Corrado Bellifemine
email: corrado.bellifemine@sorbonne-nouvelle.fr

How children with developmental language disorder use co-speech gestures to communicate

Keywords: developmental language disorder, multimodality, co-speech gestures

. Can gestures aim to compensate for linguistic difficulties, thus making children with DLD produce more gesture than TD children? We video-recorded 30 French-speaking children (15 children with DLD and 15 TD children) aged 8 to 11. Children first played a guessing game with the examiner and then described their room. For each recording, we determined the quantity and types of hand gestures produced. We then examined whether gestures were strictly related to speech and how they were integrated in children's verbal productions in the two types of activities. Results showed significant qualitative and quantitative differences between TD children and those with DLD. During the guessing game, children with DLD produced more gestures, which were mostly representational. TD children produced fewer gestures, which were mostly rhythmic and self-regulatory. However, during the description task, children with DLD used fewer gestures than TD children. Both groups produced deictic and representational gestures. Moreover, the gestures were strongly complementary to speech. The findings show the complexity of gesture-speech coordination in children with DLD. Speech elaboration is a multimodal process where gestures play an important role. However, according to the nature of the difficulties in communication, gestures can both be inhibited or strongly mobilized and facilitate expression. Gestures can therefore convey additional information to what is conveyed verbally in both types of population and are used differently according to the type of activity.

Introduction

A multimodal approach in language development

Children's language development is dynamically multidimensional (Karmiloff & Karmiloff-Smith, 2001): the phonological system is necessary for the lexicon and syntax to be acquired. Children's language development is also multimodal [START_REF] Morgenstern | Children's multimodal language development[END_REF], verbal and non-verbal modalities being interdependent. Children's communication is achieved first through gestures, facial expressions and gaze, then through speech in coordination with the other modalities. Thus, gestures are preferred during the first stages of language development, to be then primarily replaced by speech, once vocal linguistic structures are acquired and integrated. But verbal and non-verbal signals are then fully articulated as children continue using all semiotic resources at their disposal. Children modulate their gestural behavior in interaction, depending on their communicative intention, interlocutor, context, and current activity [START_REF] Cienki | Cognitive linguistics, gesture studies, and multimodal communication[END_REF]. Multimodal communication involves bodily nonlinguistic productions that can convey meaning, but also involuntary movements that are not necessarily related to the content of speech. Gestures accompanying speech are called co-speech gestures [START_REF] Colletta | Le développement de la parole chez l'enfant âgé de 6 à 11 ans: Corps, langage et cognition[END_REF].

A multimodal approach was recently integrated in the field of language disorders by authors who, in line with [START_REF] Mcneill | Hand and mind: What gestures reveal about thought[END_REF], consider speech and gestures to be part of the same system. DLD is a severe and persistent language disorder that hinders the production and/or comprehension of language at the phonological, morphosyntactic, lexical, semantic and pragmatic levels. Due to the compensatory mechanisms of the brain, children with developmental language disorder may frequently switch from one sub-category to another [START_REF] Parisse | Specific language impairment as systemic developmental disorders[END_REF][START_REF] Conti-Ramsden | Characteristics of children with specific language impairment[END_REF]. Studies on the use of gestures in children with DLD bring out varied and heterogeneous data, sometimes confirming or contrasting the various hypotheses put forward by different authors. Based on the assumption that these children produce a higher number of gestures during different types of activities such as explanations, narrative or description tasks, authors state that children with DLD use gestures as a compensation mechanism to overcome language difficulties [START_REF] Blake | Gestures accompanying speech in specifically language-impaired children and their timing with speech[END_REF]Iverson & Braddok, 2011;[START_REF] Mainela-Arnold | Gesture-speech integration in children with specific language impairment[END_REF]. Moreover, the gestures produced often convey additional information that is not transmitted verbally [START_REF] Evans | Divergence of verbal expression and embodied knowledge: Evidence from speech and gesture in children with specific language impairment[END_REF]. Other studies [START_REF] Botting | Gesture production and comprehension in children with specific language impairment[END_REF][START_REF] Wray | Gestural abilities of children with specific language impairment[END_REF] have shown that children with DLD performed equally to typically developing controls but their gestures were less precise. Gestures seem to have an important role as far as language production is concerned, but also in language comprehension, since using gesture in pedagogical contexts facilitates new words acquisition in children with and without language impairment [START_REF] Vogt | Observing iconic gestures enhances word learning in typically developing children and children with specific language impairment[END_REF][START_REF] Tellier | Dire avec des gestes. Le Français dans le monde[END_REF].

This study explores whether gesture-speech coordination in children DLD enhances their communication. To our knowledge, no study has been conducted as far as French-speaking children with DLD are concerned, so it would be interesting to observe their multimodal behavior also in comparison with typically developing children. Moreover, in France research on gestures focuses more on younger children who are still in a developing phase. Little is known about older children who are in later stages of language development, as well as children with DLD, who have already been through several years of speech therapy. Can gestures compensate for verbal difficulties, thus making children with DLD produce more gestures than TD children?

Method

To answer this question, we video-recorded 15 French-speaking children with DLD and 15 agematched typically developing children. All children were aged 8 to 11 years old. Children with DLD were all officially diagnosed by a speech therapist. The following exclusion criteria were applied: no hearing impairment, no phonatory organs' malfunction, good Nonverbal QI, no social deficit disorder, no cerebral lesion, no behavioral deficit.

Each child was video recorded during two tasks: A) each child played a guessing game with the examiner. The examiner showed 16 cards to the child. Each card contained the image of the item to be guessed. Children had to describe the image to the examiner so that he could guess the correct answer. The instructions for the game did not specify which modality should be used (gestures or speech), so children were free to use whichever strategy they preferred. B) Each child had to describe their room, while they were in another room. No detailed instructions were given during this task. The children were free to say whatever they wanted and to employ whichever modality they preferred (nonverbal or verbal).

