A lower jaw of Pondaungia cotteri from the Late Middle Eocene Pondaung Formation (Myanmar) confirms its anthropoid status

Amphipithecine primates are stem anthropoids: cranial and postcranial evidence

Since their discovery in 1927, the phylogenetic status of the Myanmar amphipithecines has been highly debated. These fossil primates are recognized either as anthropoids or as adapiform strepsirrhines. This uncertainty was largely the consequence of a limited fossil record consisting mostly of jaw fragments but lacking the critical cranial elements that might resolve this debate. We report here cranial remains associated with an ulna from a single individual pertaining to the amphipithecine Ganlea megacanina. In addition to anthropoid-like dentognathic characters, Ganlea displays several ulna and skull features that testify to its anthropoid affinities (e.g. short subvertically oriented lacrimal duct, lacrimal foramen and bone inside the orbit, maxillary contribution to the lower orbital rim, fused metopic suture). By contrast to crown anthropoids, however, Ganlea lacks postorbital closure, confirming that postorbital closure appeared later than many anthropoid dentognathic characters and evolved convergently in extant tarsiers and anthropoids. Thus, amphipithecines must now be recognized as stem anthropoids offering a unique window on the early evolution of cranial and skeletal features in anthropoids, and reinforcing the hypothesis of an origin and early diversification of anthropoids in Asia.

The face of Siamopithecus: new geometric-morphometric evidence for its anthropoid status

Amphipithecids assume a key position in early primate evolution in Asia. Here we report on new maxillofacial and associated mandibular remains of Siamopithecus eocaenus, an amphipithecid primate from the Late Eocene of Krabi (Thailand) that currently represents the most complete specimen belonging to this group. We used synchrotron microtomography and techniques of virtual reconstruction to recover the three-dimensional morphology of the specimen. Geometric-morphometric analysis of the reconstructed specimen within a comparative sample of recent and fossil primates clearly associates Siamopithecus with the anthropoids. Like modern anthropoids, Siamopithecus displays a relatively short face and highly convergent and frontated orbits, the lower rim of which lies well above the alveolar plane. The cooccurrence of spatially correlated anthropoid features and classical anthropoid dental characters in one individual represents a strong argument to support the anthropoid status of Siamopithecus. It is, thus, highly unlikely that amphipithecids are specialized adapiforms exhibiting complete convergence with anthropoids.

A new primate from the Eocene Pondaung Formation of Myanmar and the monophyly of Burmese amphipithecids

The family Amphipithecidae is one of the two fossil primate taxa from Asia that appear to be early members of the anthropoid clade. Ganlea megacanina, gen. et sp. nov., is a new amphipithecid from the late middle Eocene Pondaung Formation of central Myanmar. The holotype of Ganlea is distinctive in having a relatively enormous lower canine showing heavy apical wear, indicating an important functional role of the lower canine in food preparation and ingestion. A phylogenetic analysis of amphipithecid relationships suggests that Ganlea is the sister taxon of Myanmarpithecus, a relatively small-bodied taxon that has often, but not always, been included in Amphipithecidae. Pondaungia is the sister taxon of the Ganlea + Myanmarpithecus clade. All three Pondaung amphipithecid genera are monophyletic with respect to Siamopithecus, which is the most basal amphipithecid currently known. The inclusion of Myanmarpithecus in Amphipithecidae diminishes the likelihood that amphipithecids are specially related to adapiform primates. Extremely heavy apical wear has been documented on the lower canines of all three genera of Burmese amphipithecids. This distinctive wear pattern suggests that Burmese amphipithecids were an endemic radiation of hard object feeders that may have been ecological analogues of living New World pitheciin monkeys.

