Small mammals from Sima de los Huesos

Gloria Cuenca-Bescós & César Laplana Conesa

Paleontología. F. Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain, and U.A. CSIC-U. Zaragoza, Museo Nacional de Ciencias Naturales, 28002 Madrid, Spain

Small mammals from Sima de los Huesos A small collection of rodents from Sima de los Huesos helps to clarify the stratigraphic position of this famous human locality. The presence of Allocricetus bursae and Pliomys lenki relictus and the size of A. bursae, Apodemus sylvaticus and Eliomys quercinus suggest a Middle Pleistocene age (Saalian) to the Clays where humans have been found. ? 1997 Academic Press Limited

Jose Ignacio Canudo

Museo de Paleontología, Universidad de Zaragoza, 50009 Zaragoza, Spain

Juan Luis Arsuaga

Dpto. de Paleontología, Universidad Complutense, 28006 Madrid, Spain Received 24 April 1996 Revision received 1 November 1996 and accepted 22 March 1997 Keywords: rodents, Middle Pleistocene, Atapuerca, Sima de los Huesos, Spain, micromammal biochronology.

Journal of Human Evolution (1997) 33, 175–190

Introduction In 1974, René Lavocat wrote in this journal: ‘‘It may be rather surprising to read in a journal devoted to human evolution a paper on rodents. This contribution is justified by the fact that the study of rodents can provide excellent arguments’’ . . . of correlation and relative age assignment of fossil hominid sites (e.g., Lavocat, 1956; Chaline, 1971; Repenning & Fejfar, 1982; Carbonell et al., 1995) and can also tell us a great deal about past environments (Bishop, 1982; Andrews, 1990a,b). The Sima de los Huesos cave locality is one of the sites containing Pleistocene humans in the Sierra de Atapuerca (Burgos, Spain) karst system (Aguirre, 1995; Arsuaga et al., 1993; Bischoff et al., 1997; Carbonell et al., 1995 and references therein). In the past 5 years, the paleontological team from the Complutense University of Madrid has sieved the clays where the human fossils are recovered (about 250 kg of matrix) by means of modern sieving techniques (Daams & Freudenthal, 1988a). This yielded 43 concentrates containing a small collection of microvertebrates that helps to clarify the stratigraphic position of Sima de los Huesos locality. Collecting is continuing, and further additions to the fauna may be expected. When the small mammals were unknown in Sima de los Huesos, the carnivores were the best tool for correlation (García et al., 1997). Cuenca-Bescos´ et al. (1994) presented a preliminary report of biostratigraphical correlation based on the small mammal fossil remains. This work studies the small mammal assemblage found in the Sima de los Huesos cave site, and attempts to make biostratigraphical correlation with other Pleistocene faunas on the basis of its small mammal fauna contents. The biostratigraphy from the Gran Dolina site is still in progress of determination. It requires an enormous amount of work, partially because of the large number of small mammal fossil remains found in every stratigraphical 0047–2484/97/080175+16 $25.00/0/hu970153

? 1997 Academic Press Limited

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level (Gil & Sesé, 1991; Cuenca-Bescós et al., 1995), and partially because of the discovery, in level TD 6, of the supposed oldest human remains in the Pleistocene of Europe (Carbonell et al., 1995). This brings the problem into a wider forum of discussion than merely the small mammal paleontologists. It opens the question of which level of the Gran Dolina site the Sima de los Huesos lower unit correlates. The scarcity and poor diversity of fossil rodents and the short stratigraphical sequence of Sima de los Huesos makes difficult the most common practice applicable in mammalian correlation, the so-called first or last appearance datum. Thus, an accurate correlation, requires detailed morphological and biometrical comparative analysis of the species present in the locality. This analysis is pertinent for Allocricetus bursae from Sima de los Huesos and Gran Dolina. For the same reasons, we have compared the size of A. bursae from Sima de los Huesos with these species in other European localities.