As far as gesture types are concerned, authors have proposed several gesture classifications [START_REF] Efron | Gesture, race and culture: A tentative study of the spatio-temporal and[END_REF][START_REF] Ekman | The repertoire of nonverbal behavior: Categories, origins, usage and coding[END_REF][START_REF] Kendon | Gesticulation and speech: two aspects of the process of utterance[END_REF][START_REF] Mcneill | Hand and mind: What gestures reveal about thought[END_REF]. We propose here a simplified gesture classification:

-Deictic gestures, which include pointing and localization gestures.

-Iconic gestures, which include gestures referring to a salient feature, shape, size, mime of a referent. -Emblems, which include conventional recurrent gestures such as salutations, counting, thinking gestures, shrugs, palm ups. -Self-Adaptors, which include self-regulatory gestures such as rubbing and scratching and touching a body part to adapt oneself to the interaction. -Beats, which include gesticulation and gestures structuring speech or giving emphasis to certain words.

Thus, we hypothesized that children with DLD rely more than TD controls on gestures and that children with DLD and TD controls use different types of gestures, depending on the task. In particular, children with DLD might use more iconic gestures during the guessing game and more deictic gestures during the description task

As far as the relationship between speech and gestures is concerned, its coding was based on the classification proposed by [START_REF] Colletta | Transcription et annotation de données multimodales sous ELAN -Manuel de codage[END_REF], consisting of the following:

-Independent relation: gestures are independent from speech and they convey different meanings that are not related to each other. This is more the case for adaptors and beats. -Complementary relation: gestures complete the meaning conveyed verbally and they add information about the concept or the referent. -Substitution relation: gestures replace speech and convey meaning that is not transmitted verbally. -Redundant relation: speech and gestures convey the same meaning; the hand movement refers to a concept expressed verbally and occurring at the same time as the gesture.

Thus, we hypothesized that, during the guessing game, speech and gestures would be in a complementary or substitution relationship whereas, during the description task, speech and gestures would be in a more redundant and complementary relationship. During the guessing game children with DLD produced a gesture-utterance ratio of 1:2, as well as during the description task (guessing game ratio: 0.5; description task ratio: 0.5). Each child gestured during the guessing game but not all children gestured to describe their room. They seemed to rely more on gestures during the guessing game because their verbal productions were constrained by the task, whereas during the description task children with DLD seemed to rely on compensatory strategies to reduce difficulties and therefore, they sorted and selected what could be said without their expression being affected by the language impairment [START_REF] Delage | Relative clauses in atypical acquisition of French[END_REF].

Results

Gestureutterance ratio

During the guessing game TD children produced a gesture-utterance ratio of 1:4, whereas they produced almost one gesture per utterance during the description task (guessing game ratio: 0.2; description task ratio: 0.7). It should be noted that the TD children's descriptions were longer those of children with DLD. The more information there was, the more chances there were for cospeech gestures to occur. This could be the case for TD children. On the contrary, not all the TD children gestured during the guessing game, which could relate to a better mastery of the task, as well as better language skills. While the strategies of children with DLD were based more on the nonverbal modality, TD children gave more precise verbal cues to make the examiner guess the item.

Gesture types

Table 2. Gesture types produced during the two tasks

During the guessing game, children with DLD massively produced iconic gestures (61%). Overall, it seems that children with DLD relied more on gestures to convey meaning. Children with DLD focused mostly on a salient feature of the item to be guessed and they exploited it to provide the observer with visual non-verbal cues. The referential gestural representation of the items may derive from the fact that for these children the non-verbal modality is an alternative and a compensatory strategy accompanying their verbal productions, hindered by the language impairment. The number of adaptors (14%) could be explained by a feeling of discomfort caused by the interaction with an unknown examiner, or by moments of reflection.

As far as TD children are concerned, the most frequently produced gestures are beats (44%) and iconic gestures (26.4%). Beat gestures are not dependent on the content of speech but are used to structure and give rhythm to speech or emphasize a certain word.

During the description task children with DLD produced a much lower number of gestures compared to the number of gestures produced by typical children. During this task, the group produced as many deictic as iconic gestures (30%). Children with language disorders have trouble with spatial and temporal representation, therefore, we need to conduct specific qualitative analyses of the group performance: deictic gestures are produced more by two children in particular, while almost all children who produce gestures during this task produce iconic gestures.

Typically developing children produce a higher number of gestures. The group produced a majority of deictic gestures (40.8%) but also iconic gestures (31.9%). Children produced deictic gestures by pointing at a referent, often absent in the room or replacing the target referent by a same referent present in the room (Deixis ad fantasma, Buhler, 1934). Deictic gestures can also be finger movements tracing lines or drawing geometric forms, placing the elements of the room in the space around oneself. Above all, they can be movements of the arms or hands, to the right or to the left,

Gesture-speech relation

Since we know that, during the guessing game, children with DLD produced a majority of iconic gestures, we found a complementary or substitution relationship between speech and gestures: gestures convey either part of the message conveyed or the entire meaning of what the child wants to the verbal modality being absent. Since we know that, during the description task, children with DLD produced a majority of deictic and iconic gestures, the former have a complementary relationship with speech, while the latter are mainly in a relationship of redundancy (see Table 3).

