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Earliest Miocene hominoid from Southeast Asia.

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Earliest Miocene Hominoid From Southeast Asia
Yutaka Kunimatsu,1* Benjavun Ratanasthien,2 Hideo Nakaya,3 Haruo Saegusa,4 and Shinji Nagaoka5
Primate Research Institute, Kyôto University, Inuyama, Aichi 484-8506, Japan
Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
Faculty of Engineering, Kagawa University, Takamatsu, Kagawa 761-0396, Japan
Institute of Natural and Environmental Sciences, Himeji Institute of Technology, Sanda, Hyôgo 669-1546, Japan
Faculty of Education, Nagasaki University, Nagasaki City, Nagasaki 852-8521, Japan
Thailand; Middle Miocene; Sivapithecus; Lufengpithecus; hominoid dispersal;
A new hominoid fossil site, Chiang
Muan in northern Thailand, yielded the first finding of
a large-bodied Miocene hominoid in Southeast Asia.
This specimen (CMu6-1⬘00) was preliminarily reported
by Kunimatsu et al. ([2000a] Primate Res. 16:299).
Later, Chaimanee et al. ([2003] Nature 422:61– 65) reported additional hominoid teeth from the same site,
but all of them were collected from younger deposits
(the Upper Lignite Member, in Nagaoka and Suganuma
[2002] Primate Res 18:159 –164). The specimen described here (CMu6-1⬘00) was recovered from the Lower
Lignite Member (Nagaoka and Suganuma [2002] Primate Res 18:159 –164), which is probably several hundred thousand years older than the Upper Lignite Member (Suganuma et al. [2002] Primate Res. 18:165–173).
This article provides a detailed description of this hom-
inoid specimen and paleontological/geological data of
the fossil site at Chiang Muan. The hominoid specimen
(CMu6-1⬘00) is an isolated upper molar (right M1 or
M2), similar in size to modern orangutans (Pongo pygmaeus). This upper molar has low and voluminous
cusps, relatively thick enamel, and relatively low relief
of the dentine/enamel junction, with only a faint remnant of the lingual cingulum. The age of Chiang Muan is
estimated to be the latest Middle Miocene (ca. 11–12
Ma), based on the mammalian fossils (Nakaya et al.
[2002] Primate Res. 18:131–141) and paleomagnetic
study (Suganuma et al. [2002] Primate Res. 18:165–
173). This suggests that the Chiang Muan Hominoid in
the present study is an earlier member of Eastern Eurasian Miocene hominoids. Am J Phys Anthropol 124:
99 –108, 2004. © 2004 Wiley-Liss, Inc.
Southeast Asia is one of the few areas where nonhuman hominoids are still extant. The living Asian
hominoids include orangutans (Pongo pygmaeus) on
Sumatra and Borneo islands, and several species of
gibbons (Hylobates spp.) distributed from southern
China to the Southeast Asian archipelago. Although
Neogene hominoid fossils have long been known
from neighboring regions such as the Indian subcontinent (Sivapithecus and Gigantopithecus in the Siwaliks) and China (Lufengpithecus in Lufeng, Yuanmou, and perhaps in Kaiyuan; Harrison et al., 2002;
Lewis, 1934, 1937; Woo, 1957, 1958; Wu and Xu,
1985), Southeast Asia itself has had a very poor
record of hominoid fossils. Quaternary orangutan
fossils are known from this area (von Koenigswald,
1982; Schwartz et al., 1995; Tougard and Ducrocq,
1999; Bacon and Vu, 2001, 2002), but there had
never been any large-bodied hominoid fossil reported from the Neogene Southeast Asia until the
Thai-Japanese Paleontological Expedition Team
discovered and reported a Miocene hominoid specimen (CMu6-1⬘00) from Chiang Muan in northern
Thailand for the first time (Kunimatsu et al., 2000a;
Kunimatsu et al., 2002).
