Early Pliocene in central Myanmar

Journal of Human Evolution 84 (2015) 1e15

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First discovery of colobine fossils from the Late Miocene/Early Pliocene in central Myanmar Masanaru Takai a, *, Thaung-Htike b, Zin-Maung-Maung-Thein c, Aung Naing Soe d, Maung Maung e, Takehisa Tsubamoto f, Naoko Egi a, Takeshi D. Nishimura a, Yuichiro Nishioka a a

Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan Shwebo University, Shwebo, Myanmar Mandalay University, Mandalay, Myanmar d Defence Service Academy, Pyin Oo Lwin, Myanmar e Magway University, Magway, Myanmar f Hayashibara Museum of Natural Sciences, Setouchi 701-4212, Japan b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 August 2013 Accepted 4 April 2015 Available online 5 June 2015

Here we report two kinds of colobine fossils discovered from the latest Miocene/Early Pliocene Irrawaddy sediments of the Chaingzauk area, central Myanmar. A left mandibular corpus fragment preserving M1e3 is named as a new genus and species, Myanmarcolobus yawensis. Isolated upper (M1?) and lower (M2) molars are tentatively identified as Colobinae gen. et sp. indet. Although both forms are medium-sized colobines, they are quite different from each other in M2 morphology. The isolated teeth of the latter show typical colobine-type features, so it is difficult to identify their taxonomic position, whereas lower molars of Myanmarcolobus have unique features, such as a trapezoid-shaped long median lingual notch, a deeply concave median buccal cleft, a strongly developed mesiobuccal notch, and rather obliquely running transverse lophids. Compared with fossil and living Eurasian colobine genera, Myanmarcolobus is most similar in lower molar morphology to the Pliocene Dolichopithecus of Europe rather than to any Asian forms. In Dolichopithecus, however, the tooth size is much larger and the median lingual notch is mesiodistally much shorter than that of Myanmarcolobus. The discovery of Myanmarcolobus in central Myanmar is the oldest fossil record in Southeast Asia not only of colobine but also of cercopithecid monkeys and raises many questions regarding the evolutionary history of Asian colobine monkeys. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Colobinae Cercopithecidae Irrawaddy sediments Myanmarcolobus Late Neogene Southeast Asia

1. Introduction Colobine monkeys (Cercopithecidae, Colobinae) are now among the most diversified land mammals in South to Southeast Asia, but their evolutionary history is not well known because of their scarcity in the Asian fossil record. The known fossil record suggests that colobine monkeys originated on the African continent in the Middle Miocene (e.g., Benefit and Pickford, 1986; Nakatsukasa et al., 2010; Fleagle, 2013; Rossie et al., 2013), and some members entered Eurasia as early as the Late Miocene (Delson, 1994). The oldest Eurasian fossil colobine is Mesopithecus, a small-to-medium-sized terrestrial monkey, fossils of which have been discovered from

* Corresponding author. E-mail address: [email protected] (M. Takai). http://dx.doi.org/10.1016/j.jhevol.2015.04.003 0047-2484/© 2015 Elsevier Ltd. All rights reserved.

the Late Miocene to Late Pliocene in Europe and western Asia (Iran and Afghanistan; e.g., Heintz et al., 1981; Andrews et al., 1996; Jablonski, 2002). Recently, some researchers have suggested that “Presbytis” sivalensis, which was discovered from the Late Miocene/ Early Pliocene of Siwaliks, Indo/Pakistan in the 19th century (Lydekker, 1878), should be included in Mesopithecus (Harrison and Delson, 2007). In this paper we use ?Mesopithecus sivalensis for this small Siwalik colobine fossil, accepting the opinion of Harrison and Delson (2007). In addition, new specimens of Mesopithecus (M. cf. pentelicus) were discovered from the Late Miocene site in Yunnan Province, southwestern China, extending its geographical distribution as far as East Asia (Jablonski et al., 2011; Ji et al., 2013). After the appearance of Mesopithecus, a large-sized terrestrial colobine, Dolichopithecus, occurred in the Early Pliocene in Europe (e.g., Szalay and Delson, 1979; Delson, 1994; Jablonski, 2002). Some authorities consider that Dolichopithecus evolved from

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Mesopithecus by the end of the Miocene (Delson, 1994). Two largesized colobines, Parapresbytis and Kanagawapithecus, discovered from the Middle to Late Pliocene of East Asia (Transbaikalia and Japan, respectively) were once considered to be the subgenera of Dolichopithecus (Borissoglebskaya, 1981; Kalmykov and Maschenko, 1992; Delson, 1994; Iwamoto et al., 2005), but both are now regarded as independent genera, respectively (Jablonski, 2002; Maschenko, 2005; Egi et al., 2007; Takai and Maschenko, 2009; Nishimura et al., 2012). There is another enigmatic colobine tooth from the Early Pliocene that has been discovered in Yushe, Shaangxi Province, northern China, but no detailed descriptions have been published (Delson, 1996; Williams and Holmes, 2011). Concerning the phylogenetic relationships of these East Asian fossil colobines, Delson (1994) indicated the close relationships between Dolichopithecus, Parapresbytis, and Kanagawapithecus. However, a detailed morphological analysis of the cranial specimens using computed tomography (CT) scans revealed that Kanagawapithecus was quite different at least in cranial structure not only from Dolichopithecus and Parapresbytis but also from any extant Asian colobines (Nishimura et al., 2012). On the other hand, the oldest colobine fossils from Southeast Asia are isolated teeth and/or fragmentary jaws of Rhinopithecus discovered from the Early Pleistocene cave sediments of southern China, such as in Guangxi and Guangdong Provinces (Jin et al., 2009). Jablonski (2002) proposed an ancestoredescendant relationship between Parapresbytis and extant Rhinopithecus, but Takai and Maschenko (2009) disagreed with this hypothesis because no “intermediate” fossils have been discovered from the Pliocene sediments of East Asia to date. Moreover, it is really strange that to date no colobine fossils have been reported from the Pliocene sediments of Southeast Asia, where many extant colobine monkeys are now flourishing. The present colobine fossils from the latest Miocene/Early Pliocene of central Myanmar represent the oldest discovery in Southeast Asia not only in terms of colobines but also of any cercopithecid monkeys. 2. Materials and methods In Myanmar, it is strictly prohibited to take fossil specimens on loan outside the country, so we made high-resolution silicone molds (Seamless Silicon, Nissin Resin Co., Ltd.) of the fossils in the field. Silicon molds were also taken from the extant colobine specimens at the museums using dental silicon (Exahiflex Injection Type, GC Corp.). After returning to Japan, we made epoxy casts and scanned the surface configuration of tooth casts using a needle scanning system composed of a 3D plotter (MDX-20) and scanning software (Dr. PICZA; Roland DG Corp.), with a resolution of 0.05 mm (Figs. 4e6), and also through a One-shot 3D Measurement Macroscope (VR-3050, Keyence Corp.; Figs. 8e10). The fossil specimens were compared with epoxy casts of other extant and extinct colobine teeth. 2.1. Institutional abbreviations Institutional abbreviations used here include: AMNH: American Museum of Natural History, New York, USA; BMNH: The Natural History Museum, London, UK; BSM: Bayerische Staatssammlung €ontologie, München, Germany; FSL: Laboratoire des Scifür Pala ences de la Terre, Faculte des Sciences, Universite de Lyon, France; GIN: Geological Institute, Russian Academy of Sciences, Russia; GSI: Geological Survey of India, India; GSP: Geological Survey of Pakistan, Pakistan; IVPP: Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; JMC: Japan Monkey Centre, Inuyama, Japan; KUPRI: Kyoto University, Primate Research

