ANTHROPOLOGICAL SCIENCE Vol. 113, 33–42, 2005 A synopsis of the phylogeny and paleobiology of Amphipithecidae, South Asian middle and late Eocene primates RICHARD F. KAY1* 1Department of Biological Anthropology and Anatomy, Box 3170, Duke University Medical Center, Durham NC 27710, U.S.A. Received 4 July 2003; accepted 7 May 2004 Abstract Amphipithecidae of late middle Eocene to late Eocene of Myanmar and Thailand is a phy- logenetically enigmatic group that some place with Anthropoidea and others with Adapoidea. A link- age 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 anthro- poids. Even the stem-group anthropoid status of amphipithecids is not supported by the absence of pos- torbital 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 pos- sibility is that amphipithecids are basal haplorhines whose divergence would have predated the Tar- sius–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. Key words: Amphipithecidae, Anthropoidea, Eocene, Thailand, Myanmar (Burma) Introduction suggest a somewhat younger age than the Myanmar beds— 31 to 34 Ma (Benammi et al., 2001)—making it late Eocene Several clades of primate taxa are known from the middle to early Oligocene (Berggren et al., 1995). Thus, in total, and late Eocene of South Asia of which the Amphipithe- these extinct primates overlap and encompass the age distri- cidae is among the most diverse, including Pondaungia, bution of anthropoids described from Fayum province, Amphipithecus, Siamopithecus, and Myanmarpithecus. Egypt, and elsewhere in northern Africa and Arabia. Most of these taxa are known from teeth and jaws although Amphipithecids are known from three or perhaps four several specimens from Myanmar, assignable to Amphipith- species. From Thailand comes Siamopithecus eocaenus. ecus and Pondaungia, are known from parts of the humerus, From Myanmar come Amphipithecus mogaungensis and ulna, calcaneus, talus, face, and circumorbital region. In this Myanmarpithecus yarshensis. A third Myanmar taxon, paper I review the phylogenetic position of amphipithecids Pondaungia, seems to be represented by two species (P. cot- and, in somewhat more detail, comment on the paleobiology teri and P. savagei), although these could also represent a of this interesting clade. single sexually dimorphic species. One argument for the Myanmar amphipithecid specimens come from the former interpretation is that the ratio of the size of the lower Pondaung Formation. A fission-track age of ~37 Ma (late canine (or its root socket) to the dimensions of the molars is middle Eocene) is reported from one level in the Pondaung similar in the larger and smaller specimens. In contrast, Formation (Tsubamoto et al., 2002), concordant with the for- among extant sexually dimorphic primates, there is more mation being overlain by marine beds with foraminifera of size difference between the canines than between the molars late Eocene age (Aung, 1999; Mon, 1999). Thailand of the two sexes. amphipithecids come from coal deposits at Krabi. The mag- All amphipithecid species are known from the maxilla, netostratigraphy and paleofaunas with which it is associated mandible, and teeth, but cranial and postcranial evidence is sparser. Frontal bones of Amphipithecus have been * Corresponding author. e-mail: [email protected] described (Ciochon and Gunnell, 2002; Gunnell et al., 2002; phone: 1-919-684-2143; fax: 1-919-684-8542 Takai et al., 2003; Shigehara and Takai, 2004). Three associ- Published online 11 August 2004 ated postcranial fragments (humerus, ulna, and calcaneus) in J-STAGE (www.jstage.jst.go.jp) DOI: 10.1537/ase.04S005 belonging to a large-bodied species from Myanmar could be © 2004 The Anthropological Society of Nippon 33 34 R.F. KAY ANTHROPOLOGICAL SCIENCE either Amphipithecus or Pondaungia (Ciochon et al., 2001; Simons and Rasmussen, 1996). A resolution of this problem Ciochon and Gunnell, 2004). A talus from the Pondaung awaits recovery of new material establishing the orbital Formation also is of a size appropriate to go with Amphipith- structure of eosimiid anthropoids. ecus (Marivaux et al., 2003). One of the amphipithecid frontal fragments mentioned above preserves the dorsal endocranial