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

Abstract

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

Full text

doi: 10.1098/rspb.2009.0836
, 3285-3294 first published online 1 July 2009276 2009 Proc. R. Soc. B
Marandat, Paul Tafforeau, Aung Naing Soe, Soe Thura Tun and Aung Aung Kyaw
K. Christopher Beard, Laurent Marivaux, Yaowalak Chaimanee, Jean-Jacques Jaeger, Bernard
Myanmar and the monophyly of Burmese amphipithecids
A new primate from the Eocene Pondaung Formation of
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A new primate from the Eocene Pondaung
Formation of Myanmar and the monophyly of
Burmese amphipithecids
K. Christopher Beard1,*, Laurent Marivaux2, Yaowalak Chaimanee3,
Jean-Jacques Jaeger4, Bernard Marandat2, Paul Tafforeau5,
Aung Naing Soe6, Soe Thura Tun7and Aung Aung Kyaw8
1
Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue,
Pittsburgh, PA 15213, USA
2
Laboratoire de Pale
´ontologie, Institut des Sciences de l’E
´volution, Universite
´Montpellier 2,
Place Euge
`ne Bataillon, 34095 Montpellier, France
3
Paleontology Division, Bureau of Paleontology and Museum, Department of Mineral Resources,
Rama VI Road, Bangkok 10400, Thailand
4
Institut International de Pale
´oprimatologie, Pale
´ontologie Humaine, Evolution et Pale
´oenvironnements,
Universite
´de Poitiers, 40, Avenue du Recteur Pineau, 86022 Poitiers, France
5
European Synchrotron Radiation Facility, 38043 Grenoble, France
6
Department of Geology, Hpa-an University, Hpa-an, Myanmar
7
Myanmar Geosciences Society, MES Building, Hlaing University, Yangon, Myanmar
8
Department of Archaeology, National Museum and Historical Research (Upper Myanmar),
Ministry of Culture, Mandalay, Myanmar
The family Amphipithecidae is one of the two fossil primate taxa from Asia that appear to be early mem-
bers of the anthropoid clade. Ganlea megacanina, gen. et sp. nov., is a new amphipithecid from the late
middle Eocene Pondaung Formation of central Myanmar. The holotype of Ganlea is distinctive in
having a relatively enormous lower canine showing heavy apical wear, indicating an important functional
role of the lower canine in food preparation and ingestion. A phylogenetic analysis of amphipithecid
relationships suggests that Ganlea is the sister taxon of Myanmarpithecus, a relatively small-bodied
taxon that has often, but not always, been included in Amphipithecidae. Pondaungia is the sister taxon
of the Ganlea þMyanmarpithecus clade. All three Pondaung amphipithecid genera are monophyletic
with respect to Siamopithecus, which is the most basal amphipithecid currently known. The inclusion
of Myanmarpithecus in Amphipithecidae diminishes the likelihood that amphipithecids are specially
related to adapiform primates. Extremely heavy apical wear has been documented on the lower canines
of all three genera of Burmese amphipithecids. This distinctive wear pattern suggests that Burmese
amphipithecids were an endemic radiation of hard object feeders that may have been ecological analogues
of living New World pitheciin monkeys.
Keywords: Amphipithecidae; Eocene; Myanmar; anthropoid origins
1. INTRODUCTION
Since their initial description in the early twentieth
century, amphipithecid primates have figured promi-
nently in discussions of anthropoid origins (Pilgrim
1927;Colbert 1937; Szalay 1970,1972;Simons 1971;
Ba Maw et al. 1979;Ciochon et al. 1985). Thanks to
renewed field efforts in the Eocene Pondaung Formation
of Myanmar, a great deal of additional amphipithecid
material has been recovered and described during the
past decade ( Jaeger et al.1998,2004;Chaimanee et al.
2000a;Gunnell et al. 2002;Shigehara et al. 2002;
Marivaux et al. 2003;Takai & Shigehara 2004). This new-
found abundance of amphipithecid fossils has so far failed
to quell the longstanding debate regarding their phyloge-
netic affinities. A majority of recent workers support
anthropoid affinities for amphipithecids ( Jaeger et al.
1998,2004;Chaimanee et al. 2000a; Beard 2002,
2004; Marivaux et al.2003,2008; Beard et al.2005,
2007;Bajpai et al. 2008;Rose et al. 2009). Others
maintain that dental and gnathic similarities between
amphipithecids and early anthropoids merely reflect con-
vergent adaptations to similar diets, thereby obscuring
what they regard to be the adapiform affinities of the
former group (Ciochon & Holroyd 1994; Ciochon &
Gunnell 2002,2004; Gunnell et al.2002,2008).
Much of the ongoing disagreement about the higher-
level relationships of amphipithecids can be attributed
to the nature of their fossil record. Amphipithecids are
documented primarily on the basis of teeth and jaws
from the Pondaung Formation, although the group is
also known from the latest Eocene of peninsular Thailand
*Author for correspondence (beardc@carnegiemnh.org).
Electronic supplementary material is available at http://dx.doi.org/10.
1098/rspb.2009.0836 or via http://rspb.royalsocietypublishing.org.