Institute, Inuyama, Japan; LGI: Laboratorul de Geologie, Universitate “Al. I. Cuza,” Iasi, Romania; LPB: Laboratorul de Paleontologie, University of Bucharest, Romania; MAFI: Foldtani Inteszet um National (Geological Seice), Budapest, Huangary; MNHN: Muse e Perpignan, France; d’Histoire Naturelle, Paris, France; MP: Muse NMB: Naturhistorisches Museum of Basel, Switzerland; NMMP-KUIR: National Museum of Myanmar, PaleontologyeKyoto UniversityeIrrawaddy specimen, Myanmar; PIN: Paleontological Institute, Russian Academy of Sciences, Russia; and ZRC: Zoological Reference Collection, National University of Singapore (Raffles Museum), Singapore. 2.2. Anatomical abbreviations Anatomical abbreviations used here include: BL: buccolingual width; prd: protodonid; med: metaconid; end: entoconid; hyd: hypoconid; hyld: hypoconulid; MD: mesiodistal length; tad: talonid; and trd: trigonid. 2.3. Geological setting of Chaingzauk The present specimens were collected from Neogene Irrawaddy sediments at two sites in Myokhinthar village, Chaingzauk area, Pauk township, Magway Division, central Myanmar in February, 2009 (Fig. 1). The Irrawaddy sediments, mainly composed of fluvial sediments 2,000 to 3,000 m in thickness (Bender, 1983; Wandrey, 2006), have traditionally been subdivided into Lower and Upper Irrawaddy based on the lithological and paleontological criteria. The Lower Irrawaddy overlies the Oligocene to Miocene “Freshwater Pegu Bed” and is correlated mainly to the Dhok Pathan Formation of the Siwalik Group of India/Pakistan, suggesting a Late Miocene to Early Pliocene age based on the mammal fossils (Bender, 1983), whereas the Upper Irrawaddy is overlain by the Middle Pleistocene to Holocene Terrace deposits and is conventionally referred to the Early Pleistocene (Stamp, 1922; Chhibber, 1934; Colbert, 1938, 1943; Bender, 1983). The Chaingzauk area, located about 10 km northeast of Pauk city, has been known for yielding numerous vertebrate fossils since the 19th century (Lydekker, 1878; Cotter, 1938; Pilgrim, 1939; Matthew, 1929). The geological age of the Chaingzauk fauna was originally proposed to be Late Miocene to Early Pliocene by Pilgrim (1939) and was recently reconfirmed as near the boundary between the Late Miocene and the Early Pliocene by the presence of the combination of the following mammal taxa (Table 1): Agriotherium myanmarensis (Ursidae, Carnivora), Hystrix paukensis (Hystricidae, Rodentia), Dorcatherium cf. anthracotherioides (Tragulidae, Artiodactyla), Microbunodon milaensis and Merycopotamus dissimilis (Anthracotheriidae, Artiodactyla), Sivachoerus prior and Propotamochoerus hysudricus (Suidae, Artiodactyla), and Hexaprotodon sivalensis and H. iravaticus (Hippopotamidae, Artiodactyla) (Pickford, 1988; van der Made, 1999; Barry et al., 2002, 2007; Badgley et al., 2008; Thaung-Htike, 2008; Nishioka et al., 2011; Ogino et al., 2011; Zin-Maung-Maung-Thein et al., 2011; Tsubamoto et al., 2012). The fossil localities of the Chaingzauk area are divided into two regions (or villages), the Chaingzauk (CHZ, northern part) and Myokhinthar (MKT, southern part) villages, although there is no distinct geographical boundary between them. All of the colobine fossils described here were collected in Myokhinthar, but several important, index taxa (Agriotherium, Sivachoerus, Propotamochoerus) and many bovids were discovered from Chaingzauk. Although it is hard to correlate the sediments of the two regions because of the complicated fluvial sedimentary structure (Fig. 2), these two regions are regarded as being almost similar in age based on the mammalian fossils and overall geological setting (Zin-Maung-

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Figure 1. Index map of central Myanmar, indicating the fossil localities (after Colbert, 1943). CHZ, Chaingzauk; MKT, Myokhinthar; Gbn, Gwebin.

Maung-Thein, 2010; Nishioka et al., 2011; Ogino et al., 2011; ZinMaung-Maung-Thein et al., 2011). 3. Description of Myanmarcolobus yawensis 3.1. Systematic paleontology Order Primates Linnaeus, 1758 Family Cercopithecidae Gray, 1821

Subfamily Colobinae Jerdon, 1863 Genus Myanmarcolobus, gen. nov. Type species Myanmarcolobus yawensis, sp. nov. 3.1.1. Distribution Irrawaddy sediments. Late Miocene/Early Pliocene, central Myanmar. 3.1.2. Generic diagnosis Medium-sized colobine monkey (Table 2). Differs from all medium- to large-sized colobines in having a deeply concave median buccal cleft, a mesiodistally long trapezoid-shaped

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Figure 3. Photographs of the colobine fossils discovered in the Chaingzauk area: a) NMMP-KU-IR 1200 (Myanmarcolobus yawensis, type specimen), left mandibular fragment preserving M1e3 in occlusal (a1, stereo), buccal (a2), and lingual (a3) views; b) NMMP-KU-IR 1199 (Colobinae gen. et sp. indet.), isolated right M1 (or M2) in occlusal view (stereo); c) NMMP-KU-IR 1419 (Colobinae gen. et sp. indet.), isolated left M2 in occlusal (c1, stereo) and lingual (c2) views. Scale bar, 5 mm.

Figure 2. The columnar section at the locality of MKT 2 and 7 in Myokhinthar, Chaingzauk area. Note that IR-1199 and 1419 were discovered at MKT 2 while IR-1200 was collected at MKT 7.

median lingual notch, and very obliquely oriented transverse lophids in the lower molars. Differs from small-sized colobines, such as Presbytis and Microcolobus, in having a buccodistally protruding large hypoconulid on M3 and a distinct mesiobuccal notch in the lower molars. 3.1.3. Etymology Named after the Union of Myanmar, the country where the type specimen was collected.

Figure 4. 3D images of the colobine fossils discovered in the Chaingzauk area: a) NMMP-KU-IR 1200 (Myanmarcolobus yawensis, type specimen), left mandibular fragment preserving M1e3 in buccal (a1), occlusal (a2), and lingual (a3) views; b) NMMPKU-IR 1199 (Colobinae gen. et sp. indet.), isolated right M1 (or M2) in occlusal view; c) NMMP-KU-IR 1419 (Colobinae gen. et sp. indet.), isolated left M2 in buccal (c1), occlusal (c2), and lingual (c3) views. Scale bar, 5 mm.

township, Magway Division, central Myanmar (Fig. 1). Late Miocene/Early Pliocene. 3.2.3. Known distribution As for genus. 3.2.4. Specific diagnosis As for genus.

3.2. Myanmarcolobus yawensis, gen. et sp. nov.

3.2.5. Etymology Named from Yaw River flowing near the type locality.

3.2.1. Holotype A left mandibular fragment preserving M1e3, NMMP-KU-IR 1200. 3.2.2. Type locality MKT 7 locality (N21
300 2600 , E94
290 5500 ), about 1.5 km west of Myokhinthar village, Chaingzauk area, Pauk

3.2.6. Description and comparisons The type specimen shows typical colobine features in the lower molars: bilophodonty with relatively high cusps and a deep median lingual notch (Figs. 3a and 4). The occlusal surfaces of the lower molars slope lingually posteriorly (M3 inclines about 30
more lingually than M1;

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Figure 5. 3D images of left M1e3 teeth of fossil colobine taxa mentioned in text in comparisons with Myanmarcolobus: a) Mesopithecus monspessulanus (NMB V.j. 87, mirror image), b) Dolichopithecus ruscinensis (or hypsilophus) (PIN N 355-7), c) Myanmarcolobus yawensis (NMMP-KU-IR 1200), d) Parapresbytis eohanuman (PIN 3381-236, mirror image), e) ?Mesopithecus sivalensis (GSP 14043), and f) “Semnopithecus” palaeindicus (BMNH M15710, mirror image). Occlusal (left column) and lingual (right column) views. All images are scaled to the same M1e3 size.

