Geographical and Body Size Distributions of the Pondaung Primates with a Comment on the Taxonomic Assignment of NMMP 20, Postcra

ANTHROPOLOGICAL SCIENCE Vol. 112, 67-74, 2004

Geographical and body size distributions of the Pondaung primates with a comment on the taxonomic assignment of NMMP 20, postcranium of an amphipithecid NAOKO EGI1*, SOE THURA TUN2, MASANARU TAKAI3, NOBUO SHIGEHARA3, TAKEHISA TSUBAMOTO3

Laboratory of Physical Anthropology, Department of Zoology, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606–8502 Japan,1 Department of Geology, University of Yangon, Yangon, Myanmar,2 Primate Research Institute, Kyoto University, Inuyama, Japan3

Received 23 May 2003; accepted 1 October 2003

Abstract Relative abundance and body size were compared among six primate genera found from the Pondaung Formation (latest middle Eocene, Myanmar). Pondaungia, consisting of two species, is the most common primate in the Pondaung fauna. A high abundance of Pondaungia savagei, the larger species, is recorded at the northern fossil localities (Mogaung area). At the southwestern localities (Bahin area), the primates are taxonomically more diverse than in the other areas, and there are no significant differences in abundance of the amphipithecid genera, Myanmarpithecus, Amphipithecus, and Pondaungia. The body sizes of the three eosimiid taxa (Eosimias-like eosimiid, undescribed eosimiid, and Bahinia) and Myanmarpithecus are distinct from one another, but those of the Amphipithecus and Pondaungia species are inseparable. The postcranial bones of a large-sized primate (NMMP 20) from the Pondaung Formation, consisting of humeral, calcaneal, ulnar, and vertebral fragments, most likely belong to Pondaungia cotteri or Amphipithecus mogaungensis, based on comparisons of body mass estimates of NMMP 20 with those of the taxonomically allocated dentognathic specimens. Although NMMP 20 was previously cited as Pondaungia savagei, we consider the current evidence to be insufficient to resolve its species or generic-level taxonomic assignment.

Key words: Pondaung primates, abundance, body size range, taxonomic assignment

Introduction quently the material was described by Ciochon et al. (2001). Unfortunately, the postcranial material was found without The Pondaung Formation in central Myanmar, dating to any accompanying dental remains that would help settle its the latest middle Eocene, has yielded a diverse assemblage taxonomic assignment. No other primate specimens have of mammals, including primates (Cotter, 1914; Colbert, been recovered from the locality (Pk1). Ciochon et al. 1938; Aye Ko Aung, 1999; Tsubamoto et al., 2000, 2002; (2001) assigned NMMP 20 to Pondaungia savagei, the Tsubamoto, 2001). Two of the primates, Pondaungia and larger of the two species of Pondaungia, based on estimated Amphipithecus, have been known since the early twentieth body size and relative abundance of Pondaungia in the century (Pilgrim, 1927; Colbert, 1937). Other primate gen- Pondaung fauna, although Gunnell et al. (2000) did note that era, such as Myanmarpithecus (Takai et al., 2001), Bahinia assignment of postcranial material to Pondaungia or (Jaeger et al., 1999), an Eosimias-like eosimiid (Gebo et al., Amphipithecus was not possible due to the small size differ- 2002), and an undescribed eosimiid genus (Takai, in prep.) ence between the two genera. were discovered within the past five years. Until quite Given that the NMMP 20 specimen can, for the first time, recently, the Pondaung primates were known only from den- elucidate the postcranial morphology of the larger Pondaung tognathic remains, so their systematic position has predomi- primate, its assignment to any of the known Pondaung pri- nantly been discussed in terms of their dental morphology. mate taxa evokes two procedural questions: 1) whether or In 1997, postcranial specimens of a large primate (NMMP not the Pondaung primates are separable in terms of their 20; NMMPNational Museum of Myanmar, Primates), con- body size, and 2) whether or not there are significant differ- sisting of humeral fragments, two ulnar trochleae, a calca- ences in relative abundance of the primates of the Pondaung neal fragment, limb bone shafts, and vertebral fragments, Formation fauna, either in the composite fauna or in that of were collected from the Pondaung Formation, and subse- each area. Several new specimens of Pondaung primates have been collected since NMMP 20 was discovered. In this * Corresponding author. e-mail: [email protected] study, we clarify the relative body size range and geographic phone: 81-75-753-4094; fax: 81-75-753-4083 distributions of the Pondaung primates, using an enlarged Published online 16 April 2004 sample that includes the new material. We then reevaluate in J-STAGE (www.jstage.jst.go.jp) DOI: 10.1537/ase.00076 whether or not the current evidence can conclusively be used