Proc. R. Soc. B (2009) 276, 3285–3294
doi:10.1098/rspb.2009.0836
Published online 1 July 2009
Received 15 May 2009
Accepted 10 June 2009 3285 This journal is q2009 The Royal Society
on 10 August 2009rspb.royalsocietypublishing.orgDownloaded from

and the Oligocene of central Pakistan (Chaimanee et al.
1997,2000b;Marivaux et al. 2005). Several cranial and
postcranial fossils from the Pondaung Formation have
been allocated to Amphipithecidae, but none of these
specimens was found in direct association with diagnostic
amphipithecid dental remains, rendering all of them
controversial to a greater or lesser extent. Particularly
problematic in this regard are a partial skeleton of a
large-bodied primate (NMMP 20) and two cranial frag-
ments (NMMP 19 and NMMP 27) that have been
referred to the Amphipithecidae (Ciochon et al.2001;
Gunnell et al.2002;Takai et al.2003). The purported
amphipithecid affinities of the NMMP 20 partial skeleton
conflict with the anatomy of an isolated primate astragalus
from the Pondaung Formation, which bears diagnostic
anthropoid traits (Marivaux et al.2003). We regard the
NMMP 20 partial skeleton as that of a large-bodied sivala-
dapid adapiform, rendering it irrelevant to discussions of
amphipithecid relationships (Beard et al.2007;Marivaux
et al.2008). Similarly, the Pondaung cranial fragments
do not appear to pertain to any primate and are unlikely
to be mammalian (Beard et al.2005).
The lower-level systematics of amphipithecids from
Myanmar is also in a state of flux. The first two genera
that were proposed, Pondaungia and Amphipithecus,are
now considered to be synonymous by some experts
(Jaeger et al. 2004), a view that is endorsed here.
Questions remain regarding the number of valid species
of Pondaungia, an issue that is complicated by the possi-
bility of a high level of sexual dimorphism in this group.
More problematic is Myanmarpithecus, another fossil pri-
mate from the Pondaung Formation that was initially
described as a probable basal anthropoid of uncertain
taxonomic affinities (Takai et al. 2001). Subsequent
authors have regarded Myanmarpithecus as either an omo-
myid (Ciochon & Gunnell 2002;Gunnell et al. 2008)or
another member of the Amphipithecidae (Kay et al.
2004a,b;Marivaux et al. 2005). Here, we describe a
new genus of Amphipithecidae from the Pondaung
Formation and reassess the phylogenetic and paleobiological
affinities of this group in light of this new taxon.
2. SYSTEMATIC PALAEONTOLOGY
Class Mammalia Linnaeus, 1758
Order Primates Linnaeus, 1758
Suborder Haplorhini Pocock, 1918
Infraorder Anthropoidea Mivart, 1864
Family Amphipithecidae Godinot, 1994
Ganlea megacanina, gen. et sp. nov.
Holotype: NMMP 70, a right dentary preserving the
crowns of C
1
and M
2
and the roots or alveoli for P
2
–M
1
(figure 1). Partial alveoli for I
1–2
are also preserved.
Type locality: Ganle kyitchaung, GPS coordinates ¼
21844004.600 N, 94843025.000 E(figure 2).
Age and distribution: Late middle Eocene Pondaung
Formation, Myanmar.
Hypodigm: The holotype; NMMP 69, an isolated left
M
1
from Nyaungpinle (figure 3d); NMMP 71, an isolated
left I
2
from Nyaungpinle (figure 3e–i); NMMP 72, an iso-
lated right M
2
from Nyaungpinle (figure 3m–o); NMMP
73, an isolated left M
1
from Thamingyauk (figure 3j–l);
NMMP 74, a right dentary preserving P
3–4
from
Thamingyauk (figure 3a–c); NMMP 75, an isolated left
M
1
or M
2
from Paukkaung kyitchaung 2 (figure 3t); and
NMMP 76, an isolated left P
4
from Paukkaung kyitchaung
2(figure 3s).
Diagnosis: Amphipithecid primate smaller than
Pondaungia and Siamopithecus but larger than Myanmar-
pithecus. Symphyseal region of dentary less vertical in
orientation than in Pon daungia and Siamopithecus.C
1
,at
least in male individuals, and P
2
larger relative to molar
size than in other amphipithecids. C
1
further differs from
that of Pondaungia and Siamopithecus in having a small,
distobuccal tubercle or heel. P
2–4
relatively larger and less
compressed mesiodistally than in Pondaungia.P
3–4
with
elevated and mesially oriented preprotocristid, in contrast
to the condition in other amphipithecids. P
3
further differs
from that of Myanmarpithecus and Pondaungia in lacking a
metaconid and having a reduced talonid heel. Lower
molars differ from those of Bugtipithecus in lacking a promi-
nent lingual notch at the base of the postvallid. M
1–2
without hypoconulid, in contrast to Siamopithecus.
Etymology: The generic name derives from the village
of Ganle, situated near the type locality. The trivial name
refers to the relatively massive canine preserved in the
holotype.
Description of the holotype: The dentary is robustly
constructed, measuring 14.15 mm in depth and
6.75 mm in width just behind the symphysis. The sym-
physis is unfused, but its surface is characterized by a
highly rugose pattern of alternating ridges, pits and val-
leys that would have interlocked with corresponding
structures on the opposite side. As it is preserved, the
greatest vertical height of the symphysis is 18.05 mm. It
extends inferiorly and posteriorly to a point below the
junction of the mesial and distal roots of P
3
. The incli-
nation of the main axis of the symphysis in relation to a
horizontal line through the toothrow is 538. The
planum alveolare slopes at roughly 218. The pit for the
genioglossus muscle is notable for its depth, and it lies
above a stoutly constructed inferior transverse torus.
