Abstract
Phylogenetic relationships among extinct hominoids (apes and humans) are controversial due to pervasive homoplasy and the incompleteness of the fossil record. The bony labyrinth might contribute to this debate, as it displays strong phylogenetic signal among other mammals. However, the potential of the vestibular apparatus for phylogenetic reconstruction among fossil apes remains understudied. Here we test and quantify the phylogenetic signal embedded in the vestibular morphology of extant anthropoids (monkeys, apes and humans) and two extinct apes (Oreopithecus and Australopithecus) as captured by a deformation-based 3D geometric morphometric analysis. We also reconstruct the ancestral morphology of various hominoid clades based on phylogenetically-informed maximum likelihood methods. Besides revealing strong phylogenetic signal in the vestibule and enabling the proposal of potential synapomorphies for various hominoid clades, our results confirm the relevance of vestibular morphology for addressing the controversial phylogenetic relationships of fossil apes.
Highlights
Catarrhine primates (Old World anthropoids) include two extant subclades: cercopithecoids (Old World monkeys) and hominoids
Since our results reveal the presence of strong phylogenetic signal in the vestibular morphology, we employ maximum likelihood methods (Felsenstein, 1988; Schluter et al, 1997) to reconstruct the ancestral vestibular morphology for the last common ancestor (LCA) of main hominoid subclades, with the aim to identify phylogenetically informative characters that can be used in formal cladistic analysis
Great apes fall on positive values (Figure 2, Figure 2—figure supplement 1a) due to their stout and flattened semicircular canals (SCs) combined with an extensive vertical compression of the anterior canal, a more anterosuperior insertion of the lateral canal into the vestibule, and a greater volume of the vestibular recesses relative to the canals (Figures 3a–e, 4a–e and 5a–e)
Summary
Catarrhine primates (Old World anthropoids) include two extant subclades: cercopithecoids (Old World monkeys) and hominoids (apes and humans). Hominoids first radiated in the early Miocene of Africa (Harrison, 2010; Begun, 2013; Begun, 2015) and subsequently diversified into Eurasia during the middle and late Miocene (Alba, 2012; Begun, 2015). Their diversity and geographic distribution (humans excluded) was much greater during the Miocene than at present, being currently restricted to a few genera in southeastern Asia and Africa. The decimated current diversity of hominoids, coupled with the fragmentary nature of their fossil record, abundant homoplasy (e.g., Larson, 1998), and the lack of known fossil hylobatids prior to the latest Miocene (Harrison, 2016) make it difficult to confidently infer the phylogenetic relationships of extinct hominoids and reliably infer the morphotype of the last common ancestor (LCA)
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