Anatomy of the bony pelvis of a relatively large-bodied strepsirrhine primate from the late middle Eocene Pondaung Formation (central Myanmar)

Recent survey of the fossiliferous variegated mudstones of the PK1 locality (Sabapondaung) in the late middle Eocene Pondaung Formation (central Myanmar) has led to the recovery of a partial right innominate of a relatively large-bodied primate. Given its size and provenance, this bone probably belongs to the same individual represented by the NMMP 20 primate partial skeleton described previously from the same locality. The new fossil, which preserves the region around the acetabulum and the adjacent part of the ilium, clearly exhibits strepsirrhine rather than anthropoid affinities. This addition to our knowledge of the NMMP 20 partial skeleton allows us to reassess the different locomotor interpretations that have been proposed for this specimen. Aspects of pelvic morphology suggest that the NMMP 20 partial skeleton documents a primate that probably engaged in active arboreal quadrupedalism similar to that practiced by medium-sized Malagasy lemurids rather than lorislike slow moving and climbing. Given the conflicting phylogenetic signals provided by NMMP 39 (a talus showing anthropoid affinities) and NMMP 20 (a partial skeleton bearing adapiform affinities), it appears that two higher-level taxonomic groups of relatively large-bodied primates are documented in the Pondaung Formation. The recent discovery of two taxa of sivaladapid adapiforms from the Pondaung Formation indicates that the assumption that the NMMP 20 partial skeleton belongs to an amphipithecid can no longer be sustained. Instead, this specimen apparently documents a third large-bodied sivaladapid species in the Pondaung Formation.

Taxonomic status of purported primate frontal bones from the Eocene Pondaung Formation of Myanmar

Two isolated cranial fragments from the late middle Eocene Pondaung Formation of central Myanmar have previously been interpreted as frontal bones of the amphipithecid primate Amphipithecus mogaungensis. Aside from a few maxillary fragments, these specimens provide the only potential source of information currently available regarding the cranial anatomy of Amphipithecidae. Were this taxonomic attribution correct, these specimens would indicate that amphipithecids retained numerous primitive skull features, including the absence of a postorbital septum, the retention of a voluminous olfactory chamber, and strong separation between the forebrain and the orbital fossa. However, several anatomical details observable on these specimens are incompatible with their attribution to any primate and strongly suggest that they cannot be ascribed to Mammalia. Particularly problematic in this regard are the extreme thickness of the dermal bone, the odd structure of the alleged "frontal trigon," and the mediolateral orientation and uniquely robust construction of the descending process of the frontal bone (which partially segregates the orbital and temporal fossae). Because these isolated elements can no longer be attributed to Amphipithecus, the anatomical, phylogenetic, and behavioral inferences regarding amphipithecid paleobiology that have been drawn from these specimens can no longer be sustained.

Additional materials of Myanmarpithecus yarshensis (Amphipithecidae, Primates) from the middle Eocene Pondaung Formation

Myanmarpithecus yarshensis is an amphipithecid primate from the middle Eocene Pondaung Formation in Myanmar. It was previously known based on maxillary fragments with P(4)-M(3) and mandibular fragments with C-P(3) and M(2-3). This study reports new materials for the genus, including a humeral head fragment, a lingual fragment of the right M(2), a lingual fragment of the right M(3), and a left I(1). These new materials were collected from approximately the same point, and likely belonged to the same individual. The upper molar morphology and size of the new materials show similarity to those of the type specimen, indicating that the new materials can be assigned to M. yarshensis. The humeral head is the first postcranial element that is associated with dental materials for amphipithecids. The morphological similarity between the previously reported larger humerus and this specimen confirms the assignment of the former specimen to Amphipithecidae and suggests common locomotor adaptations in the family. The upper central incisor is large relative to the molar fragments, but is within the variation among extant platyrrhines. The tooth is spatulate-shaped and high crowned, and lacks the mesial process, indicating similarity to I(1) of haplorhines and clear differences from that of adapoids. It has been suggested that amphipithecids, including Myanmarpithecus, have affinities with notharctine adapoids, but the morphology of I(1) does not support the notharctine hypothesis of the Amphipithecidae.

Anthropoid primates from the Oligocene of Pakistan (Bugti Hills): data on early anthropoid evolution and biogeography

Asian tarsiid and sivaladapid primates maintained relictual distributions in southern Asia long after the extirpation of their close Holarctic relatives near the Eocene-Oligocene boundary. We report here the discovery of amphipithecid and eosimiid primates from Oligocene coastal deposits in Pakistan that demonstrate that stem anthropoids also survived in southern Asia beyond the climatic deterioration that characterized the Eocene-Oligocene transition. These fossils provide data on temporal and paleobiogeographic aspects of early anthropoid evolution and significantly expand the record of stem anthropoid evolution in the Paleogene of South Asia.