The lateral side of the dentary bears dual mental foramina
anteriorly, and a third emissary foramen below the mesial
root of M
1
. The anteriormost mental foramen lies
beneath the interstitial junction between C
1
and P
2
.Itis
significantly larger than the other mental foramen,
which lies beneath the junction between P
2
and P
3
.
Based on roots and/or alveoli preserved in the holotype,
the lower dental formula of Ganlea was 2-1-3-3. The
lower incisors are documented by partial alveoli located
mesial to the lower canine crown. Based on the radius of cur-
vature of the preserved lingual parts of these alveoli, it
appears that I
2
would have been slightly larger than I
1
.
Both incisors were tiny (the estimated mesiodistal dimen-
sions of the lower incisor roots are 0.85 mm for I
1
and
1.10 mm for I
2
) and oriented almost vertically within the
dentary. Given the narrow space available between the sym-
physeal surface and the lower canine crown, it is clear that
the anterior lower dentition of Ganlea megacanina was
tightly spaced. Indeed, a distinctive, vertically oriented
groove on the mesial side of the canine root and the basal
part of its crown is appropriate in position to have served
as an embrasure for the adjacent I
2
.
The lower canine is massive (length, 5.90 mm; width,
4.30 mm), being absolutely larger in terms of both
3286 K. C. Beard et al. New amphipithecid from Myanmar
Proc. R. Soc. B (2009)
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mesiodistal length and buccolingual width than the lower
canine of NMMP 24, a dentary of Pondaungia that per-
tains to an animal that was clearly much larger than
Ganlea megacanina (Gunnell et al. 2002;Jaeger et al.
2004). The apex of the canine crown has been worn
nearly flat, making it impossible to estimate the unworn
height of the canine crown. From the enamel– dentine
junction on the buccal side of the canine to the wear
(a) (b) (c) (d)
(e)(f)
(g)(h)
Figure 1. Ganlea megacanina, gen. et sp. nov.: holotype right dentary (NMMP 70) preserving the crowns of C
1
and M
2
and the
roots or alveoli for P
2
–M
1
. Partial alveoli for I
1–2
are also preserved. The specimen is presented by 3D rendering in (a) occlu-
sal, (b) inferior, (c) distal, (d) mesial, (e) buccal and ( f) lingual views. Images (a–f) have been generated from 3D data
obtained by X-ray synchrotron microtomography (SR-mCT) on the beamline ID19 at the European Synchrotron Radiation
Facility (ESRF, Grenoble, France). Images gand hare 3D rendering of NMMP 70 showing the colour-coded crowns and
roots of individual teeth, which have been virtually delimited by manual segmentation. Scale bar equals 1 cm.
New amphipithecid from Myanmar K. C. Beard et al. 3287
Proc. R. Soc. B (2009)
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facet near its apex, the crown measures 4 mm in height.
The level of the enamel–dentine junction is not uniform
about the circumference of the canine crown. Rather, this
junction extends apically on either side of the mesial
embrasure groove for I
2
noted earlier. In occlusal view
the canine is roughly ovoid in outline, with a gently
convex buccal surface and a nearly flat lingual surface.
These surfaces are separated by the vertically oriented
groove mesially and by a small heel or distension of the
crown distally. The latter structure was probably charac-
terized by a small tubercle in the unworn condition,
but this cuspule (if it actually existed) has been nearly
obliterated by the apical wear on the canine noted
previously. Similarly obscured by apical wear, there
appears to have been a distal crest that would have con-
nected the apex of the canine crown with the distal heel
or tubercle. A modest cingulid, which becomes more
marked distally, adorns the lingual side of the canine
crown, but no similar structure exists on the buccal side
of the tooth.
P
2–4
are documented in the holotype solely by their
roots and aveoli. The crowns of P
3–4
are preserved in a
referred specimen, and these are described in the follow-
ing section. We estimate that the combined mesiodistal
length of P
2–4
would have been roughly 9.25 mm. As is
the case in other amphipithecids (and eosimiids), P
2
is
single-rooted while P
3–4
are double-rooted. The single
root of P
2
is strongly compressed mesiodistally, so that
its buccolingual width greatly exceeds its mesiodistal
length. This condition also occurs in other amphipithe-
cids, but it contrasts with the presumably more
primitive condition found in eosimiids, in which the
alvelous or root for P
2
is roughly circular in cross section.
High-resolution synchrotron images reveal that the
P
2
root in the holotype of Ganlea was particularly
stout and asymmetrical in cross section. Although
Myanmarpithecus and Pondaungia share the strong mesio-
distal compression of P
2
that occurs in Ganlea, the latter
taxon is unique among amphipithecids in having a P
2
root
that is broader buccolingually than the corresponding
roots of M
1–2
.BothP
3–4
show the typical amphipithecid
pattern of having the mesial root located farther buccally
than the distal root, a condition that also occurs in
eosimiids and many other basal anthropoid taxa.
M
1
is documented in the holotype only by its roots and
alveoli. Knowledge of the crown of M
1
is based on two
referred specimens that are described in the following
section.
