We want to thank the editor Dr. Nicole Limondin-Lozouet and the two reviewers, Dr. Emmanuel Desclaux and Prof. Gloria Cuenca-Bescós, for their comments that improve the final version of the manuscript. This paper has been funded by the Spanish Ministerio de Economía y Competitividad (CGL2014-54373-P) and the Generalitat de Catalunya (2014 SGR 416 GRC and 2014-SGR900. E. Luzi is the beneficiary of a PhD scholarship funded under the Erasmus Mundus Programme - International Doctorate in Quaternary and Prehistory. The authors thank Jean Louis Perez, Caroline Guérineau, Philippe Galant, Jérôme Durbet, Miquel Nebot, Teresa Hernández and Julià González for various kinds of support. We would also like to thank Dr. Hugues-Alexandre Blain and Rupert Glasgow for French and English revisions, respectively.

1 - Introduction

1Rodents are one of the stratigraphically most significant groups of mammals in the European Pleistocene, because they have diversified more than other taxa over this relatively short geological time span. Arvicolines (voles) are particularly useful for biochronological correlation, because of the abundance of their remains and their rapid evolutionary rates. In addition, some voles undertook rapid, long-range migrations and may have had extensive geographical distributions, making interregional correlations possible (Minwer-Barakat et al., 2011). For these reasons, arvicolines have been used to establish the biostratigraphic subdivisions of the Quaternary (Chaline, 1972; van der Meulen, 1973; Agustí, 1986; Sala & Masini, 2007; Cuenca-Bescós et al., 2010; Agustí et al., 2015; among many others).

2Grotte de la Carrière is a newly discovered site in the Embullà Mountain, located between the municipalities of Ria and Corneilla-de-Conflent (Eastern Pyrenees) (fig. 1A). This mountain chain possesses a large karstic complex with more than 20 caves situated at different altitudinal levels. Réseau Lachambre Cave, with more than 26 km of galleries, is the largest of these. The research carried out by the authors since 2011 has led to the discovery of several Middle to Late Pleistocene sites (Madurell-Malapeira et al., 2015). The first paleontological survey of Grotte de la Carrière, undertaken in May 2015, resulted in the unearthing of more than 2000 large- and small-vertebrate remains in eight different stratigraphical layers. The small-mammal material recovered comes mainly from layer 4, a five-centimetre-thick layer composed of brown clays with boulders some centimetres in size comprising quartzes and calcareous schists.

3This paper aims to provide a study of the small-mammal (insectivore and rodent) faunas from Grotte de la Carrière. Particularly interesting is the correlation and chronological position of Grotte de la Carrière in relation to other Middle Pleistocene sites from southern France, Spain and Italy, based mainly on a study of their vole species. This study thus offers a good opportunity for adding to our knowledge of the small-mammal assemblages of the Middle Pleistocene of Western Europe.

2 - Material and methods

4During the excavation of Grotte de la Carrière, sediments from each layer were screen -washed in order to obtain the small -vertebrate fossil remains. Most of the material comes from layer 4. The specimens under study were sorted at the Institut Català de Paleontologia Miquel Crusafont (ICP, Barcelona, Spain). The Grotte de la Carrière - layer 4 assemblage includes a total of 91 identified small mammals corresponding to a minimum number of 42 individuals, representing at least ten taxa: Talpa europaea, Sorex sp., Microtus arvalis, Microtus agrestis jansoni, Iberomys brecciensis ( = mediterraneus; priority discussed by Cuenca-Bescós et al. 2014), Clethrionomys glareolus, Pliomys coronensis ( = lenki; priority discussed by Terzea, 1983), Apodemus gr. sylvaticus-flavicollis, Allocricetus bursae and Sciurus sp.

5The nomenclature for the description of the arvicoline teeth (only first lower molars are considered) used for the chronological inferences is that from van der Meulen (1973) and Martin (1987). Length, width, and parameter a are those proposed by van der Meulen (1973), and parameters Li and La are those proposed by Cuenca-Bescós et al. (1995). Index La/Li is the ratio between parameters Li and La (fig. 1B & C).