Table 3. Gesturespeech relation during DLD children's tasks

As far as TD children are concerned, we know that during the guessing game they produced a majority of beat gestures, therefore we found an independent relation between gestures and speech. In particular, beat gestures are independent of the content of speech but not of the utterance structure, because these gestures give rhythm to the child's speech. During the description task, TD children produced a majority of deictic gestures: these gestures mostly have a relationship of redundancy (the gesture refers to a referent already expressed verbally) and complementarity (the gesture complements the child's utterance) with the verbal modality (see Table 4). The aim of this study was to investigate the use of gesture by children with developmental language disorder, in comparison to typically developing age-matched controls. Thus, we asked how children with DLD use gestures to convey meaning during two different types of activities, namely a guessing game and a description task. We hypothesized that children with DLD would rely more on gestures than TD children, throughout the two tasks proposed. This hypothesis was partially validated: children with DLD produced a higher number of gestures (285 occurrences) than TD children (140 occurrences) during the guessing game. A Wilcoxon Test showed that these differences were significant (p = 0.01). Children with DLD produced fewer gestures (70 occurrences) than the TD group (147 occurrences) during the description task. Differences between the two groups on this task were not significant (p = 0.07) as the number of gestures was related to the number of utterances. We also asked what types of gestures children produced during the two tasks, which led us to a second hypothesis: there would be a difference in the multimodal productions during the two tasks, especially in the use of gesture types. As expected, children with DLD produced more iconic gestures (61%) during the guessing game, whereas TD children produced more beats (44%) and iconic gestures (26%). Differences were significant only as far as emblems (p = 0.03) and iconic gestures (p = 0,001) were concerned. Children with DLD produced the same number of deictic and iconic gestures (30%) during the description task, whereas TD children produced more deictic gestures during the description task (40.8%). A Wilcoxon test showed no significant differences between DLD children and TD. Finally, a Wilcoxon Test showed significant differences in relation to the tasks for the DLD group (p = 0.001).

Our results are similar to those of other authors. In general, children with DLD in our study produced more gestures in relation to speech than TD children. This result confirms other authors' studies such as [START_REF] Blake | Gestures accompanying speech in specifically language-impaired children and their timing with speech[END_REF], [START_REF] Iverson | Gesture and motor skill in relation to language in children with language impairment[END_REF][START_REF] Iverson | Gesture and motor skill in relation to language in children with language impairment[END_REF][START_REF] Mainela-Arnold | Gesture-speech integration in children with specific language impairment[END_REF]. During the description task, children with DLD produced fewer gestures than TD children but they were mostly deictic and iconic, as suggested by Blake et al.'s study. In terms of gesture-speech relation, our findings go in the same direction as Mainela-Arnold et al. ( 2014) and [START_REF] Evans | Divergence of verbal expression and embodied knowledge: Evidence from speech and gesture in children with specific language impairment[END_REF] who found that, during a narration task, children with DLD were less redundant, so gestures conveyed more meaning than speech. Even though the tasks in the other studies mentioned above were different, we can say that, globally, children with DLD use more gestures as a compensatory strategy or to convey additional meaning, given that they have difficulties conveying verbally. As far as TD children are concerned, the abundant use of beats highlights the final stage of multimodal language acquisition: beat gestures emerge from five years old [START_REF] Mcneill | Hand and mind: What gestures reveal about thought[END_REF] when almost all the linguistic structures are acquired and integrated by the child. We shall also stress the role of the task: the type of activity influences the amount and the type of gestures produced to convey meaning and the more difficult and complex is the task, the more gestures are produced or not, depending on the semantic content of communication. As was shown by the description task, children with DLD produced fewer gestures because their knowledge about space is limited, thus gestures are hindered as well as speech.

Conclusion

In conclusion, we found differences between groups, tasks and the type of gestures produced and their relation to speech. Gestures seem to be strongly complementary to speech. Thus, they are inherent to the elaboration of speech but according to the nature of the difficulties in the linguistic elaboration, gestures can either not be relied upon, which was the case during the description task, or be strongly mobilized and facilitate communication, which was the case during the guessing game.

The fact that not all children with DLD produced gestures during the guessing game, as well as the fact that not all children with DLD produced gestures during the description task, highlights the heterogeneity of this language disorder for which causes and effects are not fully known.

In this study, gestures seem to have two different functions: they are a support for children with DLD when they fail to use speech. Gestures are therefore an additional means that conveys information, sometimes absent from the child's speech. In addition, recourse to gestures takes place in particular in cases where linguistic constraints are imposed or when children encounter difficulties in expressing concepts or accessing lexicon: during the guessing game, children had to be careful not to say certain words that would have been too transparent for the aims of the activity, that is, to make the interlocutor guess a word through explanation. Gestures, even the most referential ones, help children with DLD to communicate better and they occur in multimodal productions in which their relation is typically redundant but often complementarity to speech. These gestures seem to be a support for the child to fully express concepts conveyed verbally.

These findings show the complexity of gesture-speech coordination in children with DLD. Speech elaboration is a multimodal process in which gestures play an important role. However, according to the nature of the situation or activity, gestures can be either inhibited or strongly mobilized and facilitate expression. The interaction between spontaneous gestures, speech and mental representation of referents could be a key factor to improve language mastery in children with DLD.

Table 1 . Total number of gestures and total number of utterances

 1

		GUESSING GAME	DESCRIPTION TASK
		DLD	TD	DLD	TD
	Gestures	285	140	70	147
	Utterances	571	548	140	199

Figure 1. Gestureutterance ratio

Table 4 . Gesture -speech relation during TD children's tasks TD: gesture-speech relation

 4

			GUESSING GAME			DESCRIPTION TASK
		COM	IND	RED	SUB	COM	IND	RED	SUB
	ADA	0.00% 21.43% 0.00% 0.00% 0.00%	8.16%	0.00%	0.00%
	BAT	0.00% 44.29% 0.00% 0.00% 0.00% 18.37% 0.00%	0.00%
	DEI	3.57%	0.00% 0.00% 0.00% 15.65% 0.00% 17.69% 7.48%
	EMB 0.00%	0.00% 0.00% 4.29% 0.00%	0.00%	0.00%	0.68%
	ICO 15.71% 0.00% 7.14% 3.57% 14.29% 0.00% 14.97% 2.72%
	Total 19.29% 65.71% 7.14% 7.86% 29.93% 26.53% 32.65% 10.88%
	Discussion

Acknowledgment

The author would like to thank Anne Salazar Orvig and Aliyah Morgenstern for their support, advice and suggestions.


domain: sde.be sdu sdv shs

text:
Arnaud Lenoble
email: arnaud.lenoble@mnhn.fr

Valery Zeitoun

Frédéric Laudet

Arnoult Seveau

Tasana Doyasa

Thailand ) Arnaud Chiang

Lenoble

Zeitoun Valéry

Laudet Frédéric

Asa Doy

Tasana

Natural processes involved in the formation of Pleistocene bone assemblages in continental South-East Asian caves : the

Keywords:

come   L'archive ouverte pluridisciplinaire

Introduction

To date, there is no general study describing the formation of faunistic sites in a karstic context in South east Asia. As a consequence, any bias in mechanisms which led to the accumulation of bone remains or limitations in the use of the collected series for documenting the biostratigraphy or reconstructing the paleoenvironment are not known. This present study aims to fill in these gaps in knowledge. We conducted a pluridisciplinary study at the site in the Cave of the Monk in Thaïlande. Geological and taphonomic approaches were combined in order to determine site formation processes. We discuss the implications of the formation processes in regard to the paleoenvironmental and biostratigraphic significance of the assemblage.