Fig. 4a), which is often seen in colobine monkeys. Transverse lophids run rather obliquely, especially on M2 (Figs. 5e6). The median buccal cleft is deeply concave. The M3 hypoconulid is large, protruding distally. The lower molars are as large as those of extant Nasalis, a smaller species of extant Semnopithecus, and the Late Miocene Mesopithecus (Fig. 7). They are much larger than those of extant Presbytis, Pygathrix, and Trachypithecus, and of the Late Miocene ?Mesopithecus sivalensis, but much smaller than those of the Pliocene Dolichopithecus, Parapresbytis, and extant/ extinct Rhinopithecus. Although the extant Trachypithecus sometimes retains obliquely running transverse lophids, it has a relatively shallow groove-like median buccal cleft on the lower molars. All lower molars of Myanmarcolobus retain a distinct mesiobuccal cleft, which sometimes appears in large colobine monkeys, such as Dolichopithecus, Parapresbyits, and Rhinopithecus. The distobuccal cleft is quite small on M1 but distinct on M2. The well-developed, large hypoconulid on M3 shows no size reduction seen in the extant Presbytis. The median lingual notch does not form a V shape, the typical pattern seen in most colobine monkeys, but is rather trapezoid shaped in the lingual view, in particular on M2 and M3, where the base of the notch is mesiodistally long with a gently sloped postmetacristid and nearly vertical preentocristid ridge. This trapezoid-shaped median lingual notch is a unique feature of Myanmarcolobus, whereas most colobine monkeys show a steeper, rather symmetrical V-shaped median lingual notch (Figs. 5, 6 and 8). The distal fovea is much larger and with a deeper opening distolingually than the mesial fovea in M1 and M2.

Figure 6. 3D images of left M1e3 teeth of living colobine taxa mentioned in the text in comparisons with Myanmarcolobus: a) Nasalis larvatus (ZRC 4-198, mirror image), b) Pygathrix nemaeus (NMB 10747), c) Rhinopithecus roxellanae (BMNH 3.1.2, mirror image), d) Myanmarcolobus yawensis (NMMP-KU-IR 1200), e) Semnopithecus (Kasi) johnii (BMNH 21.11.5.3, mirror image), f) Trachypithecus pileatus (BMNH 50.365, mirror image), g) Trachypithecus obscurus (ZRC 4-438, mirror image), and h) Presbytis femoralis (ZRC 4-284). Occlusal (left column) and lingual (right column) views. All images are scaled to the same M1e3 size.

4. Description of the isolated molars 4.1. Systematic paleontology Subfamily Colobinae Jerdon, 1867 gen. et sp. indet. 4.1.1. Material Isolated right M1 (or M2), NMMP-KU-IR 1199 (Figs. 3b and 4b), and left M2, NMMP-KU-IR 1419 (Figs. 3c and 4c). 4.1.2. Locality and age MKT 2 locality (N21
300 0000 , E94
300 2400 ), near Myokhinthar village, Chaingzauk area, Pauk township, Magway Division, central Myanmar (Fig. 1); Late Miocene/Early Pliocene. 4.1.3. Description and comparisons Both specimens are identified as colobine monkeys based on the bilophodonty pattern, where mesial and distal cusps are connected by transverse lophs, and the deep median lingual sulcus on the lower molar specimen. The upper molar specimen (IR-1199) is slightly worn. The mesial loph continuously connects protocone and paracone, and the

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a

b

c

d

Figure 7. Scatter plots of the dental size of colobine fossils from Chaingzauk in comparison with extant and extinct colobine genera in Asia. Nasalis includes N. larvatus. Presbytis includes P. femolaris femolaris, P. femoralis robinsoni, P. melalophos bicolor, P. siamensis cana (or catemana), and P. siamensis siamensis. Pygathrix includes P. nemaeus and P. nigripes. Rhinopithecus includes R. bieti, R. roxellana, R. avunculus, and R. brelichi. Semnopithecus includes S. entellus ajax, S. entellus priam, S. entellus schistaceus, S. entellus achates, S. (Kasi) johnii, S. vetulus nestor, S. vetulus philbricki, and S. vetulus vetulus. Trachypithecus includes T. cristatus, T. francoisi, T. leucocephalus, T. obscurus flavicauda, T. obscurus carbo, T. obscurus smithi, T. phayrei argenteus, T. phayrei shanicus, T. pileatus durga, and T. pileatus shortridgei. Data of extant specimens were measured by MT at BMNH, JMC, KUPRI, NMB, and ZRC. Classification basically follows Brandon-Jones et al. (2004). a) M1; b) M2; c) M3; and d) M1.

distal loph is cut by a shallow median groove. The distal fovea is slightly larger than the mesial one, and the central fovea is very deep. Although the median buccal notch is not so deep, the median lingual cleft is rather deep. A shallow mesiolingual notch is observed. In the lower molar specimen (IR-1419), the transverse lophids run rather obliquely, the median buccal cleft is moderately concave, the median lingual notch is very deep, and the mesiobuccal and distobuccal notches are rather distinct (Figs. 4, 8 and 9), if not quite as much as in Myanmarcolobus (IR1200). Compared with IR-1200 (Myanmarcolobus), in IR-1419 the M2 is mesiodistally much shorter (Table 2; Fig. 7), the mesial transverse lophid runs less obliquely (Fig. 10; Table 3), and the median lingual notch is not trapezoideshaped but forms a relatively symmetrical steep V shape (Figs. 4c and 8k). Although it is very difficult to make a taxonomic identification based only on these two isolated teeth, they may show some similarity to those of extinct Mesopithecus (Fig. 5e) or extant Trachypithecus (Figs. 6f, g and 8aej) rather than to those of Myanmarcolobus (Fig. 8l) in the size and shape of the lower molars (Table 4). For the present, we have tentatively treated these two specimens as colobine monkeys of undetermined genus and species.

5. Discussion 5.1. Comparisons with South Asian colobine fossils It is well known that it is very hard to identify the taxonomic position of fossil cercopithecids, including colobines, based only on dental specimens because the basic morphology of their dentition is very similar even at the subfamily level. Although the two fossil colobines reported here were easily differentiated by the lower molar morphology, we have only three specimens in hand, two of which are just isolated upper and lower molars, and there was no information on individual variation. We only know that the morphology of the M2 of IR-1419 differs from that of IR-1200 (Myanmarcolobus), and that IR-1199 (M1) and IR-1419 (M2) were collected from the same point (MKT 2), and IR-1200 was discovered at a different point (MKT 7), about two kilometers away from MKT 2. There is a possibility that the morphological difference in M2 between IR-1200 and IR-1419 may represent intraspecific variation in Myanmarcolobus, but the unique features seen in IR-1200 strongly suggests the status of a new genus for this specimen. The taxonomic position of IR-1199 and 1419 could be determined by the discovery of additional fossil materials in the future.

