Records of murine rodents (Mammalia, Rodentia) in the Pleistocene localities of Tan Vinh and Ma U’Oi (Northern Vietnam) and their implications to past distribution

Annales de Paléontologie 92 (2006) 367–383 http://france.elsevier.com/direct/ANNPAL/

Original article

Records of murine rodents (Mammalia, Rodentia) in the Pleistocene localities of Tan Vinh and Ma U’Oi (Northern Vietnam) and their implications to past distribution Présence de rongeurs murinae (Mammalia, Rodentia) dans les sites Pléistocènes de Tan Vinh et de Ma U’Oi (nord du Viêt-Nam) et leurs implications paléogéographiques Anne-Marie Bacona,*, Fabrice Demeterb, Philippe Duringerc, Stéphane Roussec, Yukio Dodod, Hirofumi Matsumurae, Vu The Longf, Nguyen Kim Thuyf, Nguyen Thi Mai Huongf, Tomoko Anezakig a UPR 2147 du CNRS, 44, rue de l’Amiral Mouchez, 75014 Paris, France Unité scientifique du muséum « Ecoanthropologie et ethnobiologie », musée de l’homme, 17, place du Trocadéro, 75116 Paris, France c Université Louis-Pasteur, institut de géologie (EOST-CGS), UMR 7517, 1, rue Blessig, 67084 Strasbourg cedex, France d Department of Anatomy and Anthropology, Tohoku University School of Medicine, 2-1 Seiryo-machi Aoba-ku, Sendai 980-8575, Japan e Department of Anatomy, Sapporo Medical University, S1, W17, Chuou-Ku, Sapporo 060-8556, Japan f Institute of Archaeology, 61, Phan Chu Trinh, Hanoi, Vietnam g Systematics and Phylogeny Section, Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan b

Received 20 July 2005; accepted 28 March 2006 Available online 29 November 2006

Abstract We describe two Vietnamese fossiliferous sites located in Hoà Binh province, northern Vietnam. The site of Tan Vinh, first described here, is a quarry opened in Triassic limestone which exposes a karstic network and its filling. One of the fissure filling contained 104 molars of Leopoldamys sabanus (Roden* Corresponding

author. E-mail address: [email protected] (A.-M. Bacon).

0753-3969/$ - see front matter © 2006 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.annpal.2006.03.019

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tia, Muridae). The biochronological age of these deposits can be estimated from late Middle Pleistocene to Holocene. The site of Ma U’Oi is a cave opened in a karstified limestone which yielded 56 molars of four species of Muridae in two assemblages: Niviventer andersoni, L. sabanus, Niviventer fulvescens among a mammal fauna dated from late Middle Pleistocene to Late Pleistocene, and L. sabanus, N. fulvescens and Hapalomys delacouri among a microvertebrate fauna dated to the late Middle Pleistocene. First, we present a description of the two sites in terms of sedimentology. Secondly, we compare molars dimensions of the most common murids, L. sabanus and N. fulvescens, recovered at Ma U’Oi and Tan Vinh, with those recovered in a Thai site. The size difference between the specimens of the two species, especially those of L. sabanus in great numbers, from the northern sites and those from the Thai site suggests a cline which can be due to latitudinal differences in palaeotemperatures. The occurrence of N. andersoni, L. sabanus, N. fulvescens in Pleistocene Vietnamese sites allow to update the past distribution of these species. © 2006 Elsevier Masson SAS. All rights reserved. Résumé Deux localités fossilifères mises au jour dans la province de Hoà Binh, au nord du Viêt-Nam, sont décrites. Le site de Tan Vinh, pour la première fois présenté ici, est une carrière formée de calcaire du Trias dont les fronts de taille exposent d’innombrables réseaux karstiques et leurs remplissages. Dans un de ces remplissages, nous avons trouvé 104 molaires de Leopoldamys sabanus (Rodentia, Muridae) dont l’âge biochronologique peut être estimé entre le pléistocène moyen récent et l’holocène. Le site de Ma U’Oi est une grotte tapissée d’une brèche typique de caverne qui a livré 56 dents appartenant à quatre espèces de Muridae. Ces espèces ont été trouvées dans deux assemblages fauniques : Niviventer andersoni, Niviventer fulvescens et L. sabanus associées à une faune de grands mammifères dont l’âge peut être estimé entre le pléistocène moyen récent et le pléistocène supérieur ; L. sabanus, N. fulvescens et Hapalomys delacouri associée à une faune de microvertébrés datée du pléistocène moyen récent. En premier lieu une description des deux sites en terme de sédimentologie est présentée. Puis, nous comparons les dimensions des molaires des deux muridés les plus communs trouvés dans les sites vietnamiens (L. sabanus et N. fulvescens), avec celles des mêmes muridés provenant d’un site fossile de Thaïlande. La différence de taille observée entre les spécimens des deux espèces provenant de sites éloignés (particulièrement L. sabanus), permet de suggérer un cline qui peut s’expliquer par les variations latitudinales des paléotempératures. Enfin, la découverte de N. andersoni, L. sabanus et N. fulvescens dans le pléistocène du Viêt-Nam nous amène à réviser la répartition passée de ces espèces. © 2006 Elsevier Masson SAS. All rights reserved. Keywords: Vietnam; Palaeoenvironment