The small vertebrate fauna Gil & Sesé (1991) give a faunal list of small mammals whose stratigraphical position in the Sima de los Huesos is unknown. This list includes the following taxa: Insectivora indet., Quiroptera indet., and Allocricetus bursae, Microtus/Pitymys sp. and Apodemus sp. among Rodentia. The cricetid Allocricetus bursae has been the object of a more complete study by Cuenca-Bescós et al. (1994) and those authors provide the following faunal list: Miniopterus schreibersi, Myotis myotis/blythi, Allocricetus bursae cf. correzensis, Pliomys sp., Arvicolidae indet., Eliomys quercinus cf. quercinus and Apodemus sp. from the layers where the human remains were excavated. In this work, the authors concluded that the Sima de los Huesos’ small mammal assemblage was correlated with the upper levels of Gran Dolina site, also in the Atapuerca karst system, and they indicate a Middle Pleistocene age for this faunal assemblage. It is beyond the scope of the present work to describe the stratigraphy of the cave at Sima de los Huesos in any detail (see Bischoff et al., 1997). Nevertheless, for the sake of clarity when correlating and the stratigraphical position of the small mammal faunas, the salient features of the stratigraphic succession will be briefly outlined. The lower sediments, or lower unit, consist of clays with macrofossils designated ‘‘Clays with macrofossils’’ and it consists of ‘‘Arcilla roja’’ and ‘‘Yellow brown mud’’ as is described in Bischoff et al. (1997). Here, this was designated as lower unit of ‘‘Clays with human and bear bones’’ and it is labelled CH&B in text and figures. In Figure 4, SH indicates Allocricetus bursae specimens from this layer. The faunal list of this lower unit, with minimum number of individuals (MNI) for rodents in brackets, is: Rodentia, Allocricetus bursae Schaub, 1930 (3), Apodemus sylvaticus (Linnaeus, 1758) (6), Pliomys lenki relictus Bartolomei et al., 1975 (1), Microtinae indet. (3), Eliomys quercinus (Linnaeus, 1766) (1); Chiroptera, Rhinolophus mehelyi Matschie, 1901, Myotis myotis/M. blythi (sensu Sevilla, 1988), Miniopterus schreibersi (Kuhl, 1819); Insectivora, Crocidura sp. These sediments have also yielded other vertebrates such as fish vertebrae and teeth (Salmo sp. and Leuciscus sp.), and undetermined small reptile bones. Fragments of gastropods and arthropods, charophytes and plant remains are also present. The samples from the lower layer are labelled after the excavation abbreviations provided by the excavation team: Q, R, S, T, SR An, SRMS, SRM(a), SRM(r), SRM(ar), SRM, SRA, SRB. The plan of the Sima de los Huesos with the small mammal samples from the lower unit (CH&B) is given in Figure 1.

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S/T 12/13

S/T 15/16

Allocricetus bursae

Allocricetus bursae Apodemus sylvaticus Myotis myots/ M. blythi Crocidura sp.

S13 y R13 Allocricetus bursae Apodemus sylvaticus Myotis sp.

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Q 25

SRMS

Apodemus sylvaticus Rhinolophus mehelyi Myotis myotis/ M. blythi

Myotis myotis/ M. blythi Miniopterus schreibersi Rhinolophus sp.

SR An Apodemus sylvaticus Eliomys quercinus Miniopterus schreibersi Sorex sp.

CPV

SRB

SRM Apodemus sylvaticus Myotis myotis/ M. blythi Miniopterus schreibersi Insectivora indet.

SR

M

9

11

13

15

17

SRA

1m

SRM (a)

Allocricetus bursae Apodemus sylvaticus Eliomys quercinus Pliomys lenki relictus Myotis sp. Miniopterus schreibersi

Apodemus sylvaticus Microtinae indet. Myotis myotis/ M. blythi Rhinolophus sp.

SRM (r)

Eliomys quercinus Apodemus sylvaticus Microtinae indet. Myotis myotis/ M. blythi Rhinolophus sp. Miniopterus schreibersi

SRM (ar)

Figure 1. Location map of the Middle Pleistocene in Sima de los Huesos, small mammals. Redrawn from Arsuaga et al. (1993).

Above these deposits is a speleothem which appears to cover the lower unit. The upper part of the sequence in Sima de los Huesos consist of dark clays with bat guano, known as the ‘‘Brown mud and bat guano’’ in Bischoff et al. (1997), and here labelled ‘‘Dark clays with bat guano’’ (DCBG). The sediments from this layer and the lower layer share the species of Chiroptera and one rodent species: Apodemus sylvaticus. No other fossil remains appear in the Bat Guano layer. This paper describes the morphological and biometrical characters of the teeth of the rodents, mainly Cricetidae and Muridae, and comparison is made to European cricetids and murids of similar age. Tooth abbreviations and dental measurements M1, M2, M3 are used for the upper molars and M1, M2, M3 for the lower molars. The teeth were measured using a calibrated micrometer eyepiece in an Olympus SZH binocular microscope. The measurements are the maximum length (L) and width (W) of the occlusal surface of the molars, and the method of taking measurements and the nomenclature of parts of the cheek teeth of the Cricetidae follows Daams & Freudenthal (1988b). Nomenclature of the teeth of the Arvicolidae is after van der Meulen (1973) and of the Gliridae after Daams (1981). The Muridae and Gliridae were measured in the same way as Cricetidae. Re-examination of the nomenclature of the elements of murid teeth has been given by Michaux (1971) and Pasquier (1974); however, the classical nomenclature is followed in the present paper (it is the most applied; e.g. van de Weerd, 1976; Martin Suárez & Mein, 1991). Measurements are given in mm (L#W).