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Figure 8. Lingual views of left M1, M2, and/or M3 of extant Trachypithecus (aej), fossil specimens of Myanmar (k and l), and extinct Dolichopithecus (mey), showing the morphological differences in the shape of the median lingual notch: a) T. cristata (KUPRI-2309); b) T. cristata (KUPRI-9494); c) T. obscurus (ZRC 4.438); d) T. obscurus (ZRC 4.439); e) T. obscurus (ZRC 4.450); f) T. obscurus (ZRC 4.458); g) T. obscurus (ZRC 4e493); h) T. phayrei (ZRC 4-545, mirror image); i) T. phayrei (ZRC 4.546, mirror image); j) T. pileatus (BMNH 1790.1630, mirror image); k) IR-1419; l) IR-1200 (Myanmarcolobus); m) D. ruscinensis (M1, ML Pp 5); n) D. ruscinensis (M2?, FSL 41045); o) D. ruscinensis (M1-2, FSL 40992, mirror image); p) D. ruscinensis (M1-2, LGI SM 1); q) D. ruscinensis (M1-2, LPB 580, mirror image); r) D. ruscinensis (M1, MAFI Ob1588-90/17, mirror image); s) D. ruscinensis (M2, MAFI Ob1588-90/18); t) D. ruscinensis (M3, MAFI Ob1588-90/19); u) D. ruscinensis (M1, MNHN-P PER004f, mirror image); v) D. ruscinensis (M2, MNHN-P PER004d, mirror image); w) D. ruscinensis (M3, MNHN-P PER004d, mirror image); x) D. ruscinensis (M1?, FSL 41177); and y) D. ruscinensis (M3, FSL 49998, mirror image). Most specimens show an asymmetrical V- or parabolic-shaped median lingual notch, while some Trachypithecus teeth (M3 in c and M2-3 in j) and Dolichopithecus teeth (M3 in t) retain a relatively long, U-shape notch. In particular, Dolichopithecus specimens show large morphological variation in the shape of the median lingual notch. All figures were taken in the same scale using the One-shot 3D Measurement Macroscope (VR-3050, Keyence corp.).

Accordingly, here we compared only IR-1200, the type specimen of Myanmarcolobus, with other colobine fossils of East Asia. As already mentioned, colobine monkeys originated in Africa in the Middle Miocene and entered Eurasia as early as the Late Miocene (e.g., Delson, 1994). The oldest colobine fossil record in Eurasia is the Late Miocene Mesopithecus in Europe as well as in western Asia, such as Maragheh (Iran) and Molayan (Afghanistan; Heintz et al., 1981; Jablonski, 2002). Considering the taxonomic similarity between the Siwalik and Irrawaddy faunas, it was expected that Myanmarcolobus might be similar to Mesopithecus of western Asia, which is a small-to-medium-sized monkey like

Myanmarcolobus (Fig. 7). However, the lower molar morphology was quite different between them: in Mesopithecus the median lingual notch is deeply incised, forming a V shape in the lingual view, and the median buccal cleft is not as deeply concave as in Myanmarcolobus (Fig. 5a). In South and East Asia, ?Mesopithecus sivalensis, another small-to-medium-sized fossil colobine, has been discovered from the latest Miocene Siwalik sediments of India/Pakistan in the 19th century (Lydekker, 1878; Fig. 5a, e). This colobine monkey was named variously as Macacus sivalensis, Semnopithecus asnoti, Cercopithecus sivalensis, or “Presbytis” sivalensis in previous works

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Figure 9. Buccal views of left M1, M2, and/or M3 of extant Trachypithecus (aej), fossil specimens of Myanmar (k and l), and extinct Dolichopithecus (mey), indicating the morphological differences in the shape of the buccal cleft. Specimen numbers and abbreviations are as for Figure 8. Note that the shape of the median buccal cleft is usually groovelike in Trachypithecus but rather concave in Dolichopithecus like in Myanmarcolobus (i). In addition, the mesial buccal cleft is more distinct in Myanmar fossils (k, i) than in Trachypithecus and Dolichopithecus, although there may be some variation in the development of the mesial buccal cleft in Dolichopithecus.

(e.g., Simons, 1970; Delson, 1975, 1994; Szalay and Delson, 1979; Barry, 1987; Jablonski, 2002), and it was recently identified as Mesopithecus sivalensis (Harrison and Delson, 2007). As a detailed description of this sample is yet to be published, we call it ? Mesopithecus sivalensis in this paper. The lower molar morphology of one newly-recovered specimen shows the same pattern seen in Mesopithecus: a deeply incised V-shaped median lingual notch and a relatively shallow buccal cleft, and the relative mesiodistal length of M2 to M1 and M3 is much shorter than in Myanmarcolobus (Fig. 5e). The dissimilarity in lower molar morphology between ?Mesopithecus sivalensis and Myanmarcolobus suggests that any close relationship between them is unlikely. In South Asia, another relatively large fossil cercopithecid, “Semnopithecus” palaeindicus, was described from the Plio/

Pleistocene “Tatrot-equivalent” of northern India (e.g., Falconer and Cautley, 1837; Pilgrim, 1915; Szalay and Delson, 1979; Jablonski, 2002). The taxonomic position of this enigmatic fossil has long been disputed: some researchers have regarded it as a colobine monkey, Semnopithecus (Falconer and Cautley, 1837; Jablonski, 2002), but others have regarded it as a cercopithecine, such as Macaca (e.g., Delson, 1975, 1980; Szalay and Delson, 1979). The morphological features of the lower molars (BMNH 15710 and 15711), such as a very shallow, obtuse median lingual notch and an untwisted tooth row, undoubtedly demonstrate that it is not a colobine but a cercopithecine monkey (Fig. 5f), although the talar specimen (BMNH 1539) assigned to this taxon shows strong similarity to that of the extant Semnopithecus entellus (Jablonski, 2002). Whatever the case, Myanmarcolobus is quite different from BMNH 15710 and 15711 in lower molar morphology.

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Figure 10. The diagram (a) and scatter plots (b) of the angles (
) of the mesial (a, angle between prd-med and med-end lines) and distal (b, angle between hyd-end and med-end lines) transverse lophids on M2 among extant and extinct colobine taxa. See Table 4 for detailed data of the specimens. Note that Myanmarcolobus (IR-1200) has very obliquely directed transverse lophids: in particular the mesial lophid angle is much more oblique than all other taxa including IR-1419.

5.2. Comparisons with northern Asian colobine fossils Several colobine fossils have been discovered in the relatively high-latitude part of East Asia as well. Parapresbyits is a relatively large, terrestrial colobine, discovered at two Middle Pliocene localities of the Transbaikal area and northern Mongolia (Borissoglebskaya, 1981; Kalmykov and Maschenko, 1992; Maschenko, 2005; Egi et al., 2007; Takai and Maschenko, 2009). In Parapresbytis, the mesiobuccal notch is often well developed, and the M3 hypoconulid is very large, protruding buccodistally in the type specimen (PIN 3381-235) as seen in Myanmarcolobus, whereas the median lingual notch forms a relatively asymmetrical V shape rather than a trapezoid shape, the M2 transverse ridges run rather perpendicularly to the tooth row, and the median buccal notch is deeply grooved rather than having the concave pattern seen in Myanmarcolobus. In addition, the M3 hypoconulid shows large variations in Parapresbytis: some specimens (e.g., PIN 3381-236; Fig. 5d) retain a very large, buccolingually wide M3 hypoconulid, which is quite different from that of Myanmarcolobus. Parapresbytis was at one time (Delson, 1994) considered a subgenus of Dolichopithecus, which is another large fossil colobine mainly distributed in Europe during the Pliocene (e.g., Szalay and Delson, 1979; Delson, 1994; Jablonski, 2002; Delson et al., 2005). Some researchers have indicated the morphological similarity in craniofacial and dental characters between Parapresbytis and extant Rhinopithecus, suggesting close phyletic relationships between them (Jablonski, 2002). However, recent morphological analysis on the cranial and dental materials of Parapresbytis revealed that Parapresbytis is definitely different from Dolichopithecus and also from Rhinopithecus in cranial and dental morphology, especially of incisors (Takai and Maschenko, 2009; Nishimura et al., 2012). Kanagawapithecus, another fossil colobine discovered from the Late Pliocene of Kanagawa Prefecture, eastern Japan, has sometimes been considered as a subgenus of Dolichopithecus as well (e.g., Delson, 1994; Iwamoto et al., 2005). However, the