Pleistocene;

Holocene;

Leopoldamys

sabanus;

Niviventer

fulvescens;

Distribution;

Mots clés : Viêt-Nam ; Pléistocène ; Holocène ; Leopoldamys sabanus ; Niviventer fulvescens ; Biogéographie ; Paléoenvironnement

1. Introduction The work that follows is based on Muridae (Rodentia) recovered in 2001 and 2002 in two sites, Ma U’Oi and Tan Vinh, in northern Vietnam, by a Vietnamese–French–Japanese team. The site of Ma U’Oi is a limestone karst cave (Roussé et al., 2003; Bacon et al., 2004; Demeter et al., 2004; Bacon et al., 2006). The landscape of this area is characterised by a typical morphology of karst peaks called “tower-karst”, developed in monotonous limestone beds thick of several hundred metres and dated to Carboniferous and Triassic. The site of Ma U’Oi yielded in two different loci inside the cave remains of murids (Bacon et al., 2004, 2006).

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From the walls of the cave, the breccia produced the in situ mammal assemblage (rhinocerotid, cervid, primate, suid, rodent) with two mandibles and 4 molars of the chesnut rat Niviventer fulvescens (Gray, 1847), the Chinese rat Niviventer andersoni (Thomas, 1911) and the longtailed giant rat Leopoldamys sabanus (Thomas, 1887). The biochronological age of this assemblage suggests an age from late Middle Pleistocene to Late Pleistocene and the U/Th dating a minimal age of 49 ± 4 kyr (data of Falguères cited in Bacon et al., 2006). The following year, the breccia of the roof produced the in situ microvertebrate fauna (small-sized cervid, primate, insectivore, reptile, amphibian, rodent) with the murids L. sabanus (14 molars, two incomplete mandibles), N. fulvescens (12 molars, two incomplete mandibles) and the marmoset mouse Hapalomys delacouri (Thomas, 1927) (1 molar). This assemblage is dated to 193 ± 17 kyr, the late Middle Pleistocene (data of Falguères cited in Bacon et al., 2006). The site of Tan Vinh was discovered while prospecting fissure fillings in quarries for their fossiliferous potential. In Southeast Asia, fissure fillings are known as sources of vertebrate fossils, especially those from the Pleistocene and Holocene (Chaimanee et al., 1993). The Tan Vinh quarry corresponds to a Triassic limestone. As the quarry is still being actively mined, we undertook a 3-day rescue excavation. The findings from Tan Vinh consist of 104 well preserved molars of a single murid L. sabanus. This abundance could be explained by the reworking of pellets regurgitated by birds of prey at the time of the filling. Taking into account this species, the biochronological age of these deposits could be from late Middle Pleistocene to Holocene (Chaimanee et al., 1993; Chaimanee, 1998). Regarding Pleistocene Vietnamese sites, these new data are important because of the scarcity of rodents in faunal lists. The aim of this brief article is threefold. First, we describe the two fossiliferous localities (Ma U’Oi and Tan Vinh) in terms of sedimentology, with a focus on Tan Vinh first mentioned here. Second, the presence of isolated molars in great numbers, especially at Tan Vinh, allows a statistical comparison with those recovered in other Middle Pleistocene localities from Thailand (Ginsburg et al., 1982; Chaimanee and Jaeger, 1993; Chaimanee et al., 1993; Tougard, 1998, 2001; Esposito et al., 1998; Chaimanee, 1998). Third, we discuss implications of N. fulvescens, N. andersoni and L. sabanus occurrences in the Pleistocene of Vietnam in terms of biochronology and past distribution. 2. Description of Vietnamese sites 2.1. The Tan Vinh site 2.1.1. Location and geological setting The Tan Vinh quarry is located in the Luong Son district, Hoà Binh province, about 50 km WNW from Hanoi, in northern Vietnam (coordinates: 20°51′38″N–105°30′02″E) (Fig. 1). Many quarries are situated along the right border of the Red River delta in the first escarpment that dominates the river plain. The Tan Vinh quarries, several metres high, contain fractured grey-dark micritic limestone attributed to the marine Triassic (Martini et al., 1998). A dense network of caves and galleries was developed through time in this geological framework (Fenart et al., 1999). Many quarries around the Tan Vinh village expose several fissures with fillings in the karstic network (Fig. 2). Most part of the fissures is full of brown to red-brown argillaceous material. Some fissures and cave fillings are several metres large and

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Fig. 1. Location of Thai and Vietnamese sites. Fig. 1. Localisation des sites thaïlandais et vietnamiens.

usually larger toward the top of outcrops. Some of them pass laterally or vertically to caves especially when quarries are open in ancient natural cliffs. 2.1.2. Description of the fissure filling The fissure filling is composed of two kinds of material (Fig. 2). The most abundant is a brown argillaceous pelite with often a quartzitic arenitic proportion and granule-sized Fe–Mnrich pisoliths concretions. This material is generally poorly consolidated. This argillaceous facies contains modern fauna. The second filling component (5% of the filling) is a yellowbrown carbonate breccia characterised by numerous calcitic veins. It consists of typical fossiliferous cave breccia cemented on walls of the fissures, with a mixing of weathered clays with

