Conceived and designed the experiments: JJJ ANS OC PC EGE RL AM AAK HS STT KLO YC. Performed the experiments: JJJ ANS OC PC EGE RL AM AAK HS STT KLO MR YC MB. Analyzed the data: JJJ ANS OC PC EGE FG HB YC MB. Contributed reagents/materials/analysis tools: FG HB KC PT. Wrote the paper: JJJ OC PC EGE FG HB.
The authors have declared that no competing interests exist.
For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a
Despite more than a century of intense research on the issue, the origin of the Pleistocene to extant orang-utan
First in 2002 and then yearly since 2006, the Myanmar-French paleontological mission has surveyed the Irrawaddy Formation outcrops of Central Myanmar with the aim of improving the comprehension of mammalian evolution in the Miocene of Southeast Asia. The present study describes a new mammal assemblage including hominoid remains collected in Irrawaddy Formation outcrops situated south of Magway city (
a: map of Southeast Asia. b: general map of Myanmar. c: local map of the region of Magway displaying the Irrawaddy Formation outcrops
Tertiary to Quaternary Irrawaddy fluvial deposits are widely exposed throughout the central basin of Myanmar. The continental deposits of the Irrawaddy Formation can reach thickness of 2000 m and span a time interval from Middle Miocene to Pleistocene
Our field research area covers around 650 square kilometers from the north of Yenangyaung to the South of Magway, where hundred meters thick sections are accessible. In that area, the deposits of the Irrawaddy Formation comprise yellow to brownish coarse cross-bedded sandstones with interstratified ferruginous conglomerates, claystones, hardened fine sandstones and red soil horizons. It frequently contains iron hydroxide-rich nodular concretions and gypsum deposits. Lateral facies variation commonly occurs along the sections. The dipping of beds is low and rarely exceeds 10°. Minor angular and erosional unconformities have been observed within the sequence.
urn:lsid:zoobank.org:act:B073A2A8-C53F-4D59-B7C8-06E50EBAB1E3
Left hemi-mandible with P3-M2 (MFI-K171, collection of the Paleontology Section of the Department of Mineral Resources (DMR), Bangkok – 10400, Rama VI Road, Thailand).
Species of
MFI-K171 is a nearly complete and undistorted left hemi-mandible (
A: lingual view. B: buccal view. C: interpretive drawing of the lingual view. D: interpretive drawing of the buccal view. E: ventral view. F: occlusal view. G: enlarged occlusal view of the tooth row. H: Detailed view of the anterior region displaying alveoli shadows. Scale bars: 5 cm for A–F and I–J and 1 cm for G–H. Abbreviations: cr, crown remnant; r, ramus. I: lingual view displaying roots shadows for P3-M3 and alveoli shadows for incisors and the canine. J: dental row with virtually extracted roots in buccal view.
MFI-K171 has an overall slender morphology owing to a shallow and thin corpus. It possesses a nearly constant depth from the distal edge of the symphysis to the M3, where it is only slightly greater (
Mandibular measurement | Distance |
Maximal length of the specimen | 102.4 |
Corpus depth at P3 | 32.60/35.92 (buccal/lingual) |
Corpus depth at P4 | 30.44/35.84 (buccal/lingual) |
Corpus depth at P4-M1 transition | 30.89/35.19 (buccal/lingual) |
Corpus depth at M1 talonid | 32.07 (buccal) |
Corpus depth at mid M2 | 31.86 (buccal) |
Corpus depth at mid M3 | 36.51 (buccal) |
Corpus depth at the distal extremity of M3 | 39.59 (buccal) |
Corpus thickness at P4 | 17.87 |
Corpus thickness at P4-M1 transition | 15.95 |
Corpus thickness at mid M1 | 16.43 |
Corpus thickness at mid M2 | 18.67 |
Corpus thickness at M3 | 21.39 |
Corpus thickness at distal extremity | 3.72 |
Length of the molar row | 41.15 |
Length of the premolar row | 19.23 |