Deep Time and the Search for Anthropoid Origins

Recent fossil discoveries, phylogenetic analyses, revised reconstructions of continental drift, and accumulating molecular evidence have all yielded new information relating to anthropoid origins within the broader context of primate evolution. There is an emerging consensus among molecular studies that four superorders of eutherian mammals can be recognized: Afrotheria, Euarchontoglires (to which primates belong), Laurasiatheria, and Xenarthra. Overall, molecular phylogenies for mammals agree with some statistical analyses of the primate fossil record in indicating an early origin for primates around 85 Ma ago, and the divergence of haplorhines and strepsirrhines at ca. 77 Ma. Such an ancient date for the origin of haplorhines is some 17 Ma prior to the first known possible primate, and some 22 Ma before the earliest fossil evidence of undoubted euprimates. Because anthropoid fossils date back at least to the late Eocene and perhaps to the middle Eocene, and given indications of an early origin for primates, it is unlikely that ancestral anthropoids arose within any other currently known clade of fossil primates (adapiforms, omomyiforms, strepsirrhines, or tarsiiforms). Implications of new molecular, morphological, and biogeographic lines of evidence are explored with respect to the likely time and place of the origin of anthropoids. Four competing, testable hypotheses are reviewed in detail: 1) the Paratethyan hypothesis, 2) the continental Asian hypothesis, 3) the Indo-Madagascar hypothesis, and 4) the African hypothesis. A case is made that current evidence best supports a relatively ancient Gondwanan origin for primates, as well as a Gondwanan (African or Indo-Madagascan) origin for anthropoids at least as old as that of any other currently documented major primate clade. Available fossil evidence at present seems to be most compatible with the African hypothesis, but it is noteworthy that primates are included not in Afrotheria but in Euarchontoglires.

The eosimiid primates (Anthropoidea) of the Heti Formation, Yuanqu Basin, Shanxi and Henan Provinces, People's Republic of China

We describe the eosimiid primate fossils collected during the course of four field seasons in the late middle Eocene Heti Formation of central China. In addition to providing new information about the anatomy of Eosimias centennicus, the Heti Formation sample documents substantial taxonomic diversity in the Asian eosimiid radiation. One new genus and three new species of Eosimiidae are proposed here. These include Eosimias dawsonae, n. sp.; Phenacopithecus xueshii, n. gen. and sp.; and Phenacopithecus krishtalkai, n. sp. The anatomy of the upper dentition of eosimiids is described in detail for the first time. As is the case for the lower dentition, a unique combination of primitive and derived traits characterizes the upper dentition of Eosimias and Phenacopithecus. Eosimiid upper molars bear many of the same derived features-including strong protocone cristae and the absence of a postprotocingulum-that have been cited as evidence for a special relationship between anthropoids and certain adapiforms. However, the upper molars of eosimiids further approximate those of other basal anthropoids in having reduced or absent conules and complete lingual cingula. These features are lacking in Periconodon and other adapiforms that have been regarded by some workers as being phylogenetically close to anthropoids. Given that similarities in upper molar anatomy are among the only derived features that can be cited in support of a possible adapiform ancestry for anthropoids, the occurrence of these same features in eosimiids significantly weakens the adapiform hypothesis of anthropoid origins. The holotype maxillary fragment of Phenacopithecus krishtalkai reveals that eosimiids possessed a relatively small infraorbital foramen and a deep lower face between the inferior orbital margin and the alveolar border. Eosimiids therefore lacked the orbital hypertrophy characteristic of living tarsiers and many fossil omomyids and microchoerids. Eosimiids apparently had relatively small orbits, suggesting that they maintained a diurnal activity cycle.

