The herpetofauna fossil remains used for this study consist of disarticulated bone fragments collected by water-screening during J.-M. Cordy's sampling of the sequence at the entrance of the caves (squares F7 and C4) and stored in the collections of the Scladina Cave Archaeological Centre (Sclayn, Belgium). The studied sample included some 123 fragments, representing eight different taxa (Table 1). The systematic nomenclature used basically follows Speybroeck et al. (2010) and Lescure and De Massary, 2012. Osteological nomenclature follows Estes (1981) and Sanchiz (1998) for amphibians, Rauscher (1992) for lizards and Szyndlar, 1984 and Szyndlar, 1991 for snakes. Measurements were made with scaled drawings using a binocular microscope with a camera lucida.

The studied material comes from the lower half of the Scladina cave sequence (layers I, V ochre, VB and VI/VIa) superimposing the top of the Sous-Saint-Paul cave sequence (layers VII to X). The sedimentary filling of these two caves is separated by a major hiatus (Haesaerts, 1992, Pirson, 2007, Pirson et al., 2008 and Pirson et al., 2014).

The stratigraphic sequence of Sous-Saint-Paul cave (Haesaerts, 1992 and Otte et al., 1983) has not recently been reviewed. A chronostratigraphic interpretation of it (Pirson, 2007, Pirson et al., 2008 and Pirson et al., 2014) suggests that layers VII to X probably date back to the end of the Middle Pleistocene [Marine Isotope Stage (MIS) 6–7, i.e. between 300 and 130 ka].

A detailed description of the geology of the layers of Scladina cave can be found in Pirson (2007) and Pirson et al. (2008). Although the stratigraphic sequence now appears considerably more complex than previously described (see Pirson, 2007, for historiographical details), we have here decided to maintain the old nomenclature associated with the works of J.-M. Cordy (Bastin et al., 1986 and Cordy, 1992). The reason for this is that the stratigraphic reappraisal was mainly undertaken inside the cave and at the present stage of research cannot be accurately correlated with the sector investigated on the terrace by J.-M. Cordy. However, a general correlation with the main lithostratigraphic units of the new stratigraphic record can be established. The chronostratigraphic interpretation of layers V ocre to VI is MIS 5 (i.e. 130–74 ka) and of layer I is MIS 3 (i.e. 60–24 ka; Pirson, 2007, Pirson et al., 2008 and Pirson et al., 2014).

AMPHIBIA Linnaeus, 1758

Amphibians are represented by 87 remains (70.7% of all the material) and have been referred to four taxa belonging to caudates and anurans.

CAUDATA Scopoli, 1777

SALAMANDRIDAE Goldfuss, 1820

Salamandra salamandra (Linnaeus, 1758)

(Fig. 1)

Referred material: one postsacral vertebra.

Description: The vertebra is characterized by its rather large size (total length 7.7 mm between pre- and post-zygapophyses). It is assigned to the Salamandra salamandra group on the basis of the following characters: opisthocoelous; neural arch is dorsoventrally flattened with a deeply concave anterior margin, at the level of the middle part of the pre-zygapophyseal articular facets and a well-developed medial notch in its posterior margin; long, narrow and low neural spine, well-developed in the middle part of the neural arch only (Estes, 1981, Ratnikov and Litvinchuk, 2007 and Sanchíz and Mlynarski, 1979). The presence of only one slightly dorsoventrally flattened rib-bearer is consistent with a postsacral position. In ventral view, no subcentral foramen is visible. Various southern former sub-species within the S. salamandra group have recently been elevated at species rank: S. atra (from the French Alps to Albany), S. corsica (Isle of Corsica, France), S. lanzai (in the Alps between France and Italy), and S. longirostris (southernmost Iberian Peninsula) (Speybroeck et al., 2010). No osteological descriptions of these new species have been yet done; consequently the fossil remains from Scladina are attributed on the basis of the geographical distribution of S. salamandra, the only species of that group currently living in northern Europe.

ANURA Duméril, 1805

Anuran remains are common in the layers of Scladina cave (86 remains). Among them, some 7 fossil remains (angulosplenial, fragments of vertebrae, fibulare and carpal) have been referred only as anurans indeterminate.

Three families are present: Pelodytidae, Bufonidae and Ranidae.

PELODYTIDAE Bonaparte, 1850

Pelodytes punctatus (Daudin, 1802)

(Fig. 2)

Referred material: one humerus and one ilium.

