UAB, 08193, Cerdanyola Del Vallès, Barcelona, Spain.
Division of Human Anatomy and Biological Anthropology, Department of Anatomy and Physiology, Faculty of Medicine, Saga University, Saga, 849-8501, Japan.
J Hum Evol. 2021 Jun;155:102982. doi: 10.1016/j.jhevol.2021.102982. Epub 2021 Apr 13.
The middle Miocene stem kenyapithecine Nacholapithecus kerioi (16-15 Ma; Nachola, Kenya) is represented by a large number of isolated fossil remains and one of the most complete skeletons in the hominoid fossil record (KNM-BG 35250). Multiple fieldwork seasons performed by Japanese-Kenyan teams during the last part of the 20th century resulted in the discovery of a large sample of Nacholapithecus fossils. Here, we describe the new femoral remains of Nacholapithecus. In well-preserved specimens, we evaluate sex differences and within-species variation using both qualitative and quantitative traits. We use these data to determine whether these specimens are morphologically similar to the species holotype KNM-BG 35250 (which shows some plastic deformation) and to compare Nacholapithecus with other Miocene hominoids and extant anthropoids to evaluate the distinctiveness of its femur. The new fossil evidence reaffirms previously reported descriptions of some distal femoral traits, namely the morphology of the patellar groove. However, results also show that relative femoral head size in Nacholapithecus is smaller, relative neck length is longer, and neck-shaft angle is lower than previously reported for KNM-BG 35250. These traits have a strong functional signal related to the hip joint kinematics, suggesting that the morphology of the proximal femur in Nacholapithecus might be functionally related to quadrupedal-like behaviors instead of more derived antipronograde locomotor modes. Results further demonstrate that other African Miocene apes (with the exception of Turkanapithecus kalakolensis) generally fall within the Nacholapithecus range of variation, whose overall femoral shape resembles that of Ekembo spp. and Equatorius africanus. Our results accord with the previously inferred locomotor repertoire of Nacholapithecus, indicating a combination of generalized arboreal quadrupedalism combined with other antipronograde behaviors (e.g., vertical climbing).
中新世中期的肯尼亚原康修尔猿（16-15 百万年前；肯尼亚纳库洛拉）以大量孤立的化石遗骸和人科化石记录中最完整的骨骼之一（KNM-BG 35250）为代表。20 世纪最后几十年，日本-肯尼亚联合考察队进行了多次野外考察，发现了大量的原康修尔猿化石。在这里，我们描述了原康修尔猿的新股骨遗骸。在保存完好的标本中，我们使用定性和定量特征来评估性别差异和种内变异。我们使用这些数据来确定这些标本在形态上是否与物种的模式标本 KNM-BG 35250 相似（后者显示出一些塑性变形），并将原康修尔猿与其他中新世人科动物和现生类人猿进行比较，以评估其股骨的独特性。新的化石证据再次证实了以前对一些股骨远端特征的描述，即髌骨关节沟的形态。然而，结果还表明，与 KNM-BG 35250 相比，原康修尔猿的股骨头相对较小，颈长相对较长，颈干角较低。这些特征与髋关节运动学有很强的功能信号相关，表明原康修尔猿近端股骨的形态可能与类似四足的行为有关，而不是更衍生的对跖运动模式。结果进一步表明，其他非洲中新世猿类（除了图尔卡纳原康修尔猿）一般都在原康修尔猿的变异范围内，其股骨整体形状类似于埃克博斯属和非洲赤道猿。我们的结果与以前推断的原康修尔猿的运动功能谱一致，表明是一种广义的树栖四足运动与其他对跖运动行为（如垂直攀爬）的结合。