Study site

The Cave of the Monk (N19° 24,603' ;E98° 48,985') is close to Ban Fa Sui, 80 km north of Chiang Ma [START_REF] Zeitoun | Découverte d'un assemblage faunique à Stegogon-Ailuropoda dans une grotte du Nord de la Thaïlande (Ban Fa Suai, Chiang Dao)[END_REF] (figure 1). The cave opening is at an altitude of 900m in a dry tropical forest. The surrounding countryside is characterised by average sized mountains, dominated by Doi Chiang Dao which at 2716 m is a major peak on the regional horizon. This limestone block is highly karstic [START_REF] Delange | Etude d'un karst nord thaïlandais : le massif de Doi Chiang Dao[END_REF], as are the surrounding limestone outcrops. The site was found within one of these karstic outcrops. The cave is in the highest section of three levels of galleries connected by separate narrow shafts. The lower section of the network is active and a tributary of the Huai Mae Pla Ao river flows through it. The Cave of the Monk is named after its entrance which is used as a meditation room. A corridor leads from this first chamber for approximately 30 meters (figure 2a). After that the gallery divides into northern and southern branches. Several meters after the corridor, the south branch of the cave can be accessed from below through a narrow passageway. This branch is accessible for approximately 40 metres. It is then necessary to crawl through a squeeze before to reach a lower chamber. It was in this chamber, which is approximately 100 metres from the entrance, that excavation led to the discovery of most of the fossils. The excavation consisted of two test-pits (figure 2b). The first was near the entrance to the room (test 1) and the second deep within the chamber (test 2). The total surface covered was 5 m 2 . The paleontological remains were found within the first 50 cm of sediment. To ensure that the recovery of material was complete all of the articles found during the dig were removed after having noted their exact position. Then, each layer of removed sediment was sieved with water and a 1.3 mm sieve and once dry all remains larger than this were kept. A large number of species and genera were identified within the assemblage (cf. Zeitoun et al., elsewhere in this volume). The level of identification at the genus level was significantly high : 31.6 %, but it was low at the species level: 9.1 %. The assemblage includes remains of Stegodon, Panda and Pongo, that is one fossil species and two species now extinct in this region. On this basis the assemblage can be classed as type Ailuropoda-Stegodon. The absence of archaic species suggests that this assemblage is characteristic of the faunistic group known as Yenchingkou II which, according to [START_REF] Han | -Pleistocene mammalian faunas of China. In Palaeoanthropology and Palaeolithic Archaeology in the Peoplees Republic of China[END_REF] was present in the late Pleistocene in southern China. Nevertheless, we can not be overly confident with this assessment because modern Hyena, Crocuta crocuta ultima, which replaced Hyena sinensis [START_REF] Kurten | The status affinities of Hyaena sinensis Owen and Hyaena ultima Matsumoto[END_REF][START_REF] Ginsburg | ) -A middle Pleistocene (Loangian) cave fauna in northern Thailand[END_REF], is the characteristic species of this biozone and we did not identify this taxon in the assemblage. Only one tooth fragment of a Hyenidae was collected but it was not possible to precisely determine its taxonomic origin.

Materials and methods

Geological study

The site context was described by examining the organisation of the karstic network, the morphology of the cave and its infilling. A cave temperature profile was also determined by measuring the minimum and maximum daily temperatures at different places within the cave. The stratigraphy of the site is based on the test pit sections. The deposits were described directly on site by noting their general organization, the texture of sediment and the clast morphology, the characteristics of the stratification and the occurrence of sedimentary features as grain size sorting or grading. Sediment colour was determined by reference to the Munsell colour code [START_REF] Munsell | Soil Chart Color[END_REF]. The macroscopic description was completed with several laboratory analyses: particle size distribution of the deposit matrix (i.e. the sediments less than 2 mm) was determined by mechanical sieving and laser diffractometre analysis for the finest fraction (<50 µm), X-ray diffraction was used to identify mineral species, and thin sections, prepared from undisturbed blocks of sediment impregnated with polyester resin, were observed with a petrographic microscope. The genesis of the so characterized deposits has been interpreted by comparison with actual analogues.

Taphonomic study

Artefacts found on the surface in the north branch of the cave will not be taken into consideration in this study. The studied series, 3709 remains, was collected from the surface in the entrance to the chamber and during the excavation. Each paleontological remain was examined by eye and if necessary with a magnifying glass. For each bone or tooth we noted: the state of fragmentation, the colour and the surface state. For this last parameter we were looking for any man-made alterations (e.g. Traces of fire/combustion, knife marks, percussion marks), biological alterations (digested or regurgitated bones, gnawing, edge damages, punctures) and alterations caused by corrosion (polish, smoothing, patina). Finally the dimensions of each remain were measured with a caliper.

Results

Geological study

The Cave of the Monk and the south branch in particular, is a natural gallery with a relatively constant diameter. Large speleothems and gours occur frequently. The lower chamber, however, is uncemented. There, the soil surface is clayey and consists of juxtaposed shallow basins (10-20 cm), less than one-meter large and bordered by flattened ring of compacted sediment. During the first exploration of the cave, one of these troughs was surrounded by porcupine quills (figure 2b). At several places in the cave, evidence of old infilling preserved against the well and generally cemented by secondary calcite can be observed. These outliers consist of bedded sands and pebbles indicating an ancient alluvial stage. In the shaft above the narrow opening to the south branch, this conglomerate is overlain with fine sand and silt finely laminated. The cave appears to have had a complex sedimentary history with at least 4 phases:

1.