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Figure 2. Occlusal view of the lower cheek teeth of Allocricetus bursae from Sima de los Huesos: left mandible with M1, M2, M3: SH Clays with human and bear bones (CH&B) T15/16. Bar 1 mm.

Repository The small mammal specimens described are provisionally housed in the Museo Paleontológico de la Universidad de Zaragoza.

Systematic palaeontology Family, Cricetidae Rochebrune, 1883; species, Allocricetus bursae Schaub, 1930; Figure 2. Material and measurements M1: 2·03#1·28; 2·08#1·26; M2: 1·65#1·26; 1·58#1·32; 1·58#1·25; M3: 1·50#1·20; 1·47#1·23; 1·65#1·28; M1: -#1·34; M2: 1·47#1·38. Cricetids appear exclusively in the CH&B layer. Description and discussion The species A. bursae is a well-known cricetid of small size from the Lower and Middle Pleistocene localities of Near East, Central and West-South Europe. It was described for the first time by Schaub (1930) in the early Pleistocene (Nagyhársányhegy phase, early Biharian) locality of Brassó (Rumania). The teeth of A. bursae from Sima de los Huesos are comparable to the A. bursae assemblages from the European upper Middle Pleistocene. There are some peculiarities that characterize A. bursae from this age: The anterolophulid is long and complete in M1, some extant Cricetulus migratorius Pallas, 1773 may have no anterolophulid and, if present, it is shorter. The same occurs in Allocricetus ehiki Schaub, 1930 from the Lower Pleistocene (Hír, 1993b). The mesolophid is present only in M3; in earlier assemblages, the mesolophid may be present in M2 (Hír, 1993a,1994). The posterolophid (or posterior cingulum) is present in M1, M2 and M3. The posterolophid is medium sized, it does not reach the lingual border. In the Middle Pleistocene, A. bursae shows no hypoconid in M1 (Chaline, 1971, 1972) but it is present in M2 as can be seen in the assemblage of Sima de los Huesos (Figure 2). In advanced forms of Allocricetus as A. jesreelicus Bate, 1943, from the Upper Pleistocene of Israel (Tchernov, 1968a,b), the posterior cingulum is less developed and C. migratorius differs from the fossil Allocricetus species in the absence (or reduction) of the posterior cingulum in M1 (Ellerman, 1941). The extant hamster, C. migratorius, the Upper Pleistocene species A. jesreelicus and the Lower Pleistocene species A. ehiki have a very small hypoconulid in M2 or lack it entirely.

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Probably, the Pleistocene species A. bursae is related to the recent C. migratorius living today in SE Europe, Asia Minor and N Asia (Ellerman, 1941; Tchernov, 1968a,b; Macdonald, 1984; Hír, 1989, 1993a, 1994). The extant C. migratorius range from Greece to Chinese Turkestan; and in Israel, exists today in all the Mediterranean regions of the country, mainly in the macchia and wooden macchia regions or in bare fields (Tchernov, 1968a). Schaub (1930) remarked on the lack of differences in the tooth morphology of Allocricetus from Cricetulus, and several authors disputed the validity of the Allocricetus genus (see Sutcliffe & Kowalski, 1976). Nevertheless, both taxa can be distinguished on the basis of the longitudinal measurements of the teeth and toothrows, and the statistical morphological differences (Hír, 1993a,b, 1994). The tooth size is a character commonly used for discriminating Cricetidae species (Freudenthal & Cuenca-Bescós, 1984). The size of A. bursae from Sima de los Huesos (Figures 2–4) is slightly larger than A. bursae from Arago (Chaline, 1971), and as far as the size and morphology of M1, M2, M3 is concerned, it shows closest resemblance with A. bursae correzensis from the French localities La Fage and Orgnac 3 (Chaline, 1972) and Abri Vaufrey II (Marquet, 1989), the Spanish localities Cueva del Agua (López Martínez & Ruiz Bustos, 1977), Gran Dolina (Atapuerca), upper levels TD 10 or between TD 10 and TD 11 (work in prep.). Aspects of the size variation of Allocricetus bursae during the Pleistocene The small hamsters of the genus Allocricetus are well known in several Lower to Middle Pleistocene European sites although the mean size of Allocricetus bursae is not the same at all the localities. Figure 3(a) shows the variation of the size of the first lower molar by means of the L/W ratio. Figure 3(b) shows the localities grouped by ‘‘stages’’. Correlation and chronostratigraphical order is based on the literature of each locality (see below) and the correlation charts or discussions provided by several authors (Cooke, 1984; Nilsson, 1983; Fejfar & Heinrich, 1990; Kolfschoten 1990, 1992). It should be noted in this arrangement of the European localities that the afore-mentioned chronostratigraphical order is not discussed here because the authors usually correlate in terms of presence/absence of a given taxa, and Sima de los Huesos has no index taxa in terms of the European Pleistocene chronostratigraphy where the genus Arvicola is widely discussed (Kolfschoten, 1990, 1992, 1993; Abbassi & Desclaux, 1996). The size of A. bursae from the lower unit or clays which includes the human and bears from Sima de los Huesos were compared with Allocricetus assemblages studied by several authors from European localities where this cricetid is abundant [Figure 3(a, b)], as well as with A. bursae from the upper levels of Gran Dolina site in Atapuerca (Figure 4) and the extant hamster Cricetulus migratorius from Syria and Turkey (Hír, 1993a). The oldest localities with Allocricetus are Osztramos 3 (or Esztramos) and Villány from Hungary, Praetiglian/Tiglian or Villányan (Van der Meulen, 1973; Hír, 1993b). Kamyk from Poland and Varbeshnitsa from Bulgaria are considered Eburonian (equivalent to the Gunz I? or Villányan; Kowalski, 1958, 1960); the cricetid studies were carried out by Fahlbusch (1969) and Popov (1988), respectively. The Cromerian localities with Allocricetus are Bourgade from France (Chaline, 1972) and Kozi Grzbiet from Poland (Pradel, 1988). The Cromerian is correlated with the Biharian by Kretzoi & Vértes (1965) and Van der Meulen (1973). The Biharian locality of Brassó, typical locality of Allocricetus bursae, is not considered because of the scarcity of data. The Elsterian A. bursae was studied by Ruiz Bustos & Michaux (1976) in the Spanish locality Cúllar de Baza I, and by Hír (1989) in the sequence of Tarkö (Hungary), and correlated with the Toringian (Mindel). Holsteinian localities (Mindel/Riss) are Pongor from Hungary (Hír,