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Fig. 2. Scenario for the formation of the Tan Vinh deposits: A. Complete or partial filling of a fissure in the karstic network with the fossiliferous cave breccia facies (Late Pleistocene); B. Erosion of the precedent filling, some relicts of breccia stay caught on the wall or ground of the fissure; C. Complete filling of the karst by the recent brown clay facies (Holocene). Fig. 2. Scénario simplifié illustrant la formation des dépôts du gisement de Tan Vinh : A. Remplissage complet ou partiel du réseau karstique par la brèche fossilifère (pléistocène supérieur) ; B. Érosion du remplissage précédent, seules quelques reliques de brèche restent accrochées sur les parois ou au fond de la fissure ; C. Remplissage complet des fissures par de l’argile brune récente (holocène).

granule-sized Fe–Mn-rich pisoliths, reworked speleothems, clasts of dark limestone and fossil remains of mammals. All murid teeth come from this breccia. Some clasts of the breccia are sometimes reworked in the argillaceous facies. 2.1.3. Interpretation The breccia is in fact a relict facies and the mode of deposit could be the following: (1) Filling of the fissures with the fossiliferous breccia, perhaps during an uplift of the base level (Fig. 2A). (2) Opening of the fissure and clearing out of the most part of the breccia during a new water circulation phase. The cave filling is karstified in the same way as the former karst system (Fig. 2B). During this clearing, 95% of the material into the fissure is eroded. Some breccia stays cemented on the wall of the fissure. (3) New filling of fissures and cave with the brown argillaceous material produced by weathering of surrounding soils (Fig. 2C). 2.2. The Ma U’Oi site 2.2.1. Location and geological setting The Ma U’Oi cave is situated in the Man Duc village, Tan Lac district, Hoà Binh province, 25 km SSW from Hoà Binh city, northern Vietnam (coordinates: 20°37′22″N, 105°16′40″E) (Fig. 1). Around the site, the bedrock consists of grey-dark micritic marine limestone attributed

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to the Triassic (Martini et al., 1998). A dense network of caves and galleries developed through the time in this framework, partially driven by faults and fractures (Fenart et al., 1999). In the neighbourhood of Man Duc village, several caves expose the karstic network and its fossiliferous filling (Fig. 3A). The caves are partly filled with brown to red-brown argillaceous and breccia material with numerous iron pisoliths. The largest karstic fillings reach several metres thick. 2.2.2. Description of the filling of Ma U’Oi cave The Ma U’Oi cave consists of two distinct corridors (A and B) composed of several rooms (Fig. 3B). The fossiliferous facies shows a quite constant composition in all rooms. The facies, a calcaro-pelitic fossiliferous breccia, is characterised by a relative apparent monotony, a shortscale lateral and vertical extension and a variable potential of preservation. In all excavated rooms, the fossiliferous level forms a thick layer (ranges from 0.5 to 1.5 m) covering the vault, the upper part of the walls and the floor. All murids have been recovered in the breccia from the roof of the room A1 (in situ microvertebrate fauna) and from the walls of the rooms A1 and A2 (in situ mammal assemblage) (Fig. 3). U/Th datings have been performed on two samples. The first one from the upper part of the fossiliferous breccia (coarse-grained sparite from stalagmitic floor) reveals an age of 193 ± 17 kyr, i.e. late Middle Pleistocene for the microvertebrate fauna. The second sample, sparite from speleothems partially covering the fossiliferous breccia, gives for filling alteration an age of 49 ± 4 kyr (i.e. late Late Pleistocene). This estimate corresponds to the minimal age of the mammal assemblage.

Fig. 3. A. Synthetic scenario of the Ma U’Oi site showing the location of the excavated fossiliferous level and the two alluvial terraces (Terrace 1 and 2, lying respectively at 92 and 43 m above the contemporary alluvial plain). Both of alluvial terrace depositional units are closely associated to endokarstic deposits (fossiliferous cave breccia and speleothems). The crosses indicate the location of the breccia from which were extracted rodents teeth, in the rooms A1 (in situ microvertebrate fauna) and A2 (in situ mammal assemblage). B. Plan of Ma U’Oi cave. Fig. 3. A. Aperçu schématique du site de Ma U’Oi montrant la position du niveau fossilifère étudié, ainsi que l’association entre les dépôts endokarstiques (brèche fossilifère et spéléothèmes) et les niveaux étagés des terrasses alluviales (terrasses 1 et 2, reposant respectivement à 92 et 43 m au dessus du niveau de la plaine actuelle). Les croix indiquent la localisation de la brèche d’où ont été extraites les dents de rongeurs, dans la salle A1 (faune in situ de microvertébrés) et dans la salle A2 (assemblage in situ de mammifères). B. Plan de la grotte de Ma U’Oi.