P3-M3 length | 61.02 |
I1 mesial margin-M3 distal margin length | 70.56 |
Alveolar medio-external breadth of the incisors | 8.86 |
Alveolar medio-external breadth of I1-C | 14.37 |
Symphysis section long axis | 34.81 |
Symphysis section short axis | 17.33 |
Symphysis section height | 29.62 |
Symphysis section length | 30.13 |
Level | MFI-K171 | TF 6223 |
|
|
|||
P4 | 33.14 | 38.88 | - |
M1 trigonid | 33.04 | 40.61 | 29.29–43.65 |
29.29–31.89(n = 5)/41.67–43.65(n = 3) | |||
Mid-M3 | 36.51 | 40.19 | 26.29–41.29 |
26.29–30.48(n = 5)/37.88–41.28(n = 2) | |||
|
|||
P4 | 17.87 | 21.23 | - |
M1 trigonid | 15.98 | 19.84 | 13.10–20.18 |
13.10–17.37(n = 5)/16.15–20.18(n = 4) | |||
Mid-M3 | 21.39 | 31.43 | 20.52–26.32 |
20.52–23.41(n = 5)/24.69–26.32(n = 4) | |||
|
|||
P4 | 2.89 | 3.30 | - |
M1 trigonid | 2.88 | 3.46 | 2.28–3.38 |
2.28–2.74(n = 5)/2.83–3.38(n = 3) | |||
Mid-M3 | 3.19 | 3.42 | 2.10–3.19 |
2.10–2.65(n = 5)/2.58–3.19(n = 2) | |||
|
|||
P4 | 1.56 | 1.80 | - |
M1 trigonid | 1.39 | 1.69 | 1.14–1.37 |
1.14–1.35(n = 5)/1.19–1.37(n = 4) | |||
Mid-M3 | 1.87 | 2.67 | 1.75–1.91 |
1.75–1.87(n = 5)/1.76–1.91(n = 4) | |||
|
|||
P4 | 54.10 | 54.60 | - |
M1 trigonid | 46.45 | 48.85 | 38.73–58.97 |
38.73–50.48(n = 5)/49.26–58.97(n = 3) | |||
Mid-M3 | 58.59 | 78.20 | 60.04–84.07 |
70.60–84.07(n = 5)/60.04–68.22(n = 2) |
depth/squareroot(M1 length*M1 breadth).
thickness/squareroot(M1 length*M1 breadth).
thickness/depth*100.
Corpus depths are means of buccal and lingual measurements. Corpus measurements and indices of
Another characteristic of MFI-171 is its low surface relief: the fossae for the masseter and the pterygoid muscles are shallow and the post C-P3 buccal depression is not well marked, unlike in TF 6223. On the lingual side of the jaw, the mylohyoid line is discernible. It starts from the inferior transverse torus and disappears under the M3. Below the mylohyoid line, the bone shows a shallow, narrow and short depression (submandibular fossa). In most other places, the bone is rather flattened. On the ventral and lingual margins of the corpus, no imprint for the anterior digastric muscle insertion is distinguishable (see
MFI-K171 is sufficiently well preserved in its anterior region to provide a good estimate of the symphyseal section outline. The specimen displays only a partial genial fossa because the break is not perfectly oriented along the midsagittal plane (
The genial fossa is oriented distally and superior and inferior transverse tori are equally developed. MFI-K171 has a much shorter symphysis than TF 6223, especially at the level of the planum alveolare: the long axis in TF 6223 is 56% longer than that of MFI-K171. The inclination of the planum alveolare is similar between the two specimens.
The general outline of the symphyseal section of MFI-K171 is closer to that of TF 6223 than to any other Asian fossil hominoids, with subequal transverse tori, shallow genial fossa, and a supero-inferiorly convex anterior portion (
The angulation (measured between the long axis of the outline and alveolar margin plane and/or the occlusal plane) where obtained from CT-scans (
Only a few hominoids such as the African and Asian
In order to quantify the symphysis outline of MFI-K171 and compare it to those of other hominoids, we undertook an elliptic Fourier analysis on normalized Fourier coefficients, following the methodology of
A principal component analysis (PCA) was then performed on the Fourier coefficients. The PCA yielded seven significant axes expressing 95% of the total variance. The first three components represent 85% of the total variance (respectively 53%, 19%, and 13% of the total variance). The four other significant components represent in total 10% of the total variance (3.6%, 3.1%, 1.8% and 1.3%).
