Reassessing hominoid phylogeny: evaluating congruence in the morphological and temporal data

Abstract

The phylogenetic relationships of fossil and extant members of the primate superfamily Hominoidea are reassessed by using both conventional (morphological) cladistic and stratocladistic (incorporating morphological and temporal data) techniques. The cladistic analysis recovers four most parsimonious cladograms that distinguish postcranially primitive (“archaic”) and derived (“modern”) hominoid clades in the earliest Miocene of East Africa and supports distinct hominine and pongine clades. However, the relationships among the pongines and hominine clades and other Eurasian hominoids remain ambiguous and there is weak support (Bremer decay indices, reduced consensus, and bootstrap proportions) for several other parts of the proposed phylogeny. An examination of the partitioning of homoplasy across the two major hominoid clades recovered in the cladistic analysis indicates that the majority of the observed homoplasy resides in the postcranially derived clade. An examination of the partitioning of homoplasy across anatomical regions indicates that dental characters display a significantly higher level of homoplasy than postcranial characters. A rarefaction analysis demonstrates that the higher homoplasy associated with the dental characters is not the result of sampling biases, indicating that postcranial skeletal characters are likely the more reliable phylogenetic indicators in the hominoids. The branching order of the most parsimonious cladograms shows better than average congruence with the observed ordering of first appearances in the fossil record, implying that the hominoid fossil record is surprisingly good. As with morphologic parsimony debt, most of the stratigraphic parsimony debt in these cladograms is associated with the “modern” hominoid clade. A stratocladistic analysis of the data recovers a single most parsimonious phylogenetic tree with a different cladistic topology from the morphological cladogram. The most striking difference is the elimination of the postcranially primitive clade of hominoids in the early Miocene in favor of a pectinate succession of taxa. The relative position of the late-appearing taxon Oreopithecus is also altered in the stratocladistic hypothesis. Topological differences between the cladistic and stratocladistic hypotheses highlight two intervals of significant discord between the morphological and temporal data—the early Miocene of eastern Africa and the late Miocene of Eurasia. The first discrepancy is likely the result of poor preservation and morphological homoplasy in Morotopithecus , as the fossil record in the early Miocene of eastern Africa for the ingroup is rather good. The second discrepancy is likely the result of the unusual preservation conditions associated with the late Miocene hominoid Oreopithecus .