© 2004 The Anthropological Society of Nippon 67 68 N. EGI ET AL. ANTHROPOLOGICAL SCIENCE to assign NMMP 20 to a particular Pondaung primate taxon. ness of the strata, from the fossil bearing horizon to the base of the overlying Yaw Formation, is much greater in the Relative Abundance of the Pondaung Primates Mogaung area than in the other two areas. Nannoplanktonic fossils in rock samples from the Mogaung area are repre- The Pondaung Formation is lithologically divided into sented by index taxa of NP 15 to 18, while rock samples two parts, “the Lower Member” and “the Upper Member.” from the Bahin and Pangan areas predominantly contain All of the primate fossil-bearing horizons occur in the lower index nannoplanktonic fossils of NP 17 to 20. However, half of “the Upper Member” (Aye Ko Aung, 1999, in press). those from the Pangan area also contain nannoplanktonic This level is exposed at numerous places in the Pondaung fossils of NP 14 to 16 and NP 18 to 22 (Hla Mon, 1999). area, and there are many vertebrate fossil localities. The fos- Although resolution of relative age estimations based on sil localities are geographically divided into three areas, these index fossils is not high, and some of the samples Mogaung, Bahin, and Pangan (Figure 1; Pondaung Fossil apparently combine rocks of the Pondaung and other Paleo- Expedition Team, 1997; Aye Ko Aung, 1999; Tsubamoto, gene formations thus obscuring biostratigraphic relation- 2001). Although we have not yet reached a full understand- ships especially in the case of the Pangan area, the ing of the geological structure of the Pondaung Formation, nannoplanktonic fossils indicate that sediments of the some data suggest that the fossil horizons exposed in the Pondaung Formation of the Mogaung area are generally Mogaung area are lower in the sequence than those exposed older than those of the other two areas. in the Bahin and Pangan areas. Aye Ko Aung (1999, in press; The Pk1 locality (Sabapontaung kyitchaung in the local Aung Naing Soe et al., 2002) demonstrated that the thick- language), where NMMP 20 was found, is located in the

Figure 1. Map of Pondaung area. The rectangles with thick gray border indicate the three main fossil locality assemblages (Mogaung, Bahin, and Pangan areas). Ellipses are fossil localities, and the locality numbers catalogued by Kyoto University are indicated in italics. Localities with black colored ellipses yielded primate fossils (listed in Table 1). Squares are townships and villages. Vol. 112, 2004 RELATIVE OCCURRENCES OF THE PONDAUNG PRIMATES 69