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2.2.3. Interpretation The present-day disposition of the breccia up to the vault of the cave seems to indicate first a quite complete filling of the cave by sediments (at least 3 or 4 m thick) before being partially eroded. The outcropping of the breccia (i.e. thin relicts on walls, roof or ground) suggests at least one episode of removing of karstic sediments since first deposit of the breccia (i.e. fossiliferous facies). Such features are now well-known in karstic environment (Bacon et al., 2004) and suggest that karst filling is the result of several episodes of sedimentation interrupted by non-deposition and erosion periods (Roussé et al., 2003). Inside the breccia, close imbrication of clastic materials (limestone, Fe–Mn-rich pisoliths, speleothems) with bones and teeth, attest to a sedimentological origin for the breccia (downstream water circulations inside the caves). General aspects of the fossiliferous breccia and relations between endokarstic (activity inside the cave) and exokarstic (alluvial terraces) environments are described in Roussé et al. (2003); Bacon et al. (2004). 3. Molars description of L. sabanus and N. fulvescens 3.1. Material and methods At Tan Vinh, we collected several kilos of breccia and dissolved them with formic acid (10%). After washing the sediment with running water and drying, we sorted it using a sieve of 2 mm. At Ma U’Oi, the breccia was crushed in small fragments, washed in the water of the nearby river, dried and screened with same sieves. We used a binocular and a digital counter for measuring teeth. Two dimensions have been taken: maximal length (mesiodistal) and maximal width (buccolingual). A statistical analysis has been realised on raw data by using range of variation, mean and standard deviation (Tables 1 and 2). Microphotographs of isolated teeth were realised with the Scanning Electron Microscope (JEOL JSM-25SIII). Teeth have not been metallised. Fossil data (description, statistical parameters) of rodents from Thai localities are taken from Chaimanee (1998) and compiled in Tables 1 and 2 (raw data are not available). They concern localities of Snake cave (main and upper layers), Kanchanaburi 2, Khao Toi 1 and Khao Rupchang. Data of modern species are also taken from this reference, but their origin is unknown. 3.2. Results We attributed 14 molars and two fragmentary mandibles (one with m1–m2 and one with m1) from Ma U’Oi and all of the isolated 104 molars from Tan Vinh to L. sabanus on the basis of descriptions of comparable fossil specimens in Chaimanee (1998). Upper and lower molars are large (Fig. 4). In M1 and M2, central cusps are larger than labial ones. We found the same features as those described in Chaimanee (1998) (p. 115): On the first row (of M1), cusp t1 is separated from t2 by a deep groove. Cusp t3 is reduced and fused with t2. On the second row, cusp t4 and t6 are more distal than the central cusp t4 is separated from t5 by a deep groove. On the third row, cusp t8 is large (…). There is no posterior cingulum. In M2, the cusp t3 is absent and the cusp t4 is rounded and separated from t5 by a deep groove. Lin-

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Table 1 Measurements (length and width) of molars of modern and fossil L. sabanus. Measurements from Ma U’Oi and Tan Vinh have been taken by the authors; those from Snake cave and Kanchanaburi 2 are from Chaimanee (1998). Living specimens are also compiled in Chaimanee (1998) but their origin is unknown. N = number of specimens; x = mean; S.D. = standard deviation (only for sample sizes superior or equal to 10) Tableau 1 Mesures (longueurs et largeurs) des molaires de L. sabanus fossile et actuelle. Les mesures des spécimens de Ma U’Oi et de Tan Vinh ont été prises par les auteurs ; celles de Snake cave et de Kanchanaburi 2 sont extraites du travail de Chaimanee (1998). Les mesures des spécimens actuels proviennent également de Chaimanee (1998) mais leur origine est inconnue. N = nombre de molaires ; x = moyenne ; S.D. = Ecart-type (uniquement pour les effectifs supérieurs ou égaux à 10) Localités M1

M2

M3 m1

m2

m3

Ma U’Oi Tan Vinh SC main layer SC upper layer Kanchanaburi 2 Living Ma U’Oi Tan Vinh SC main layer SC upper layer Kanchanaburi 2 Living Tan Vinh Ma U’Oi Tan Vinh SC main layer SC upper layer Living Ma U’Oi Tan Vinh SC main layer SC upper layer Living Tan Vinh

N 4 16 36 11 2 2 4 19 24 10 3 3 3 6 29 27 5 3 4 30 27 10 3 7

R 4.52–5.05 4.21–5.36 4.29–5.18 4.21–4.82 4.12–4.40 4.63–5.20 3.74–4.26 2.92–4.55 2.98–3.62 3.11–3.58 2.75–3.06 3.24–3.80 2.33–2.69 3.99–4.63 4.07–4.69 3.45–4.00 3.68–4.04 3.89–4.04 3.17–3.73 3.08–3.93 2.61–3.49 2.78–3.16 2.93–3.22 2.43–3.04

Length (mm) x 4.85 4.92 4.74 4.49 4.26 4.92 3.98 3.78 3.37 3.33 2.87 3.45 2.48 4.33 4.39 3.77 3.85 3.96 3.50 3.46 2.96 2.97 3.09 2.9

S.D. – 0.28 0.25 0.22 – – – 0.35 0.16 0.16 – – – – 0.17 0.18 – – – 0.21 0.18 0.13 – –

R 3.06–3.62 2.85–3.31 2.56–3.00 2.49–2.79 2.53–2.61 2.72–3.00 2.88–3.04 2.77–3.23 2.48–2.90 2.29–2.96 2.39–2.70 2.74–3.27 2.29–2.47 2.49–2.99 2.53–3.29 2.11–2.72 2.35–2.58 2.20–2.84 2.76–3.18 2.49–3.41 2.39–2.82 2.46–2.87 2.18–2.93 2.26–2.75