M
2
(length 4.70 mm; width 4.50 mm) is a relatively
quadrate, low-crowned tooth characterized by poorly
defined cusps and weakly developed crests (figure 3p–r).
The M
2
crown in the holotype is moderately worn,
obscuring some details of its morphology (NMMP 72 is
a relatively unworn M
2
that is described in the following
section). The mesiodistally compressed trigonid shows
no evidence of having a paraconid. The protoconid
appears to have been slightly larger than the metaconid
(at least in terms of its basal circumference), and the
two cusps were partly separated by a longitudinal valley.
A tiny mesial cingulid occurs in front of the metaconid.
The talonid is broad, surrounded by low crests, and
simple in construction. It bears a low entoconid and a
much higher hypoconid. The cristid obliqua meets the
postvallid very buccally, so that the hypoflexid is extre-
mely shallow. Several minor folds of enamel run from
the hypoconid and the cristid obliqua toward the central
part of the talonid basin. A small interstitial wear facet
on the distal side of the talonid demonstrates that M
3
was present.
Description of the referred specimens: NMMP 71
(figure 3e–i) is an isolated left lower incisor (apical mesio-
distal length, 1.90 mm; basal labiolingual breadth,
1.85 mm) that we tentatively identify as I
2
on the basis
of the mesiodistal dimension of its root (1.10 mm),
which matches the size of the partial I
2
alveolus in the
holotype lower jaw (see earlier mentioned). The crown
is broken apically, but that which remains can be
described as being spatulate in shape. In mesial or distal
92°
28°
24°
20°
16° Yangon Thailand
Laos
Myanmar
Mandalay
Thadut
Paukkaung
12
34
4
2
3
1
Bahin Pangan
Nyaungpinle Paukkaung Kyitchaung n°2
Ganle Thamingyauk
Kanle
Chaungzongyi
Thamingyauk
21°
45'
Magyigan
Than-UDaw
94°45'
4 km
Pale
Padaukkon
Bay
of
Bengal
96° Legan
China
India
N
Figure 2. Location map for the fossiliferous localities in the Bahin (Nyaungpinle, Paukkaung Kyitchaung 2, Ganle) and Pangan
(Thamingyauk) areas of central Myanmar.
3288 K. C. Beard et al. New amphipithecid from Myanmar
Proc. R. Soc. B (2009)
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view, the crown is roughly wedge-shaped, being broader
at its base than near its apex. The enamel–dentine junc-
tion is not uniformly distributed about the base of the
crown. Rather, it extends farther toward the root on the
labial and lingual surfaces of the crown. Distally and
(especially) mesially, the enamel– dentine junction arcs
toward the apex of the tooth, thereby covering less of
the root. The labial surface of the crown is gently
convex, while the lingual surface is more irregular, but
generally concave. The lingual surface of the crown is
dominated by a central, pillar-like structure that is
bounded mesially and distally by well-developed cingu-
lids. The latter structures are connected by a more
modest cingulid near the lingual base of the crown.
(a)
(b) (c)
(d) (e) ( f) (g) (h) (i)
(j) (k)(l)
(s)
(m)(n) (o)
(t)
(r)(q)( p)
Figure 3. Ganlea megacanina, gen. et sp. nov.: (a–c) right dentary fragment bearing P
3–4
(NMMP 74) in (a) occlusal, (b) lin-
gual and (c) buccal views; (d) left M
1
(NMMP 69) in occlusal view; (e–i) left lower incisor (NMMP 71) in (e) occlusal, ( f)
lingual, (g) labial, (h) mesial and (i) distal views; ( j–l) left M
1
(NMMP 73) in ( j) occlusal, (k) buccal and (l) lingual views;
(m–o) right M
2
(NMMP 72) in (m) occlusal, (n) buccal and (o) lingual views; (p–r) right M
2
of the holotype (NMMP 70) in
(p) occlusal, (q) buccal and (r) lingual views; (s) left P
4
(NMMP 76) in occlusal view; (t) left M
1
or M
2
(NMMP 75) in occlusal
view. Scale bar equals 2 mm. The 3D renderings (d–r) have been obtained by X-ray SR-mCT. Original art (drawings a–c,s–t)
by Laurence Meslin, copyright CNRS-Meslin.
New amphipithecid from Myanmar K. C. Beard et al. 3289
Proc. R. Soc. B (2009)
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NMMP 74 (figure 3a–c) is a fragmentary dentary
preserving the crowns of P
3–4
, both of which are
double-rooted. P
3
(length, 2.80 mm; width, 2.90 mm) is
distinctive in showing strong basal distensions of enamel
both buccally and lingually. The lingual base of the P
3
crown is notably more asymmetrical than its buccal
counterpart, because the degree of enamel distension is
far more pronounced distally than mesially on the lingual
side of the tooth. Similar P
3
morphology occurs in
Myanmarpithecus and Pondaungia, but Siamopithecus
lacks the pronounced basal distension of P
3
enamel that
characterizes all three Burmese amphipithecids. The tri-
gonid of P
3
bears an elevated paraconid that is situated
directly mesial to the protoconid. The latter two cusps
are connected by the preprotocristid, yielding a relatively
trenchant structure that approximates a blade-like mor-
phology. The lingual side of the trigonid bears a relatively
complete cingulid, but there is no development of a meta-
conid. The lingual cingulid is stronger distally than
mesially, and it traces the general contour of the base of
the crown. As such, the lingual cingulid reaches its
inferiormost point near the junction of the trigonid and
talonid. From there, it continues superiorly to define
the lingual side of the abbreviated talonid. The talonid
itself lacks a distinct basin. Rather, it forms a heel-like
structure that consists of the hypoconid, the distalmost
part of the lingual cingulid, and a vertically oriented
crease that separates the trigonid and the talonid. A
short, almost vertically oriented crest unites the hypoconid
with the protoconid.