Bahin area. Ciochon et al. (2001) mentioned the greater more common than Amphipithecus mogaungensis. abundance of Pondaungia specimens compared with the In the Bahin area, where NMMP 20 was collected, all other Pondaung primates, and added a comment that a man- Pondaung genera are represented. Amphipithecus, Myan- dible of Pondaungia (P. savagei) had been found at a nearby marpithecus, and Pondaungia are represented by four, three, locality (Pk2) in the Bahin area. Although this evidence was and two individuals, respectively. As mentioned above, sin- used as the basis upon which they made their taxonomic gle individuals of each eosimiid taxon has been collected. assignment of NMMP 20 to Pondaungia, no data on the rel- All of these primate fossils, except one specimen, have been ative abundance of primate fossils from the Pondaung area collected from localities a few kilometers west of Pauk- were presented. kaung and Bahin villages (Figure 2). Among these primate- Our current sample of the Pondaung primates includes a bearing localities, Pk2, Pk3, and Pk5 are similar in strati- total of 33 specimens. Table 1 shows the abundance of each graphic level to Pk1 (Maung Maung, 2003). Of the two indi- primate species based on the number of individuals instead viduals of Pondaungia, one (NMMP 24) was found at Pk2, of the number of specimens. Some individuals have several as noted by Ciochon et al. (2001). An additional Pondaungia specimen numbers because they were collected by different specimen (NMMP 41) has been collected from Pk5. How- researchers or on different dates. Thus, counting the number of specimens will bias the relative abundance of the primates. The sample of 33 specimens consists of 24 individuals from six genera. Pondaungia has been divided into two species, a smaller P. cotteri and a larger P. savagei, by Gun- nell et al. (2002). We follow their classification for the specimens included in their study. Concerning the specimen collected after their study (NMMP 41), the species-level taxonomy is left as indeterminate. When all three areas are combined, Pondaungia savagei and Amphipithecus mogaungensis are the most abundant species in the fauna, represented by six and seven individuals, respectively. The other species are represented by smaller numbers of individuals, three each for Myanmarp- ithecus yarshensis and for Pondaungia cotteri and one each for the eosimiid taxa (Bahinia, Eosimias, and the undescribed new genus). Pondaungia is found to be the most Figure 2. Detailed map of the Bahin and Paukkaung localities in abundant primate in the Pondaung Formation, as suggested the Bahin area. Closed circles are the fossil localities, and the black by Ciochon et al. (2001). Pondaungia savagei is the most circles are the primate-bearing localities. Locality names are indicated abundant species of the current sample, but it is only slightly in italics. NMMP 20 was found at the Pk1 locality.