Width (mm) x 3.21 3.09 2.79 2.65 2.61 2.86 2.93 2.95 2.63 2.55 2.51 2.99 2.36 2.70 2.77 2.41 2.43 2.52 2.98 3.07 2.62 2.64 2.59 2.51

S.D. – 0.13 0.12 0.08 – – – 0.12 0.10 0.06 – – – – 0.16 0.15 – – – 0.48 0.11 0.11 – –

gual cusps of m1 are more mesial than labial cusps. The second and third rows are chevronshaped. Cv5 is present on m1 and m2. Among the microvertebrate fauna from Ma U’Oi, 12 isolated teeth and two mandibles with m1–m2 are affiliated to N. fulvescens (Fig. 5). The morphological differences with L. sabanus are tenuous. However, concerning the size, there is no overlap between the two species, N. fulvescens being markedly smaller than L. sabanus (Tables 1 and 2). We affiliated these small teeth to N. fulvescens on the basis of description of Chaimanee (1998) (p. 122). In short, M1, long and narrow, display central cusps larger than labial and lingual ones. In unworn M1, the lingual cusps t1 and t4 are clearly separated from the central cusps. The second row is chevron-shaped and the third row is characterised by an enlarged cusp t8 connected to a reduced cusp t9. In M2, the cusps t1 and t8 are rounded and large and t9 is absent. m1 are small and narrow with lingual cusps more mesial than labial cusps. The second and third rows of cusps show chevron-shaped laminae. m2 are slightly larger than m1 (Table 2). The presence of Cv5 is variable on m1 and m2.

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Table 2 Measurements (length and width) of molars of modern and fossil N. fulvescens. Measurements from Ma U’Oi and Tan Vinh have been taken by the authors; those from Snake cave, Khao Toi 1, Khao Rupchang are from Chaimanee (1998). Living specimens are also compiled in Chaimanee (1998) but their origin is unknown. N = number of specimens; x = mean; S.D. = standard deviation (only for sample sizes superior or equal to 10) Tableau 2 Mesures (longueurs et largeurs) des molaires de N. fulvescens fossile et actuelle. Les mesures des spécimens de Ma U’Oi et Tan Vinh ont été prises par les auteurs ; celles de Snake cave, Khao Toi 1, Khao Rupchang sont extraites du travail de Chaimanee (1998). Les mesures des spécimens actuels ont été trouvées également chez Chaimanee (1998) mais leur origine est inconnue. N = nombre de spécimens ; x = moyenne ; S.D. = Écart-type (uniquement pour les effectifs supérieurs ou égaux à 10) Localités M1

M2

m1

m2

Ma U’Oi SC main layer SC upper layer Khao Toi 1 Khao Rupchang Living Ma U’Oi SC main layer SC upper layer Khao Toi 1 Khao Rupchang Living Ma U’Oi SC main layer SC upper layer Living Ma U’Oi SC main layer SC upper layer Living

N 2 47 17 4 3 7 2 17 3 3 3 8 5 20 9 7 7 29 5 5

R 3.31–3.62 2.99–3.50 3.04–3.34 2.83–3.25 2.89–3.06 3.13–3.46 2.19–2.75 1.98–2.35 2.04–2.18 1.96–2.13 2.05–2.12 1.99–2.33 2.63–2.96 2.40–2.76 2.53–2.72 2.38–2.71 1.75–2.44 1.77 2.18 1.98–2.23 1.88–2.14

Length (mm) x S.D. 3.46 – 3.20 0.12 3.15 0.09 3.06 – 2.95 – 3.20 – 2.47 – 2.17 0.09 2.12 – 2.03 – 2.09 – 2.11 – 2.81 – 2.59 0.08 2.61 – 2.54 – 2.05 – 1.99 0.11 2.11 – 1.98 –

R 2.03–2.05 1.56–1.85 1.54–1.74 1.67–1.84 1.57–1.61 1.59–1.77 1.62–2.29 1.50–1.82 1.55–1.70 1.40–1.52 1.52–1.63 1.52–1.69 1.57–1.85 1.34–1.71 1.44–1.63 1.39–1.73 1.65–1.99 1.53–1.76 1.61–1.77 1.50–1.65

Width (mm) x S.D. 2.05 – 1.71 0.07 1.65 0.06 1.76 – 1.60 – 1.68 – 1.95 – 1.68 0.10 1.63 – 1.45 – 1.58 – 1.64 – 1.72 – 1.51 0.09 1.50 – 1.55 – 1.74 – 1.64 0.06 1.70 – 1.60 –

We report ranges of variation, means and standard deviations of molars dimensions of L. sabanus (Table 1) and N. fulvescens (Table 2) found in Vietnamese (Ma U’Oi and Tan Vinh) and Thai sites (Snake cave (SC) upper layer and main layer, Kanchanaburi 2, Khao Toi 1, Khao Rupchang). Except the sample size of Tan Vinh and Snake Cave (superior to 15 specimens), all other data (modern and fossil species) are only represented by small samples (less than three specimens), which limit the meaning of statistical parameters and their comparison. Nevertheless, we can notice some variations between L. sabanus of different localities. All specimens considered, upper and lower molars from Vietnamese sites (especially Tan Vinh) tend to be slightly greater than those from the Thai site Snake cave (data from Kanchanaburi are too sporadic) for both dimensions (Fig. 6). Concerning N. fulvescens, molars from Ma U’Oi are also slightly greater than those from Thai sites, but samples are small. If we consider the two late Middle Pleistocene localities, Ma U’Oi (193 ± 17 kyr) and Snake Cave (169 ± 15 kyr, Esposito et al., 1998; Chaimanee, 1998), these small size differences between individuals of same species could be interpreted as a cline. Indeed, these two sites are clearly located at different latitudes, the northern site Ma U’Oi (and also the close Tan Vinh) and the southern site (Snake Cave) being around 1000 kilometres apart. Thus, we