Description: Humerus. The humerus is small and presents a rather robust and straight shaft in ventral view. The condyle is more or less spherical and slightly outwardly displaced in relation to the main axis of the diaphysis. Within the genus Pelodytes, the robustness of this element permits attribution to P. punctatus (Sanchíz et al., 2002).

Ilium. The ilium is fragmentary and consists of the middle part of this element: the anteriormost part and the acetabulum are missing. As in the genus Pelodytes, it lacks a dorsal ilial crest (crista dorsalis) and a dorsal prominence (tuber superior). The ilial shaft (pars cylindriformis) is well curved.

BUFONIDAE Gray, 1825

Bufo bufo (Linnaeus, 1758)

(Fig. 2)

Referred material: one pterygoid, one squamosal, 12 vertebrae, one sacrum, three urostyles, one scapula, one clavicle, one coracoid, four humeri, six radio-ulna, seven ilia, two femurs, four tibio-fibula, two fibulare and two carpals.

Description: The osteology of Bufo has been discussed in detail by several authors (e.g., Bailon, 1999, Blain et al., 2010, Böhme, 1977, Holman, 1998, Ratnikov, 2001 and Sanchíz, 1977). The following discussion is limited to the most representative elements of our assemblage.

Humerus. Humeri have a shaft that is rectilinear and more or less curved in females; the condyle is laterally (radially) displaced. The humerus in Bufo bufo and Bufo viridis generally has a straighter diaphysis than in Bufo calamita. In male B. bufo, the medial crest (crista medialis) is flat and restricted to the distal part of the epiphysis, whereas in B. viridis this crest is long and dorsally curved.

Ilium. The presence of a dorsal prominence (tuber superior) and absence of an ilial crest (crista dorsalis) are characteristic of the genus Bufo. In B. bufo, the dorsal prominence is low and rounded, whereas in B. viridis, it is slightly higher and frequently provided with a secondary anterior tubercle and in B. calamita, it is higher and pointed. Moreover, in B. viridis, a deep pit (fossa preacetabularis) is present, and in B. calamita, a strongly developed ventrolateral crest (calamita blade or calamita ridge) is generally visible on the anterior half of the shaft.

Femur. The femur is a relatively long element and is robust and sigmoid. In B. bufo it usually has a low ridge (deltoid crest) that is proximally flattened and forms a triangle in medial view whereas this ridge is higher, sharper and slightly bifurcated in B. viridis and higher, narrow and straight in B. calamita (Bailon, 1999).

The other elements, which are often fragmentary, show the general morphology of the genus Bufo. Attribution to B. bufo is mainly based on their robustness rather than on their size; fossils of B. bufo in Scladina do not show the particularly large size (especially for females) of the southern representatives of the species.

RANIDAE Rafinesque-Schmaltz, 1814

Rana temporaria Linnaeus, 1758

(Fig. 2)

Referred material: one exoccipital, one atlas, one coracoid, three ilia, one tibio-fibula, three fibulare and three carpals.

Description: Ilium. Like in European ranids, ilia are characterized by the presence of an ilial crest on the shaft, a short ischial process (pars ascendens), a well-developed tuber superior and a posteromedial surface that is smooth and without any interilial sulcus (Bailon, 1999). The ilial crest in brown frogs (genus Rana) is lower and not as vertical as in green frogs (genus Pelophylax) and the corpus ossis ilii is slender (if observed on the juncture; d/t, sensu Gleed-Owen, 2000). In brown frogs, the d/t value lies between 2.75 and 4.00 whereas in green frogs d/t is between 2.12 and 2.88 (Gleed-Owen, 2000). The fossil ilia from Scladina have d/t values between 3.10 and 3.87. Within the genus Rana, attribution at the species level is rather difficult, but factors such as size or robustness may suggest an assignation to Rana temporaria. Also the height of the ilial crest is generally lower in R. temporaria whereas it is higher in other western European species (Bailon, 1999, Esteban and Sanchíz, 1985, Esteban and Sanchíz, 1991, Gleed-Owen, 1998 and Gleed-Owen, 2000; and personal observations).

Tibio-fibula. This element is very elongated, with relatively short longitudinal sulci at the distal and proximal ends. The diaphysis at the level of the foramen nutricium seems to be more slender in brown frogs than in green frogs.

Other elements have a size and certain slenderness that match with an attribution to R. temporaria. The exoccipital is not fused with the prootic, as is the case in ranids as opposed to bufonids (Bailon, 1999).

REPTILIA Laurenti, 1768

Non-avian Reptilia are represented in Scladina by lacertid and anguid lizards and ophidians.