The paleobiology of Amphipithecidae, South Asian late Eocene primates

Analysis of the teeth, orbital, and gnathic regions of the skull, and fragmentary postcranial bones provides evidence for reconstructing a behavioral profile of Amphipithecidae: Pondaungia, Amphipithecus, Myanmarpithecus (late middle Eocene, Myanmar) and Siamopithecus (late Eocene, Thailand). At 5-8 kg, Pondaungia, Amphipithecus, and Siamopithecus are perhaps the largest known Eocene primates. The dental and mandibular anatomy suggest that large-bodied amphipithecids were hard-object feeders. The shape of the mandibular corpus and stiffened symphysis suggest an ability to resist large internal loads during chewing and to recruit significant amounts of muscle forces from both the chewing and non-chewing sides of the jaw so as to increase bite force during mastication. The large spatulate upper central incisor of Pondaungia and projecting robust canines of all the larger amphipithecids suggest that incisal food preparation was important. The molars of Siamopithecus, Amphipithecus, and Pondaungia have weak shearing crests. This, and the thick molar enamel found in Pondaungia, suggests a diet of seeds and other hard objects low in fiber. In contrast, Myanmarpithecus was smaller, about 1-2 kg; its cheek teeth suggest a frugivorous diet and do not imply seed eating. Postcranial bones (humerus, ulna, and calcaneus) of a single large amphipithecid individual from Myanmar suggest an arboreal quadrupedal locomotor style like that of howler monkeys or lorises. The humeral head is rounded, proximally oriented, and the tuberosities are low indicating an extremely mobile glenohumeral joint. The great thickness of the midshaft cortical bone of the humerus implies enhanced ability to resist bending and torsion, as seen among slow moving primate quadrupeds. The elbow joint exhibits articular features for enhanced stability in habitually flexed positions, features also commonly found in slow moving arboreal quadrupeds. The short distal load arm of the calcaneus is consistent with, but not exclusive to, slow, arboreal quadrupedalism, and suggests no reliance on habitual leaping.

The anthropoid status of a primate from the late middle Eocene Pondaung Formation (Central Myanmar): tarsal evidence

Primate dental and postcranial remains from the Eocene Pondaung Formation (Myanmar) have been the subject of considerable confusion since their initial discoveries, and their anthropoid status has been widely debated. We report here a well preserved primate talus discovered in the Segyauk locality near Mogaung that displays derived anatomical features typical of haplorhines, notably anthropoids, and lacks strepsirhine synapomorphies. Linear discriminant and parsimony analyses indicate that the talus from Myanmar is more similar structurally to those of living and extinct anthropoids than to those of adapiforms, and its overall osteological characteristics further point to arboreal quadrupedalism. Regressions of talar dimensions versus body mass in living primates indicate that this foot bone might have belonged to Amphipithecus. This evidence supports hypotheses favoring anthropoid affinities for the large-bodied primates from Pondaung and runs contrary to the hypothesis that Pondaungia and Amphipithecus are strepsirhine adapiforms.

Chronology of primate discoveries in Myanmar: influences on the anthropoid origins debate

The history of primate paleontology in Asia is long and complex, beginning with the first discoveries of fossil primates on the Indian subcontinent in the early 1830's. The first Eocene mammals from Asia were collected in Myanmar and described in 1916, while the first primates, Pondaungia and Amphipithecus, were described in 1927 and 1937, respectively, both from the Pondaung Formation in Myanmar. For the next 60 years, these two Pondaung taxa remained as the only known Eocene primates from Myanmar and one of the few records of Eocene primates from all of Asia. Taxonomically, Pondaungia and Amphipithecus were linked with a number of different groups, including archaic, hoofed ungulates (condylarths), adapiform primates, omomyid primates, and anthropoids. While no consensus existed, Pondaungia and Amphipithecus were most commonly compared with anthropoids. Beginning in the late 1990s, new primates were discovered in Myanmar, including smaller-bodied forms such as Bahinia and Myanmarpithecus. Also, new and better specimens of the larger-bodied Pondaungia and Amphipithecus began to appear, including the first cranial and postcranial fragments. Evaluations based on these new specimens, especially the postcrania, indicate that the two larger-bodied Myanmar taxa are adapiform primates that show their closest affinities to North American notharctines. The smaller-bodied taxa remain enigmatic, but may share their closest affinities with North American and Asian omomyid primates and Asian Tarsius. None of the known Asian primate taxa appear closely related to African anthropoids, which suggests that true anthropoids did not reach Asia until the latest Oligocene or earliest Miocene. These facts make an Asian origin for Anthropoidea unlikely. Additional and earlier evidence from both Asia and Africa is required before the ultimate origin of anthropoids can be determined. It appears possible that true anthropoids were an ancient radiation that may have been part of a Gondwanan (southern hemisphere) community that is, at present, poorly sampled and little understood.