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Fig. 4. Microphotographs of isolated teeth of L. sabanus realised with a Scanning Electron Microscope (× 15). Fig. 4. Photographies des dents isolées de L. sabanus réalisées au Microscope Electronique à Balayage (× 15).

suggest that these size differences could be an adaptive response to a latitudinal variation of temperatures. 4. Biochronology and past distribution of N. fulvescens and L. sabanus While N. fulvescens and L. sabanus possess nowadays large distributions, in the Indochinese and part of Himalayan subregions for the former, Indochinese and Sundaic subregions for the latter (Corbet and Hill, 1992; Musser and Carleton, 1993), their Pleistocene distributions are still poorly known (Fig. 7).

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Fig. 5. Microphotographs of isolated teeth of N. fulvescens realised with a Scanning Electron Microscope (× 20). Fig. 5. Photographie des dents isolées de N. fulvescens réalisées au microscope électronique à balayage (× 20).

Concerning Vietnam, the findings from Tan Vinh (late Middle Pleistocene to Holocene) and Ma U’Oi (late Middle Pleistocene) bring new data about this past distribution. Indeed, L. sabanus had never been found so far north in the Indochinese subregion and also so far in the Pleistocene of Vietnam (Tham Kuyen and Keo Leng produced two unidentified species Rattus sp. and Mus sp. (Cuong, 1985; Olsen and Ciochon, 1990) (Table 3). Only, the Lang Trang fauna (cave II, breccia 5) dated to Late Pleistocene yielded the species Rattus sabanus (Long et al., 1996) (Fig. 7B). Concerning N. fulvescens, its presence at Ma U’Oi is the first ever mentioned in the Pleistocene of Vietnam. However, its presence so far north in the Indochinese area is not new as it has been already listed at Baiyanjiao, Yanhui and Washuwan in southern China for the Middle Pleistocene (Zheng, 1993) (Fig. 7A).

378 A.-M. Bacon et al. / Annales de Paléontologie 92 (2006) 367–383 Fig. 6. Graphics showing statistical results of Table 1 (mean and variation of each dimension (L: length, W: width) calculated for molars of L. sabanus from northern Vietnamese sites (Ma U’Oi and Tan Vinh) and the southern Thai site (Snake Cave, main layer (SCml) and upper layer (SCul)). Means of each group are linked with a line for a better comparison. Fig. 6. Graphique montrant les résultats statistiques du tableau 1 (moyenne et intervalle de variation pour chaque dimension (L : longueur, W : largeur) réalisés sur les molaires de L. sabanus provenant des sites vietnamiens au nord (Ma U’Oi et Tan Vinh) et du site thailandais localisé plus au sud (Snake Cave, main layer (SCml) et upper layer (SCul)). Les moyennes de chaque groupe sont reliées par un trait pour une meilleure comparaison.