Altogether, they only represent some 36 remains (29.3% of all the material) and have been referred to four taxa.

“Lacertilians”

LACERTIDAE Batsch, 1788

Lacerta cf. agilis Linnaeus, 1758

(Fig. 3)

Referred material: one dentary.

Description: A single dentary is present in layer I of Scladina cave. It possesses the morphological characteristics of the Lacertidae, bearing pleurodont, isodont, cylindrical and mono- or bicuspid teeth (most of the apices are smooth) and with a Meckelian sulcus open along its entire length. The posteriormost part of the element is broken. The corpus of the bone seems to be rather short and robust (total length = 7.5 mm; maximum height = 2.83 mm). Seventeen tooth positions have been preserved. No labial foramen is visible in lateral view; they are probably hidden by sediments. The element is cautiously attributed to Lacerta agilis on the basis of the robustness of the bone as well as its size (probably equal or superior to 10 mm for the complete dentary). The dentaries of Podarcis muralis and Zootoca vivipara are generally more slender and smaller, and those of L. gr. viridis/bilineata and Timon lepidus are more robust (Rauscher, 1992).

ANGUIDAE Gray, 1825

Anguis fragilis Linnaeus, 1758

(Fig. 3)

Referred material: one cervical vertebra, eight trunk vertebrae, eight caudal vertebrae and one osteoderm.

Description: Vertebrae. All the vertebrae are small (centrum length < 3 mm) and are procoelous with the condyle and cotyle dorsoventrally flattened. In lateral view, the neural spine is generally long, moderately high and, when entire, it forms an interzygapophyseal point, the posterior part of which overlies the posterior edge of the neural arch. In ventral view, the centrum is generally longer than wide and possesses a flat ventral surface and two lateral margins parallel almost their entire length. The lateral foramina are not always visible but are generally small and located in the anterior half of the centrum.

The single cervical vertebra is rather short and robust, and its centrum presents the base of a posteroventrally directed hypapophysis. Of the eight caudal vertebrae, five correspond to the small anterior part of a caudal vertebra broken at the level of the autotomy suture. Three caudal vertebrae are sub-complete, more elongated than the trunk and cervical vertebrae, and show the base of two haemapophyses fused in the posterior half of their centrum and of flattened transverse processes in the anterior part of the centrum.

Osteoderm. A single left laterodorsal osteoderm is represented as a fossil in Scladina cave. It is small (maximum length = 3.1 mm) and has a somewhat semicircular shape. The anterior edge is thicker and smooth, and the posterior part of the external surface is rough and consists of a radiating network of channels and intervening ridges. The absence of a longitudinal carina and the small size of the element is consistent with attribution to A. fragilis. Osteoderms of the genus Dopasia (sensu Augé, 2005), sometimes referred as Ophisaurus (sensu Klembara, 2014) and Pseudopus are generally larger and their mediodorsal osteoderms, but not the lateral and medioventral ones, bear a longitudinal carina on the posterior part (Hoffstetter, 1962 and Rauscher, 1992). Ornamentation in Pseudopus is generally more pronounced (Augé, 2003).

SERPENTES Linnaeus, 1758

Only 17 snake remains (13.8% of all the material) have been found in Scladina cave. These are mainly represented by vertebrae. Members of the families Colubridae and Viperidae have been identified.

COLUBRIDAE Oppel, 1811

Zamenis longissimus (Laurenti, 1768)

(Fig. 4)

Referred material: four trunk vertebrae.

Description: The fossil trunk vertebrae attain a relatively large size (centrum length between 5.9 and 4.0 mm, sensu Szyndlar, 1984) and do not bear a hypapophysis on the centrum, as in “colubrine” snakes. Zamenis longissimus vertebrae are characterized by a deep and rounded haemal keel that is spatulate at the caudal end. The pre-zygapophyseal processes are relatively short and show a rounded tip (but slender and pointed in the smallest specimen; Bailon, 1991 and Szyndlar, 1984). As is usual in large specimens, the zygosphene is generally straight anteriorly (Szyndlar, 1991). No comparisons have been made with the recently elevated at species rank Z. lineatus (formerly included with Z. longissimus), but this snake has been disregarded on the basis of its geographical distribution restricted to southern Italy and Sicily (Razzetti and Zanghellini, 2006).

VIPERIDAE Oppel, 1811

Vipera cf. berus (Linnaeus, 1758)

(Fig. 4)

Referred material: four trunk vertebrae.