Table 1. Primate fossils from the Pondaung Formation Total Mogaung area Bahin area Pangan area # # specimen (locality) # specimen (locality) # specimen (locality) cf. Eosimias 1 0 1 NMMP 23* (Pk2) 0 Eosimiidae indet. 1 0 1 NMMP 31 (Pk2) 0 Bahinia 1 0 1 NMMP 13, 14, 15, 16 (Bh1) 0 Myanmarpithecus 3 0 3 NMMP 8, 9, 10 (Bh1); 0 NMMP 11 (Bh1); NMMP 21 (Pk2) Amphipithecus 7 3 AMNH 32520 (Thdn); 4 NMMP 7 (Bh1); 0 NMMP 2 (Thdn); NMMP 18, 19** (Pk2); NMMP 6 (Thdn) NMMP 27** (PA1); NMMP 30 (Pk3) Pondaungia 10 6 2 2 Pondaungia cotteri 3 2 NMMP 4 (Lma); 0 1 GSI D201, D202, NMMP 22 (Lma) D203 (PGN1) Pondaungia savagei 6 4 NMMP 1, 3 (Lma); 1 NMMP 24 (Pk2); 1 NMMP 12 (PGN2) NMMP 5 (Lma); NMMP 17 (Thdn); NMMP 25 (Lma); Pondaungia sp. 1 0 1 NMMP 41 (Pk5); 0 Amphipithecidae indet. 1 0 1 NMMP 20* (Pk1) 0 The number of the primate species found from each area is based on individuals. * and ** indicate postcranial and cranial specimens, respectively. The other specimens include dental material. Institutional abbreviations: AMNHAmerican Museum of Natural History, GSIGeological Survey of India, NMMPNational Museum of Myanmar, Primates. 70 N. EGI ET AL. ANTHROPOLOGICAL SCIENCE ever, this does not mean that Pondaungia is the most abun- ships used in this study are those of Egi et al. (2004), which dant primate at this stratigraphic level. Every Pondaung were based on an extant sample of prosimians and small to primate genus, except Bahinia, is known from Pk2, and medium sized anthropoids. The dental specimens of the Amphipithecus has been collected from both Pk2 and Pk3. Pondaung primates included in this study are: Pondaungia No eosimiid specimen has been collected from the other cotteri—GSI D201 and D203; Pondaungia savagei— two areas, so primate samples from the Pangan and NMMP 1, 3, 5, 12, 17, 24 and 25; Pondaungia sp.—NMMP Mogaung areas are taxonomically less diverse than those 41; Amphipithecus mogaungensis—AMNH 32520, NMMP from the Bahin area. From the Pangan area, only Pondaun- 2, 6, 7, 18 and 30; Myanmarpithecus yarshensis—NMMP 8, gia has been found. The sample is represented by only two 9 and 10; Bahinia pondaungensis—NMMP 14, 15 and 16. individuals, one Pondaungia savagei and one P. cotteri. The measurements of these specimens were obtained from Dental specimens from the Mogaung area are represented by Egi et al. (2004), and from the literature listed therein. For nine individuals, six Pondaungia and three Amphipithecus. NMMP 24, 25 and 41, measurements were taken by one of Among the six individuals of Pondaungia, four are P. sav- us (M.T. or N.E.) directly on the specimens during the agei, and two have been assigned to P. cotteri. course of the present study. Crown areas in squared millime- When all the localities are combined, the dominance of ters for these specimens are: M1 of NMMP 24, 32.5, M2 of 1 the genus Pondaungia is evident. However, there are some NMMP 24, 44.9, M1 of NMMP 25, 36.8, M of NMMP 41, differences in the occurrence of primate fossils among the 48.1, M2 of NMMP 41, 50.4. The body mass of the unde- three geographic areas. The more frequent occurrence of scribed eosimiid (NMMP 31) was estimated from the crown smaller primates in the Bahin area than in the other areas is area of M3 because no other tooth is available. The body probably influenced, to some extent, by collecting biases. mass estimate for the Eosimias-like eosimiid specimen Despite the dominance of Pondaungia in Mogaung (and (NMMP 23), which is a calcaneal fragment, was obtained Pangan) areas, Amphipithecus and Myanmarpithecus are from Gebo et al. (2002). just as abundant as Pondaungia in the Bahin area, where The estimated body mass for the Pondaung primates are NMMP 20 was found. The differences in the occurrence of presented in Figure 3 and Tables 2 and 3. The six Pondaung the larger species between the Mogaung and Bahin areas primate genera are separable into the smaller eosimiids and may be an artifact of small sample sizes, or it may reflect a the larger amphipithecids. All the eosimiid species are change of relative abundances through time. inferred to have weighed less than 1 kg. Among them, Bahinia is the largest, weighing approximately 0.6 kg, and Comparison of Estimated Body Mass the body mass for the Eosimias-like eosimiid is estimated as among the Pondaung Primates 0.11 kg (Gebo et al., 2002). Body size of the undescribed new eosimiid falls between those of the other two eosimiids. Body size ranges are compared among the Pondaung pri- Among the amphipithecids, Myanmarpithecus is estimated mates. Body mass is estimated from the crown areas of the to have weighed about 1.8 kg, and is clearly smaller than upper and lower first and second molars, whichever are Amphipithecus and Pondaungia. Although the sample size available. These four molars were chosen because these for each genus is small and the confidence intervals of the teeth are known to have lower intraspecific variation than dental based body mass estimates are large, it seems that the other teeth (Gingerich and Schoeninger, 1979; Egi et al., body size of each Pondaung primate taxa is distinct, except 2002, 2004). The body mass to tooth crown area relation- with the larger two genera.

Figure 3. Comparison of estimated body mass of NMMP 20 and that of the known Pondaung primate taxa. Body mass is plotted in logarithmic scale. See Tables 2 and 3 for the raw data. The dotted line for cf. Eosimias indicates the range of body mass estimates derived from the various calcaneal dimensions. Thin lines indicate the 95% confidence intervals of the body mass estimates based on molar crown areas, calculated using the nested degree of freedom according to the phylogeny of the comparative sample. The thick line for NMMP 20 indicates the 95% confidence inter- val of the body mass estimates derived from the humeral dimensions. Vol. 112, 2004 RELATIVE OCCURRENCES OF THE PONDAUNG PRIMATES 71