3 - Biochronological remarks

6Small mammals, and particularly arvicolines, evolved rapidly during the Quaternary, so their record provides an important basis for stratigraphic divisions and correlations between distant areas. In particular, the quick evolutionary radiation of the ‘Microtus group’ (which includes forms ascribed to Microtus, Allophaiomys, Stenocranius, Terricola, Iberomys and Pallasiinus) constitutes a very useful tool for correlating European Pleistocene faunas. In our case, the most diagnostic species from a chronological point of view are the voles Microtus agrestis jansoni and Iberomys brecciensis (fig. 2A).

3.1 - Microtus agrestis jansoni (Chaline, 1972)

7Microtus agrestis morphotype jansoni was first described by Chaline (1972) on the basis of material from Grotte de l’Escale (Saint-Estève-Janson, Bouches-du-Rhône, France) as a vole with agrestis-like morphology: m1 that presents a posterior loop, 5 closed triangles with a clear labio-lingual asymmetry, alternatingly confluent T6 and T7, and an asymmetric anterior cap. In particular, the jansoni-type is characterized by a middle-large size, a deep LRA4, the presence of T9 in the ACC and a broad LRA5. In some cases, the populations of the late Middle Pleistocene develop a small BRA4 on T6, resulting in a T8 that recalls the mimomyan-fold. This archaic character is rare in Late Pleistocene populations (1/1000). Chaline (1972) and Cuenca-Bescós et al. (1999) suggest a trend toward a decrease in size for this sub-species during the Middle Pleistocene.

8Other populations of M. agrestis jansoni have been identified in the Middle and Late Pleistocene sites of Caune de l’Arago (Brunet-Lecomte & Paunesco, 2004), La Fage (Mourer-Chauvire et al., 2003), Grotte des Cèdres (Defleur et al., 1990) and Combe Grenal (Chaline, 1972) in France, and in the Middle Pleistocene sites of Galeria, Zarpazos, Gran Dolina TD10, Sima del Elefante TE18-19 (Cuenca-Bescós et al., 1999, 2010; Galindo-Pellicena et al., 2011; López-García et al., 2011), Mollet (López-García et al., 2014) and Valdavara-3 in Spain.

9The specimens from Grotte de la Carrière identified as Microtus agrestis jansoni present all the morphological characters proper to this sub-species. One specimen also shows a T8 which, taking into account the number of remains recovered, suggests a Middle Pleistocene age. From a biometric point of view, the mean length of m1 (2.796 mm) is lower than those from the type-population of L’Escale (2.87 mm) and from TE 18-19 (2.886 mm) and Zarpazos (2.849 mm), and it is close to those from Mollet (2.775 mm), TD10 (2.776 mm) and Valdavara-3 (2.801 mm). The labio-lingual asymmetry is more pronounced in Grotte de la Carrière (La/Li = 57) than in the samples from Mollet, TD10, Zarpazos, Valdavara-3 and TE 18-19 (La/Li = 41.5, 51.5, 51.6, 52.5 and 54 respectively). The population of M. agrestis from layer IIb of Teixoneres Cave (López-García et al., 2012) (Late Pleistocene, Spain) is smaller and more symmetrical (L = 2.662 mm; La/Li = 64.1) than those of the Middle Pleistocene (fig. 2B). Thus, a morphometric comparison between these populations indicates that Grotte de la Carrière has an age close to Valdavara-3 and TD10 and younger than Zarpazos (Falguères et al., 2013; Demuro et al., 2014), ranging from 360 to 250 ka.

3.2 - Iberomys brecciensis (= Mediterraneus) (Giebel, 1847)

10Microtus (Iberomys) brecciensis was described by Chaline in 1972 as a subgenus of Microtus species. Chaline proposed a specimen drawn by Cuvier (1823) as the holotype, and Sète as the type locality, a karst fissure of imprecise location where lagomorphs have been found.

11The distinctive morphological traits of I. brecciensis are the T4 and T5 that are closed in all specimens. In some specimens, BRA4 forms a reduced re-entrant angle, and in most m1, T6 is clearly separated from the anterior cusp due to the strong development of the re-entrant angle LRA4. These characteristics allow our material to be attributed to the species I. brecciensis, thus distinguishing it, moreover, from the present-day species I. cabrerae and from the fossil species from the Early Pleistocene I. huescarensis.