Since 1996, the Thai-Japanese Paleontological
Expedition Team (TJPET) has found a number of
fossils at several Late Cenozoic sites in northern
Thailand (Kunimatsu et al., 2000c; Saegusa et al.,
1999). During the field season of January–February 2000, we recovered an isolated upper molar
(CMu6-1⬘00) of a large-bodied fossil hominoid at a
Miocene site in Chiang Muan, Phayo Province
(Fig. 1). In the same year, this finding was preliminarily reported in the 16th Congress of the Primatological Society of Japan at Nagoya, Japan
(Kunimatsu et al., 2000a), and then, the discovery
of this specimen as well as other mammalian fossils was announced in a number of scientific meetings in Japan and elsewhere (Kunimatsu et al.,
Grant sponsor: Japanese Ministry of Education, Culture, Sports,
Sciences, and Technology; Grant numbers: 06041079. 09041161,
*Correspondence to: Yutaka Kunimatsu, Primate Research Institute, Kyôto University, Kanrin, Inuyama, Aichi 484-8506 Japan.
Received 3 October 2002; accepted 1 May 2003
DOI 10.1002/ajpa.10344.
Published online 8 September 2003 in Wiley InterScience (www.
Fig. 1. Map of Eastern Eurasia and distribution of Miocene catarrhine sites. Solid circles, fossil sites yielding large-bodied
hominoids (note that pliopithecids are also known from Lufeng and Yuanmou). Open circles, fossil sites yielding pliopithecids but no
large-bodied hominoids. Hatched oval indicates Siwalik region where large-bodied hominoids and small catarrhines were discovered.
Chiang Muan is marked with a star.
2000b, 2001, 2002a,b, 2003a,b; Nakaya et al.,
2001, 2002a–c Kunimatsu et al., 2003). Later,
Chaimanee et al. (2003) separately reported additional hominoid specimens from Chiang Muan and
provisionally assigned them to Lufengpithecus as
a new species (cf. Lufengpithecus chiangmuanensis). However, all of their specimens are said to
have been found from higher levels than the first
hominoid specimen (CMu6-1⬘00), and are probably
several hundred thousand years younger than the
latter (Suganuma et al., 2002). At present, it is
uncertain whether the first hominoid specimen
(CMu6-1⬘00) from the older deposits and the additional specimens from the younger deposits belong to the same species or not. In this article, we
provide a detailed description of the first hominoid
specimen (CMu6-1⬘00) and related information on
the mammalian fauna and geology of Chiang Muan.
The Chiang Muan basin is a small intermountain
basin located in Amphoe Chiang Muan, Changwat
Phayao. It is approximately 570 km north of
Bangkok, and 150 km east of Chiang Mai. The basin
is 250 –300 m in altitude, spanning 7.5 km (eastwest) by 22.5 km (north-south), and it is troughshaped, trending northwards. It originated in a
north-south fault graben flanked by mountains under 750 m in altitude, which are comprised of marine and nonmarine Mesozoic sandstones, conglomerates, and andesitic tuff (Lampang Group). The
bottom of the basin is filled with lacustrine to fluviolacustrine Tertiary deposits more than 200 m thick
(Chiang Muan Formation in this article). They are
overlaid with Quaternary fluvial deposits (less than
20 m). The thickness of the Chiang Muan Formation
indicates a long-term, slow, and continuous subsidence of the basin.
The Chiang Muan Formation is well-exposed in
the large pit of the Chiang Muan Lignite Mine.
Nagaoka and Suganuma (2002) recognized five
semiconsolidated and unconsolidated members: the
Under Burden (UB), Lower Lignite (LL), Inter Burden (IB), Upper Lignite (UL), and Over Burden
(OB), in ascending order (Fig. 2). The columnar section in Chaimanee et al. (2003) is basically similar to
that in Nagaoka and Suganuma (2002), but they
used slightly different terms. The Lower Lignite
Member in Nagaoka and Suganuma (2002) corresponds to the lower lignite seams in Chaimanee et
al. (2003), while the Upper Lignite Member includes
both of the upper and middle lignite seams in the
latter. In this article, we follow Nagaoka and Suganuma (2002).