An ancient alluvial period during which an underground stream deposited a bed of sand and pebbles, 2.

Sedimentation due to flooding of the cave network, perhaps in relation to a subsequent event where the water level sunk back into the massif, during which suspended material was deposited, 3.

A period of sediment remobilization, probably by draining in lower karstic levels, 4.

A period of karstic fossilisation during which the speleothems formed. The temperature measurements made in the area around the entrance during january, in the cold dry season, showed a daily cycle with variations between 14 and 18° C (figure 3). The minimum temperatures were recorded at the beginning of the morning and the maximum temperature at the end of the afternoon, showing that the cave reaches a rapid equilibrium with the outside temperatures, which were identical. Air currents generated by these temperature fluxes run through most of the network. In the southern corridor these currents loose intensity after a division in two passages. They are no longer noticeable in the second half of the north branch. The temperature of the deep karst, regardless of seasonal fluctuations, is 20.5° C. This value was determined by measuring the temperature of the stream water at its resurgence. This same temperature was also measured in the lower chamber, where no daily fluctuations were measured. We conclude that this chamber is not affected by air currents and that its thermic cycle is the same as the deep karst, with a constant year round temperature. The infilling of the fossiliferous room has been described on the section of the first test pit. The bedrock was reached at a depth of 0.8 to 1 m. Its surface is irregular and presents a block crust made up of a centimetre thick alteration rim with alternating compact white and powdery black laminae. The mineralogical determinations indicated that it is mostly composed of phosphates (table1). The infilling consists of 3 stratified units (figure 4).

1.

The third unit is only found in the hollows in the rocky substratum. The unit is 20 cm thick. It consists of horizontally bedded lenses of well-sorted calcareous granules and pebbles sorted by lenses with horizontal bedding and filled with a clayey red brown sand. The structure and composition of this deposit are the same as those of the breccia conglomerate observed against the walls of the cave.

2.

The second unit overlays the first deposit as well as the highest parts of the bedrock. The sediment is a yellow-brown to yellow (10 YR 6/8) clayey sand which is more or less indurated. X-ray diffraction determined that the major minerals are phosphates (tableau 1) which, in thin sections, look either like beige to yellow isotropic mass impregnating the deposit, or like a fibrous isopac coatings of hydroxylapatite. Subhorizontal layers of sediment which is aggregated or rich in granules were also observed in some spots. Under the microscope, the lithology of the granules is variable: pelite, sandstone and quartzite. Several pieces of granules are scattered in the deposit and have a very well developed phosphate-rich alteration rim (table 1).

3.

The first unit contains the paleontological remains. It is 0.2 to 0.5 m thick. The irregular and sharp lower limit indicates an erosional contact. The deposit is a yellow-brown (75 YR 4/6) to red brown (7,5 YR 5/6) and, sometimes, grey brown sandy clay with few pebbles. The general facies is a stratified lenticular deposit. The lenses are no more than 10 cm thick. They are arranged in series of horizontal or slightly inclined conformably overlying lenses. The sets of lenses extend for several metres and their thickness reaches approximately 20 to 30 cm. Each set is separated by sharp or erosional surface (figure 4 &5). In detail, each lens is formed by the superposition of two facies: The base and the body of the lenses consist of millimetre to centimetre thick clay aggregates. These aggregates are sorted and a single grading, most often normal, occurs frequently. Example of recurrent grading has been observed in some lenses. Aggregation is clear at the coarse-grained basal part of the lenses and lessens progressively towards the top. Associated to the coarser aggregates are small limestone pebbles which are smooth and sometimes completely weathered. The clast morphology, small triangular or square plates, indicates that these stones are derived of the surrounding rock that is fractured by a joint pattern. Dental remains were preferentially associated with the coarse-grained parts of lenses. In thin sections, aggregates are heterogeneous, due to variations in texture and colour. Also of note is the clay orientation observed art the periphery of the aggregates (figure 6). The upper part of lenses is composed of compact and massive clay (figure 7). This bed varies in thickness from 2 to 5 cm. It is especially pronounced when it forms the upper surface of a set of lenses. The lower boundaries of these beds are progressive where as the upper limit is sharp and sometimes highlighted by a pattern of desiccation cracks. Locally, intercalated laminae some centimetres thick can be distinguished. These have wavy borders and stand out due to variations in colour and texture. A clay orientation is also observed under the microscope; clays are orientated on the periphery of grains (sand or bone) or according to the bedding plane and, in the case of intercalated laminae, following the undulations of the sediment. In this massive sediment, porosity is weak, and consists of cracks parallel to the bedding plane. The microscopic examination of the slides has shown an alteration of the paleontological material. This degradation was more or less pronounced but affected both bone and dental remains (figure 8). It is characterised by 1) cracking, 2) digestion holes along the walls, 3) the development of brown spots in a dentritic network and 4) the appearance of darkening zones with a loss of birefringence. Our interpretation of the deposition mechanisms is the following:

At the bottom of the sequence (unit 3), sands and pebbles are evidences, preserved in the bedrock depressions, of an ancient alluvial period, which is also represented by for the cemented conglomerate observed intermittently along the walls of the cave. The second unit was originally a deposit of fine material transported by flow, as shown by several intercalate beds of granules. As is the case of the silt overlaying the alluvial deposits in the well, this is evidence of deposition related to cave flooding at a time where the river flowed in a lower karstic level. These sediments have undergone significant diagenesis. This is shown by the phosphate formation (mostly hydroxylapatite, cf. table 1). These phosphates are derived from animal guano, very likely bat, because of the occurrence of Dittmarite in the mineralogical array which is an ammoniated phosphate of animal origin [START_REF] Hill | Cave minerals of the world[END_REF]. The diagenesis is pronounced. Among the phosphates identified are several mineralogical species that imply a complete decarbonatation of the sediment (tarakanite, leucophosphite and montgomeryite, cf. [START_REF] Karkanas | Diagenesis in prehistoric caves : the use of minerals that form in situ to asses the completeness of the archaeological record[END_REF]. This type of transformation indicates that a hiatus took place between the edification of this unit and the overlying unit 1. The unit 1 deposit is attributable to an accumulation of dug sediment by burrowing animals. Indeed, the round millimetric to centimetric aggregates facies observed, and which are commonly found in karstic context [START_REF] Goldberg | -Some micromorphological aspects of prehistoric cave deposits[END_REF], are associated with burrow infilling [START_REF] Karkanas | Site formation processes in Theopetra Cave : a record of climatic change during the late pleistocene and early holocene in site formation processes in Theopetra cave[END_REF]. This interpretation is also supported by the grain size sorting of the aggregates. The strips of digging debris which accumulate when a burrowing animal digs show a longitudinal sorting where the coarsest material ends up on the edge of the rejected layer. The accretion of this debris then leads to the superposition of material in progressively decreasing size [START_REF] Lenoble | Etude géoarchéologique[END_REF].

The progressive nature between the clay aggregates and the solid clay facies underneath it indicates that the solid clay layer was produced by the compaction of the aggregated sediment. The orientation of clay minerals observed under the microscope suggests that the deformed sediment is in a plastic state. The ill-defined bedding and the flattening observed (indicated by the wavy edges of the intercalated fine layers) are also evidence of this deformation. The compaction and the fissural porosity in accordance with the bedding plane suggest that it is a trampled horizon [START_REF] Goldberg | Micromorphology study of a bedouin tent floor[END_REF]. So we deduce that these compact beds are formed by an originally aggregated material. The association between lenses of aggregates and beds of clay thus represent an episode of burrowing (production of aggregates) followed by a period of occupation of a burrow (formation of a trampled horizon). The succession of many lenses means that there were many burrowing events. The size and morphology of the digging can be determined from the geometry of the erosive contact between each set of lenses. These are suggestive of shallow depressions extending for about one metre. This morphology is identical to the troughs which presently structure the ground of the lower chamber. The sediment rings which delimit the troughs on the soil surface represent the strips of accumulated debris which have secondary been compacted by trampling. The stacking of a series of lenses indicated multiples phases of digging where the debris filled in the existing topography. These beds are significantly smaller than those described for brown bears [START_REF] Fosse | Ursidés pléistocènes des Pyrénées : éléments de paléontologie et de paléobiologie[END_REF]. They were thus made by a medium sized animal. The porcupine quills surrounding on of these beds when the room was discovered suggests the digging was done by this rodent. This interpretation is supported by the present-day descriptions of the Hystricidae lair. Hughes reported a similar organisation of burrows and a central area flattened by trampling and used for sleeping: « Inside the lair was a circular raised pieces of clean ground well consolidated by the porcupines that had lain there sleeping » (Hugues in Brain, 1981: 112). Two other arguments also support this interpretation. First of all this area of the cave is exceptional in that the temperature does not vary, making it attractive for occupation by an animal. Secondly, unlike other galleries where puddles of water are present at some times during the year, the absence of concretions, on the ceiling or floor, is evidence that dripping is rare in this chamber which would also make it a more favourable place for a lair. The sedimentological study indicated that the fossil deposit (unit 1) is associated with the use of the lower chamber as a lair. The formation of this deposit was late in the history of the karst. Indeed it was at the moment that the network became fossilised, meaning that there was no longer any alluvial deposition taking place. The cave has probably been frequented for a long time judging by the large number of beds which have remodelled the upper part of the room infilling and which reach a thickness of half a metre. This use of the cave appears to have continued to the present day since we found porcupine quills on the floor during our first exploration of the cave.

Taphonomic study

The series of remains is mostly teeth (82.7%). A large majority is dental fragments made of enamel and dentine, but sometimes only enamel (table 2). The size of these fragments obviously varies greatly depending on the taxonomical origin of the remains. Nevertheless these are only rarely larger than 3cm. The majority of bone remains are small splinters for which identification is difficult. As for the teeth, their size is often less than 3 cm (figure 9). The largest bone artefact found, a fragment of large mammal long bone diaphysis, is not longer than 5.5 cm. Most of the identified bones are complete or almost complete and are not very diverse. For the most part, these are (table 3): petrosal, phalanx, metapode and calcaneous bones. We did not identify any traces of man-made alterations of bone, whether it be burn, cutting or percussion marks. Similarly, no modifications due to the action of carnivores: teeth marks, perforations, grooves, crenelated edges, traces of digestion, were found. Alterations of biological nature were found in abundance, however, and are due to gnawing (table 4). Typically, this gnawing is seen as flat to concave plurimillimetric to centimetric facets, bearing groups of striations (figure 10a). Small numbers of these striations are grouped within shallow grooves, which are parallel to each other and sometimes slightly curved. Grooves are several millimetres wide and their bottom is slightly concave in a transverse plane. From the size and morphology of these grooves these could be identified as gnawing marks made by a porcupine [START_REF] Brain | Porcupines as bone collectors in African caves[END_REF][START_REF]Le rôle des animaux et des causes naturelles dans la cassure des os[END_REF]. The list of fauna from the site includes two taxa which could be the culprits of this gnawing: Hystrix brachyura and Atherurus macrorus (cf. Zeitoun et al., this volume). Almost all of the bone fossils (78%) have traces of gnawing. When exhaustive, these gnawing cause the modification of the bone shape. Two noteworthy morphologies are produced by exhaustive gnawing:

-small compact prisms of bone the outside of which is formed exclusively of subvertical facets. These are 1 to 2 cm thick and approximately the same width with a length shorter than 3 cm. These pieces can have been completely shaped by gnawing (figure 10b), but sometimes the non -altered bone in which the prism was sculpted can be seen at the bottom or at the top surface. The ridges are arranged in a radial pattern. Some facets no more than a few millimetres wide show evidence of previous gnawing.