reexamination of the inner structure of the Kanagawapithecus skull using X-ray CT demonstrated that it is quite different from the structural pattern seen in Dolichopithecus and Mesopithecus but rather similar to African colobines (Nishimura et al., 2012). Unfortunately, the Kanagawapithecus specimen consists only of the cranial material preserving upper dentitions, so it is impossible to compare directly with Myanmarcolobus. However, Kanagawapithecus is larger in upper molar size than Parapresbytis (Iwamoto et al., 2005; Takai and Maschenko, 2009), which is much larger in the sizes of M1-3 and M1 examined than those of Myanmarcolobus (Fig. 7). It is very unlikely that Myanmarcolobus is closely related to Kanagawapithecus. Thus, the two East Asian fossil colobines, Parapresbytis and Kanagawapithecus, were once regarded as the subgenera of the European taxon Dolichopithecus, but both are now generally admitted as independent genera mainly based on cranial morphology. On the other hand, it is interesting that Myanmarcolobus shows similarity in lower molar morphology to Dolichopithecus in having relatively obliquely running transverse ridges, a mesiodistally long asymmetrical median lingual notch, a largely concave median buccal cleft, and a distinct mesiobuccal notch on the lower molars (Figs. 5, 8 and 9). Myanmarcolobus is most similar to Dolichopithecus, especially to the specimens from the Early Pliocene of southeastern Europe, such as Dolichopithecus hypsilophus (Fig. 5b) and Dolichopithecus balcanicus, among fossil colobines discovered in Eurasia (Koufos et al., 1991; Maschenko, 1991, 2005; Delson et al., 2005; Spassov and Geraads, 2007). However, large size differences in the lower molars between Myanmarcolobus and Dolichopithecus and the cohesiveness of lower molar size in Dolichopithecus suggest heterogeneity between them (Fig. 7). The trapezoid-shaped median lingual notch (Fig. 8l) and more obliquely running mesian transverse ridge (Fig. 10; Table 3) also indicate an independent generic status for Myanmarcolobus. Obviously, the generic status of Myanmarcolobus could be more firmly determined by additional fossil material, such as other teeth and/or cranial specimens, in the future.

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M. Takai et al. / Journal of Human Evolution 84 (2015) 1e15

Table 1 Faunal lists of some localities of central Myanmar.a Chaingzauk

Primates Cercopithecidae Colobinae gen. et sp. indet. Semnopithecus sp. indet. Carnivora Herpestidae Urva sp. indet. Felidae Machairodontinae gen. et sp. indet. Ursidae Agriotherium myanmarensis Percrocutidae Percrocuta sp. indet. (brachydont form) Hyaenidae Ictitherinae gen. et sp. indet. gen. et sp. indet. Rodentia Hystrichidae Hystrix paukensis Hystrix sp. indet. (brachydont form) Hystrix cf. brachyura Muridae Hapalomys cf. longicaudatus Maxomys sp. nov. Rattus jaegeri cf. Rattus sp. indet. Spalacidae Cannomys cf. badius Sciuridae Menetes sp. indet. Lagomorpha Leporidae gen. et sp. indet. Artiodactyla Anthracotheriidae Merycopotamus dissimilis Microbunodon milaensis Bovidae Pachyportax latidens Pachyportax giganteus cf. Proamphibos sp. indet. cf. Hemibos sp. indet. Proleptobos birmanicus Sivaportax dolabella gen. et sp. indet. (large form) Hippopotamidae Hexaprotodon cf. iravaticus Hexaprotodon sivalensis Hexaprotodon palaeindicus Suidae Sivachoerus prior Propotamochoerus hysudricus cf. Sus sp. indet. Tragulidae Dorcatherium cf. anthracotherioides Dorcabune sp. indet. Perissodactyla Chalicotheriidae gen. et sp. indet. Rhinoceratidae Dicerorhinus gwebinensis Rhinoceros sp. indet. Proboscidea Mastodontidae Sinomastodon sp. indet. Stegodontidae Stegodon sp. indet. a

Gwebin area Gwebin

Thanbyingyaung

Peikswe

X

X

X

X

X X X X X X

X

X X

X X

X X X X

X

X X

X

X X X X X X X X

X X

X X

X X

X X X

X X X

X

X X X

X

X

X X

X X

X X

X

X

? X

X

X

X

X X

Thanbyingyaung and Peikswe are adjacent to Gwebin area and considered almost similar in age to the Gwebin sediments (Nishioka, 2013).

X

M. Takai et al. / Journal of Human Evolution 84 (2015) 1e15

11

Table 2 Dental measurements of colobine fossils discovered from Chaingzauk, central Myanmar, compared with extant Asian genera.a M1

M1 BL

MD colobine indet. IRe1199 7.62 IRe1419 Myanmarcolobus IRe1200 Dolichopithecus mean 9.05 (17) range 8.0e10.0 SD 0.63 CV 0.07 Mesopithecus mean 6.94 (20) range 6.09e7.56 SD 0.32 CV 0.05 Nasalis mean 7.15 (11) range 6.83e7.54 SD 0.22 CV 0.03 Pygathrix mean 6.76 (11) range 6.50e7.03 SD 0.18 CV 0.03 Rhinopithecus mean 7.92 (32) range 6.57e9.49 SD 0.72 CV 0.09 Semnopithecus mean 7.24 (28) range 6.01e8.96 SD 1.02 CV 0.14 Trachypithecus mean 6.19 (36) range 5.45e6.93 SD 0.33 CV 0.05 Presbytis mean 5.56 (9) range 5.23e5.82 SD 0.2 CV 0.04