Description: The trunk vertebrae show the typical characteristics of the family: presence of a straight and distally pointed hypapophysis; neural arch dorsoventrally flattened; centrum convex in transverse section and not well-marked lateral margins; developed condyle and cotyle; and upwardly inclined articular surface of the zygapophyses. Vertebral morphology permits two groups to be differentiated within the European vipers: the “Vipera aspis complex” and the “Vipera berus complex”. Even if partially broken, the neural spine of the trunk vertebrae is very low and the hypapophysis is sigmoid-shaped with an obtuse apex like in the “V. berus complex” (Szyndlar, 1984). European members of the “V. berus complex” (V. berus, Vipera ursinii and Vipera seoanei) display homogenous vertebra morphology and are hardly distinguishable from one another (Szyndlar, 1984 and Szyndlar and Rage, 1999). Nevertheless, the morphology of the fossil vertebrae fits well with V. berus, the only adder currently present in northern Europe.

SERPENTES indet.

Referred material: one cervical vertebra, four trunk vertebrae, one caudal vertebra and four ribs.

All the remains without significant characters and clearly referable to the above-identified taxa or with juvenile characters have been referred to as Serpentes indeterminate.

The Scladina and Sous-Saint-Paul caves assemblage provides a good opportunity to improve our understanding of the Belgian herpetofauna at the end of the Middle Pleistocene and in the Late Pleistocene. On the whole, four taxa of amphibians and four of reptiles have been identified: their presence in each sampled layer is summarized in Table 1. Scladina cave thus represents the first citation in the Belgian fossil record for the amphibian S. salamandra, and also the first fossil mention in the Pleistocene of Belgium, for L. cf. agilis, Anguis fragilis, Z. longissimus and V. cf. berus. Scladina and Sous-Saint-Paul caves represent the first citation in the Belgian fossil record for P. punctatus. Interestingly, Scladina (layer V ocre, MIS 5) also represents one of the northernmost fossil mentions for the Fire Salamander (S. salamandra) although it lies within its current distribution in Europe. Moreover, the probable presence of the European Adder (V. berus) in Scladina (layers VB and VI-VIa, MIS 5) is also noticeable because today this snake is infrequent and classified as endangered in Belgium, probably due to anthropic pressure (Wallonie, 2010 and Ursenbacher, 2010).

The main peculiarity of the assemblage is the coexistence of taxa still living in the area (S. salamandra, B. bufo, R. temporaria and A. fragilis) with others that today have a southern and/or western distribution, such as the Parsley Frog (P. punctatus) and the Aesculapian Snake (Z. longissimus).

P. punctatus today ranges from Spain up to the North of France, including France, Spain, Portugal and a small part of northwestern Italy (Piedmont and Liguria; Gasc et al., 1997; Duguet and Melki, 2003). In the northeastern part of its modern range, P. punctatus curiously does not cross the border between France and Belgium, following the political frontier exactly. In the fossil record, outside its current range Pelodytes sp. is known from the Middle Pleistocene of Kozi Grzbiet (Poland; Sanchíz and Szyndlar, 1984), and P. punctatus is recorded from the Middle Pleistocene of Steinbruch Schmidt (Stuttgart, southwestern Germany; Böttcher, 1994) and from the Middle Pleistocene (MIS 13, i.e. 528 ka) of Westbury cave (Units 11–15; Somerset, England; Gleed-Owen, 1998, Gleed-Owen, 1999 and Holman, 1998). Its presence in layers Vb (MIS 5) and VII (probably MIS 6/7) of Scladina cave thus suggests a more expanded range to the northeast of its modern distribution during the Late Middle and Early Late Pleistocene (Fig. 5).

The continuous area of Z. longissimus covers most of France except the North (about up to the latitude of Paris), the Spanish Pyrenees and the eastern part of the Spanish north coast, Italy (except the South), all of the Balkan peninsula down to Greece and Asia Minor, and parts of central and eastern Europe up to about the 49th parallel (Gasc et al., 1997; Naulleau, 2010). Further, there are (or were in historical times) a number of isolated populations north to modern northern range limit: in western Germany (Schlangenbad, Hirschhorn and Burghausen), Switzerland (Lorrach/Basel), the Northwest of the Czech Republic (Karlovy Vary) and South Poland (Zloty potok, Zamojszczynza, Zarzecze, Powroznik and Bieszczady; Musilová et al., 2007; Fig. 6). The northernmost historical occurrence (18th and 19th centuries) was in Vordingborg (Denmark; Boulenger, 1913 and Hvass, 1942). Although some authors (e.g., Laughlin, 1962) have hypothesized that parts of the geographical distribution of the species may be the result of the intentional keeping and subsequent release of these snakes by Romans from the temples of Asclepius, the classical god of medicine, the fossil evidence shows that this snake was present north of its current distribution in Europe during the Pleistocene interglacials and the Holocene (Böhme, 2000, Gleed-Owen, 1998, Gleed-Owen, 1999, Holman, 1998, Ivanov, 2007 and Szyndlar, 1984).