At the mine, lignite seams are being excavated by
the Chiang Muan Mine Co., Ltd. (CMMC), leaving
slopes covered with thin remains of the lignite
seams where fossils, including mammals, reptiles,
birds, and fish, have been collected (Kunimatsu et
al., 2000c; Nakaya et al., 2002a). The hominoid specimen (TJPET field no. CMu6-1⬘00) was discovered
on the surface on January 22, 2000 by Nikorn
Wongchai, a geologist of CMMC, when he was looking for fossils with the members of TJPET on a slope
of the mining pit. The place of discovery is positioned
at the southern end of the mining pit (TJPET locality name CMu 6: N 18° 56⬘ 08⬙, E 100° 14⬘ 07⬙) and
corresponds to the Lower Lignite. The surface of the
slope around this locality is covered with the remnants of lignite, and it is approximately parallel to
the strata, so that the fossils collected on the surface
are thought to be contemporaneous to each other.
From locality CMu6, some vertebrate teeth and
postcranial fragments had previously been found by
the mine staff and were preserved in the fossil collection of the CMMC office. Judging from the columnar section in Chaimanee et al. (2003), their additional hominoid specimens were collected from the
Upper Lignite in Nagaoka and Suganuma (2002).
The hominoid specimen (CMu6-1⬘00) is the
heavily worn crown of a right upper M1 or M2 (Fig.
3). It appears to be low-crowned, though we should
be careful, since heavy occlusal wear may sometimes
have an effect on the appearance of the crown
height. The paracone is missing. The protocone and
hypocone are worn flat, with large areas of dentine
exposed on both cusps. These dentine exposures are
hollowed deeply, but they are not connected with
each other. The metacone still retains a considerable
relief, with a very tiny dentine exposure near the
apex. The cusps appear to have been low and voluminous. The remaining part of the crown (mesiodistal length 11.8 mm by buccolingual breadth 14.0
mm) indicates that this hominoid specimen is equivalent in dental size to extant orangutans (Fig. 4).
Fig. 2. Columnar section of Chiang Muan Formation. Under
Burden (UB) is less than 20 m thick, reddish to grayish in color,
and comprises silt to sand. Sedimentary environment is lowenergy-fluvial to lacustrine. Lower Lignite (LL) consists of two
lignite layers, each of which is ca. 10 m thick, suggesting a forest
swamp paleoenvironment. Inter Burden (IB) is ca. 50 m thick,
comprised of reddish brown to gray silt and sand. Sedimentary
environment is low-energy-fluvial, and there would have been
frequent dry periods. Upper Lignite (UL) is ca. 85 m thick, and
comprises gray silt-clayey sediments that contain gastropod fossils and are interbedded with more than 10 layers of lignite, each
of which is less than 10 m thick. Paleoenvironment is inferred to
be intermittent forest swamp and lacustrine. Over Burden (OB) is
30 m thick, consisting of yellowish to reddish brown silt-sand,
indicating low-energy-fluvial environment. It is overlaid by Quaternary high-energy-fluvial sand and gravel sediments (after Nagaoka and Suganuma, 2002).
When compared to other Eastern Eurasian Miocene
hominoids, the Chiang Muan molar is plotted near
Sivapithecus indicus and Lufengpithecus lufengensis (Fig. 5, Table 1). The hominoid sample from
Kaiyuan (cf. Lufengpithecus keiyuanensis), which is
Fig. 3. A: Occlusal view of Chiang Muan Hominoid (CMu61⬘00). B: Three-dimensional virtual image generated by AVS
Medical Viewer based on pQCT data (peripheral quantitative
computed tomography, Norland and Stratec Co., Ltd.). C: Crosssection of crown through apices of metacone (Me) and hypocone
(Hy), indicated by plane in B.
Fig. 4. Dental size. CMH, Chiang Muan Hominoid (CMu61⬘00). Pongo UM1 and UM2, upper M1 and M2 of extant orangutans (Pongo pygmaeus), respectively. Extant orangutan sample
includes both sexes.
geographically the closest and similar in age to
Chiang Muan, is considerably smaller. However, it
should be noted that the presently available maxillary specimen from Kaiyuan (YVO720) is a female,
based on its canine size and shape. The lower dentitions of Lufengpithecus keiyuanensis show large
sexual dimorphism (Woo, 1957, 1958; Zhang, 1987).