Only the outlying individuals are represented for the extant hominoids. For each component, extreme outlines and expressed variance are given.
Given the substantial distance between the two
Incisor alveoli are deep and possess ovoid sections with a labio-lingual long axis and a mesio-distal compression. Both incisor alveoli bear small absolute dimensions (
Teeth and alveoli | Mesio-distal length | Bucco(labio)-lingual length (trigonid/talonid) | Height |
I1 (alveoli) | 2.19 | 5.78 | - |
I2 (alveoli) | 3.17 | 7.6 | - |
C (alveoli) | 6.45 | 8.05 | - |
P3 | 13.5 | 9.68 | 8.89 (Protoconid) |
P4 | 8.19 | 9.92 | 7.30 (Protoconid) |
M1 | 12.29 | 11.05/10.33 | 5.91 (Metaconid) |
M2 | 13.92 | 12.75/11.46 | 6.15 (Metaconid) |
M3 (dentine section) | 14.2 | 11.93/9.25 | - |
Incisor comparisons between MFI-K171 and
The canine alveolus revealed by X-ray microtomography has a substantial volume in comparison to the roots/alveolus of the other teeth (
The canine alveolus has a triangular outline with rounded corners, comparable to that of
The P3 is a sharp tooth (height/mesio-distal length = 0.66) dominated by a large and moderately elevated protoconid whose buccal face is distinctly slanted. The lingual face of the protoconid is rectilinear and shows an angle of about 30° to the dental row axis. It displays a low and thin cingulum between a small and low parastyle and the disto-lingual border of the tooth. The preprotocristid is mesially oriented and ends into the parastyle. The metacristid lacks a distinct metaconid and becomes bifurcated distally. The postprotocristid, only slightly worn, is curved lingually to the disto-lingual border of the tooth. The talonid basin corresponds to a narrow and shallow furrow between the postprotocristid and the metacristid. A narrow honing facet is observable on the mesiobuccal side of the tooth. It extends over the entire height of the crown. The P3 of MFI-K171 is different from those of
The P4 has a large and buccally-bulged protoconid and a smaller metaconid separated by a shallow mesio-distal groove. The metaconid is slightly mesial to the protoconid. The talonid is large, closed, and lower than the trigonid. The postprotocristid joins a distolingual crest which closes the deep talonid basin by joining the metaconid. There is no cingulid. The talonid of the P4 of MFI-K171 is higher in relation to the trigonid than those of
The P4 of MFI-K171 can be distinguished from those of
Only remnants of enamel wrinkling are visible on the M1 because of its stage of wear (small dentine pits apparent on the protoconid and hypoconid). The buccal face of the tooth is markedly slanted unlike in TF 6223,
The M2 of MFI-K171, nearly unworn, shows strong cusp relief, markedly wrinkled enamel, and is substantially wider in the trigonid region than in the talonid as in the M1. The wrinkling is better expressed around the large central fovea (in particular on the medial face of the entoconid which shows three furrows) and between the protoconid and the metaconid. As on the M1, there is no buccal cingulid. This combination of features is different from that of
The M3 has a triangular section at the cervix. The surface area of this tooth at the cervix is similar to the M1 crown surface area (at the cervix) and about 22% smaller than that of the M2 (at the cervix). Nevertheless, it is reasonable to consider that the crown of the M3 was close in size to that of the M2.
