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.

Significance: Reconstructing the phylogenetic relationships of extinct apes is challenging due to their fragmentary fossil record and the recurrent independent evolution of morphological features. Given the relevance of the phylogenetic signal of the bony labyrinth, here we assess the phylogenetic affinities of the late Miocene great apes Hispanopithecus and Rudapithecus by studying their inner ear morphology. Our results are consistent with the distinct generic status of these dryopiths, which further differ from the derived condition of orangutans and most closely resemble African apes. However, the latter appear largely primitive (similar to the last common ancestor of great apes and humans). Hence, our results do not conclusively favor a closer relationship with African apes as opposed to great apes as a whole.

The systematic status of the small-bodied catarrhine primate Pliobates cataloniae, from the Miocene (11.6 Ma) of Spain, is controversial because it displays a mosaic of primitive and derived features compared with extant hominoids (apes and humans). Cladistic analyses have recovered Pliobates as either a stem hominoid or as a pliopithecoid stem catarrhine (i.e., preceding the cercopithecoid–hominoid divergence). Here, we describe additional dental remains of P. cataloniae from another locality that display unambiguous synapomorphies of crouzeliid pliopithecoids. Our cladistic analyses support a close phylogenetic link with poorly-known small crouzeliids from Europe based on (cranio)dental characters but recover pliopithecoids as stem hominoids when postcranial characters are included. We conclude that Pliobates is a derived stem catarrhine that shows postcranial convergences with modern apes in the elbow and wrist joints—thus clarifying pliopithecoid evolution and illustrating the plausibility of independent acquisition of postcranial similarities between hylobatids and hominids.

Revealing the evolutionary processes which resulted in the derived morphologies that characterize the Neanderthal clade has been an important task for paleoanthropologists. One critical method to quantify evolutionary changes in the morphology of hominin populations is through evaluating morphological phenotypic diversity (i.e., disparity) in phylogenetically informative bones as a close proxy to neutral evolutionary processes. The goal of this study is to quantify the degree of disparity in the Neanderthal clade. We hypothesize that a reduction in bony labyrinth disparity is indicative of the underlying genetic variation resulting from bottleneck events. We apply a deformation-based geometric morphometric approach to investigate semicircular canal and vestibule shape of a chronologically broad sample of individuals belonging to the Neanderthal lineage. Our results identify a significant reduction in disparity after the start of Marine Isotope Stage 5 supporting our hypothesis of a late bottleneck, possibly leading to the derived morphology of Late Pleistocene Neanderthals.