Quaternaire, Hors-série, (4), 2011, p. 107-116
NEW INSIGHTS ON THE CAVE BEAR POPULATION FROM THE URŞILOR CAVE, ROMANIA n Marius ROBU 1, Alexandru PETCULESCU 1, Cristian PANAIOTU 2, Doris DÖPPES 3, Vlaicu MARIUS 1, Virgil DRAGUŞIN 1, 5, Marius KENESZ 4, Oana Teodora MOLDOVAN 6 and Silviu CONSTANTIN 1, *
ABSTRACT The first two palaeontological excavation campaigns held in 2010 at the Urşilor Cave, Bihor Mountains, Romania brought new information concerning the cave occupation by Ursus spelaeus during the Upper Pleistocene. The excavation is located in the Lower Passageway (Scientific Reserve) and extends over 7 m2 with the lowest point reached during the campaigns at ~125 cm below surface. The overwhelming majority of the fossil material extracted belongs to the cave bear of all age categories. The skeletal elements found in anatomical connection, the analysis of the long bones orientation, and their relatively good preservation indicate that the bones were deposited under a low-energy hydraulic regime and subsequently covered by lacustrine sediments during at least three flooding episodes. The morphodynamic analysis of the fourth cave bear premolars from the uppermost three layers indicates an MIS 3 age. The P4 index however comes in disagreement with the K-index value for the 4th metatarsal which indicates a low evolutionary level for the cave bear population from Urşilor cave. Key-words: Ursus spelaeus, taphonomy, biochronological estimation, magnetic susceptibility, Upper Pleistocene, Urşilor Cave, Romania.
RÉSUMÉ NOUVELLES DONNÉES SUR LES OURS DES CAVERNES D’URŞILOR CAVE, ROUMANIE Les deux premières campagnes de fouilles paléontologiques, qui ont eu lieu en 2010, dans la Grotte Urşilor, Monts de Bihor, Roumanie, ont apporté de nouvelles données concernant l‘occupation de la grotte par Ursus spelaeus pendant le Pléistocène supérieur. La fouille est située dans la Galerie Inférieure (Réserve Scientifique) et s’étend sur 7 m2. Le point le plus bas atteint pendant les campagnes est à 125 cm en-dessous de la surface. L’écrasante majorité des fossiles récoltés appartient à l’ours des cavernes appartenant à toutes les catégories d’âge. Les éléments de squelettes trouvés en connexion anatomique, l’analyse de l’orientation des os longs, le degré de conservation des os indiquent que le niveau ossifère a été lentement recouvert de sédiments lacustres pendant au moins trois épisodes d’inondation. L’analyse morphodynamique des quatrièmes prémolaires d’ours des cavernes provenant des trois premières couches indique le MIS 3. L’indice pour la P4 est, cependant en désaccord avec la valeur K-indice du quatrième métatarsien d’ours des cavernes, qui indique un faible niveau d’évolution de la population d’ours des cavernes de la Grotte Urşilor. Mots-clés : Ursus spelaeus, taphonomie, susceptibilité magnétique, estimation biochronologique, Pléistocène supérieur, Grotte Urşilor, Roumanie.
1 - INTRODUCTION Urşilor Cave (Peştera Urşilor = Bears Cave) in Bihor Mountains, North-Western Romania is an important cave bear site in South-Eastern Europe. Its reputation owes to the large number of cave bear remains as well as to cave bear activity traces such as scratch marks, footprints and claw marks, hair imprints, bear nests, and polished rocks (=Bärenschliffe).
The first excavation campaigns at Urşilor Cave were carried out in the late 1970s and early 1980s by Terzea (1978) and Jurcsak et al. (1981) in test-pits located within the Bones Passage (fig. 1), close to the actual entrance of the cave. A rich Würmian and Holocene fauna was found both within the sediment and on the cave floor: Talpa europea Linnaeus 1758, Glis glis (Linnaeus, 1766), Apodemus sylvaticus (Linnaeus, 1758), Clethrionomys glareolus Schreber, 1780, Arvicola terrestris Linnaeus,
“Emil Racoviţă” Institute of Speleology, 13 Septembrie 13, Bucharest, Romania Bucharest University, Faculty of Geology and Geophysics, N. Bălcescu 1, Bucharest, Romania. Reiss-Engelhorn-Museen, Zeughaus, C 5, 68159 Mannheim, Germany. 4 “Babes-Bolyai” University, Faculty of Geography, Mihail Kogalniceanu 1, Cluj-Napoca, Romania. 5 “Babes-Bolyai” University, Faculty of Biology and Geology, Gheorghe Bilaşcu 44, Cluj-Napoca, Romania. 6 “Emil Racoviţă” Institute of Speleology, Cluj Branch, Clinicilor 5, Cluj-Napoca, Romania. * Corresponding author; [email protected]
1 2 3
Manuscrit reçu le 06/12/2010, accepté le 01/06/2011
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108 1758, Microtus arvalis (Pallas, 1778), M. agrestis (Linnaeus, 1761), M. oeconomus (Pallas, 1776), Chionomys nivalis (Martins, 1842), Chiroptera representatives, Canis lupus Linnaeus, 1758, Vulpes vulpes (Linnaeus, 1758), Crocuta crocuta spelaea (Goldfuss, 1823), Panthera leo spelaea Goldfuss, 1810, and Ursus spelaeus Rosenmüller, 1794. From the analysis of the stratigraphy, the faunal and microfaunal remains in the test-pits, Terzea (1978) and Jurcsak et al. (1981) described a succession of four climate fluctuations all assigned to the Würmian. From the bottom to the surface, the deposits were considered to record two oscillations from a temperate climate to a much colder and humid one. Over time, Urşilor Cave was the subject of several studies focusing on palaeontology (Terzea, 1978, 1989; Jurcsak et al., 1981, Diedrich et al., 2008; 2009; Robu et al., 2009a, 2009b), geomorphology, tectonics and hidrology (Vălenaş, 1979), sedimentology (Hadnagy, 1977) and paleoclimate reconstructions (Onac et al., 2002). However, until 2009 no systematic excavations were carried out within the so-called Scientific Reserve (the Lower Passageway) (fig. 1), where significant cave bear remains and their activity traces were documented. This paper presents the results of a new excavation started in 2010 and integrating a multidisciplinary approach to the study of the cave bear accumulation and cave evolution within the paleoenvironmental context of the Late Pleistocene. In Romania, such complex
