Systematics of Miocene apes: State of the art of a neverending controversy

The Miocene primate Pliobates is a pliopithecoid

“…The spread of cladistics promoted the view that postcranial similarities between these clades are synapomorphic 45 , 49 , but the discovery that the pongine Sivapithecus displayed a much more primitive postcranium than expected 50 reopened this debate during the 1990s 11 . Subsequent discoveries of Sivapithecus 51 and the stem hominid Pierolapithecus 52 , 53 further reinforced the previous contention 11 , 54 that such similarities may be largely homoplastic 12 – 15 . However, cladistic analyses performed during the last decades 14 , 55 , 56 have continued to support a close relationship between hylobatids and hominids to the exclusion of all Early and most Middle Miocene apes despite molecular evidence indicating that they diverged during the Early Miocene 57 , 58 .…”

“…Deciphering the phylogenetic relationships among pliopithecoids, crown catarrhines, and other Miocene catarrhines is not the main aim of this work but the results of our cladistic analyses support the view that pliopithecoids (including Pliobates ) are stem catarrhines and that previous results indicating a stem hominoid status 1 are probably attributable to the independent acquisition in crouzeliids of postcranial ape-like features. This interpretation illustrates the confounding effect that postcranial convergences might also have when inferring the internal phylogeny of living and fossil hominoids 11 – 15 , not only between extinct taxa such as Oreopithecus and crown hominids, but also between hylobatids and hominids. The spread of cladistics promoted the view that postcranial similarities between these clades are synapomorphic 45 , 49 , but the discovery that the pongine Sivapithecus displayed a much more primitive postcranium than expected 50 reopened this debate during the 1990s 11 .…”

“…In our opinion, these contradictions stem from the fact that Pliobates displays a mosaic of primitive (stem catarrhine-like) and derived (crown hominoid-like) features 1 , particularly in the postcranium, so that different topologies may be favored depending on the emphasis put on these features. Although the results based on all available evidence should be preferred on cladistic epistemological grounds, the fact that postcranial features alone yield a completely different topology for Pliobates and that postcranial homoplasy has repeatedly been noted as misleading in hominoid phylogenetics 11 – 15 suggest otherwise. The cranial morphology of Pliobates is also ambiguous because some similarities with hylobatids (anteriorly situated orbits, broad interorbital distance, short face, low zygomatic roots) are also displayed by the pliopithecoid Epipliopithecus 27 , stem hominoids such as nyanzapithecids 2 , and small-bodied catarrhines from East Africa such as the dendropithecid Micropithecus 28 .…”

“…However, cladistic analyses performed during the last decades 14 , 55 , 56 have continued to support a close relationship between hylobatids and hominids to the exclusion of all Early and most Middle Miocene apes despite molecular evidence indicating that they diverged during the Early Miocene 57 , 58 . Hominoid phylogenetic inference might be affected by a problem of long-branch attraction between hylobatids and hominids due to the numerous postcranial similarities presumably evolved in parallel between these lineages 15 . Uncertainties surrounding the origin of hylobatids and the lack of associated postcrania for many Miocene apes precludes adequately testing this hypothesis, which is nevertheless supported by preliminary results of tip-dating Bayesian analyses (Fig.…”

“…The contradictory results yielded by previous cladistic analysis for Pliobates —i.e., stem hominoid 1 vs. pliopithecoid 2 , 3 largely stem from the different emphasis put by the respective authors on postcranial features. The original topology recovering Pliobates as a hominoid was largely driven by the possession of numerous purported crown hominoid postcranial synapomorphies, which many authors consider homoplastic (i.e., independently evolved) to a large extent among various extant ape lineages 11 – 15 . Given the impossibility of disentangling homologous from homoplastic features a priori, an alternative approach to test whether Pliobates is a pliopithecoid would be to focus on dental morphology—as it is on this basis that pliopithecoids are distinguished from other catarrhines and considered to constitute a clade 8 , 16 – 20 .…”