tr 7.10

M2 BL

ta

MD

M3 BL

trd

tad

MD

trd

BL tad

MD

trd

tad

6.99 7.72

6.36

6.17

7.01

5.32

5.54

8.18

6.18

6.10

10.28

6.44

5.70

8.57 (16) 7.4e9.4 0.54 0.06

8.25 (15) 6.8e9.0 0.59 0.07

9.22 (27) 8.1e10.3 0.47 0.05

6.75 (24) 6.0e7.6 0.42 0.06

7.08 (24) 6.2e8.0 0.49 0.07

10.3 (27) 9.5e11.7 0.59 0.06

7.98 (26) 7.0e8.7 0.5 0.06

8.05 (26) 7.1e9.0 0.53 0.07

12.78 (27) 10.94e14.7 0.88 0.07

8.3 (18) 7.6e8.9 0.37 0.04

7.92 (22) 7.0e8.7 0.49 0.06

7.14 (14) 5.98e7.63 0.41 0.06

6.89 (14) 5.79e7.62 0.44 0.06

6.75 (23) 5.57e7.55 0.49 0.07

5.40 (23) 4.41e7.0 0.59 0.11

5.55 (23) 4.52e6.22 0.47 0.09

7.39 (22) 5.55e8.16 0.55 0.07

6.38 (22) 4.96e7.37 0.63 0.1

6.53 (21) 5.17e7.37 0.64 0.1

9.18 (21) 8.18e10.33 0.6 0.07

6.39 (14) 5.41e7.17 0.57 0.09

5.95 (15) 5.03e6.67 0.51 0.09

6.3 (11) 5.96e7.04 0.31 0.05

6.44 (11) 6.04e6.87 0.28 0.04

7.19 (11) 6.71e7.54 0.32 0.04

5.11 (11) 4.82e5.53 0.22 0.04

5.61 (11) 5.33e5.92 0.23 0.04

7.84 (11) 7.21e8.34 0.38 0.05

6.16 (11) 5.68e6.68 0.31 0.05

6.29 (11) 5.83e6.68 0.27 0.04

9.98 (11) 9.39e11.04 0.61 0.06

6.19 (11) 5.78e6.74 0.36 0.06

6.2 (11) 5.78e7.01 0.37 0.06

6.4 (11) 5.86e6.73 0.28 0.04

6.19 (11) 5.64e6.61 0.27 0.04

6.84 (11) 6.37e7.16 0.27 0.04

5.22 (11) 4.57e5.59 0.28 0.05

5.28 (11) 4.76e5.68 0.29 0.05

7.33 (11) 6.73e7.68 0.34 0.05

5.86 (11) 5.37e6.17 0.27 0.05

5.99 (11) 5.38e6.41 0.34 0.06

9.15 (10) 8.50e10.09 0.57 0.06

5.92 (10) 5.45e6.34 0.26 0.04

5.8 (10) 5.28e6.21 0.30 0.05

7.71 (28) 6.62e8.69 0.61 0.08

7.57 (26) 6.68e9.00 0.62 0.08

7.80 (30) 6.43e8.92 0.71 0.09

5.86 (28) 5.30e6.65 0.35 0.06

6.35 (29) 5.85e7.14 0.35 0.06

8.67 (22) 7.11e9.78 0.68 0.08

7.06 (21) 6.40e8.14 0.48 0.07

7.22 (21) 6.44e8.25 0.5 0.07

10.86 (18) 9.10e12.59 1.03 0.09

7.34 (16) 6.28e8.18 0.57 0.08

7.07 (15) 6.03e7.86 0.50 0.07

6.76 (27) 5.42e8.41 0.95 0.14

6.52 (28) 5.41e7.72 0.73 0.11

7.31 (26) 6.10e9.07 0.99 0.14

5.46 (26) 4.48e6.94 0.76 0.14

5.7 (26) 4.60e7.35 0.87 0.15

7.84 (31) 6.30e10.23 1.15 0.15

6.38 (31) 5.05e8.89 0.98 0.15

6.49 (31) 5.16e8.99 1.02 0.16

9.67 (28) 7.49e13.03 1.59 0.16

6.37 (28) 5.04e8.15 0.90 0.14

6.18 (28) 4.74e7.78 0.90 0.15

6.26 (35) 3.21e7.30 0.69 0.11

6.05 (36) 5.16e6.86 0.41 0.07

6.29 (36) 5.43e7.07 0.37 0.06

4.92 (35) 4.19e5.65 0.44 0.09

5.12 (34) 4.18e6.04 0.46 0.09

6.60 (36) 5.65e7.46 0.42 0.06

5.68 (35) 4.80e6.67 0.46 0.08

5.7 (34) 4.65e6.62 0.45 0.08

7.97 (34) 6.06e9.33 0.67 0.08

5.59 (33) 4.60e6.37 0.44 0.08

5.35 (34) 4.48e6.23 0.49 0.09

5.69 (9) 5.29e5.96 0.25 0.04

5.47 (9) 5.009e5.83 0.26 0.05

5.64 (9) 5.40e5.87 0.17 0.03

4.47 (9) 4.26e4.67 0.13 0.03

4.61 (9) 4.44e4.73 0.11 0.02

5.72 (9) 5.34e6.22 0.32 0.06

4.9 (9) 4.58e5.14 0.19 0.04

5.04 (9) 4.76e5.29 0.19 0.04

6.09 (9) 5.67e6.86 0.41 0.07

4.72 (9) 4.53e5.14 0.19 0.04

4.5 (9) 4.07e4.86 0.28 0.06

a Nasalis includes N. larvatus. Presbytis includes P. femolaris femolaris, P. femoralis robinsoni, P. melalophos bicolor, P. siamensis cana (or catemana), and P. siamensis siamensis. Pygathrix includes P. nemaeus and P. nigripes. Rhinopithecus includes R. bieti, R. roxellana, R. avunculus, and R. brelichi. Semnopithecus includes S. entellus ajax, S. entellus priam, S. entellus schistaceus, S. entellus achates, S. (Kasi) johnii, S. vetulus nestor, S. vetulus philbricki, and S. vetulus vetulus. Trachypithecus includes T. cristatus, T. francoisi, T. leucocephalus, T. obscurus flavicauda, T. obscurus carbo, T. obscurus smithi, T. phayrei argenteus, T. phayrei shanicus, T. pileatus durga, and T. pileatus shortridgei. Dolichopithecus includes D. ruscinensis and D. balcanicus. Mesopithecus includes M. pentelicus and M. monspessulanus. Data of extant and extinct specimens were measured by MT at BMNH, JMC, KUPRI, NMB, ZRC, and MNHN. Data of two extant genera, Dolichopithecus and Mesopithecus, were measured by MT or taken from Heintz et al. (1981), Koufos et al. (1991), Spassov and Geraads (2007), and PRIMO (Primate Morphometrics Online), the NYCEP Primate Morphometric database. MD: mesiodistal length (mm). BL: buccolingual width (mm). tr: trigon. ta: talon. trd: trigonid. tad: talonid. SD: standard deviation. CV: coefficient of variation.

5.3. Comparisons with the Pleistocene and extant Asian colobines Despite the high diversification of living species, the Neogene fossil record of cercopithecid monkeys (including colobines and cercopithecines) in Southeast Asia is very limited. Although the fossil records in Southeast Asia drastically increase after the Early Pleistocene, most of the Pleistocene colobine fossils have been reported from the cave deposits of southern China (including Taiwan) and Indonesian islands, such as Java and Sumatra (e.g., Colbert and Hooijer, 1953; Szalay and Delson, 1979; Jablonski and Tyler, 1999; Tougard, 2001; Jablonski, 2002; Jin et al., 2009; Takai and Maschenko, 2009; Chang et al., 2012). In particular, the fact that

the Pleistocene cave deposits of the Guangxi Zhuang Autonomous Region and Guangdong Province have produced numerous isolated teeth of cercopithecid monkeys such as Rhinopithecus, Pygathrix, Trachypithecus, and Macaca together with extinct hominoids from the same deposits is well known (Gu et al., 1996; Jablonski, 2002; Jin et al., 2009). However, these colobine fossils show no similarity to Myanmarcolobus but undoubtedly resemble extant Asian genera in lower molar morphology (Takai et al., 2014). Moreover, Myanmarcolobus shows neither a tendency for hypoconulid reduction on M3, a typical feature of the extant Presbytis, nor the basal swelling of the tooth crown (exodaenodonty), a typical character of the extant Semnopithecus and Rhinopithecus. Only

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M. Takai et al. / Journal of Human Evolution 84 (2015) 1e15

Table 3 The measurements of the angles (
) of the mesial (a, angle between prd-med and med-end lines) and distal (b, angle between hyd-end and med-end lines) transverse lophids on M2 among extant and extinct colobine taxa.a Category fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil fossil odd-nose colobine odd-nose colobine odd-nose colobine odd-nose colobine odd-nose colobine odd-nose colobine odd-nose colobine odd-nose colobine langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur langur African colobine African colobine African colobine African colobine African colobine African colobine African colobine a

Taxon

Species

a

b

No.

Sex

Myanmarcolobus colobine Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Dolichopithecus Mesopithecus? Mesopithecus? Mesopithecus Mesopithecus Mesopithecus Mesopithecus Mesopithecus Parapresbytis Parapresbytis Parapresbytis Parapresbytis Nasalis Nasalis Pygathrix Rhinopithecus Rhinopithecus Rhinopithecus Simias Simias Presbytis Presbytis Presbytis Presbytis Presbytis Presbytis Presbytis Presbytis Semnopithecus Semnopithecus Semnopithecus Semnopithecus Semnopithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Trachypithecus Colobus Colobus Colobus Piliocolobus Piliocolobus Procolobus Procolobus

yawensis indet. ruscinensis ruscinensis ruscinensis ruscinensis ruscinensis ruscinensis ruscinensis ruscinensis ruscinensis sivalensis sivalensis monspessulanus monspessulanus monspessulanus pentelicus pentelicus eohanuman eohanuman eohanuman eohanuman larvatus larvatus nemaeus roxellana roxellana roxellana concolor concolor femolaris robinsoni femolaris femolaris femolaris siamensis catemana siamensis paenulata potenziani potenziani potenziani entellus entellus “entellus” priam johnii cristata cristata obscurus obscurus obscurus obscurus obscurus phayrei phayrei pileatus pileatus guereza polykomos polykomos badius badius verus verus