-flat splinters with crenelated edges. Their width and thickness can reach several centomtres whereas their width is never greater than ½ cm. The facets forming the edge of the pieces are slightly inclined with respect to the flat plane. The ridges are also arranged radially. The teeth have also been gnawed (table 5). In general the surface of the dentine has been nibbled at but occasionally the tooth has been reduced to its crown (figure 10c). In rare cases even the enamel has been attacked. These traces are often found in the area surrounding the fracture point suggesting that already broken teeth were gnawed. Half of the teeth were gnawed, as well as 21 % of the teeth fragments without any obvious differences between the different categories of large mammals (Ungulates, Carnivores and Primates). The proportion of rodent teeth that had been chewed was, however, very low at only 2.2 %.

Very few alterations were noted after the gnawing on the bones or teeth. Thus gnawing marks were not interrupted by fractures. The modifications identified concern the surface patina of the remains. Most of the bones are light coloured and smooth. A small fraction, less than 5% of the bone remains, however, are distinguished by their brown colour and a polish which has also blunt the gnawing marks (figure 11). Some of the teeth, especially suids molars and several fragments of walls from muntjac teeth, also have the same brown colour and a smoothing out of the relief caused by gnawing.

Altogether, these observation show that the porcupine is the principal, if not only, agent to have modified the bones. This alteration led to a considerable reduction in size of the bone fragments, which are mostly less then 3 cm. This exploitation was not only of bone because teeth roots have also been gnawed. The lack of evidence suggesting that any other actors (human or carnivore) have been involved in the accumulation or transformation of the remains is remarkable. The presence of smoothed or even polished pieces is not sufficient evidence to conclude that another taphonomic actor played a role, because these modifications could have been made during the occupation by the rodents.

Discussion

The sedimentological study concluded that an animal lair, most probably of a porcupine, was present. Our taphonomic approach corroborates this interpretation because the principal actor who modified the bones was indeed a porcupine. The recognition that the site contains the deposits of a lair suggests that the bones in the cave have a purely biological relationship. Furthermore, this interpretation takes into account the fact that the bones were transported into the deep karst context. The porcupine is an animal renowned for accumulating faunal remains in its dens [START_REF] Brain | Porcupines as bone collectors in African caves[END_REF]. Its contribution to the formation of paleontological sites has been especially studied in South Africa and the Middle East (Alexander, 1956;[START_REF] Brain | Porcupines as bone collectors in African caves[END_REF]Maguire, 1976;[START_REF] Maguire | The Makapansgat limework grey breccia: hominids, hyaenas, hystricids or hillwash? Palaeont[END_REF][START_REF] Monchot | Un assemblage original au Paléolithique moyen : le repaire à Hyènes, porcs-épics et hominidés de la grote Geula (Mont-Carmel, Israël)[END_REF]Rabinovitch and Horowitz, 1994). Alexander (1956) observed evidence that objects weighing as much as 2 kg had been moved. Thus, all of the bone remains discovered at the site in the lower chamber of the Cave of the Monk were accumulated by this animal. Studies describing present-day alterations to bone fossils are carried out in South Africa and the Middle East however. These studies are far to report features similar to those found in South-East Asia. Particularly, none of these studies reports an almost complete disappearance of the post-cranial skeleton. Nevertheless, the example of the Cave of the Monk is not unique. A number of authors have reported the occurrence of gnawing on bone fossils from caves in the tropical Far East (eg. [START_REF] Bacon | New palaeontological assemblage, sedimentological and chronological data from the Pleistocene Ma U'Oi cave (northern Vietnam)[END_REF][START_REF] Bien | -Cave and rockshelter deposits in Yunnan[END_REF]von Koenigswald, 1938-39;[START_REF] Long | The fossil mammal fauna of the Lang Trang caves, Vietnam, compared with southeast asian fossil and recent mammal faunas: the geographical implications[END_REF][START_REF]Fossils mammals from the Kwangsi Caves[END_REF][START_REF]Le rôle des animaux et des causes naturelles dans la cassure des os[END_REF][START_REF] Tougard | Abnormal fossil upper molar of Pongo from Thailand Quaternary climatic changes in Southeast Asia as a possible cause[END_REF][START_REF] Vos | Reconsideration of Pleistoene cave faunas from South China and their relation to the faunas from Java[END_REF][START_REF] Young | On the mammalian fauna at Koloshan near Chingking, Schezuan[END_REF]. In all these cases, the authors noted the destruction of the teeth roots. Some of these authors argue that the destruction of bones in these sites could be explained by a differential dissolution (e. g. [START_REF] Tougard | Les faunes de grands mammifères du Pléistocène moyen terminal de Thaïlande dans leur cadre phylogénétique[END_REF]. We can accept this hypothesis because some bones are preserved, even if reduced, and their surfaces don't shows dissolution marks. This is confirmed by microscopic observations of sediment slides where an alteration of bones and teeth is noted but is not different between this two categories. The preservation of bones fragments is documented in others South-East Asian caves as well and it is also noteworthy that the same prism shapes or crenelated splinters that we have described were previously observed by [START_REF]Le rôle des animaux et des causes naturelles dans la cassure des os[END_REF] and [START_REF] Young | On the mammalian fauna at Koloshan near Chingking, Schezuan[END_REF] in paleontological material collected in caves in South China. The complete transformation of bones by porcupine gnawing is thus not unique to the Cave of the Monk but a widespread phenomenon throughout all of Indochina. No ethological study of Asian porcupine could explain this phenomenon. One hypothesis explains this characteristic by the lack of available bone in the tropical forest environment compared to the semi-arid environments, where the available actualist studies were carried out. This shortage could explain the increased consumption of bones collected by Porcupines in South-East Asia. The sedimentological study shows evidence that numerous beds were dug between which there were periods during which the den was occupied as shown by the development of a trampled surface. This type of functioning implies a long formation time. It is possible to understand this time length by relating the number of remains which may be found at the site with the rate of introduction of remains established by studies on modern porcupine dens. In the Cave of the Monk, about 3,500 dental fragments were found in 5 m 2 . The surface of the lower chamber that has a surface patterned by beds, and thus functioned as a den, is slightly larger than 50 m 2 . Thus we can reasonably assume that we excavated slightly less than one tenth of the deposit and that a complete collection of all material would be about 35,000 dental remains. The Nossob den, studied by [START_REF] Brain | Porcupines as bone collectors in African caves[END_REF], gives an example of the time necessary to accumulate remains in the cave. Teeth are introduced into the den in the form of pieces of cranial mandible. The figure given by the author for the accumulation of these pieces is 80 per century (cf. Brain, op. cit.). A minimalist hypothesis of 8 teeth per cranial fragment leads to a figure of 640 teeth being introduced per century. Thus the time necessary to introduce 35,000 dental remains in a den is more than 5,000 years. Considering that the cave was probably not occupied continuously, we can estimate that the time necessary to form the site is in the order of one or several tens of thousands of years. This hypothesis should be confirmed by dating the remains held at the bottom and top of the fossil deposit. Such a duration for site formation has two consequences on the significance of the assemblage collected. First of all, this time frame is longer than periods of climatic fluctuation which could have led to changes in the environment. Consequently if the assemblage is considered as a homogeneous group then species which actually lived in very different environments could be clumped together. Furthermore, the time frame is large enough so that taxa which lived in different eras and consequently different biozones, could be found associated in the same assemblage. This problem of non homogeneity in paleontological assemblages echoes the remarks of [START_REF] Patte | Comparaison des faunes de mammifères de Lang Son (Tonkin) et du Se Tchouen[END_REF] and De [START_REF] Vos | Reconsideration of Pleistoene cave faunas from South China and their relation to the faunas from Java[END_REF], for whom unexpected associations in Pleistocene paleontological assemblages recovered from South-East Asian caves reflected mixes within the series. The identification of the porcupine as the principal agent in forming Pleistocene paleontological sites supports J. De Vos's hypothesis and indicates that the assemblages can not be considered, from the biochronological and especially the paleoenvironmental point of view, as homogeneous series.