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2.2 2.1 2.0 1.9 1.8 1.7

1.5

Kamyk Varbeshnitsa Kozi Grzbiet Cúllar Baza I Tarkö 1 Tarkö 1 2–10 Tarkö 11–12 Tarkö 13–15 Tarkö 16–18 Pongor Aridos 1 Camp de Peyre Abri Vaufrey VIII St. Esteve Janson Abri Vaufrey IV Zamborino Arago Cueva del Agua Orgnac 3 TD10T5 La Fage SH B&H Clays Abri Vaufrey II Grotte Suard La Carigüela Abri Gaudry

1.6

(b) 2.1 2.0 1.9 1.8 1.7

Weichselian

Saalian

Holsteinian

Elsterian

Cromerian

Eburonian

1.6

Figure 3. (a) The size of Allocricetus bursae from Sima de los Huesos [lower layer, Clays with human and bear bones (CH&B) and size trends (length/width of M1) in the Pleistocene Allocricetus bursae. (b) Localities arranged in chronostratigraphical succession as currently known. Data from Fahlbusch (1969), Popov (1993), Hír (1993a), López Martínez (1980), Chaline (1971, 1972), Marquet (1989), Pradel (1988), Ruiz Bustos & García Sánchez (1977), López Martínez & Ruiz Bustos (1977) and Ruiz Bustos & Michaux (1976).

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ml SH

1.2 TD 10 T1

1.3 SH

Width (mm)

1.2 TD 10 T5

1.3 SH 1.2

TD 10 T15

1.3 SH 1.2 TD 10 T17 1.9

2

2.1

Length (mm) Figure 4. Length/width scatter diagrams of Allocricetus bursae from Gran Dolina (level TD 10, samples T1, T5, T15, T17 from top to bottom) and Sima de los Huesos lower unit (Clays with human and bear bones), here labelled SH.

1989), Aridos 1 from Spain (López-Martínez, 1980) and the French localities St Esteve Janson and Camp de Peyre [Chaline (1972) and Marquet (1989), respectively]. The Saalian localities (Riss) with A. bursae are the Arago levels (Chaline, 1971; Cattani et al., 1994), La Fage, Orgnac 3, La Colombière (Chaline, 1972) and Abri Vaufrey (Marquet, 1989) in France and the Spanish localities Solana del Zamborino and Cueva del Agua (López Martínez & Ruiz Bustos, 1977). By the end of the Saalian and the beginning of the Weichselian (Würm), Allocricetus is represented in the Spanish localities Pinilla del Valle (Toni & Molero, 1990) and La Carigüela (Ruiz Bustos & Garcia Sánchez, 1977) in the French localities Grotte Suard, Roc en Pail, La Roche Cotard and Abri Gaudry (Marquet, 1989) and the Polish Raj Cave (Pradel, 1988). Two extant populations of Cricetulus from Krak des Chevaliers (Syria) and Meydan (Turkey) were measured by Hír (1993a).