Among the additional hominoid samples from
Chiang Muan, there are two upper M2s (Chaimanee
et al., 2003). The larger M2 (TF6169) is similar in
size to the first hominoid specimen (CMu6-1⬘00), but
more elongated mesiodistally (MD/BL ratio, 93.3%
vs. 84.3% for TF6169 and CMu6-1⬘00, respectively).
The smaller M2 (TF6176) is much smaller than
CMu6-1⬘00, and its crown area (MD ⫻ BL) is only
63.0% of the latter. In size and crown proportion
(MD/BL ratio), TF6176 is similar to the upper M1
and M2 of the Kaiyuan palate (YVO720) (Fig. 5).
The MD/BL ratios are 96.2% for TF6176, and 95.2%
and 93.8% for M1 and M2 of YVO720, respectively.
The lingual cingulum of CMu6-1⬘00 appears to be
much reduced, though the heavy occlusal wear might
have affected the cingular expression to a certain degree. It is completely absent on the lingual aspect of
the protocone, but there still remains a trace of the
cingulum on the mesiolingual corner. In Late Oligocene and Early Miocene East African hominoids, the
lingual cingulum is much more strongly developed,
forming a continuous ledge on the mesial to lingual
aspects of the protocone, which sometimes extends
onto the lingual aspect of the hypocone (Andrews,
1978). Middle Miocene East African hominoids such as
Kenyapithecus (Leakey, 1961) and Nacholapithecus
(Ishida et al., 1999) have a reduced lingual cingulum
that is usually limited to the mesiolingual corner of the
crown. Especially, it is nearly absent in K. wickeri
(Harrison, 1992; Pickford, 1985, 1986). The lingual
cingulum of upper molars is strongly reduced in Sivapithecus and Lufengpithecus from Eastern Eurasia. As
far as we can see from published photographs (Fig. 3 in
Chaimanee et al., 2003), at least one upper molar
(TF6169) appears to have a small cingular remnant on
the mesial aspect of the protocone. Modern great apes
also show a reduction of the lingual cingulum on their
upper molars, though cingular remnants to various
degrees may be observed in some individuals. These
remnants are less frequently developed in orangutans
than in African great apes (Swindler, 1976).
On the distal aspect of the crown, a large interstitial wear facet (6.8 mm wide by 3.4 mm high) developed. Because of the poor preservation of the specimen, precise measurement of enamel thickness is
impossible. However, as far as can be known from
the noninvasive observation of cross-sectional images of the crown using peripheral quantitative computed tomography (pQCT; Norland and Stratec Co.,
Ltd.), the enamel of CMu6-1⬘00 would have been
thicker than that of thinly enameled hominoids like
the African great apes, hylobatids, and Dryopithecus. On the other hand, the enamel is probably as
moderately thick as in extant orangutans
(Schwartz, 2000). The cross-sectional images also
revealed that CMu6-1⬘00 has relatively low relief of
the dentine/enamel junction, differing from the high
relief in African great apes.
It is often difficult to determine precise affinities
of hominoids based on a single isolated upper molar.
In addition, the present specimen is missing one
fourth of the crown and is heavily worn. Therefore,
we treated this upper molar (CMu6-1⬘00) just as the
“Chiang Muan Hominoid” (Kunimatsu et al., 2000a,
b, 2002a,b, 2003a,b). Nonetheless, the limited morphological data from the present specimen (low and
voluminous cusps, much reduced lingual cingulum,
flat dentine/enamel junction, and probably moder-
Fig. 5. Upper molar size in Eastern Eurasian Miocene hominoids. UM1, upper first molar; UM2, upper second molar; Chiang
Muan, right upper molar (CMu6-1⬘00) in this study; Chiang Muan TF, hominoid specimens in Chaimanee et al. (2003); Kaiyuan, cf.
Lufengpithecus keiyuanensis; Lufeng, Lufengpithecus lufengensis; S., Sivapithecus; Yuanmou, Lufengpithecus yuanmouensis. All are
average values except for Chiang Muan, Chiang Muan TF, and Kaiyuan.