Endocranial cast and morphology of the olfactory bulb of Amphipithecus mogaungensis (latest middle Eocene of Myanmar)

A detailed endocranial cast of the olfactory bulb of Amphipithecus mogaungensis, a latest middle Eocene primate from the Pondaung Formation (Myanmar), was studied in comparison with some Paleogene primates, the olfactory bulb of which has been reported. The olfactory bulb of Amphipithecus is located just anterior to the postorbital constriction, that is, within the interorbital septum. It is relatively large and pedunculate, not overlapped by the frontal lobe, and consists of two parallel aligned bodies. The relative volume of the olfactory bulb shows the same pattern as in adapiforms, but the location and bilobed form are more similar to those of omomyoids than of adapiforms.

The upper dentition and face of Pondaungia cotteri from central Myanmar

A specimen of Pondaungia from the late middle Eocene Pondaung Formation in central Myanmar includes maxillary fragments and parts of the dentition, some hitherto undocumented, including the upper central incisor, canine, premolars and molars. Pondaungia has a large spatulate I1 closely resembling that of crown anthropoids. It possesses a stout projecting upper canine (like anthropoids) but differs from that tooth of crown anthropoids in lacking a strong mesial groove. There are three upper premolars of which P2 is distinctly smaller than P3 or P4. P3 has a buccolingually oriented mesial profile and an inflated distal profile resembling that of parapithecids and crown anthropoids. The distolingual molar cusp is a hypocone and is not homologus with the "pseudohypocone" of notharctines because the cusp is neither twinned with the protocone nor attached to a Nannopithex-fold. Pondaungia has a stout zygomatic root with a strongly demarcated muscle scar for the superficial masseter situated well above the occlusal plane. The inferior orbital margin is not preserved but the inflated suborbital region allows for the inference that the orbit was small. This specimen is not sufficiently well preserved to identify if there was postorbital closure. However, a specimen of the frontal bone of Amphipithecus shows that its orbital septum was absent or poorly developed. If, as commonly supposed, Pondaungia andAmphipithecus are sister taxa, postorbital closure was probably absent in Pondaungia. The large incisors, molars with poorly developed crests and thick enamel, together with the stoutly developed and strong dorsal component of the force vector of the superficial masseter muscle suggest that Pondaungia had a diet low in fiber, but that included hard food objects like nuts or seeds. The present material adds to the structural similarities between Pondaungia and anthropoids, but whether these similarities are due to shared descent or functional and adaptive convergence remains unresolved.

Molecular estimates of primate divergences and new hypotheses for primate dispersal and the origin of modern humans

The concept of recent hominoid divergences has been a mainstay in molecular primatology since the 1970's. However, the ages allocated to the calibration points used to establish these divergence times and the estimates resulting from their application, notably the commonly accepted divergence between Pan (chimpanzees) and Homo 5 million years before present (MYBP), are now palaeontologically refutable. Here we estimate the ages of various primate divergences using three references with a more detailed fossil record than any of the traditional primate calibration points. Our findings suggest that the latter yield datings that are too recent by a factor of about two. For example, our estimates place the divergence between Pan and Homo 10.5-13 MYBP. The revised estimates of primate divergence times suggest a new hypothesis for primate evolution and dispersal: that the divergence between strepsirhines (lorises, lemurs) and anthropoids was contemporary with the break-up of Southern continents about 90 MYBP, with strepsirhines becoming isolated on Madagascar and later dispersing to Africa (and Asia) and anthropoids evolving in South America and subsequently colonizing Africa (and Asia), or possibly North America. In addition we present a new hypothesis, which accommodates the strikingly similar coalescence times for human mitochondrial DNA and the Y-chromosome. This hypothesis posits a common mitochondrial and Y-chromosome bottleneck about 400,000 years ago, associated with the origination of the human 2n = 46 karyotype, obstructing genetic exchange with the 2n = 48 Homo contemporaries.