Table 2. Body mass estimates (kg) for Pondaung primates taxa N body mass range (95% CI) estimator comparative sample cf. Eosimias 1 0.052–0.18 (n/a) calcaneal dimensions strepsirhines mean0.11 Eosimiidae indet. 1 0.42 (0.31–0.55) M3 crown area prosimians 1 2 Bahinia 1 0.55–0.66 (0.40–0.94) M , M , M1 crown areas prosimians 1 2 Myanmarpithecus 1 1.5–2.1 (0.78–3.3) M , M , M2 corwn areas prosimians; anthropoids 1 2 Amphipithecus 6 4.9–7.0 (2.3–9.0) M , M , M1, M2 crown areas prosimians; anthropoids Pondaungia 1 2 Pondaungia cotteri 1 3.9–5.9 (1.8–8.6) M , M , M2 corwn areas prosimians; anthropoids 2 Pondaungia savagei 7 5.5–8.8 (3.2–12.6) M , M1, M2 crown areas prosimians; anthropoids Pondaungia sp. 1 6.4–6.9 (3.1–12.0) M1, M2 crown areas prosimians; anthropoids N denotes the number of individuals that were included in the species. The body mass estimates for cf. Eosimias are from Gebo et al. (2002). The estimates for the other taxa are from Egi et al. (2004). Confidence intervals were calculated using the nested degree of freedom (Smith, 1994), accounting for the phylogeny of the comparative samples. See Table 3 for the body mass estimates of NMMP 20.

Table 3. Body mass estimates (kg) for NMMP 20 NMMP 20 body mass estimate equations estimator body mass (95% CI) sample N equation r SEE humerus cortical area 4.57 (4.11–5.02) prosimians, platyrrhines 46 logeY1.29logeX3.85 0.97 0.29 polar second moment of area 3.90 (3.74–4.06) prosimians, platyrrhines 46 logeY0.68logeX4.34 0.98 0.25 total periosteal area 3.62 (3.35–3.92) prosimians, platyrrhines 46 logeY1.37logeX2.91 0.98 0.24 head surface area 4.80 (4.46–5.17) prosimians, monkeys 75 logeY1.56logeX0.53 0.98 0.32 calcaneus cuboid facet height (C6) 4.87 strepsirhines 23 logeY2.70logeX2.46 0.98 0.28 cuboid facet area (index 6) 4.98 strepsirhines 23 logeY1.43logeX2.55 0.97 0.32 The body mass estimate equations of the humeral diaphyseal cross-sectional properties and calcaneal dimensions were obtained from Runestad (1994) and Dagosto and Terranova (1992), respectively. The body mass to humeral head surface area relationship was calculated using the data listed in Swartz (1989), Runestad (1994), and Rafferty (1996).