101.73 92.75 98.75 95.05 93.14 92.15 91.23 94.29 95.13 89.93 91.59 91.73 92.02 89.50 95.86 94.61 93.44 95.06 91.53 92.50 98.86 91.27 91.21 89.14 92.59 92.91 98.54 93.04 94.57 92.82 93.15 93.19 94.16 97.76 96.23 96.97 94.11 98.18 88.90 93.57 98.75 98.03 91.64 93.94 95.17 93.57 93.60 91.07 95.25 91.90 94.36 96.13 99.21 92.81 91.92 91.72 97.41 93.41 93.56 94.14 95.75

98.84 97.35 99.05 96.29 92.08 97.28 99.84 92.79 94.39 94.34 91.62 92.79 90.83 88.02 96.20 92.06 87.83 91.10 92.41 92.16 98.33 90.54 93.18 96.31 97.50 93.49 95.80 94.89 95.27 92.72 93.28 91.58 96.46 96.32 97.01 95.18 96.56 93.74 89.68 94.44 95.95 97.51 95.88 92.39 96.13 93.56 93.64 91.54 96.54 95.04 95.77 96.53 97.63 93.73 96.00 90.99 97.97 97.19 92.10 96.23 97.33

NMMP-IR-1200 NMMP-IR-1419 BMNH 36367 PIN N355-7 FSL 40992 FSL 41177 FSL 41045 LGI SM1 LPB 589 MAFI Ob1588-90/18 MNHN-P PER 004e GSP 14043 GSI D184 NMB Vj 87 (right side) NMB Vj 87 (left side) NMB Vj 130 BSM AS II 60 MP 881 PIN 3381-235 (mean of both sides) PIN 3381-236 (mean of both sides) GIN No.12 GIN U 986/38(6) ZRC 4.197 ZRC 4.198 NMB 10747 IVPP without No. BMNH 8.10.9.1 BMNH 1999.3.1.2 PRI-1264 PRI-1270 ZRC 4.276 ZRC 4.252 PRI-4564 PRI-4568 PRI-4555 PRI-1163 PRI-1175 PRI-1184 PRI-1545 PRI-5307 GSI-F201 (subfossil) ANTH 007 BMNH 21.11.5.3 PRI-9494 PRI-2309 ZRC 4.438 ZRC 4.439 ZRC 4.493 ZRC 4.450 ZRC 4.458 ZRC 4.545 ZRC 4.546 BMNH 50.365 BMNH 1979.1630 PRI-8696 PRI-1093 PRI-1101 PRI-458 PRI-462 PRI-364 PRI-374

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? F M M M M F M F F M M M F F M M ? F ? M M F F M F F M F F F M F F F F F M F M

Odd-nosed colobines and langurs are the two main extant colobine groups in Asia. Odd-nose colobine: odd-nosed monkeys in Asia; langur: langurs in Asia.

Trachypithecus sometimes retains the relatively long asymmetrical median lingual notch; however, it is not trapezoid shaped and is much shorter than that of Myanmarcolobus. On the other hand, many colobine fossils were recently discovered in the same area of central Myanmar by the expedition team of the present authors (Takai et al., 2012; Nishioka, 2013). The Late Pliocene Gwebin locality, about 20 km SSE of Chaingzauk (Fig. 1), has been famous for producing rich vertebrate fossils since

the 20th century, and more than a dozen teeth of relatively large colobine monkeys were collected from a single point through screening and washing by the MyanmareJapan joint team. All of these specimens have now been identified as Semnopithecus based on the morphological features of the upper and lower dentitions. It looks rather strange that the colobine fossils discovered from the two late Neogene sites (Chaingzauk and Gwebin) in central Myanmar show no special similarity between them.

M. Takai et al. / Journal of Human Evolution 84 (2015) 1e15

13

Table 4 The distribution of several morphological characters on lower molars of extant and extinct colobine monkeys.a

fossil taxa

living taxa

a

Taxon

Mesiobuccal cleft

Median buccal cleft

Distobuccal cleft (M1, 2)

Median lingual notch

Direction of lophids

M3 hypoconulid

Myanmarcolobus (IR-1200) Gen. indet. (IR-1419, M2) Mesopithecus (n ¼ 10) Dolichopitheus (n ¼ 13)

deep cingulum moderate cingulum shallow/absent moderate/distinct

deeply concave moderately concave groove/concave shallow concave

shallow groove/distinct moderate groove absent/shallow groove shallow groove

very oblique oblique transverse oblique/transverse

large e large large

Parapresbytis (n ¼ 8) Nasalis (n ¼ 3) Pygathrix (n ¼ 6) Rhinopitheus (n ¼ 7) Simias (n ¼ 5) Semnopitheus (n ¼ 8) Trachypithecus (n >10)

moderate/shallow absent absent shallow/moderate absent shallow/moderate shallow/absent

groove-like shallow groove groove-like concave/groove groove-like concave groove-like

absent/shallow groove absent absent absent/shallow groove absent absent/shallow groove shallow groove/absent

oblique/transverse transverse slightly oblique slightly oblique transverse slightly oblique oblique/transverse

large large large large large large large

Presbytis (n >10)

absent

groove-like

absent

trapezoid shape V shape V shape aymmetrical V/U shape V shape V shape V shape V shape V shape V shape asymmetrical V shape V shape

transverse

absent/tiny

See Figure 6 for the morphological variation of the shape of the median lingual notch in Dolichopithecus and Trachypithecus.

5.4. Faunal transition and environmental change in central Myanmar The Chaingzauk and Gwebin faunas, both of which produced colobine fossils, have been studied by the MyanmareJapan joint research teams since 2002 (Thaung-Htike et al., 2005, 2007, 2008; Takai et al., 2006, in press; Zin-Maung-Maung-Thein, 2010, ZinMaung-Maung-Thein et al., 2010, 2011; Nishioka et al., 2011; Ogino et al., 2011; Tsubamoto et al., 2012; Nishioka, 2013). Although both faunas consist of a mixture of forest dwellers and open land inhabitants, the faunal members are rather different from each other, indicating a faunal turnover in central Myanmar during the Pliocene (Table 1; Nishioka, 2013). For example, the Chaingzauk fauna is more similar to that of the Siwalik faunas of South Asia than to the faunas of southern China or Southeast Asia (Zin-MaungMaung-Thein, 2010), whereas the Gwebin fauna shows more similarity to the Southeast Asian fauna than to the Siwalik fauna (Nishioka, 2013, 2015). The discrepancy between the Chaingzauk and Gwebin faunas suggests a rapid shift in the faunal interchange from a Myanmar-South Asia connection to a Myanmar-southeast Asia link, probably caused by the appearance of some geographical barriers, such as the establishment of the huge Brahmaputra River and the uplift of the Indo-Burman Ranges between South Asia and Myanmar. For example, Semnopithecus, the Hanuman langur, is now widely distributed on the west side of the Brahmaputra, whereas Trachypithecus pileatus, the capped leaf monkey, ranges on the east side, suggesting the importance of the Brahmaputra as a geographical barrier for zoogeography (Osterholz et al., 2008). Recent molecular biological studies estimate that two extant Asian colobine cladesdthe odd-nosed monkeys (Rhinopithecus, Pygathrix, Nasalis, and Simias) versus the Trachypithecus/Presbytis/ Semnopithecusddiverged by 8.8 Ma (Sterner et al., 2006; Osterholz et al., 2008; Springer et al., 2012), which is older than the geological age of the Chaingzauk fauna, and suggest that T. pileatus is a hybrid species between ancestral Semnopithecus and Trachypithecus (Osterholz et al., 2008; Roos et al., 2011). The probable change in the course of the large river, the Brahmaputra, originally advocated by Chhibber (1934:32), may have played an important role in the faunal transition that occurred during the Pliocene in Southeast Asia, including Myanmar (see also Meijaard and Groves, 2006). The morphological similarities and dissimilarities among Myanmarcolobus, Trachypithecus, and Semnopithecus may reflect the complicated evolutionary history of Asian colobines and