P
4
(length, 3.05 mm; width, 3.10 mm) shows greater
enamel distension buccally than lingually, thereby dis-
playing the muted exodaenodont condition that is typical
of most basal anthropoids. The trigonid is more nearly
molariform than that of P
3
, because the metaconid is rela-
tively well developed. The latter cusp is situated inferiorly
and distally with respect to the protoconid. A modestly
developed crest runs from the apex of the protoconid to
the base of the metaconid. As is the case for P
3
, the pre-
protocristid is somewhat elevated and it extends almost
directly mesially to unite with a small paraconid. The lin-
gual cingulid is restricted to the trigonid, where it forms a
thick shelf extending distally and inferiorly from the
paraconid. Because the lingual cingulid fails to unite the
paraconid with the metaconid, the trigonid is open
lingually. The talonid of P
4
is abbreviated, but better
developed than that of P
3
. It is dominated by the hypoco-
nid, which occurs at roughly the same height on the
crown as the metaconid. Two moderately developed
crests emanate from the hypoconid to line the buccal
and distal margins of the talonid. The short cristid obli-
qua climbs the trigonid to become cofluent with the
base of the protoconid. The postcristid runs lingually
and inferiorly from the hypoconid, connecting that cusp
with a tiny entoconid. The talonid itself consists of a
short, arcuate valley between the trigonid and the
postcristid.
NMMP 69 (figure 3d) (length, 4.30 mm; width,
3.90 mm) and NMMP 73 (figure 3j–l) (length,
4.20 mm; width, 3.80 mm) are isolated left M
1
s referred
to Ganlea megacanina on the basis of their appropriate
size and morphology. NMMP 69 shows slightly less
wear than NMMP 73, but otherwise the two specimens
are remarkably similar in morphology. The trigonid
is less compressed mesiodistally than is the case for M
2
in the holotype (see earlier mentioned), being roughly
triangular in occlusal outline. The protoconid and
metaconid are low, rounded cusps separated by either a
sinuous valley (NMMP 69) or a tiny depression
(NMMP 73). In terms of basal circumference, the proto-
conid is appreciably larger than the metaconid, but there
is no apparent difference in the height of these cusps.
Weakly developed crests, including an arcuate crest defin-
ing the mesial margin of the trigonid and a transverse
crest marking the distal side of the trigonid, connect the
protoconid with the metaconid. There is no development
of a distinct paraconid. The talonid is remarkably broad
and encircled by weak crests. The hypoconid and the cris-
tid obliqua are much taller than the entoconid and its
associated crests. The cristid obliqua is relatively straight,
and it joins the postvallid very buccally, resulting in an
extremely shallow hypoflexid. The hypoconulid is not
developed as a distinct cusp.
NMMP 72 (figure 3m–o) (length, 4.45 mm) is an
isolated right M
2
from Nyaungpinle that appears to be
an unerupted tooth germ. We tentatively refer this specimen
to Ganlea megacanina here. Although the tooth is broken
buccally, it appears to have been relatively narrower than
M
2
in the holotype. Its unworn condition is reflected by
the presence of numerous enamel crenulations.
NMMP 76 (figure 3s) (length, 2.85 mm; width,
4.65 mm) is an isolated left P
4
from Paukkaung
kyitchaung 2. The crenulated crown is nearly rectangular
in occlusal outline, although its lingual margin is rounded
and slightly narrower than its buccal counterpart. The
buccal margin of the crown is dominated by the paracone,
the base of which is buccolingually compressed. Pre- and
post-paracristae run mesially and distally from the apex of
the paracone toward the margins of the tooth. The mesial
cingulum is thick and continuous, running lingually from
the terminus of the preparacrista to a point directly mesial
to the protocone. The distal cingulum is similar in thick-
ness but less distinct because it is interrupted by multiple
enamel crenulations. The protocone is a low, rounded
cusp situated near the mesiolingual margin of the
crown. The preprotocrista is low but extensive, running
buccally more or less parallel to the mesial cingulum
until it reaches the base of the paracone. A short postpro-
tocrista is confluent with the distal cingulum. The central
part of the crown is covered by an irregular pattern of
enamel crenulations that defies any systematic attempt
at description.