Conclusion

Both geological and taphonomic studies carried out on the infilling and fossil material respectively, show that the Pleistocene faunal site at the Cave of the Monk was accumulated by a porcupine. The criteria for this diagnosis are both sedimentological: facies of debris from a burrowing animal, digging morphology, as well as taphonomic: modifications to bones by this rodent. The series of faunal remains shows a large degree of transformation of the bones which were reduced to small faceted splinters and the consumption of teeth roots. These characteristics are common at paleontological cave sites in the Indochina region and distinguish them from accumulations by rodents described in South Africa or the Middle East. We think that this is linked to the environment in the tropical forests of South East Asia. This finding has double implications on the paleoenvironmental interpretations which can be deduced from this type of series. On one hand the assemblage is a good environmental indicator, in the sense that the accumulations generated by the Porcupine are thought to have sampled the existing taxa from the environment without bias. On the other hand, the series was composed over a long period of time, in the order of one or several 10s of thousands of years. This time frame is greater than that of climatic events which faunal associations may reflect. Consequently, the assemblage can not be considered as a homogeneous reference for reconstructing environments. Methods for extracting the information available from these types of assemblages are yet to be.

Figure 1 :

 1 Figure 1: Site location.

Figure 3 :

 3 Figure 3 : Daily temperature fluctuations (°C) measured at different places in the cave.

Figure 4 :

 4 Figure 4 : Stratigraphy of the deposits in the lower chamber of the Cave of the Monk observed on the east section of the first test pit. The numbers indicate the stratified units.

Figure 5 :

 5 Figure 5: Detailed structure of stratified unit 1 observed at survey site 2.

Figure 6 :

 6 Figure 6: Microfacies of the fossiliferous unit (unit 1). Aggregated clay facies: note the smoothed surface of the aggregates (a) and the orientation of the clayey matrix at the periphery of the aggregates (b).

Figure 7 :

 7 Figure 7 : Microfacies of the fossiliferous unit (unit 1). Solid clay facies: note the irregular lamination with variations in the colour of the fine fraction and in the quantity of sand, and the sediment compactness which is associated with a fissural porosity parallel to the bedding plane.

Figure 8 :

 8 Figure 8: Details of a boney remain found in unit 1. Alteration is characterised by fine cracking at the bone periphery (detachment of thin slices) and the development of brown areas.

Figure 9

 9 Figure 9 Distribution of bone fragment length.

Figure 10 :

 10 Figure 10 : Example of gnawed bones. A: fragment of long bone diaphysis gnawed at its ends. B: a gnawed tooth root. C: a bone showing multiple gnawed facets.

Figure 11 :

 11 Figure 11 : A smoothed bone showing old traces of gnawing marks.

Table 1 :

 1 Minerals identified by Xray diffraction. Phosphated minerals are indicated in bold. +++ : very common ; ++ : common ; + : slightly common ; -: rare ; --: traces.

Table 2 :

 2 The kind of remains found.

	Bone		Teeth
	complete		fragments
		enamel	enamel & dentine
		769	1,958
	297		2,727
	472	3,024
		Total 3,496

Table 3 :

 3 The kind and number of average and large sized mammal bones (rondents are not included).

		petrosal	phalanx	metapode	calcaneus	indet	indet
						fragment	fragment
						>3cm	<3cm
	N	71	9	5	5	18	354	462
	%	15.4	1.9	1.1	1.1	39	76.6	100

Table 4 :

 4 Gnawing tracks NR is the number of remains ; NRr is the number of remains showing traces of gnawing; Rr is the rate of gnawing, in percentage. It represents the ratio of NRr/Nr.

		NR	NRr	Rr
	Fragmentary bones	472	368	78.0%
	Teeth	3,024	562	18.6%
	Complete tooth	297	149	50.2%
	Enamel	769	0	0
	Enamel & dentine	1,958	413	21.1%