TABLE 1. Mesiodistal and buccolingual dimensions of upper molars (mm)1
Chiang Muan CMu6-1⬘00
Chiang Muan TF6169
Chiang Muan TF6176
Kaiyuan YVO7202
Yuanmou hominoids
Lufengpithecus lufengensis
Sivapithecus sivalensis
Sivapithecus indicus
Sivapithecus parvada
MD mean s.d.
0.71 7.6–11.4 118
1.08 8.7–14.1 136
0.78 11.2–13.3
1.16 13.5–16.0
BL mean
0.52 n.a.
0.56 n.a.
1.02 14.4–16.7
0.49 16.9–17.6
This study
Chaimanee et al. (2003)
Chaimanee et al. (2003)
Zhang (1987)
Zhang (1987)
Liu et al. (2000)
Liu et al. (2000)
Wu & Oxnard (1983)
Wu & Oxnard (1983)
Kay (1982)
Kay (1982)
Kay (1982)
Kay (1982)
Kelly (1988)
Kelly (1988)
n.a.; not available.
Mean values between right and left sides of single individual.
Mean values for combined sexes recalculated from statistic data in Wu and Oxnard (1988).
ately thick enamel) suggest that the Chiang Muan
Hominoid would have belonged to the same group as
the other large-bodied Miocene hominoids in Eastern Eurasia, such as Sivapithecus and Lufengpithecus. Although some additional hominoid specimens
from Chiang Muan were reported and assigned to a
new species, cf., Lufengpithecus chiangmuanensis
(Chaimanee et al., 2003), all of them are said to have
been collected from the Upper Lignite, and are probably several hundred thousand years younger than
CMu6-1⬘00 from the Lower Lignite (Suganuma et
al., 2002). Taking into account such a considerable
gap in age, these two samples from different lignite
units might represent two different taxa. However,
the present samples are too poor to determine
whether they are the same or different species.
The mammalian fossils from Chiang Muan have
yet to be studied in detail, but some useful data are
available from our preliminary observations. The
present nonprimate mammalian samples from
Chiang Muan include proboscideans, tragulids,
suids, rhinocerotids, and bovids (Nakaya et al.,
2001, 2002a–c ).
The proboscidean material is characterized by the
tetralophodont intermediate molars, the bunodont
molar cusps with a relatively simple configuration,
and the number of molar lophs (4.5 in upper M3, and
5 in lower M3). These features suggest that the
Chiang Muan proboscidean is a primitive tetralophodont gomphothere. At present, the Chiang Muan
material is most likely attributed to Tetralophodon
xiaolongtanensis (Chow and Chang, 1974), which
was previously known only from Xiaolongtan,
Kaiyuan District, Yunnan Province, China. Tetralophodon xiaolongtanensis was initially established as
a trilophodont gomphothere (Chow and Chang,
1974; Tobien et al., 1986), because only the third
molar showing relatively simple crown structure
was known at that time. Later, after the finding of
tetralophodont intermediate molars from the type
locality, the species was transferred from genus
Gomphotherium to Tetralophodon (Dong, 1987; Tobien et al., 1988). As noted by Dong (1987) and
Tobien et al. (1988), Tetralophodon xiaolongtanensis
can be distinguished from Tetralophodon longirostris from the European Vallesian in having a lesser
number of lophs (-ids) and a simpler loph structure.
Thus, Tetralophodon xiaolongtanensis is more primitive than T. longirostris and may indicate a slightly
older age than the Vallesian, possibly dating to the
latest Astracian (MN 7 ⫹ 8).
An upper molar of a small tragulid was discovered
from the same locality (CMu6) as was the hominoid
molar. It is identified as a small species of Dorcatherium. Although a number of Dorcatherium fossils
have been reported from the Siwaliks, many of them
have not yet been formally named (Barry, 1995).
Hence, a detailed comparison of the Chiang Muan
tragulid with the Siwalik Dorcatherium is difficult
at present. Because the Dorcatherium molar from
Chiang Muan is very small and low-crowned, it is
quite probable that the Chiang Muan tragulid is
assigned to one of the following four species from the
Siwaliks: Dorcatherium very small sp. A, Dorcatherium very small sp. B, D. minimus, or D. nagrii. The
temporal distribution of small and low-crowned Dorcatherium dates earlier than 11 Ma in the Siwaliks
(Barry, 1995).