Among Amphipithecus mogaungensis and the two species bly correspond to the degree of body size variation in the of Pondaungia, P. cotteri is the smallest and P. savagei is the species. largest. The smallest body weight estimate for Pondaungia Within the genus Pondaungia, mesiodistal length of M2 in cotteri is 3.8 kg, and the largest for P. savagei is 8.8 kg, indi- the larger maxillary specimen (NMMP 12) is 19% longer cating that these amphipithecids were large compared with than that in the smaller specimen (GSI D203). Mesiodistal other contemporaneous primates. The occurrence of a high length of M2 in the largest mandibular specimen (NMMP proportion of large-sized primates may be noted as one of 17) is 16% longer than that in the smallest specimen (GSI the characteristics of the Pondaung mammalian fauna. D201) (Figure 4). As a result, the body mass estimates of the 2 The estimated body mass of Amphipithecus and Pondaun- larger individuals based on M and M2 crown areas (NMMP gia differs considerably depending on the choice of teeth 12 and 17) are about one and one half times greater than examined, even when the teeth come from the same jaw. Such methodological limitations enhance the apparent over- lap of body size ranges between Pondaungia cotteri and P. savagei, and between Amphipithecus mogaungensis and the two Pondaungia species. Although the actual body mass range of each species might have been more distinct, sepa- rating Amphipithecus from Pondaungia using estimated body size seems impossible. Both Amphipithecus and Pondaungia show individual variation. Within Amphipithecus mogaungensis, the lengths of M1 and M2 of the larger individuals (AMNH 32520 and NMMP 2) are approximately 8% longer than those of the smaller individual (NMMP 30). The resulting body mass Figure 4. Comparison of molar crown sizes between the smallest and the largest Pondaungia specimens. (A) Left M1–2 of Pondaungia estimates based on M1 and M2 crown areas of the larger indi- 1–2 viduals (AMNH 32520 and NMMP 2) are 28% and 22% cotteri (GSI D203); (B) Left M of Pondaungia savagei (NMMP 12); (C) Reversed image of left M2–3 of Pondaungia cotteri (GSI larger than those based on the respective tooth crown areas D201); (D) right M1–3 of Pondaungia savagei (NMMP 17). of the smaller individual (NMMP 30). These values proba- Scale1cm. 72 N. EGI ET AL. ANTHROPOLOGICAL SCIENCE those of the smallest individuals (GSI D203 and D201). 1997). Within the specimens that have been assigned to Pondaun- In this study, body mass of NMMP 20 is estimated based gia savagei by Gunnell et al. (2002), the ratio of body mass on humeral diaphyseal cross-sectional properties, humeral estimates between the large (NMMP 17) and small individu- head surface area, and calcaneocuboid facet height and sur- als (NMMP 24) is 32% based on M1 and 15% based on M2, face area. Humeral length was not used as a body mass esti- which are similar to body size variation estimated for mator in this study. The humerus of NMMP 20 was reported Amphipithecus. Comparing the smallest individual of to be complete in Ciochon et al. (2001), but a small section Pondaungia savagei (NMMP 24) with P. cotteri (GSI of the shaft appears to be missing. This can be seen from the D201), the difference of body mass estimates based on M2 circumferences of the two broken ends which are not the crown area is 30%. These observations suggest that interspe- same, and from the position of origin of the supinator crest cific differences in body size between the two Pondaungia that would be extremely proximal if the humerus is assumed species is not very marked compared to intraspecific varia- to be complete. The equations for estimating body mass tion within P. savagei. The large size variation within the from humeral diaphyseal cross-sectional properties and cal- genus probably supports the recognition of two species. caneal dimensions were obtained from Runestad (1994) and However, with the currently available samples, we cannot Dagosto and Terranova (1992), respectively. Body mass was set a threshold of body size that best distinguish between the calculated from humeral head surface area using the data two species. This is because complications exist such as the listed in Swartz (1989), Runestad (1994), and Rafferty body mass estimates vary according to the tooth type used, (1996). Table 3 summarizes the body mass estimates of interspecific variation in size appears to be small relative to NMMP 20. The extant comparative sample consists of pros- intraspecific variation, and the presence of individuals with imians and monkeys for the humeral, and strepsirhines for intermediate body size (e.g., NMMP 24, 41). the calcaneal measurements. The humeral and calcaneal measurement items used in this study are shown in Figure 5. Taxonomic Assignment of NMMP 20 The shaft cross-sectional properties