Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Edifici ICTA-ICP, c/ Columnes s/n, Campus de la UAB, 08193 Cerdanyola del Vallès, Barcelona, Spain.
Univ. Bordeaux, CNRS, MCC, PACEA, UMR 5199, F-33600, Pessac, France.
J Hum Evol. 2021 Feb;151:102930. doi: 10.1016/j.jhevol.2020.102930. Epub 2021 Jan 7.
Pliopithecoids are an extinct group of catarrhine primates from the Miocene of Eurasia. More than 50 years ago, they were linked to hylobatids due to some morphological similarities, but most subsequent studies have supported a stem catarrhine status, due to the retention of multiple plesiomorphic features (e.g., the ectotympanic morphology) relative to crown catarrhines. More recently, some morphological similarities to hominoids have been noted, raising the question of whether they could be stem members of this clade. To re-evaluate these competing hypotheses, we examine the morphology of the semicircular canals of the bony labyrinth of the middle Miocene pliopithecid Epipliopithecus vindobonensis. The semicircular canals are suitable to test between these hypotheses because (1) they have been shown to embed strong phylogenetic signal and reliably discriminate among major clades; (2) several potential hominoid synapomorphies have been identified previously in the semicircular canals; and (3) semicircular canal morphology has not been previously described for any pliopithecoid. We use a deformation-based (landmark-free) three-dimensional geometric morphometric approach to compare Epipliopithecus with a broad primate sample of extant and extinct anthropoids. We quantify similarities in semicircular canal morphology using multivariate analyses, reconstruct ancestral morphotypes by means of a phylomorphospace approach, and identify catarrhine and hominoid synapomorphies based on discrete characters. Epipliopithecus semicircular canal morphology most closely resembles that of platyrrhines and Aegyptopithecus due to the retention of multiple anthropoid symplesiomorphies. However, Epipliopithecus is most parsimoniously interpreted as a stem catarrhine more derived than Aegyptopithecus due to the possession of a crown catarrhine synapomorphy (i.e., the rounded anterior canal), combined with the lack of other catarrhine and any hominoid synapomorphies. Some similarities with hylobatids and atelids are interpreted as homoplasies likely related to positional behavior. The semicircular canal morphology of Epipliopithecus thus supports the common view that pliopithecoids are stem catarrhines.
巨猿是已灭绝的类人猿，生活在中新世的欧亚大陆。50 多年前，由于一些形态相似性，它们与长臂猿有关联，但大多数后续研究支持它们是原始类人猿的地位，这是因为相对于冠类人猿，它们保留了多个原始特征（例如，外鼓室形态）。最近，人们注意到它们与人类有一些形态相似性，这引发了一个问题，即它们是否可能是这个分支的原始成员。为了重新评估这些相互竞争的假说，我们检查了中中新世巨猿 Epipliopithecus vindobonensis 迷路半规管的形态。半规管适合用来检验这些假说，因为：(1) 它们已经被证明具有强烈的系统发育信号，并且能够可靠地区分主要分支；(2) 以前已经在半规管中确定了几个潜在的人科同源特征；(3) 以前没有描述过任何巨猿的半规管形态。我们使用基于变形（无标志）的三维几何形态测量方法，将 Epipliopithecus 与现生和已灭绝的灵长类动物的广泛灵长类样本进行比较。我们使用多元分析来量化半规管形态的相似性，通过 phylomorphospace 方法重建祖先形态，根据离散特征识别出类人猿和人类的同源特征。Epipliopithecus 的半规管形态最接近阔鼻猴和 Aegyptopithecus，这是因为它保留了多个类人猿的共源特征。然而，Epipliopithecus 最合理的解释是一个比 Aegyptopithecus 更衍生的原始类人猿，因为它具有一个冠类人猿的同源特征（即圆形的前管），同时缺乏其他类人猿和任何人类的同源特征。与长臂猿和原猴类的一些相似性被解释为可能与位置行为有关的同形特征。因此，Epipliopithecus 的半规管形态支持巨猿是原始类人猿的常见观点。