The suid species from Chiang Muan are relatively
small in size. At present, we think that there are
three suid taxa in the Chiang Muan fossil sample;
Propotamochoerus/Hippopotamodon spp. and Suidae indet. (Nakaya et al., 2002a). Propotamochoerus
hysudricus is distributed between the Nagri to Soan
Formations of Late Miocene in the Siwaliks (Pickford, 1988). The temporal distribution of Hippopotamodon sivalense in the Siwaliks is very similar to
that of Propotamochoerus hysudricus, with the
known range between 7–10 Ma, but older and
younger specimens may be found (Pickford, 1988).
The known specimens from Chiang Muan are intermediate in size between P. hysudricus and H.
sivalense. It is interesting that Propotamochoerus
and Hippopotamodon are also known from Lufeng (8
Ma), Yuanmou (9 Ma), and Kaiyuan (10 –12 Ma) in
southwestern China, whose fauna include large-bodied hominoid fossils (Dong, 1987; Han, 1985; Ni and
Qiu, 2002; Pan, 1997a; Pickford and Liu, 2001;
Zhang, 1974).
Previous authors (Ducrocq et al., 1994; Jaeger et
al., 1985; Mein and Ginsburg, 1997; Pope and Bernor, 1990) estimated relatively old ages (14 –18 Ma)
for a number of Miocene fossil sites in northern
Thailand, such as Ban San Klang and Huai Siew in
the Pong Basin, Mae Long and Na Sai in the Li
Basin, and Mae Moh and Had Pu Dai. According to
faunal analysis (Nakaya et al., 2002a–c, unpublished findings), Chiang Muan is younger than these
fossil sites, most likely equivalent to MN 7 ⫹ 8 in the
European MN zones, though the MN zones are
based on European fauna and there are some uncertainties in applying them to Eastern Eurasian faunas. The fossil mammalian fauna of Chiang Muan
given by Chaimanee et al. (2003) differs from the
results of our own study (Nakaya et al., 2002a–c,
unpublished findings), but the available information
in their article is too little to compare with our data.
A paleomagnetic study at Chiang Muan by the ThaiJapanese Paleontological Expedition Team (Suganuma et al., 2002) revealed a normal-reverse-normal polarity sequence correlated to C5A to C5
chrons, suggesting that the Tertiary sediments at
Chiang Muan were deposited between 12–10 Ma.
The paleomagnetic data given by Chaimanee et al.
(2003) are slightly different in detail, with a wider
range of the estimated age for the Chiang Muan
deposits (10 –13.5 Ma). Based on the mammalian
fauna (Nakaya et al., 2002a–c, unpublished findings), we think that the latest Middle Miocene
(11–12 Ma) is the most likely age for the Chiang
Muan Hominoid (CMu6-1⬘00).
Suteethorn et al. (1990) reported the occurrence of
a small hominoid-like primate from Ban San Klang,
an early Middle Miocene site in northern Thailand.
They named it Dendropithecus orientalis, considering the Ban San Klang primate to be congeneric
with Dendropithecus macinnesi, an Early Miocene
small catarrhine from East Africa. However, the
hominoid status of East African Miocene small catarrhines such as D. macinnesi has been doubted
(Harrison, 1988). In addition, Harrison and Gu
(1999) concluded that the Ban San Klang primate is
not Dendropithecus but is recognized as a species of
Dionysopithecus, i.e., a pliopithecid. The Pliopithecidae are now regarded as a primitive catarrhine
group that may have diverged earlier than the split
between the Cercopithecoidea and Hominoidea (Andrews et al., 1996). Hence, there had not been any
true hominoid fossil reported from the Neogene
Southeast Asia before the discovery of the Chiang
Muan Hominoid. The hominoid molar (CMu6-1⬘00)
from Chiang Muan is the first reported Miocene
hominoid in Southeast Asia (Kunimatsu et al.,
2000a). Additional hominoid fossils were later reported by Chaimanee et al. (2003) from the same
site, although all of them had been collected from
younger deposits than CMu6-1⬘00. Partly because of
the considerable temporal gap between these two
materials (probably several hundred thousand
years; Suganuma et al., 2002), and partly because of
the fragmentary nature of the first specimen, it is
difficult to determine whether or not these two materials belong to a single or different species. It is
necessary to recover more samples from the Lower
Lignite Member through further fieldwork.