were calculated from the external and internal anteroposterior and mediolateral diam- Specimen NMMP 20, the postcranial fragments of a eters (Runestad, 1994), and the measurements were taken larger primate without associated dental material, was origi- just distal to the termination of the deltopectoral crest where nally assigned to Pondaungia savagei based on the supposed a natural break was available. The humeral head surface area abundance of Pondaungia in the fauna and on the large esti- was calculated from the anteroposterior and mediolateral mated body size (Ciochon et al., 2001). Subsequent publica- chords and depth (Runestad, 1994; Rafferty, 1996). The cal- tions have followed this taxonomic assignment, at least at caneocuboid facet height (C6) and width (C5) were mea- the generic level (Ciochon and Gunnell, 2002a, b; Gunnell et al., 2002; Kay et al., in press). We discuss here whether or not the relative abundance and body size distribution data of the Pondaung primates, presented in the previous sections, actually support Ciochon et al.’s (2001) taxonomic assignment. Concerning relative abundance of the Pondaung primates, our observations indicate that Pondaungia savagei and Amphipithecus mogaungensis are the most frequently found species in the fauna. In the Bahin area, where NMMP 20 was collected, four, three, and two individuals, respectively, of Amphipithecus, Myanmarpithecus, and Pondaungia, have been collected. Therefore, the current data on the relative abundance of primate fossils do not support an assignment of NMMP 20 to Pondaungia rather than to the other genera. The species level taxonomy for one of the Pondaungia specimens from the Bahin area has not been determined. This precludes an assessment of relative abundance at the species level. A secure classification of Pondaungia at the species level, and a larger sample that can provide a more reliable basis for evaluation of relative abundance are necessary before relative abundance can be used in the taxonomic assignment of NMMP 20 to any species. Figure 5. Measurements taken on NMMP 20. Diagrams are the left humerus in posterior view (A) and in medial view (B), reversed Two disparate body sizes were indicated for NMMP 20 by image of shaft cross-section of the right humerus (C), shaft cross-sec- Ciochon et al. (2001): one was 5 to 6 kg (the range of body tion of the left humerus (D), and the left calcaneum in superior (E) and mass was plotted from 5.5 to 6 kg in Figure 2 of Ciochon et distal (F) views. Lines with arrows indicate measurements taken in this al., 2001) estimated from humeral length and mid-shaft study: humeral head width (A), humeral head length and depth (B), diameters, and the other was their assessment that the external and internal anteroposterior and mediolateral diameters of the shaft (C and D), and calcaneocuboid articular surface height and width humeral size of NMMP 20 is comparable to that of Lemur, (F). The dark colored areas indicate broken or damaged parts. with a body mass of around 2.2 kg (Smith and Jungers, Scale1cm. Vol. 112, 2004 RELATIVE OCCURRENCES OF THE PONDAUNG PRIMATES 73 sured following Dagosto and Terranova (1992), and the Amphipithecus and Myanmarpithecus are as abundant as calcaneocuboid facet area (index 6) was calculated as the Pondaungia in the area where NMMP 20 was found. The product of the two measurements. current evidence is insufficient to assign NMMP 20 to a spe- The body mass estimates of NMMP 20 based on the shaft cific taxon, and its taxonomic assignment should be left as cross-sectional properties are around 4 kg, while the humeral an indeterminate amphipithecid until further evidence can head gives a larger body mass estimate, 4.8 kg. The differ- solve this problem. ence between the estimates derived from the two humeral parts may be related to an increased mobility of the shoulder Acknowledgements joint, or to the subadult age of the individual which is hinted at by the trace of an epiphyseal line around the humeral We thank the following personnel who have helped our head. The body mass estimates of NMMP 20, derived from field expedition in the Pondaung area and research at the the calcaneal measurements, agree better with the estimate National Museum of Myanmar in Yangon: Brig.