Amphipithecidae of late middle Eocene to late Eocene of Myanmar and Thailand is a phylogenetically enigmatic group that some place with Anthropoidea and others with Adapoidea. A linkage with adapoids is hard to demonstrate because it relies largely on a series of similarities that are arguably symplesiomorphies of Primates as a whole. The possibility that amphipithecids are specially related to crown anthropoids (e.g. Aegyptopithecus) is suggested by some shared-derived dental and gnathic anatomy. The postcranial anatomy indicates that the amphipithecids, if they are anthropoids, are probably a distantly related stem group outside the clade of African late Eocene-to-Recent anthropoids. Even the stem-group anthropoid status of amphipithecids is not supported by the absence of postorbital closure and enlarged olfactory bulbs, since postorbital closure and reduced olfactory bulbs characterize a more inclusive crown haplorhine clade of Tarsius plus Anthropoidea. An appealing possibility is that amphipithecids are basal haplorhines whose divergence would have predated the Tarsius–Anthropoidea split. Larger amphipithecids equal or exceed the body size of the largest known Eocene primates. Dental and mandibular anatomy suggests these large-bodied amphipithecids were fruit and hard-object (nut) feeders. A more primitive contemporary amphipithecid, Myanmarpithecus, was smaller, about 1–2 kg, and its cheek teeth suggest a frugivorous diet but do not imply seed eating. The humerus and calcaneus of a large amphipithecid from Myanmar (Pondaungia or Amphipithecus) suggest a slow-moving arboreal quadrupedal locomotion like that of lorises. A talus of an amphipithcid is more suggestive of an active arboreal quadruped.