approaches in karst environments were applied for the sites of Peştera cu Oase (Trinkaus et al., 2005; Rougier et al., 2007; Zilhao et al., 2007; Quilès et al., 2006; Richards et al., 2008; Petrea et al., 2006) and Cioclovina Uscată Cave (Häuselmann et al., 2010, Harvati et al., 2007, Petculescu et al., 2010).
2 - MATERIALS AND METHODS 2.1 - THE SITE Urşilor Cave is located at the geomorphological contact between the Bihor Mountains and the Beiuş Depression (North-Western Romania, fig. 1), at 428 meters a.s.l. The cave is carved in the Upper Jurassic re-crystallized limestones and includes at least two underground karstification levels. The upper level, hydrologically inactive, is a showcave and the lower, hydrologically active, is protected as a Scientific Reserve. Both cave levels include an important and complex settlement of cave bears including assemblages, skeletons in anatomical connection and palaeoichnological traces (footprints, scratches, hibernation nests, fur traces, and polished rocks). The small underground stream (~3-5 l/s in average) flows along the main passage in the Scientific Reserve to sink at the base of a 15 m-high wall in the Excavation Chamber. From here on, it flows through inaccessible
Fig. 1: Location and map of the Urşilor Cave (redrawn after Rusu & Racoviţă, 1981), with a detailed survey and long section of the Excavation Chamber. Fig. 1 : Localisation et carte de la Grotte Urşilor (redessiné d’après Rusu & Racoviţă, 1981) avec le plan de détail et le profil longitudinal de la Salle des Fouilles.
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109 passages underneath the touristic level to reappear in the Huda de la Chişcău resurgence cave. The morphology of the cave at the sinking point suggests that the drainage may have been set off by rock collapses along a local tectonic line. The collapses should have dammed the underground stream, at least at high water levels, leading to the formation of a series of dam-lakes upstream. A persistent clay-mark level, which may be noticed on passage walls in the Excavation Chamber and the passages upstream at heights up to ~7 m, supports this hypothesis. In the Excavation Chamber, the floor consists of an accumulation of sediments and fossil remains with a thickness of ~1.5-2 meters. 2.2 - THE METHODS
The excavation site is located at the base of the 15-m wall that separates the lower and upper levels of the cave. Currently, the excavation area has almost 7 m2 and consists of seven quadrants, of 1 m2 each (fig. 1). Quadrants A1, B1 and C1 are disposed longitudinally while D1 through D4 are disposed transversally with respect to the main passageway. The area is no longer influenced by the river activity, although small river channels displaying angular pebbles were surveyed at depths of ~ 90 cm. In the excavation, the fossil bones were recorded, photographed and surveyed with respect to the excavation grid and using a 10 × 10 cm subgrid. A zero level (datum) point was materialized on the wall, in topographic station 900 and the findings were leveled with respect to this point using a laser beam level. The orientation of almost 340 long bones was measured to test for the inferred fluviatile transport. The bone surveying was done using pictures at high resolution and measuring the azimuth with a compass. The standard error was less then 5°. In order to asses the age and timing of the bone accumulation, bone subsamples were taken for subsequent radiocarbon dating. Speleothem calcite samples for U-series dating were collected from stratigraphically-relevant locations both within the excavation and from places that may pre- or post-date the sediment and bones accumulation. Finally, since previous rockmagnetic studies on cave sediments (e.g. Ellwood et al., 2001) pointed out that magnetic susceptibility magnitudes may be used as a relevant paleoclimate proxy, sediment samples were taken from four selected profiles along the underground stream. Oriented samples weighing cca 30 grams were taken at intervals typically ranging between 5 cm and 10 cm from the fluviatile terraces. The rockmagnetism profile closest to the excavation was taken from the southern end of the Excavation Chamber, across an exposed sediment face with a height of ~2 m (fig. 1). In the laboratory, the magnetic susceptibility of the samples was measured at 3 frequencies (976 Hz, 3904 Hz and 15616 Hz) using the multifunction kappabridge MFK1A (AGICO). With the same instrument we measured also the anisotropy of the magnetic susceptibility.