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Outside of Vietnam, the only well documented murid assemblages come from Pliocene to Holocene sites of Thailand (Chaimanee, 1998). This author reported the presence of L. sabanus in Thai sites dated from Middle Pleistocene to Holocene (Fig. 7). Among all murids found at Snake cave [fauna dated to late Middle Pleistocene (Tougard, 1998, 2001) and to 169 ± 15 kyr by U/Th method (Esposito et al., 1998)], L. sabanus is rather abundant (with N. fulvescens, Rattus sikkimensis and R. rattus) (Chaimanee, 1998), that is also confirmed by Ma U’Oi and Tan Vinh data. It is also present in other sites in Central and Peninsular Thailand, but the data are sporadic (Chaimanee, 1998). This author also showed that N. fulvescens was present southwards into the Malay peninsula since the Middle Pleistocene (Fig. 7, Ban Nasan, Khao Toi 1 and Khao Rupchang sites). However, the reconstruction of past distribution of these species varies in accordance with systematics of the modern taxa (Lekagul and McNeely, 1977; Corbet and Hill, 1992; Nowak, 1999). Indeed, if modern N. fulvescens and N. bukit are considered as separated species (as represented in Fig. 7), the record of this fossil species behind the limit of the Isthmus of Kra is new for the Pleistocene, as it extends southwards. On the contrary, if N. fulvescens and N. bukit are considered as conspecific and grouped in a single species N. fulvescens with a larger distribution as far as the Sondaic subregion (Java, Sumatra, Bali), the fossil specimens do not question the past distribution of the taxon (see Chaimanee (1998) for exhaustive references about this question). No fossil records of L. sabanus and N. fulvescens older than the Middle Pleistocene have been listed in Southeast Asia, but the oldest occurrence of the genus Leopoldamys (L. minutus n. sp.) is mentioned at Saraburi in Thailand, a site dated to Late Pliocene (Chaimanee, 1998) and both genera Leopoldamys and Niviventer are present in the Indochinese area at the Longgupo locality, dated to the Early Pleistocene (Zheng, 1993). According to a recent phylogeographical analysis based on mitochondrial DNA (Gorog et al., 2004), L. sabanus may have dispersed throughout its current Indochinese and Sundaic areas in the early Pliocene “before the long-standing connections between Indochina, Java, Sumatra, Borneo and the Malay Peninsula were severed” (Gorog et al., 2004: p. 103), suggesting a vicariance history rather than a dispersal. The fossil record tends to reflect a similar conclusion (Chaimanee, 1998). N. andersoni is an endemic species present only in limited Chinese areas, from East Tibet to southern and central provinces (Yunnan, Sichuan, South Gansu and Shaanxi) (Corbet and Hill, 1992; Musser and Carleton, 1993). Until now, it was only mentioned in different Chinese Pleistocene localities, from the limit Pliocene/Pleistocene to the beginning of the Holocene, between 1.8 myr and 10 kyr (Zheng, 1993). So, the Vietnamese record of N. andersoni at Ma U’Oi is the first mention of this species in Quaternary deposits outside China (Bacon et al., 2004). It attests of a southernmore distribution of this species in the Indochinese subregion in the past. 5. Contribution to reconstruction of past environments The murids record of Ma U’Oi is far for being exhaustive and their interest in palaeoenvironmental reconstruction can only be succinct. Among the in situ mammal fauna, three murids are listed (Bacon et al., 2004). L. sabanus is a large-bodied arboreal rat, still today largely widespread in Southeast Asia, Indochinese (Vietnam, Cambodia, Laos, Thailand and Bangladesh) and Sundaic subregions (Java, Malay Peninsula, Sumatra, Borneo and many small islands) (Medway, 1972; Musser, 1982; Corbet and Hill, 1992; Van der Meulen and Musser, 1999). It is adapted to all types of forests and is common in lowlands and foothills of ever-

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Fig. 7. Current distributions of N. fulvescens and L. sabanus represented by grey and N. andersoni represented by triangles from Corbet and Hill (1992). The numbers correspond to Pleistocene localities (Bacon et al., 2004; Chaimanee, 1998; Zheng, 1993; Long et al., 1996). Map A: 1-Ma U’Oi (late Middle Pleistocene), 2-Snake cave (late Middle Pleistocene), 3-Kanchanaburi 2 (Middle Pleistocene), 4-Khao Songto, 5-Ban Nasan (Middle Pleistocene), 6-Khao Toi 1 (Middle Pleistocene), 7-Khao Rupchang (Middle Pleistocene), 8-Baiyanjiao (Middle Pleistocene). Map B: 1-Ma U’Oi (late Middle Pleistocene), 2-Tan Vinh, 3-Lang Trang (Late Pleistocene), 4-Snake cave (three localities, late Middle Pleistocene), 5-Kanchanaburi 1 (Holocene) et Kanchanaburi 2 (Middle Pleistocene), 6-Khao Tinpet (Middle Pleistocene), 7-Khao Toi 1 (Middle Pleistocene). Fig. 7. Distributions géographiques actuelles de N. fulvescens et L. sabanus représentées en grisé, et de N. andersoni représentée par des triangles d’après Corbet et Hill (1992). Les chiffres correspondent aux localités pléistocènes (Bacon et al., 2004 ; Chaimanee, 1998 ; Zheng, 1993 ; Long et al., 1996). Carte A : 1-Ma U’Oi (Pléistocène moyen récent),

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Table 3 List of murids in Pleistocene Vietnamese (Cuong, 1985; Bacon et al., 2004, 2006) and Thai sites (Chaimanee, 1998). Snake cave (ML: Main Layer; UP: Upper Layer); K2: Kanchanaburi 2 Tableau 3 Listes des Muridae découverts dans les sites pléistocènes vietnamiens (Cuong, 1985 ; Bacon et al., 2004, 2006) et thaïlandais (Chaimanee, 1998). Snake cave (ML : Main Layer ; UP : Upper Layer) ; K2 : Kanchanaburi 2 Taxa Rattus sp. R. sikkimensis R. rattus Mus sp. M. shortridgei M. pahari M. cooki M. cervicolor Vandeleuria oleracea Hapalomys delacouri Chiropodomys gliroides Bandicota savilei B. indica Hadromys humei Berylmys berdmorei Maxomys surifer Niviventer fulvescens N. andersoni N. gracilis Leopoldamys sabanus