-Gen. Than made from humeral head surface area. The values estimated Tun, Maj. Bo Bo (Office of Chief Military Intelligence, Min- from the shaft cross-sectional properties are probably close istry of Defence, Myanmar), Ms. Yumi Kaneko (Myanmar to the body mass of the individual at its death, assuming that Embassy in Tokyo), Dr. Tin Thein, Mr. Chit Sein (University long bone shaft diaphyses behave plastically when com- of Yangon), Dr. Aye Ko Aung (Dagon University), Dr. pared with external articular size and shape (Ruff and Maung Maung (University of Mandalay), Mr. Aung Naing Runestad, 1992). In this case, it seems that the values esti- Soe (University of Pathein), and Dr. Hisashi Suzuki (Monta- mated from the humeral head and calcaneal measurements nuniversitaet). Financial support was provided by Overseas more likely represent the body mass of NMMP 20 when it Scientific Research Fund (No. 09041161, No. 14405019), would have reached a full adult age. Therefore, it can be said and the MEXT Grant-in-Aid for COE Research (No. that NMMP 20 belonged to an animal with an adult body 10CE2005) for the 21st Century COE Program (A2 to Kyoto mass of a little less than 5 kg. University) and for JSPS Fellows (No. 15004748). The estimated body mass of NMMP 20 is much larger than that of the eosimiids and Myanmarpithecus yarshensis, but do not exceed the body mass estimates of Pondaungia References savagei. The estimated body mass of NMMP 20 best fits Aung Naing Soe, Myitta, Soe Thura Tun, Aye Ko Aung, Tin with that of Pondaungia cotteri, but it also overlaps with the Thein, Marandat B., Ducrocq S., and Jaeger J.-J. (2002) Sedi- lower end of the range of body mass estimates of Amphipith- mentary facies of the late middle Eocene Pondaung Forma- ecus mogaungensis. tion (central Myanmar) and the paleoenvironments of its It has been suggested that body mass estimates based on Anthropoid Primates. Comptes Rendus Palevol, 1: 153-160. some limb bone dimensions, such as the cross-sectional Aye Ko Aung (1999) Revision on the stratigraphy and age of the primates-bearing Pondaung Formation. In: Office of Strategic properties of the long bone shafts and articular sizes, are Studies, Ministry of Defence, Myanmar Government (ed.), substantially more reliable as indicated by the lower stan- “Proceedings of the Pondaung Fossils Expedition Team,” dard error of estimates than those based on dental measure- Myanmar Government, Yangon, pp. 131–151. ments (Damuth and MacFadden, 1990). In addition, a study Aye Ko Aung (in press) The primate-bearing Pondaung Formation of body mass estimates for Proconsul by Rafferty et al. in the upland area, northwest of central Myanmar. In: Ross C. (1995) demonstrated that body mass estimates derived from and Kay R. (eds.), “Anthropoid Origins: New Visions,” Klu- wer Academic/Plenum, New York. skeletal dimensions are consistent with each other, but that Ciochon R.L., Gingerich P.D., Gunnell G.F., and Simons E.L. dental size overestimates body mass in the smallest species (2001) Primate postcrania from the late middle Eocene of and underestimates body size in the larger species. Judging Myanmar. Proceedings of the National Academy of Sciences from these suggestions, the body mass estimates of NMMP of the United States of America, 98: 7672-7677. 20 probably more accurately represent the actual body mass Ciochon R.L. and Gunnell G.F. (2002a) Chronology of primate of the individual than would be possible from estimates discoveries in Myanmar: influence on the anthropoid origins based on molar crown areas. Body size of NMMP 20 was debate. Yearbook of Physical Anthropology, 45: 2-35. Ciochon R.L. and Gunnell G.F. (2002b) Eocene primates from originally estimated to fall within the range of Pondaungia Myanmar: historical perspectives on the origin of Anthro- savagei (Ciochon et al., 2001). However, the estimated body poidea. Evolutionary Anthropology, 11: 156-168. mass for the postcranium derived in this study is smaller Colbert E.H. (1937) A new primate from the upper Eocene than their value, and our results suggest that the possibility Pondaung Formation of Burma. American Museum Novi- of NMMP 20 belonging to Pondaungia savagei is low, tates, 951: 1-18. unless the species had a strong tendency for a macrodont Colbert E.H. (1938) Fossil mammals from Burma in the American Museum of Natural History. Bulletin of American Museum of dentition. Natural History, 74: 255-436. In conclusion, based on the comparison of body mass esti- Cotter G. de P. (1914) Some newly discovered coal-seams near the mates, NMMP 20 most likely belongs to Pondaungia cotteri Yaw River, Pakokku district, Upper Burma. Records of Geo- or Amphipithecus mogaungensis. The relative abundance of logical Survey of India, 44: 163-185. the Pondaung primate taxa does not provide sufficient evi- Dagosto M. and Terranova C.J. (1992) Estimating the body size of dence for choosing between Pondaungia or Amphipithecus Eocene primates: a comparison of results from dental and postcranial variables. International Journal of Primatology, as the likely taxon of NMMP 20. Although Pondaungia is 15: 307-344. the most common primate genus of the whole combined- Damuth J. and MacFadden B.J. (1990) Body Size in Mammalian area fauna, P. cotteri is much rarer than P. savagei, and Paleobiology: Estimation and Biological Implications. Cam- 74 N. EGI ET AL. ANTHROPOLOGICAL SCIENCE

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