Although small primitive catarrhines such as the
Pliopithecidae already immigrated from Africa to
both Western and Eastern Eurasia in the Early Miocene (Andrews et al., 1996; Harrison and Gu, 1999),
the oldest of the known large-bodied fossil hominoids in Eastern Eurasia is Sivapithecus from the
Chinji Formation (12.5 Ma) of the Siwaliks (Kappelman et al., 1991). In a recent review of Asian fossil
hominoids, Kelley (2002) recognized three species of
Sivapithecus: S. sivalensis (ca. 8.5–9.5 Ma), S. indicus (ca. 10.5–12.5 Ma), and S. parvada (ca. 10 Ma),
though he himself admitted that the Siwalik hominoid fossils still need revision.
In the Chinese fossil record, the oldest large-bodied hominoid is “Dryopithecus” keiyuanensis, and is
comprised of several associated lower teeth and a
palate from Xiaolongtan, Kaiyuan District, Yunnan
Province (Woo, 1957, 1958; Zhang, 1987). Recent
authors (Zheng and Zhang, 1997; Harrison et al.,
2002) included this material in Lufengpithecus. Its
age is estimated to be equivalent to MN9 in European land mammal units (ca. 10 –11 Ma) by Dong
(1987) and Harrison et al. (2002), or slightly older
(MN 7 ⫹ 8) by Qiu and Qiu (1995).
There are three other sites in Yunnan Province
which have yielded Neogene hominoid fossils:
Lufeng, Yuanmou, and Baoshan. Lufengpithecus
lufengensis from the type locality (Lufeng) is considered to be 8 Ma old. The hominoid material from
Yuanmou is also assigned to Lufengpithecus, though
its specific taxonomy is still debated (Harrison et al.,
2002). The age of Yuanmou was thought to be considerably younger (ca. 5 Ma), but a recent analysis of
micromammalian fossils from the Yuanmou Basin
(Ni and Qiu, 2002) suggests a slightly older age (9
Ma) than Lufeng. The hominoid material from
Yangyi in Baoshan District is not yet described, but
its age is said to be much younger (3–5 Ma) than the
others (Harrison et al., 2002).
Among these Miocene hominoid sites in Yunnan
Province, Kaiyuan is geographically the closest to
Chiang Muan. The distance between these two sites
is only ca. 650 km. In addition, our faunal analysis
at Chiang Muan shows a faunal similarity to
Kaiyuan (Nakaya et al., 2002a). The estimated ages
of these two sites are similar (Nakaya et al., 2002a;
Suganuma et al., 2002). However, Chaimanee et al.
(2003) did not refer to the Kaiyuan hominoid material (cf. Lufengpithecus keiyuanensis), despite their
assigning the additional hominoid fossils from the
Upper Lignite Member of Chiang Muan to a new
species which is provisionally included in Lufengpithecus (cf. Lufengpithecus chiangmuanensis). Considering the geographical and temporal closeness of
these two sites, it is critical in creating a new species
to make clear that the Chiang Muan material is
considerably different from the Kaiyuan material.
The important characters of cf. Lufengpithecus
chiangmuanensis are a mesiodistally broad lower
central incisor (TF6178) and a male lower canine
with a rounded cross-section (TF6171-1), which
might indicate some similarity to extant orangutans. However, these parts are not preserved in the
Kaiyuan material. According to the description and
photographs in Chaimanee et al. (2003), the morphology of the postcanine teeth of cf. L. chiangmuanensis appears to be basically similar to that of
cf. L. keiyuanensis, as well as the molar size and
degree of sexual dimorphism (Woo, 1957, 1958;
Zhang, 1987; Harrison et al., 2002; Kunimatsu, personal observations). Therefore, there is still ambiguity in the taxonomy of cf. L. chiangmuanensis. Detailed comparison to the Kaiyuan hominoid material
has yet to be done. Unless the distinction between
the hominoid fossils of these two sites is made clear,
cf. L. chiangmuanensis has to be treated as a junior
synonym of cf. L. keiyuanensis, because the latter
name apparently has priority.