Ma U’Oi

Tan Vinh

Tham Kuyen X

X

X

Keo Leng X

Snake Cave ML

Snake cave UL

K2

X X

X

X X X X X X X

X X X X X X X

X X X X X

X X

X

X X

X

X

X

X X

? X

X

X

X X X

X

X X

green forests (Corbet and Hill, 1992). So, it does not provide any pertinent environmental information, as it is present in northern seasonal forest as well in southern rain forest. N. fulvescens occurs in various kinds of forests in both lowlands and mountains in the north of the Isthmus of Kra as far as the Himalayan forest zone, following also the eastern boundary of the Palaearctic Region (Corbet and Hill, 1992). It seems adapted to a more seasonal climate or to a climate with other seasonality. The presence of N. andersoni at Ma U’Oi is more informative. According to Musser and Chiu (1979), “Both andersoni and excelsior inhabit the high mountains along the eastern edge of the Tibetan Plateau and the Himalayas” and, farther, “Examples of andersoni have been collected from elevations ranging from 6000 to 10,000 ft” (2000 to 3300 m). Corbet and Hill (1992) confirm that N. andersoni can be observed at altitudes of 1800–3000 m. The presence of this murid at Ma U’Oi which attests a more southern distribution of this species in the past, also suggests a more southern boundary of montane forest vegetation with drier conditions (and that before 49 ± 4 kyr, the minimal age of the fauna). It also reflects that the montane vegetation zone was probably lower in altitude due to cooler temperatures. This seems to be in accordance with palaeoenvironmental reconstruction (Van der Kaars and Dam, 1995), which show a marked climatic change between 74,000 yrs and the last glacial peak around 20,000 yrs with drier conditions. 2-Snake cave (pléistocène moyen récent), 3-Kanchanaburi 2 (pléistocène moyen), 4-Khao Songto, 5-Ban Nasan (pléistocène moyen), 6-Khao Toi 1 (pléistocène moyen), 7-Khao Rupchang (pléistocène moyen), 8-Baiyanjiao (pléistocène moyen). Carte B : 1-Ma U’Oi (pléistocène moyen), 2-Tan Vinh, 3-Lang Trang (pléistocène supérieur), 4-Snake cave (trois localités du pléistocène moyen), 5-Kanchanaburi 1 (holocène) et Kanchanaburi 2 (pléistocène moyen), 6-Khao Tinpet (pléistocène moyen), 7-Khao Toi 1 (pléistocène moyen).

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The microvertebrate in situ fauna at Ma U’Oi seems to indicate a more forested environment, not contradictory with the late Middle Pleistocene (a period corresponding to a short interglacial episode). N. fulvescens and L. sabanus are not the only rodents present in this locality. The third murid rodent listed at Ma U’Oi H. delacouri is a specialised arboreal rat which inhabits today tropical forest and bamboo forest in small zones of the Indochinese area (Central Vietnam, Northern Laos, Hainan) Corbet and Hill (1992). The fauna is also composed of sciurid rodents with three taxa of flying squirrels Hylopetes phayrei, Hylopetes sp., and a Petauristinae indet., which reflect evergreen forest habitat. Shrews were present at Ma U’Oi with Crocidura sp. which inhabits lowland and montane forests. This record can be seen as an “impoverished” version of the microvertebrate fauna found at Snake cave (Ginsburg et al., 1982; Chaimanee et al., 1993; Chaimanee, 1998), the Ma U’Oi species (Bacon et al., 2004, 2006), especially flying squirrels, suggesting a comparable habitat with the presence of evergreen forest. 6. Conclusion These original data from Ma U’Oi and Tan Vinh bring the first information concerning record and past distribution of the two murids L. sabanus and N. fulvescens in Vietnam. The comparison of molar dimensions between rodents of these Vietnamese sites and those of the southernmore thai site (Snake Cave) emphasizes the possibility of clines. However, we can not go deeper in the discussion as the sample size for each species has to be increased. Acknowledgments The authors want to present their gratitude to people who gave them the possibility to undertake these fieldworks in Vietnam: Bui Thi Xuan, Bui Van Hop and Quach Van Ach, Quach Dinh Thi from the Hoà Binh Museum, Bui Giang Huong, Bui Manh Hung and Bui Van Khai from the Commune Department of Culture and Mrs. Tran Thi Lan Anh from the National Centre for Social Sciences and Humanities (CNSSH). Thanks to C. Falguères for datings (Institut de Paléontologie humaine, Paris); A. Gorog, J. de Vos, S. Sen and the referee M. Michaux for correction of the manuscript; D. Fouchier (UPR 2147) and A. Bouzeghaia (Institute of Geology, Strasbourg) who realised drawings; C. Chancogne (National Museum of Natural History, Paris) for SEM photographs. This mission was financed by the Collège de France (Chaire de Paléoanthropologie et de Préhistoire); UPR 2147 of CNRS; DRI of CNRS (projects no. 12746, no. 13669); the Earth Sciences Doctoral School of Louis Pasteur University (F. Beck and M. Cara), Strasbourg; the Department of Anatomy and Anthropology, Tohoku University School of Medicine, Sendai, Japan; the Department of Anatomy, Sapporo Medical University, Japan. References Bacon, A.-M., Demeter, F., Roussé, S., Long, V.T., Duringer, P., Antoine, P.-O., Thuy, N.K., Huong, N.T.M., Dodo, Y., Matsumura, H., Schuster, M., Anezaki, T., 2006. New palaeontological assemblage, sedimentological and chronological data from the Pleistocene Ma U’Oi cave (Northern Vietnam). Palaeogeography, Palaeoclimatology, Palaeoecology 230, 280–298. Bacon, A.M., Demeter, F., Schuster, M., Long, V.T., Thuy, N.K., Antoine, P.O., Sen, S., Nga, H.H., Huong, N.T.M., 2004. The Pleistocene Ma U’Oi cave, northern Vietnam: palaeontology, sedimentology and palaeoenvironments. Geobios 37, 305–314.

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