Primate postcrania from the late middle Eocene of Myanmar

Fossil primates have been known from the late middle to late Eocene Pondaung Formation of Myanmar since the description of Pondaungia cotteri in 1927. Three additional primate taxa, Amphipithecus mogaungensis, Bahinia pondaungensis and Myanmarpithecus yarshensis, were subsequently described. These primates are represented mostly by fragmentary dental and cranial remains. Here we describe the first primate postcrania from Myanmar, including a complete left humerus, a fragmentary right humerus, parts of left and right ulnae, and the distal half of a left calcaneum, all representing one individual. We assign this specimen to a large species of Pondaungia based on body size and the known geographic distribution and diversity of Myanmar primates. Body weight estimates of Pondaungia range from 4,000 to 9,000 g, based on humeral length, humeral midshaft diameter, and tooth area by using extant primate regressions. The humerus and ulna indicate that Pondaungia was capable of a wide variety of forelimb movements, with great mobility at the shoulder joint. Morphology of the distal calcaneus indicates that the hind feet were mobile at the transverse tarsal joint. Postcrania of Pondaungia present a mosaic of features, some shared in common with notharctine and adapine adapiforms, some shared with extant lorises and cebids, some shared with fossil anthropoids, and some unique. Overall, Pondaungia humeral and calcaneal morphology is most consistent with that of other known adapiforms. It does not support the inclusion of Pondaungia in Anthropoidea.

A new anthropoid from the latest middle Eocene of Pondaung, central Myanmar

A new genus and species of medium-sized fossil primate, Myanmarpithecus yarshensis, is described from the lastest middle Eocene sediments of Pondaung, central Myanmar (Burma). The specimens consist of right maxillary fragments with P(4)-M(3)and a left mandibular corpus with C-P(3)and M(2-3). To date, three purported anthropoids have been discovered from the Pondaung Formation: Pondaungia and Amphipithecus (Amphipithecidae) and Bahinia (Eosimiidae). Myanmarpithecus differs from these other Pondaung primates in having cingular hypocones on upper molars and in lacking paraconids on M(2-3). Although Myanmarpithecus resembles some utahiin omomyines in superficial aspects of the morphology of M(2-3)(i.e., mesiodistally compressed molar trigonid and enamel crenulation), the morphological analysis of upper molars and lower premolars indicates that it is neither an omomyoid nor an adapoid but is more derived than fossil prosimians (such as adapoids, omomyoids, and tarsiers) and more anthropoid-like. On the other hand, it is more primitive (prosimian-like) than early anthropoids from the late Eocene/early Oligocene of the Fayum, Egypt. Myanmarpithecus is likely to be an early, primitive anthropoid ("protoanthropoid").

Diets of fossil primates from the Fayum Depression of Egypt: a quantitative analysis of molar shearing

Over the last 90 years, Eocene and Oligocene aged sediments in the Fayum Depression of Egypt have yielded at least 17 genera of fossil primates. However, of this diverse sample the diets of only four early Oligocene anthropoid genera have been previously studied using quantitative methods. Here we present dietary assessments for 11 additional Fayum primate genera based on the analysis of body mass and molar shearing crest development. These studies reveal that all late Eocene Fayum anthropoids were probably frugivorous despite marked subfamilial differences in dental morphology. By contrast, late Eocene Fayum prosimians demonstrated remarkable dietary diversity, including specialized insectivory (Anchomomys), generalized frugivory (Plesiopithecus), frugivory+insectivory (Wadilemur), and strict folivory (Aframonius). This evidence that sympatric prosimians and early anthropoids jointly occupied frugivorous niches during the late Eocene reinforces the hypothesis that changes in diet did not form the primary ecological impetus for the origin of the Anthropoidea. Early Oligocene Fayum localities differ from late Eocene Fayum localities in lacking large-bodied frugivorous and folivorous prosimians, and may document the first appearance of primate communities with trophic structures like those of extant primate communities in continental Africa. A similar change in primate community structure during the Eocene-Oligocene transition is not evident in the Asian fossil record. Putative large anthropoids from the Eocene of Asia, such as Amphipithecus mogaungensis, Pondaungia cotteri, and Siamopithecus eocaenus, share with early Oligocene Fayum anthropoids derived features of molar anatomy related to an emphasis on crushing and grinding during mastication. However, these dental specializations are not seen in late Eocene Fayum anthropoids that are broadly ancestral to the later-occurring anthropoids of the Fayum's upper sequence. This lack of resemblance to undisputed Eocene African anthropoids suggests that the "progressive" anthropoid-like dental features of some large-bodied Eocene Asian primates may be the result of dietary convergence rather than close phyletic affinity with the Anthropoidea.