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Figure 5. Occlusal view of Apodemus sylvaticus. (a) Left mandible with M1 and M2 from the lower layer (CH&B: SRMT1). (b) Right maxilla with M1 and M2 from the upper layer [Dark clays with bat guano (DCBG); SRB bat guano].

When the series of localities is arranged in the established chronological order [Figure 3(a, b)], the trend towards size increase in Allocricetus bursae is not a gradual one as Chaline (1972) remarks. In the upper Middle Pleistocene (La Fage, Sima de los Huesos), they are definitely larger than in localities of earlier age, but in the latest Middle Pleistocene there is a dwarfing (Grotte Suard and La Carigüela), with a minimum at Abri Gaudry. In older localities, in the late Lower Pleistocene-early Middle Pleistocene, differences in size are less outstanding than in the upper Middle Pleistocene [Figure 3(a, b)]. Family, Muridae Thomas, 1896; species, Apodemus sylvaticus (Linnaeus, 1758); Figure 5. Material and measurements CH&B: M1: 1·88#1·28; 2·12#1·37; M2: 1·31#1·14; 1·35#1·20; M3: 1·00#0·90; M1.:1·80#1·13; 1·82#1·05; 2·06#1·19; 1·95#1·13; M2: 1·26#1·14; 1·20#1·10; 1·35#1·26; 1·42#1·19; 1·28#1·16; M3: 0·98#0·93; 1·00#0·90.

      

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DCBG: M1: 1·80#1·20; 1·95#1·43; M2: 1·35#1·19; 1·40#1·29; M1: 1·83#1·10; 1·68#1·04; 1·73#1·08; 1·76#1·07; M2: 1·28#1·10; 1·23#1·08; 1·20#1·07; M3: 1·01#0·98. Description The M1 shows a very strong and high anterocentral cusp (Figure 5). The anteroconid complex is well developed. The anterolingual and anterolabial cusps, the protoconid and metaconid are arranged in an X-shape. In some specimens, the anterolingual and anterolabial cusps are separated by a narrow and deep furrow. Hypoconid and entoconid are arranged in a broad chevron. The posterior cusp (or terminal heel) is low, round shaped and well developed. There are two (in most specimens) to three (scarce) labial accessory cusps. The anterior is the biggest and is round in shape, and the posterior (c1) may be elongated and connected to the hypoconid by a low and narrow ridge. M2 shows the t9 (a postero-lingual accessory cusp) to be well developed, almost identical in size to the t6 (an antero-lingual accessory cusp). Discussion After the work done by Pasquier (1974) and Darviche (1978), the Apodemus species from the Pleistocene and Holocene of Europe are reasonably well known. The research done by these authors gives the possibility of separating the species A. sylvaticus from A. flavicollis Melchior, 1834, which are both very similar in size and morphology. The chief character, the expansion of the t9 on M2, together with the size, separates the species. A. sylvaticus is slightly smaller than A. flavicollis but it shows a bigger t9 on M2. In size and morphology, A. sylvaticus from Sima de los Huesos CH&B layer [Figure 6(a, b)] is close to A. sylvaticus from Cueva del Agua (López Martínez & Ruiz Bustos, 1977), Orgnac 3, Prince Grimaldi and La Grotte du Lazaret de Nice (Pasquier, 1974). The size of the M1 or A. sylvaticus from Westbury sub Mendip Bed 10 (L/W=1:54, Westbury 3; Bishop, 1982) is similar to the size of the M1 of A. sylvaticus from Sima de los Huesos. The specimens from the upper layer (DCBG) are smaller than any of the compared assemblages [Figure 6(a)]; morphologically, they are related to A. sylvaticus by the large t9. The size of A. sylvaticus from Sima de los Huesos was compared with the size of A. sylvaticus remains in owl pellets recovered by the present authors in 1992–93 (hibernating community of Asio otus near the Ebro river, la Alfranca, Zaragoza). Aspects of the size variation of Apodemus sylvaticus during the Pleistocene As with the small hamsters, the mean size of A. sylvaticus is not the same at all the localities. Figure 6(a) shows the variation of the size of the first upper molar by means of the L/W ratio. Figure 6(b) shows the localities grouped by ‘‘stages’’. Correlation and chronostratigraphical order is based on the literature of each locality and the correlation charts or discussions provided by several authors (see discussion in the Allocricetus bursae paragraph). Family, Arvicolidae Gray, 1821; species, Pliomys lenki relictus Bartolomei et al., 1975; Figure 7(a). Description and discussion A single, right M2 from the lower layer (CH&B) shows the roots and a very small amount of crowncementum in the synclines or re-entrant angles. The differentiation of enamel thickness is typical for Pliomys, the cover is slightly thinner at the posterior sides of the anticlines. There are two labial and two lingual anticlines. The triangles have a narrow connection between