surface of the olfac- Phylogenetic Position of Amphipithecidae tory fossa and frontal pole of the cerebrum (Takai et al., 2003). The olfactory bulbs apparently were quite large— The phylogenetic position of amphipithecids is debated. within the range of extant strepsirrhines, and comparable to A cladistic analysis of dental, cranial, and postcranial anat- those of Eocene omomyids and adapoids, but distinctly omy by Kay et al. (2004c) examined the possibilities. Con- larger than Fayum anthropoids like Apidium and Aegyptop- sidering the collective evidence, Kay et al. (2004c) found it ithecus. Again, this reinforces the point of view that amphip- to be slightly more parsimonious (owing to dental charac- ithecids are more primitive than Fayum and more recent ters) to root amphipithecids within the anthropoid clade, anthropoids but does not rule out a haplorhine status. especially with Propliopithecidae, the earliest catarrhine In summary, the dental, cranial, and postcranial evidence anthropoids from the African Oligocene. Dental evidence point in very different directions: the dental evidence sug- provides the only support for a crown anthropoid hypothe- gests a link to crown anthropoids; the postcranial evidence sis. Some or all amphipithecids bear a strong resemblance to suggests that amphipithecids could be anthropoids but are propliopithecids, sharing with them deep jaws, spatulate and outside the more inclusive clade of crown and African stem enlarged upper central incisors, robust canines with a anthropoids; the orbital and olfactory anatomy suggests that rounded oval cross-section, P3 with a convex distal margin, the group, while possibly haplorhine is outside the crown p4 with a metaconid but lacking a paraconid, low crowned haplorhine clade. molars without paraconids, with little disparity between trig- A very different phylogenetic placement of the amphipi- onid and talonid heights, and the presence of wear facet X on thecid clade is as a sister group to one or another group of the molars (Ducrocq, 1998, 1999; Jaeger et al., 1998a, b; adapoid primates. The case for a relationship to notharctine Chaimanee et al., 2000; Shigehara et al., 2002; Kay et al., adapoids from North America was made by Gunnell, Cio- 2004c). However, a careful evaluation of the total available chon, and colleagues (Ciochon et al., 2001; Gunnell et al., anatomical evidence leads to the conclusion that a linkage 2002). Such an argument was based mainly on overall large with catarrhine anthropoids is unlikely because it would size and postcranial primitiveness. Additionally, synapo- require many convergences in the orbital anatomy (lack of morphies of the dentition were proposed, especially the pres- postorbital closure, a feature of stem anthropoids). Further- ence of a ‘pseudohypocone’ in amphipithecids and some more, the humerus and calcaneus lack the shared-derived advanced notharctines. Ducrocq (1999) and later Shigehara features characteristic of late Eocene and early Oligocene et al. (2002) reviewed the latter proposed similarity and dis- African oligopithecids, parapithecids, and propliopithecids counted it. (Kay and Williams, 1994; Ciochon and Gunnell, 2004; A possible phyletic link has been suggested between Seiffert et al., 2004). This interpretation is reinforced by a amphipithecids and non-notharctine adapoids of Europe like recently described amphipithecid talus which, while more Adapis, Leptadapis, Pronycticebus, and their relatives on diagnostically anthropoid, does not associate exclusively other continents such as Mahgarita (North America) and with crown anthropoids (Marivaux et al., 2003). Thus, this Aframonius (Africa). Kay et al. (2004c) reported that such a postcranial evidence in total indicates that the amphipithec- link is less parsimonious than the anthropoid hypothesis but ids might be stem anthropoids outside the clade of African has the advantage of not requiring parallel evolution of pos- Eocene-to-Recent crown anthropoids (Kay et al., 2004c). torbital closure. At that time, we indicated our preference for A major challenge for the anthropoid status of amphipith- this second, admittedly less parsimonious, interpretation that ecids comes