The upper molar morphology of Ganlea is documen-
ted by NMMP 75 (figure 3t), an isolated left M
1
or M
2
(length, 4.15 mm; width, 5.25 mm). The crown is
bunodont, bears crenulated enamel, and is basically
tritubercular. The paracone is slightly larger than the
metacone, and both buccal cusps are situated near the
buccal margin of the crown, rather than being located
more internally as is often the case in Pondaungia. Con-
ules are not apparent. The protocone is situated mesial
of the midline, such that it is closer to the paracone
than the metacone. The pre- and post-protocristae are
evident, but neither of these crests are well defined. The
postprotocrista runs distally before turning buccally to
become confluent with a lingual crest from the metacone
(hypometacrista). There is no evidence of a pseudohypo-
cone. The mesial cingulum is relatively strong and
3290 K. C. Beard et al. New amphipithecid from Myanmar
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continuous, while the distal cingulum is narrower and
interrupted by numerous enamel crenulations. A tiny cus-
pule that could be regarded as an incipient hypocone
occurs near the lingual termination of the distal cingu-
lum. Buccal and lingual cingula are either extremely
weak or entirely absent.
Discussion: The adult body mass of Ganlea megaca-
nina can be estimated on the basis of regressions of
body mass as a function of M
1
area in living primates
(Conroy 1987). Using the anthropoid regression equation
provided by Conroy (1987), we derive a mean adult body
mass estimate of roughly 2.4 kg. The all-primate
regression equation provided by Conroy (1987) yields a
slightly lower estimate of mean adult body mass of
roughly 1.9 kg. Hence, Ganlea would have been about
the same size as the New World monkey Pithecia.
3. PHYLOGENETIC ANALYSIS
In order to assess the impact of Ganlea on the
evolutionary relationships of Amphipithecidae, we per-
formed a phylogenetic analysis based on a data matrix
including 39 taxa and 326 characters (see the electronic
supplementary material). Twelve maximally parsimo-
nious trees were recovered. These trees have a tree
length of 1584, a consistency index of 0.3226 and a
retention index of 0.5467. A strict consensus tree that
summarizes the phylogenetic resolution obtained by our
analysis is depicted in figure 4.
Notable results from this analysis include the novel
finding that all three Burmese amphipithecids (Pondaun-
gia,Myanmarpithecus and Ganlea) are monophyletic
with respect to the Thai genus Siamopithecus. To reflect
their seemingly close phylogenetic relationships, we refer
all three Burmese amphipithecids to the subfamily
Amphipithecinae, while Siamopithecus is classified here
in a separate amphipithecid subfamily, Siamopithecinae.
Many previous workers have failed to recognize that
Myanmarpithecus is an amphipithecid (Takai et al. 2001;
Ciochon & Gunnell 2002; Gunnell et al.2002,2008).
Those who have accepted the amphipithecid affinities of
Myanmarpithecus have typically regarded it as lying
outside a putative clade of large-bodied forms including
Pondaungia and Siamopithecus (Kay et al. 2004b;
Marivaux et al. 2005). All Burmese amphipithecids (or
Amphipithecinae) share a distinctive, derived suite of
features in the lower premolar dentition that readily dis-
tinguishes them from Siamopithecus and other early
anthropoids. In general, the crowns of P
2–4
show a
greater degree of mesiodistal compaction in Amphipithe-
cinae (and particularly in Pondaungia) than is the case in
Siamopithecus (table 1). This mesiodistal compaction is
manifest in several morphological characters. For
example, the root or alveolus for P
2
in Amphipithecinae
is mesiodistally compressed, such that its buccolingual
breadth exceeds its length. Additionally, the bases of the
crowns of P
2-3
in Amphipithecinae are distended distolin-
gually, often incorporating a strong lingual cingulid into
this distolingual lobe. Finally, the talonids of P
3–4
are
extremely abbreviated in Amphipithecinae, such that
they consist of little more than transverse furrows running
lingually and inferiorly from the hypoconid. The talonid
of P
4
in Siamopithecus is less abbreviated, so that it retains
a small but distinct talonid basin.
Recognizing the amphipithecid affinities of Myanmar-
pithecus diminishes the possibility that amphipithecids
are adapiforms rather than anthropoids. Previous workers
who have argued for the adapiform affinities of amphi-
pithecids have always maintained that Myanmarpithecus
pertains to some other higher-level primate taxon, such
as Omomyidae (Ciochon & Gunnell 2002;Gunnell
et al. 2008). The dentition of Myanmarpithecus diverges
radically from that of adapiform primates, rendering
detailed comparisons virtually meaningless (Takai et al.
2001). Our phylogenetic analysis conflicts with the
hypothesis that amphipithecids are related to adapiforms
and places them in or near crown anthropoids instead.
Indeed, all 12 of the most parsimonious trees used to gen-
erate the strict consensus tree shown in figure 4 recognize
amphipithecids as being nested within crown clade
anthropoids. These trees differ only in recognizing a
closer relationship between amphipithecids and proplio-
pithecids (as originally suggested by Jaeger et al. 1998)
or a closer relationship between amphipithecids and pla-
tyrrhines. Accordingly, current evidence indicates that
amphipithecids are much more advanced anthropoids
than eosimiids. Additional evidence, particularly from
the postcranium and skull of amphipithecids, is needed
to test this hypothesis.
Propliopithecidae
Platyrrhini
Siamopithecus
Pondaungia
Myanmarpithecus
Oligopithecidae
Parapithecidae
Eosimiidae
Tarsiidae
Omomyidae
Adapidae
Notharctidae
outgroups
Amphipithecidae
Figure 4. Strict consensus of 12 equally most parsimonious
trees of 1584 steps each (CI ¼0.32; RI ¼0.54). This
cladogram is a simplified tree highlighting the principal
dichotomies among higher taxonomic primate groups. Further
information is available as electronic supplementary material.