The roots of MFI-K171 (
The combination of features displayed by the mandible MFI-K171 (absence of an imprint for the anterior digastric muscle, the symphyseal outline and inclination, and the association of certain dental traits such as buccal slanted protoconids on P3 and P4, narrow and deep talonid basin on P3, deep and closed talonid basin on P4, protoconid and metaconid close together on P4, deep central fovea on molars) excludes any close affinity with the Asian Neogene hominoid genera
Although the teeth of MFI-K171 and the
Numerous dental differences in the molars (smaller central fovea) and premolars (smaller distal basin and less slanted protoconid on the P3; P4 with a smaller talonid basin, a lower mesiodistal∶buccolingual ratio) support a specific distinction between MFI-K171 and the material assigned to
MFI 89 (
A: right M2 MFI89 in occlusal view. B: interpretive drawing of MFI89. C–D: interpretive drawings of
A: lithology and stratigraphic position of the sampled levels. B: latitude of the virtual geomagnetic pole vs. stratigraphic position. C: polarity column (black bar: normal polarity zone) and potential correlations with the GPTS of
MFI89 is close in size to M2s of presumed male
The cusp organisation of MFI 89 strongly resembles that of the M2s of
The molar MFI 89, because of its strong resemblance with
A magnetic polarity stratigraphy of the section of MFI89 was established on 20 distinct levels along a 97 m thick section (
A–C: Orthogonal vector diagrams (closed/open symbols correspond to the horizontal/vertical component), stereoplots (crosses: upper hemisphere, circles: lower hemisphere), intensity and step plots for representative samples after thermal and alternating field demagnetization. D: Equal-area stereographic projections of site mean ChRM directions. Open triangle: site mean direction (Declination = 7.3°; Inclination = 23.9°; α95 = 7; k = 23; n = 20), Ellipse: 95% confidence ellipse for mean direction. Solid star: direction derived from the 10-Ma apparent polar wander path. E: Isothermal remanent magnetization (IRM) acquisition curves (normalized values) for two representative samples. F–G: Stepwise thermal demagnetization of the differential IRM components (X, Y, and Z). 99B022A: medium grained sandstone. 99B039A: grey claystone.
Site | Height(m) | Incl. | Decl. | α95 | k | λVGP |
1 | 0 | 56.32 | 351.64 | - | - | 79.14 |
2 | 2 | 22.41 | 11.65 | - | - | 75.78 |
3 | 3 | 19.31 | 31.26 | - | - | 55.25 |
4 | 4.5 | 41.62 | 358.83 | 17.7 | 49 | 86.43 |
5 | 9.5 | 10.06 | 4.68 | 14.0 | 79 | 74.28 |
6 | 14.2 | 21.81 | 32.32 | 17.3 | 52 | 57.73 |
7 | 15.5 | 14.47 | 8.07 | 13.5 | 84 | 75.03 |
8 | 20 | 20.49 | 3.25 | 13.2 | 88 | 79.97 |
9 | 24 | 20.49 | 6.63 | 14.2 | 76 | 78.53 |
10 | 28.5 | 9.89 | 355.82 | 23.3 | 29 | 74.33 |
11 | 32.5 | 2.17 | 5.07 | 13.4 | 85 | 70.34 |
12 | 35 | 31.7 | 13.65 | - | - | 76.50 |
13 | 45 | 47.39 | 3.51 | 9.0 | 190 | 80.99 |
14 | 60 | 3.74 | 15.69 | 9.8 | 160 | 66.18 |
15 | 62 | 33.67 | 2.28 | 9.7 | 164 | 87.26 |
16 | 64 | 23.24 | 23.05 | 19.1 | 43 | 66.49 |
17 | 73.5 | 23.37 | 4.24 | 18.9 | 44 | 81.09 |
18 | 82 | 22.56 | 2.98 | 15.4 | 65 | 81.15 |
19 | 87.5 | 21.8 | 1.75 | - | - | 81.17 |
20 | 97 | 19.43 | 342.07 | 41.7 | 10 | 70.00 |
Height: stratigraphic height above the first level sampled; Incl.: mean tilt corrected inclination in degree to the horizontal; Decl.: mean tilt corrected declination in °E; α95: mean direction 95% confidence ellipse; k: Fisher precision parameter; λVGP: paleolatitude of the virtual geomagnetic pole.
