Adaptive explanation for the origins of the anthropoidea (primates)

Phylogenetic analysis of anthropoid relationships

The relationships of anthropoids to other primates are currently debated, as are the relationships among early fossil anthropoids and crown anthropoids. To resolve these issues, data on 291 morphological characters were collected for 57 taxa of living and fossil primates and analyzed using PAUP and MacClade. The dental evidence provides weak support for the notion of an adapid origin for anthropoids, the cranial evidence supports the tarsier-anthropoid hypothesis, and the postcranial evidence supports a monophyletic Prosimii and a monophyletic Anthropoidea. Combining these data into a single data set produces almost universal support for a tarsier-anthropoid clade nested within omomyids. Eosimias and Afrotarsius are certainly members of this clade, and probably basal anthropoids, although the Shanghuang petrosal may not belong to Eosimias. The tree derived from the combined data set resembles the tree derived from the cranial data set rather than the larger dental data set. This may be attributable to relatively slower evolution in the cranial characters. The combined data set shows Anthropoidea to be monophyletic but the features traditionally held to be anthropoid synapomorphies are found to have evolved mosaically. Parapithecines are the sister taxon to crown anthropoids; qatraniines and oligopithecids are more distantly related sister taxa. There is support for a relationship of a Tarsius + Anthropoidea clade with either washakiines on Uintanius. These elements of tree topology remain fairly stable under different assumptions sets, but overall, tree topology is not robust. Previously divergent hypotheses regarding anthropoid relationships are attributable to the use of restricted data sets. This large data set enables the adapid-anthropoid hypothesis to be rejected, and unites Tarsius, Anthropoidea and Omomyiformes within a clade, Haplorhini. However, relationships among these three taxa cannot be convincingly resolved at present.

Anthropoid origins

Recent fossil discoveries have greatly increased our knowledge of the morphology and diversity of early Anthropoidea, the suborder to which humans belong. Phylogenetic analysis of Recent and fossil taxa supports the hypotheses that a haplorhine-strepsirrhine dichotomy existed at least at the time of the earliest record of fossil primates (earliest Eocene) and that eosimiids (middle Eocene, China) are primitive anthropoids. Functional analysis suggests that stem haplorhines were small, nocturnal, arboreal, visually oriented insectivore-frugivores with a scurrying-leaping locomotion. A change from nocturnality to diurnality was the fundamental adaptive shift that occurred at the base of the tarsier-eosimiid-anthropoid clade. Stem anthropoids remained small diurnal arborealists but adopted locomotor patterns with more arboreal quadrupedalism and less leaping. A shift to a more herbivorous diet occurred in several anthropoid lineages.