geographical changes that occurred in Southeast Asia during the Pliocene. The analyses of stable carbon and oxygen isotopes extracted from the tooth enamel of mammal fossils also demonstrated that the paleoenvironment of the Chaingzauk fauna was a mixture of closed (forest) and open (grassland) habitat under the wet and dry seasonality caused by a monsoon climate (Zin-Maung-MaungThein, 2010; Zin-Maung-Maung-Thein et al., 2011), although the present-day Chaingzauk area in west-central Myanmar shows a relatively arid environment with thorn scrub, grassland, and shrubland. The Late Miocene/Early Pliocene Chaingzauk fauna likely represents a transitional period from closed forests to relatively open grasslands like those of present-day central Myanmar, which was caused by the uplift of the Indo Burman Ranges due to the Himalayan Orogeny during the Late Miocene-to-Pliocene (ZinMaung-Maung-Thein, 2010; Zin-Maung-Maung-Thein et al., 2011). The transition from Myanmarcolobus in the Late Miocene/Early Pliocene Chaingzauk to Semnopithecus in the Late Pliocene Gwebin (Takai et al., in press) may reflect the environmental deterioration and the evolutionary adaptation of Asian colobine monkeys in Southeast Asia. The morphological similarities between the European Dolichopithecus and the Southeast Asian Myanmarcolobus likely present a geographical issue in the evolutionary history of Asian colobine monkeys. To date, only Mesopithecus-like colobine fossils have been discovered from the Late Miocene sediments of South Asia, where many detailed paleontological investigations have been carried out (e.g., Pilgrim, 1910; Colbert, 1935, 1938, 1943; Delson, 1975; Barry, 1987; Barry et al., 2002; Harrison and Delson, 2007). The lack of Dolichopithecus- and/or Myanmarcolobus-like fossils in South Asia strongly suggests another dispersal route for the group between Europe and Southwest Asia. An extinct, ancestral colobine clade, including Dolichopithecus, Myanmarcoloubs and possibly Parapresbytis, may have been distributed across the northern area of central Eurasia in the latest Miocene-to-Pliocene. In fact, a large cercopithecine, Paradolichopithecus sushkini has been discovered from the Late Pliocene in Kuruk-Say, southern Tajikistan (Trofimov, 1977, 2005; Nishimura et al., 2007; Takai et al., 2008). Future discovery of colobine fossils from uninvestigated areas in central Eurasia, together with detailed morphological analyses of the Pliocene colobine fossils discovered from Eurasia, such as Dolichopithecus, Myanmarcolobus, Parapresbytis and Kanagawapithecus, will likely add new insights into the complexities of the evolution of the Asian colobines.

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Acknowledgments We are grateful to Aung-Aung-Kyaw, Hla-Shwe, Myat-Swe, Kyaw Myo Win, Kyaw Soe Win, Zin-Oo, Kyaw Khaing and many other staff of the Department of Archaeology, Ministry of Culture, Myanmar for their help in our paleontological studies in Myanmar, and also all research members who participated in the field works in Myanmar. We thank E. Delson (AMNH); M. Pickford, B. Senut, P. Tassy, and C. Sagne (MNHN); Changzhu Jin and Yingqi Zhang (IVPP); Baoguo Li and Xiaoguang Qi (Northwest University, Xi'an, China); D. Shimizu and Y. Shintaku (JMC); J. de Vos and R. van Zelst (National Natuurhistorisch Museum, Leiden, Netherlands); R. Kruszynski and P. Jenkins (BMNH); E.V. Maschenko (PIN); Lim Kok Peng Kelvin (National University of Singapore, Singapore); and C. Nahallage (University of Sri Jayewardenepura, Sri Lanka) for graciously providing access to the specimens examined at their respective institutions. We thank the reviewers (E. Delson and an anonymous reviewer), Associate Editor, and JHE Editor for helpful comments and suggestions on a previous version of this paper. E. Delson kindly provided us with the casts of European colobine fossils and measurements data of PRIMO (Primate Morphometrics Online, the NYCEP Primate Morphometric database). Financial supports were provided by the Ministry of Education, Culture, Sports, Science and Technology, Tokyo (MEXT): Grants-in-Aid for Scientific Research to M.T. (Nos. 16405018, 20405015 and 26304019). References Andrews, P., Harrison, T., Delson, E., Bernor, R.L., Martin, L., 1996. Distribution and biochronology of European and Southwest Asian Miocene catarrhines. In: Bernor, R.L., Fahlbusch, V., Mittman, H.-W. (Eds.), The Evolution of Western Eurasian Neogene Mammal Faunas. Columbia University Press, New York, pp. 168e206. Badgley, C.B., Barry, J.C., Morgan, M.E., Nelson, S.V., Behrensmeyer, A.K., Cerling, T.E., Pilbeam, D., 2008. Ecological changes in Miocene mammalian record show impact of prolonged climatic forcing. Proc. Natl. Acad. Sci. 105, 12145e12149. Barry, J.C., 1987. The history and chronology of Siwalik cercopithecids. Hum. Evol. 2, 47e58. Barry, J.C., Morgan, M.E., Flynn, L.J., Pilbeam, D., Behrensmeyer, A.K., Raza, S.M., Khan, I.A., Badgley, C., Hicks, J., Kelley, J., 2002. Faunal and environmental change in the Late Miocene Siwaliks of northern Pakistan. Paleobiology 28, 1e71. Bender, F., 1983. Geology of Burma. Gebrüder Borntraeger, Berlin. Benefit, B.R., Pickford, M., 1986. Miocene fossil cercopithecoids from Kenya. Am. J. Phys. Anthropol. 69, 441e464. Brandon-Jones, D., Eudey, A.A., Geissmann, T., Groves, C.P., Melnick, D.J., Morales, J.C., Shekelle, M., Stewart, C.-B., 2004. Asian primate classification. Int. J. Primatol. 25, 97e164. Borissoglebskaya, M.B., 1981. New species of monkey (Mammalia, Primates) from the Pliocene of northern Mongolia. In: Trudy Sovmestnoi Sovetsko-Mongolskoi Paleontologicheskoi Ekspeditsii. Treatises of the Paleontological Institute, RAS15. Nauka, Moscow, pp. 97e107 (in Russian). Chang, C.-H., Takai, M., Ogino, S., 2012. First discovery of colobine fossil from the middle Pleistocene of southern Taiwan. J. Hum. Evol. 63, 439e451. Chhibber, H.L., 1934. Geology of Burma. Macmillan and Co. Ltd, London. Colbert, E.H., 1935. Siwalik mammals in the American Museum of Natural History. Trans. Am. Phil. Soc. 26, 1e401 (New Series). Colbert, E.H., 1938. Fossil mammals from Burma in the American Museum of Natural History. Bull. Am. Mus. Nat. Hist. 74, 259e434. Colbert, E.H., 1943. Pleistocene vertebrates collected in Burma by the American Southeast Asiatic Expedition. Trans. Am. Phil. Soc. 32, 395e429 (New Series). Colbert, E.H., Hooijer, D.A., 1953. Pleistocene mammals from the limestone fissures of Szechwan, China. Bull. Am. Mus. Nat. Hist. 102, 1e134. Cotter, G.D.P., 1938. The geology of parts of the Minbu, Myingyan, Pakokku, and lower Chindwin Districts, Burma. Mem. Geol. Survey India 72, 1e136. Delson, E., 1975. Evolutionary history of the Cercopithecidae. Contrib. Primatol. 5, 167e217. Delson, E., 1980. Fossil macaques: phylogenetic relationships and a scenario of deployment. In: Lindburg, D.G. (Ed.), The Macaques: Studies in Ecology, Behavior, and Evolution. Van Nostrand Reinhold Company, New York, pp. 10e30. Delson, E., 1994. Evolutionary history of the colobine monkeys in paleoenvironmental perspective. In: Davies, A.G., Oates, J.F. (Eds.), Colobine Monkeys: Their Ecology, Behaviour, and Evolution. Cambridge University Press, Cambridge, pp. 11e43.

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