The associated mammal fauna collected during our fieldwork is homogeneous along the Magway sections and among the investigated area. It includes a proboscidean belonging to the genus
MAMMALIA |
|
Hominidae |
|
|
|
Suidae |
|
cf. |
Palaeochoeridae |
Tragulidae |
Gen. et sp. indet. (medium-sized) |
Bovidae |
Antilopini indet. |
Gen. et sp. indet. |
Gen. et sp. indet. 2 |
Anthracotheriidae |
|
|
Equidae |
Rhinocerotidae |
Gen. et sp. indet. |
Chalicotheriidae |
Chalicotheriinae |
Gen. et sp. indet. |
|
Fam. Gen. et sp. indet. |
REPTILIA |
|
Trionychidae |
CHONDRYCHTHYES |
|
Carcharhinidae |
|
ICHTHYES |
|
Fam. Gen. et sp. indet. |
This associated fauna, among which hipparionin fossils are most common, is younger than 10.7 Ma, the observed first appearance datum (FAD) of these equids in the Siwaliks of Pakistan
Because the Burmese fauna includes several shared or closely-related species with the Siwaliks of Pakistan, the first and last appearance data (LAD) of the Pakistani taxa are used to provide the biochronological bracket. This choice is also motivated by fossil richness and chronological precision of the sites of this region
The stable isotopes from enamel and dentine of 6
Tooth enamel of large herbivores such as
The δ13C values obtained from tooth tissues and dentary bone of
Specimen | Tissue | CaCO3( |
δ13CPDB(‰) | δ18OPDB(‰) | δ18OVSMOW(‰) |
IRWD 1 | Enamel | 4.0 | −9.9 | −3.9 | 26.9 |
IRWD 2 | Enamel | 4.0 | −11.4 | −4.3 | 26.4 |
IRWD 3 | Enamel | 4.9 | −12.1 | −4.9 | 25.8 |
IRWD 4 | Enamel | 4.4 | −11.7 | −6.8 | 23.8 |
IRWD 5 | Enamel | 5.2 | −11.0 | −8.8 | 21.8 |
IRWD 6 | Enamel | 3.6 | −11.1 | −4.5 | 26.2 |
|
4.3 | −11.2 | −5.5 | 25.2 | |
|
0.6 | 0.7 | 1.7 | 1.8 | |
IRWD 1 | Dentine | 7.3 | −13.1 | −7.4 | 23.2 |
IRWD 2 | Cement | 6.8 | −14.4 | −6.7 | 24.0 |
IRWD 3 | Cement | 5.3 | −15.3 | −8.5 | 22.1 |
IRWD 4 | Bone (dentary) | 9.0 | −14.3 | −6.6 | 24.0 |
IRWD 5 | Dentine | 6.7 | −13.7 | −8.0 | 22.6 |
IRWD 6 | Dentine | 6.1 | −13.6 | −7.6 | 23.0 |
|
6.9 | −14.1 | −7.5 | 23.2 | |
|
1.1 | 0.7 | 0.7 | 0.7 |
The genus
New specimens discovered in the Irrawaddy Formation, in Central Myanmar, document a new species of the large bodied hominoid genus
Biogeographically, the fauna associated with
The extensive exposures of Irrawaddy Formation, combined with their long temporal range (middle Miocene to Pleistocene), suggest a high potential for the understanding of Asian hominoids evolution.
The
The electronic version of this document does not represent a published work according to the International Code of Zoological Nomenclature (ICZN), and hence the nomenclatural acts contained in the electronic version are not available under that Code from the electronic edition. Therefore, a separate edition of this document was produced by a method that assures numerous identical and durable copies, and those copies were simultaneously obtainable (from the publication date noted on the first page of this article) for the purpose of providing a public and permanent scientific record, in accordance with Article 8.1 of the Code. The separate print-only edition is available on request from PLoS by sending a request to PLoS ONE, 1160 Battery Street, Suite 100, San Francisco, CA 94111, USA along with a check for $10 (to cover printing and postage) payable to “Public Library of Science”.
In addition, this published work and the nomenclatural acts it contains have been registered in
We thank the Ministry of Culture of the Union of Myanmar for supporting the project and the organization of the fieldwork campaigns, MM. Stéphane Dovert, Fabrice Etienne and Emmanuel Mouriez, Mrs Wah Wah Tin and Shwe Zin Nyunt from the French Embassy in Yangon for their help to our project, Jay Kelley (Arizona State University) for fruitful discussions and comments, J. Baruchel and the ID 17 and 19 beamline staff of the ESRF (Grenoble) for their assistance in X-ray imaging, J. Barry (Harvard University) for discussion and providing comparative material, X. Valentin (iPHEP, Univ. Poitiers) for material preparation, C. Fontaine and A. Decarreau (HydrASA, Univ. Poitiers) for providing X-Ray diffraction data, B. Steinhilber (Univ. Tübingen) for technical assistance in stable isotope analysis of