Although the precise taxonomic affinity of the
Chiang Muan Hominoid (CMu6-1⬘00) is uncertain
due to the poor preservation of the present material,
the estimated age for Chiang Muan (ca. 11–12 Ma)
suggests that the Chiang Muan Hominoid is very
likely one of the early hominoid immigrants into
Eastern Eurasia, and no doubt it is the earliest
Hominoidea sensu stricto ever discovered in Southeast Asian countries (Fig. 6).
In addition, the Chiang Muan Hominoid (CMu61⬘00) is the first Miocene hominoid fossil reported
from the south of the Tropic of Cancer in Eastern
Eurasia. The previously known hominoid fossil sites
in South Asia and China are all located north of the
Tropic of Cancer. Consequently, Chiang Muan is the
southernmost Miocene hominoid site in Eurasia.
The presence of the Chiang Muan Hominoid indicates that by the latest Middle Miocene, hominoids
had already expanded their distribution into more
southern areas of Eastern Asia than previously
At present, the fossil record, including the hominoid fossils from Chiang Muan, seems to indicate
that the hominoid dispersal into Eastern Eurasia
occurred around 13 Ma (Sivapithecus), while largebodied hominoids (Griphopithecus) entered into Europe and Anatolia by 16 –17 Ma (Andrews et al.,
1996; Heizmann and Begun, 2001). If this were the
Fig. 6. Temporal range of Chiang Muan Hominoid and Neogene catarrhines in Eastern Eurasia. After Barry et al. (1995), Ducrocq
et al. (1995), Harrison and Gu (1999), Harrison et al. (1991), Kappelman et al. (1991), Pan (1994, 1997b, 1998), Pilbeam et al. (1996),
Qiu and Qiu (1995), Steininger et al. (1996), and Suteethorn et al. (1990).
case, there would have been a 3– 4-million-year time
lag between the hominoid dispersals into the eastern and western parts of the Eurasian continent.
Yet, the fossil records of hominoids in Eastern Eurasia are insufficient to answer with certainty
whether such a time lag is real or superficial. The
Eastern Eurasian Miocene hominoids might have
evolved from earlier Western Eurasian forms like
Griphopithecus, or they might have separately immigrated from Africa (Kelley, 2002). The present
evidence is insufficient to give a clear answer to this
While further investigations are, of course, needed
to determine the phylogenetic status and more precise age of the Chiang Muan Hominoid (CMu6-1⬘00),
this finding, as well as the additional isolated hominoid teeth from younger deposits at Chiang Muan,
shows a good potential in Thailand for discovering
hominoid fossils that will enable us to understand
more about the evolutionary history of hominoids in
Eastern Eurasia.
Arong Sritulakarn, Anuvart Wongwan, and Amrit
Suvunsavate) for their support during our field research in Thailand. We also appreciate the assistance given by Thanuchai Silaratana and Bantita
Udomkan of Chiang Mai University, and Mototaka
Saneyoshi, Yuusuke Nakano, and Yasunori Horikiri
of Shimane University. Y. K. also thanks Yang
Changman of the Raffles Museum of Biodiversity at
the National University of Singapore, Boeadi of the
Zoological Museum at Bogor in Indonesia, Lu
Qingwu and Pan Yuerong of the Institute of Vertebrate Paleontology and Paleoanthropology in China,
and Samir Sen Gupta of the Geological Survey of
India, for allowing him to examine extant and fossil
specimens under their care. We owe much to Nobuo
Shigehara and Osamu Takenaka of the Primate Research Institute (PRI), Kyôto University, for their
support of our overseas research. We thank Michael
A. Huffman of the PRI for correcting the Englishlanguage usage of our manuscript, and two reviewers for their useful comments.
We thank the staff of the Department of Geological Sciences, Chiang Mai University and the Chiang
Muan Mine Co., Ltd. (especially Nikorn Wongchai,
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