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La Alfranca

SIMA HUESOS DCBG

Le Lazaret

SIMA HUESOS CH&B

Prince Grimaldi

Orgnac 3

Cueva de Agua

Les Valérots

St. Esteve Janson

1.4

(b)

1.6

1.5

Holocene

Weichselian

Saalian

Holsteinian

Eburonian

1.4

Figure 6. (a) The size of Apodemus sylvaticus from Sima de los Huesos [lower, Clays with human and bear bones (CH&B); upper, Dark clays with bat guano (DCBG) layers] and size trends (length/width) in Middle Pleistocene to recent Apodemus sylvaticus assemblages. (b) Localities arranged in chronostratigraphical succession as currently known. Data from Pasquier (1974) except for Cueva del Agua (Lopez Martinez & Ruiz Bustos, 1977) and La Alfranca (from pellets of Asio otus).

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Figure 7. (a) Occlusal view of M2 of Pliomys lenki relictus (CH&B: SRMab). (b) Occlusal view of M2 Eliomys quercinus (SRMar). Bar 1 mm.

them. The lingual triangles have rounded tips, and the labial ones are gently pointed. The rounded tips and the enamel thickness points to an individual of old age. P. lenki relictus is a characteristic but not very common rooted arvicolid from the Middle Pleistocene of Europe (Bartolomei et al., 1975). P. lenki with crowncementum on the rentrant angles has been described in Isernia, Italy (Sala, 1983), in La Grotte du Lazaret de Nice, France and Lezetxiki, Spain (Bartolomei et al., 1975) as P. lenki relictus. The presence of crowncementum is interpreted as a trait shown at the end of the evolutionary lineage of this species. Nevertheless, Isernia La Pineta is older than P. lenki assemblages of modern age which lacks this character. Moreover, P. lenki lacking crowncementum is reported from Upper Pleistocene localities in Spain as Cueva Millán (Alvarez et al., 1992). Other Upper Pleistocene localities with P. lenki in Spain are Amalda and Ekain in the North (Sánchez Gon˜i, 1993) and La Carihuela and Cueva Hora in the South (Alvarez et al., 1992). It can be assumed that the Middle Pleistocene is characterized by at least two Pliomys (sub)species, one could add crowncementum in the synclines. Microtinae indet. Three isolated teeth are all the remains of arvicolids that can be identified as microtines by the absence of roots and the presence of crowncementum in the re-entrant angles. Family, Gliridae Thomas, 1897; species, Eliomys quercinus (Linnaeus, 1766); Figure 7(b). Material and measurements CH&B: M2: 1·50#1·64; M2: 1·29#1·53. Description and discussion Two isolated teeth, a right M2 [Figure 7(b)] and a right M2 from the lower layer (CH&B), are the record of the dormouse from Sima de los Huesos. The M2 shows a complete endoloph, and the posterior and anterior centroloph are absent. M2 has a very simple occlusal pattern, the centrolophid is absent and the metalophid, which is only connected to the protoconid, is discontinuous. The size and morphology of E. quercinus from Sima de los Huesos resembles that of E. quercinus helleri from the Middle Pleistocene assemblage Le Lazaret (Chaline, 1972). The Middle Pleistocene orchard dormouse are larger than those from the Upper Pleistocene as Santenay (Chaline, 1972), Cueva Millán (Alvarez et al., 1992) and the living populations