During the Pleistocene, Z. longissimus was present in England during the Middle Pleistocene interglacials in Barnham (Norfolk; MIS 11, i.e. 427 ka), Beeches Pit (Suffolk; MIS 11), and Cudmore Grove (Essex; MIS 9, i.e. 334 ka; Gleed-Owen, 1998, Gleed-Owen, 1999 and Holman, 1998). In Germany, it was present during the Middle Pleistocene (Weimar-Ehringsdorf, Gamsenberg and Stuttgart-Bad Cannstatt), at numerous early Late Pleistocene sites often attributed to the Eemian stage (MIS 5e, i.e. 130–115 ka; van Kolfschoten, 2000), such as Schönfeld-Calau (Brandenburg), Lobsing (Bavaria), Taubach (Thuringia), Burgtonna (Thuringia), Neumark-Nord (Saxony-Anhalt), etc., and in one layer, probably MIS 4 in age (i.e. 74 to 60 ka), from Gamsenberg (Thuringia; Böhme, 2000 and Holman, 1998). In central Europe, Z. longissimus has been reported from the Early Pleistocene of Ivanovce (Slovakia) and the Middle Pleistocene of Stránská Skála Hill, the Mladeč caves and Za Hájovnou cave (all in Moravia; Ivanov, 2007). Finally, in Poland it is represented during the Early Pleistocene (Kadzielnia, Zalesiaki B, Kamyk and the Zabia cave), the late Early or early Middle Pleistocene (Zalesiaki A), the Middle Pleistocene (around 500 ka, Kozi Grzbiet), the early Late Pleistocene (Eemian, MIS 5e?; Rzasnik and Wierzbica I) and the Late Pleistocene (MIS 3, Weichselian) (the Zamkova Dolna cave; Szyndlar, 1984).

All this suggests that the range of Z. longissimus repeatedly contracted and then expanded again over the course of the Pleistocene and Holocene (Musilová, 2011, Musilová et al., 2007 and Musilová et al., 2010), very probably in relation with the alternating climatic conditions during the glacial/interglacial cycles. As a consequence, the occurrence of Z. longissimus in Scladina cave (layer V ocre, MIS 5) is in accordance with previous fossil mentions of the species to the north of its current distribution in northern Europe during the early Late Pleistocene (in Germany and Poland, though neither in England nor the Czech Republic), documenting for the first time the occurrence of this snake in Belgium (Fig. 6).

Together, the taxa represented in layers V ocre to VI (MIS 5, Late Pleistocene) fit well with a variety of climatic conditions, maybe warmer conditions than at present in the case of layer V ocre. These species reflect multiple environments including a slow-water stream within a forest area and humid meadows. These various environments may have formed a mosaic on the landscape or been correlated with climatic fluctuations during MIS 5. The Fire Salamander (S. salamandra) lives in hilly areas in European forests. It prefers deciduous forests, since it hides in fallen leaves and around mossy tree trunks. It needs small brooks or ponds with clean water in its habitat for the development of its larvae. The Common Toad (B. bufo) is also found largely in forested areas, especially in wet locations with dense herbaceous vegetation. The Aesculapian Snake (Z. longissimus) prefers warm, moderately humid, forested habitats with proper insolation and varied but not sparse vegetation that provides sufficient variation in local microclimates. It generally avoids open environments. Other taxa, such as the Slow Worm (A. fragilis) and the Common Frog (R. temporaria), may be found in more open environments, such as humid meadows and forest edges. The Parsley Frog (P. punctatus) is found in open or semi-open, even arid landscapes, and the common Adder (V. berus) is found in a variety of habitats, generally dry, cool or humid and with sparse vegetation: wastelands, heathland and gorse and forest edges or scrubby environments. Z. longissimus is the most thermophilous element from the faunal list, and taking into account its modern distribution in Europe, it suggests that temperatures may have been 1 to 2 °C higher than at present in southern Belgium during the formation of layer V ocre.