Table 1. Quantification of the degree of lower premolar
compaction among Amphipithecidae, based on the ratio of
lower premolar length versus M
2
length.
Species specimen
length,
P
2–4
(mm)
length,
M
2
(mm)
ratio,
P
2–4
:M
2
Ganlea
megacanina
NMMP 70 9.25 4.70 1.97
Siamopithecus
eocaenus
TF 7624 13.67 6.75 2.02
Pondaungia
cotteri
(large)
NMMP 17 9.26 8.20 1.13
Pondaungia
cotteri
(large)
NMMP 24 8.42 7.50 1.12
Pondaungia
cotteri
(small)
NMMP 30 8.64 6.70 1.29
New amphipithecid from Myanmar K. C. Beard et al. 3291
Proc. R. Soc. B (2009)
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4. FEEDING ADAPTATIONS
The unique morphology of the teeth and jaws of amphi-
pithecids has led many workers to regard them as hard
object feeders that specialized on seeds and fruits with
tough, resistant exteriors (Gunnell et al.2002;Ciochon &
Gunnell 2004;Kay et al. 2004a). The most detailed
analysis of feeding adaptations in amphipithecids pub-
lished to date is that of Kay et al. (2004a), who cite
upper incisor morphology, molar shearing development,
molar enamel thickness and mandibular morphology as
evidence favoring hard object feeding for this group.
Here, we explore the implications of the highly specialized
lower canine morphology and lower canine wear
pattern found in Ganlea and other amphipithecids for
reconstructing their dietary habits.
The holotype of Ganlea megacanina is unique among
Amphipithecidae in having a greatly enlarged lower
canine relative to M
1
, which can be quantified using
Gingerich’s (1981) canine molar ratio (or CMR)
(table 2). We interpret this as evidence that the holotype
represents a male individual. However, some of the other
amphipithecid specimens in our comparative sample, nota-
bly including the holotype of Myanmarpithecus yarshensis
and a referred lower jaw of Siamopithecus eocaenus, prob-
ably also represent male individuals, yet their CMR
values are much lower than that of the holotype of
Ganlea megacanina (table 2). This suggests that the lower
canine of Ganlea megacanina was hypertrophied beyond
the level associated merely with canine dimorphism.
Among living anthropoid primates, taxa that habitually
use their canines to open hard objects such as highly resist-
ant fruits have stouter canines that confer resistance to
bending or breaking in both the mesiodistal and buccolin-
gual planes (Plavcan & Ruff 2008). The hypertrophied
lower canine of Ganlea could therefore reflect a similar
functional adaptation in this amphipithecid.
The unusual apical wear pattern that occurs on the
lower canine of Ganlea megacanina is consistent with
this view. Apical wear such as that on the lower canine
of Ganlea megacanina can only result from repetitive con-
tact with hard food items that abrade the tooth crown.
Normal tooth-on-tooth wear facets (attrition facets) are
oriented more obliquely with respect to the tooth crown
(Kay & Hiiemae 1974). Modern primate seed predators
such as New World monkeys of the tribe Pitheciini
habitually use their upper and lower canines to open
hard, tough fruits to obtain the seeds contained inside
(Kinzey 1992). We interpret both the hypertrophy of
the lower canine in Ganlea megacanina and its heavy
apical wear as evidence that this taxon engaged in
pitheciin-like seed predation in which the canines were
used to husk the hard exteriors of resistant fruits.
Although other amphipithecids lack the extreme
canine robusticity seen in Ganlea (table 2), many of
these taxa also show remarkably heavy apical wear on
their canines, suggesting that they too engaged in
pitheciin-like husking of hard fruits. For example, the
holotype of Myanmarpithecus yarshensis (NMMP 9)
shows extremely heavy apical wear on its lower canine
(Takai et al. 2001), as does one of the few specimens of
Pondaungia (NMMP 24) that preserves the lower canine
crown intact (Gunnell et al. 2002;Jaeger et al. 2004).
The heavy apical wear patterns on the lower canines of
all three genera of Burmese amphipithecids suggest that
the entire group was an endemic radiation of hard
object feeders. Variation in canine robusticity among
Burmese amphipithecids resembles that found among
living pitheciins, in which Chiropotes and Cacajao show
extreme canine hypertrophy while Pithecia has only mod-
estly enlarged canines (Kinzey 1992). The degree of
canine hypertrophy shown by Ganlea closely matches
that which occurs in the Miocene pitheciin Cebupithecia
sarmientoi, while less specialized amphipithecids resemble
the Miocene pitheciin Nuciruptor rubricae in this regard
(table 2). The extant pitheciin Chiropotes satanas shows
an even greater degree of canine hypertrophy than does
Ganlea (table 2). Although our reconstruction of dietary
adaptations in amphipithecids is generally consistent
with that of Kay et al. (2004a), consideration of the
heavy apical wear on the lower canine of Myanmarpithecus
yarshensis suggests that this taxon was also a specialized
seed predator, rather than a generalized frugivore as
Kay et al. (2004a)infer.
5. DISCUSSION
The discovery of Ganlea provides some welcome resolution
to the ongoing debate regarding the phylogenetic position
of amphipithecids with respect to other primates, while
at the same time it clarifies the evolutionary relationships
within this extinct group of primates. Ganlea can be
referred with confidence to the Amphipithecidae on the
basis of its dental morphology, which shares numerous fea-
tures in common with Pondaungia and Myanmarpithecus.