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(Chaline, 1972). The reduction of the size of E. quercinus is shown by Chaline (1972) in the Pleistocene French localities. E. quercinus from Sima de los Huesos is slightly smaller than E. quercinus granatensis (López Martínez & Ruiz Bustos, 1977) from Cueva del Agua and it shows a less complex morphology. Taphonomical remarks All through the Sima de los Huesos lower unit, or clays with macrofossils (CH&B), the small mammal fossil remains are scattered with no concentration either spatially (Figure 1) or vertically through the section. Considering the poorly fossiliferous contents (in small mammal terms), and following Andrews (1990b), the degree of richness provides an indication of the distance the bones are from their source, since the richer areas should be nearer. It can be inferred that the source was far from the actual site. Preservation and colour is similar in both macro- and microfossils, and one can deem that they were deposited under similar conditions and probably at the same time. Digestion of the teeth is almost absent only one microtine specimen from the lower unit shows light to moderate digestion. None of the teeth still in place in the jaws of A. bursae and A. sylvaticus show digestion signs. Breakage is extensive but that could be the damage caused by attrition during the transport of the sediments from one part of the cave to another, and/or during the sieving-washing process. The teeth are well preserved; on average, the roots are complete and the mandibles have the molars and incisor (i.e., Allocricetus bursae in Figure 2). The specimens of A. sylvaticus are well preserved in both levels. There are complete mandibles with the teeth (Figure 5). The amount of skeletal elements is very low and the only elements apart from isolated teeth that are at all abundant are mandibles. The bats are relatively better preserved and represented than the rodents. The good preservation of bats and their large proportion in relation to the rodent remains indicates that bats were accumulated in a place where an hibernating colony was living (Kowalski, 1995). Further transport took them together with other fossil remains. If bats were accumulated in scats or pellets of avian or mammalian predators, the bones should be digested and breakage would be heavier. The authors’ hypothesis is that a large number of bat carcases and some rodent corpses were accumulated somewhere in or near the Sima de los Huesos cave, maybe an upper chamber which lost some of this material into the lower chamber (the Sima de los Huesos is the lowermost known cave from the Atapuerca karst system; Arsuaga et al., 1993), and accumulated together with the sediments containing the humans and macromammals. Few scats or owl pellets from this area could be transported together with the small mammal remains. In the clays with Bat Guano unit, the concentration of small bones is higher, making it possible to name it ‘‘bat earth’’ because bats are the most abundant mammal remains. Murids are not as complete as the bat remains but all mandibles are nearly complete. In general, the small mammal remains from the upper unit give a general impression of completeness and good preservation. The degree of breakage is minor, and the numbers and proportions of the main skeletal elements is higher than in the lower unit. Mandibles and maxilars are complete, even an entire skull, and the long, postcranial elements are preserved with the epiphyses intact. Following the terminology of Andrews (1990a,b), the degree of breakage of the small mammal bones is less in the upper layer than in the lower one. General taphonomical features give the impression that the source of bone was very near during the deposition of the Clays with Bat Guano layer, that is the bats were accumulated in the bottom or very near the cavern where they were living. Similar accumulation of bat bones occurs today in winter (hibernating) colonies of cave bats, the skeletons from summer bat colonies should be dissolved by the guano

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produced by the bats (Kowalski, 1995). In summary, the upper layer of the Sima de los Huesos represents the bottom of a cavern with a bat colony living there during the winter and summer seasons. Rodents could visit the place sporadically during the winter season. The main entry was not far from the bat chamber but it would have been too small to permit the entrance of any vertebrate animal larger than the small mice. The age of Sima de los Huesos From the above taphonomical observations, the authors believe that the small mammal remains from the lower unit of Sima de los Huesos, that is the layer where the humans have been found, are contemporaneous with those of the humans, being accumulated at the same time. However, the exact time of emplacement in the Sima is currently unknown. The age of the rodent fauna will be discussed here. The rodent fauna from the late Middle Pleistocene is typified by the rich assemblages from the French localities La Fage and La Grotte du Lazaret de Nice (Chaline, 1972; Dubar, 1995; Abbassi & Desclaux, 1996) and Gran Dolina levels upper TD 8–TD 11 (Gil & Sesé, 1991; Cuenca-Bescós et al., in prep.) among other European localities. Works by Kolfschoten (1985, 1990, 1992, 1993) show that The Netherlands and Western Germany also have good Middle Pleistocene sequences of mammal faunas. In Great Britain, the Middle Pleistocene faunas are summarized by Sutcliffe & Kowalski (1976) and more recently by Stuart (1982). Localities of the Middle Pleistocene from Hungary, as Tarkö among others, are revised by Jánossy (1986). The Rumanian Middle Pleistocene is summarized by Terzea (1993). Some of the characteristic rodents of this age are Arvicola, Allocricetus bursae, Apodemus sylvaticus, Pliomys lenki and Eliomys quercinus. In Spain, A. bursae and P. lenki are characteristic elements of the late Middle Pleistocene rodent assemblages (Agustí & Moyà-Solà, 1992). The paleontological record of Allocricetus bursae ranges from the early Lower Pleistocene to the late Middle Pleistocene in Europe and Israel. Remains of Apodemus sylvaticus are common from the early Middle Pleistocene onwards in Europe, and the assemblages of the late Middle Pleistocene are larger than in any other age (Figure 6). Pliomys lenki relictus with crowncementum is known in the Middle Pleistocene localities of Isernia, Le Lazaret and Lezetxiki VI–IV. Recent analysis of palynological and radiometrical data from Lezetxiki gives an older age for the lower levels than in previous works (Sánchez Gon˜i, 1993 and references therein). La Grotte du Lazaret de Nice and the lower levels of Lezetxiki are correlated with the oxygen isotopic stage 5 (Dubar, 1995; Sánchez Gon˜i, 1993). The upper levels (TD 8b–TD 11) of Gran Dolina most probably correlate with Sima de los Huesos lower unit, and after Cattani et al. (1994), those levels correspond to the oxygen isotopic stages 11–8. Evolution (morphological change within species) Although many mammal species responded to Pleistocene climatic change by leaving a given area, and the LAD, FAD of a given species in an area is the most useful tool for correlation, many other species stayed where they were. One example is the hamster Allocricetus bursae, which remained in southern-central Europe throughout the Lower and Middle Pleistocene. Allocricetus bursae and Apodemus sylvaticus show a size increase at the end of the Middle Pleistocene [Figures 3(a, b) and 6(a, b)] but, in general, show changes during the Pleistocene (Kurtén, 1960; Pasquier, 1974; Michaux & Pasquier, 1974; this work, Figures 3 and 6). When the series of localities is arranged in the established chronological order (see discussions above), either following the correlation proposed by the authors (see legend of figures) or the synthesis of authors as Nilsson (1983), Cooke (1984), Klein (1989), Agustí & Moyà-Solà (1992) and