12Other populations of I. brecciensis have been identified in Middle Pleistocene sites such as Caune de l’Arago, Orgnac and Le Lazaret (Hanquet, 2011; Hanquet & Desclaux, 2011) in France, Valdemino or Montagnola Senese II in Italy (López-García et al., 2015), and Galeria, Zarpazos, Gran Dolina TD10, Sima del Elefante TE18-19 (Cuenca-Bescós et al., 1999, 2010; Galindo-Pellicena et al., 2011; López-García et al., 2011) and Mollet (López-García et al., 2014) in Spain.

13The specimens from Grotte de la Carrière identified as Iberomys brecciensis present all the morphological characters proper to this species, suggesting a Middle Pleistocene age for layer 4. From the biometric point of view, m1 (mean length 2.830 mm) is longer than those from the sites of Valdemino (2.69 mm) and Mollet (2.7 mm), shorter than those from Orgnac (2.96 mm), Lazaret (3.15 mm), TE 18-19 (2.91 mm) and Galeria (3.12 mm), and similar to those from Arago I (2.89 mm), L’Escale (2.89 mm), Montagnola Senese II (2.83 mm) and TD10 (2.88 mm). The labio-lingual asymmetry is less pronounced in Grotte de la Carrière (La/Li = 47.6) than in Galeria (La/Li = 48.2), but more pronounced than in Valdemino, Montagnola Senese II, TD10, TE18-19 and Mollet (36.8, 41.8, 42.7, 45.2 and 45.9 respectively). The populations of I. cabrerae from the Late Pleistocene sites of Cova del Gegant (L = 3.31 mm; La/Li = 54.7), Abric Romaní (L = 3.35 mm; La/Li = 56.9) and Gorham’s cave (L = 3.40 mm; La/Li = 55.07) (López-García et al., 2008; López-García, 2011) are larger and more asymmetrical than those of the Middle Pleistocene (fig. 2B). Thus, morphological and biometric comparisons between these populations indicate that Grotte de la Carrière has an age close to TD10, Galeria and TE18-19, older than Mollet, and younger than Valdemino and Montagnola Senese II (López-García et al., 2011; Maroto et al., 2012; Falguères et al., 2013; Demuro et al., 2014; ; de Lombera-Hermida et al., 2015; López-García et al., 2015), ranging from 450 to 215 ka.

14In summary, the small-mammal association from layer 4 of Grotte de la Carrière fits within the range of typical associations from the Middle Pleistocene faunas of the southwestern Mediterranean and can be included in FU6 (ranging from 600 to 125 ka) as defined by Cuenca-Bescós et al. (2010), where the characteristic species of this Faunal Unit are I. brecciensis, M. arvalis, M. agrestis jansoni, Pliomys coronensis and Allocricetus bursae. Thus, the Grotte de la Carrière association is also very similar to other Middle Pleistocene sites from the south of France, such as Caune del Arago or Grotte du Lazaret (Hanquet, 2011; Hanquet & Desclaux, 2011), and Spain, such as Gran Dolina (TD10), Galeria and Sima del Elefante (TE18-19) from the Sierra de Atapuerca (Cuenca-Bescós et al., 1999, 2010; Galindo-Pellicena et al., 2011; López-García et al., 2011). All these data, together with the morphological and biometric studies of the species Iberomys brecciensis and Microtus agrestis jansoni, suggest a rough age for layer 4 of between 450 and 220 ka (fig. 2C). The chronology proposed on the basis of the micromammal assemblage is in accordance with the large mammals recovered and identified from this layer, Ursus deningeri, Panthera fossilis and Canis mosbachensis being the most characteristic species.

4 - Conclusions

15Our study of the small-mammal assemblage from layer 4 of Grotte de la Carrière allows the following conclusions to be drawn:

• -1/ Ten small-mammal (insectivore and rodent) species are currently known to be present in Grotte de la Carrière - layer 4: Talpa europaea, Sorex sp., Microtus arvalis, Microtus agrestis jansoni, Iberomys brecciensis, Clethrionomys glareolus, Pliomys coronensis, Apodemus gr. sylvaticus-flavicollis, Allocricetus bursae and Sciurus sp.

• -2/ Within the context of the small- and large-mammal assemblages from layer 4 of Grotte de la Carrière, the evolutionary states of the vole species Microtus agrestis jansoni and Iberomys brecciensis are indicative of a chronological age within the range of 450 and 220 ka .