Ganlea has the same lower dental formula that typifies all
amphipithecids (and many other basal anthropoid taxa),
and its single P
2
root is strongly compressed mesiodistally
(rather than being circular in cross section), as is also the
case in other amphipithecids. However, its lower premolar
series shows a lower degree of mesiodistal compaction
Table 2. Quantification of Gingerich’s (1981) canine molar ratio (CMR) among Amphipithecidae and Pitheciini.
species specimen(s) length width, C
1
(mm
2
) length width, M
1
(mm
2
) CMR
Ganlea megacanina NMMP 70, 69, 73 25.4 16.8 1.51
Myanmarpithecus yarshensis NMMP 9, 37 8.1 10.5 0.77
Siamopithecus eocaenus TF 7624 32.0 39.0 0.82
Pondaungia cotteri (large) NMMP 24 22.4 34.4 0.65
Pondaungia cotteri (small) NMMP 61, 63 13.1 26.5 0.49
Nuciruptor rubricae IGM 251074 14.6 15.5 0.94
Cebupithecia sarmientoi UCMP 38762 20.8 13.3 1.56
Chiropotes satanus CM 51862 33.4 15.8 2.11
Chiropotes satanus CM 76820 33.4 15.7 2.13
3292 K. C. Beard et al. New amphipithecid from Myanmar
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(both in terms of the crowns and the roots) than is the case in
Pondaungia, which has severely compressed its lower premo-
lars relative to M
2
length (table 1). In this respect, Ganlea
resembles Myanmarpithecus and Siamopithecus,butthis
resemblance is probably only due to symplesiomorphy.
Canine morphology suggests that Ganlea is the sister group
of Myanmarpithecus, because both taxa share a distinctive dis-
tobuccal distension of the canine crown that yields a sinuous
apical wear facet in older individuals. The loss of hypoconu-
lids on M
1–2
, the greater degree of mesiodistal compaction of
the lower premolars, and the strong distolingual distension of
enamel on P
2-3
that are shared by all of the amphipithecids
from Myanmar appear to be derived characters linking
these taxa to the exclusion of Siamopithecus.
The inclusion of Ganlea and Myanmarpithecus in
Amphipithecidae makes it less probable that this extinct
group of primates is closely related to adapiforms, as
some recent workers have suggested (Ciochon et al.
2001;Ciochon&Gunnell2002,2004;Gunnellet al.
2002,2008). Even those scholars who have emphasized
similarities between certain adapiforms and large amphi-
pithecids such as Pondaun gia admit that Myanmarpithecus
is unlikely to be related to the former group (Ciochon &
Gunnell 2002;Gunnell et al.2008). In many respects
Ganlea is metrically and morphologically intermediate
between Pondaungia and Myanmarpithecus, and our phylo-
genetic analysis suggests that all three of these Burmese
taxa are nested within Amphipithecidae. Fossils of all
three genera of Burmese amphipithecids show heavy
apical wear on their lower canines, suggesting that all Bur-
mese amphipithecids used their canines to husk the hard
exteriors of fruits to extract the nutritious seeds contained
inside. This apparent shared dietary specialization for hard
object feeding corroborates our phylogenetic analysis,
suggesting that the Burmese amphipithecid radiation was
ecologically analogous to the radiation of modern New
World pitheciin primates. Seed predation is an uncommon
dietary strategy among primates, and there is no evidence
that adapiforms ever invaded this dietary niche.
In terms of both abundance and alpha-level diversity,
amphipithecids are the dominant primate group in the
Pondaung Formation, although both eosimiids and sivalada-
pids occur there in much lower numbers ( Jaeger et al. 1999;
Gebo et al. 2002;Ta k a i et al.2005;Beard et al. 2007). At first
glance, the diversity and abundance of amphipithecids
appear to be at odds with the specialized dietary adaptation
posited for them here. However, modern pitheciins of the
Amazon Basin have radiated into three genera of seed preda-
tors that utilize different parts of the floodplain and different
foraging strategies to minimize interspecific competition
(Ayres 1989). The amphipithecids of the Pondaung For-
mation inhabited a paleo-Irrawaddy fluvial system that
may have resembled the modern Amazon Basin in terms
of seasonal flooding and general environmental conditions
(Aung Naing Soe et al. 2002).Thedegreetowhichsedimen-
tary and taphonomic processes may have biased the fossil
record of the Pondaung Formation can only be determined
by further field investigations.
We thank the many colleagues who helped us in the field,
including Ste
´phane and Agnes Dovert, Mana Rugbumrung,
Cornelis Schipper and Xavier Valentin. L. Meslin produced
the original art included in figure 3. Richard Cifelli and two
anonymous reviewers provided helpful comments on an
earlier draft of the manuscript. Special thanks are extended to
the villagers of Bahin, Paukkaung, Nyaungpinle and
Magyigan, whose kindness and enthusiasm made our work a
pleasure to undertake. This research was supported by
funding from the US National Science Foundation (BCS
0820602, BCS 0309800), the French CNRS-Eclipse II
Programme and the Thai-French TRF-CNRS Biodiversity
Project (PICS Thaı¨l ande).
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