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Stringer & Gamble (1993), the picture of size evolution seems to be a series of oscillations. There is a relative maximum in the size of the assemblages of the species Allocricetus bursae, Apodemus sylvaticus and probably Eliomys quercinus at the end of the Middle Pleistocene. The size of those species from Sima de los Huesos CH&B layer holds for this maximum [Figures 3(b) and 6(b)]. The maximum size of Allocricetus bursae from Sima de los Huesos and other localities of Figure 3 (see discussion above) could be related to the Saalian cold phase in the regional climatic stratigraphy of Europe. Following Kurtén (1960), the size oscillations in mammals may be due to climatic changes, and their true significance was made evident by the study of the size gradients in the living relatives (Cricetus cricetus) of the fossil forms by the author; the recent hamsters show the existence of a north-south cline, with the southern forms smaller than the northern ones. After Kurtén (1960), the existence of a west-east cline is suggested by the somewhat smaller size of the Belgian specimens compared with the German. Also, Barnosky (1994) has demonstrated that Microtus pennsylvanicus Ord, 1815, the meadow vole from North America, responded to the climatic perturbations of its environment by apparently increasing its length with the deterioration of climate conditions. Thus, the correlation of the size increase of Allocricetus and the cold increase during the Saalian seems probable. Moreover, Eliomys quercinus also shows increasing size at the end of the Middle Pleistocene in localities such as Cueva del Agua, and in Sima de los Huesos, the size is similar to that in Cueva del Agua. The size of the extant forms shows dwarfing when compared with the Middle Pleistocene assemblages. Conclusions From these data, it can be concluded that the human locality of Sima de los Huesos (CH&B layer), by its rodent assemblage, could be Saalian in age. It is somewhat younger than Arago (Tautavel, France), Cueva del Agua (Sierra Alfaguara, Granada, Spain) and Orgnac 3 (France), similar in age to the upper levels of Gran Dolina (Atapuerca, Spain) and La Fage (Corrèze, France), and somewhat older than the Lezetxiki cave in the north of Spain and Le Lazaret (Nice, France). Acknowledgements The excavations are supported by the Junta de Castilla y León and the Research Project by the Ministerio de Educación y Ciencia (DGICYT, Project No. PB93-0066-C03). References Abbassi, M. & Desclaux, E. (1996). Arvicola Lacepede, 1799 (Rodentia, Mammalia) de quatre sequences du sud-est de la France et de Ligurie datant de la fin du Pleistocene Moyen et du debut du Pleistocene Superieur. Quaternaire 7, 1, 29–37. Alvarez, M. T., Morales, A. & Sesé, C. (1992). Mamíferos del yacimiento del Pleistoceno superior de Cueva Millan (Burgos, Espan˜a). Estudios geol. 48, 193–204. Aguirre, E. (1995). Atepuerce (Burgos, España): en contributión a las Ciencias del Cuaternerio. Reviste Españole de Paleontologíe 10, 58–82. Agustí, J. & Moyà-Solà, S. (1992). Mammalian dispersal events in the Spanish Pleistocene. Courier Forschungsinstitut Senckenberg 153, 69–77. Andrews, P. (1990a). Small mammal taphonomy. In European Neogene Mammal Chronology (E. H. Lindsay et al., Eds), 487–494. Andrews, P. (1990b). Owls, Caves and Fossils: predation, preservation and accumulation of small mammal bones in caves, with analysis of the Pleistocene cave faunas from Westbury-sub-Mendip, Somerset, UK. British Museum (Natural History), NHM, London.

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