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The morphodynamic analysis for the upper and lower fourth premolars (P4/4) was done applying the method described by Rabeder & Tsoukala (1990). The method is based on the evolutionary trend in the occlusal plan for the upper and lower P4. The more recent the cave bear specimen, the more evolved is the fourth premolar (broader surface, with more additional cusps). The morphodynamic analysis on the cave bear’s fourth premolar followed five steps: (1) Identification of morphotypes; (2) Ordering of the morphotypes by following a morphodynamic scheme; (3) Statistical analysis; (4) Determination of the morphodynamic indexes using the equation: MphtProduct x 100 %, where: MphtProduct is the P4/4amount product of all the upper or lower P4 morphotypes and P4/4amount represents the total number of the upper or lower P4 analyzed. (5) Standardization of the obtained P4/4 index with the most relevant site, Gamsulzen Cave, with a P4/4 index = 225.12 (Rabeder, 1999). The equation used was: P4/4 index Urşilor x 100 %, the P4/4 index for P4/4 index Gamsulzen Gamsulzen Cave site is the landmark for the Upper Pleistocene cave bear populations, one of the youngest in Alps. Canine as well as metapodial bones were measured according to Tsoukala & Grandal d’Anglade (2002). Scatter diagrams were plotted for the upper and lower canine measurements in order to emphasize the sexual dimorphism in cave bears. Following the Simpson’s method (1941), ratio diagrams were plotted for all the cave bear metapodials (the greatest length, the smallest breadth of diaphysis and the K-index) in order to compare, metrically, the cave bear population from Urşilor Cave with other similar European sites (Gamsulzen, Austria; Potočka zijalka, Slovenia; Nerubajskoe, Ukraine). For those three ratio diagrams, the standard used was the cave bear fauna (Ursus ingresus, Rabeder et al., 2004) from Gamsulzen Cave. All measurements were taken with an electronic caliper with a standard error of 0.1 mm. Two metapodial parameters were calculated as well: the K-index and the index of plumpness. The K-index was calculated according to the method of Gužvica & Radanović-Gužvica (2000): Dtprox x DAPprox K = –––––––––––––––– , L where Dtprox – the proximal breadth, DAPprox – the proximal height, L - the greatest length. The index of plumpness was calculated according to Withalm (2001): Dtdist Ip = –––––– x 100, L where Dtdist – the distal breadth and L – the greatest length.
110 3 - RESULTS 3.1 - TAPHONOMY Five sediment layers were identified in the excavation so far. The uppermost three layers (0-70 cm depth) are rich in fossil bones, the overwhelming majority of these belonging to cave bear. The fourth sediment layer is sterile of fossil bones and is situated between 70 and 100 cm in depth. The matrix of the first four layers consists of very fine clay of different colors (fig. 2). The bone-preservation degree decreases from the surface downwards with distinct sedimentological limits. The fifth layer shows a different facies and consists of a sandy-clayey sediment that includes fossil remains starting with a depth of 20-25 cm from its top. Within this layer the fossil remains are, in contrast, very well preserved and have a blackish color. The long bones show a dip angle with respect to the horizontal plan suggesting a higher-energy hydraulic regime as compared to the upper layers.
Therefore, almost 340 long bones were surveyed in order to establish if a fluvial transportation occurred. A rose diagram (fig. 3) was plotted in order to test the correlation between the supposed fluvial direction and the orientation of the long bones. The rose diagram indicates a very low correlation with the direction of the underground river, which, together with the presence of the clay sediment suggests a depositional setting with a low hydraulic energy, at least for the upper layers.
Fig. 3: Rose-diagram of the orientation of the cave bear long bones at the excavation area (Urşilor Cave, Scientific Reserve) plotted versus the orientation of the underground stream (grey sector). Fig. 3: Orientation générale des os longs des ours de cavernes de la zone fouillée par rapport à la direction du ruisseau souterrain (Grotte Urşilor, Réserve Scientifique) (secteur gris).
Fig. 2: Stratigraphic log of the sediments from the excavation area (Square B1) in the Scientific Reserve, Urşilor Cave. Fig. 2 : Profil stratigraphique de la zone fouillée (carré B1) de la Grotte Urşilor, Réserve Scientifique.
Almost 1500 bone remains were extracted from the excavation area. With only two exceptions (a cave hyena canine and a fox long bone) the bone remains belong exclusively to Ursus spelaeus. One of the basic issues posed by this bone accumulation was the understanding of its genesis. Although the working-hypothesis assumed fluviatile transport, the evidence gathered during the first two campaigns suggest that a non-fluviatile component cannot be excluded, at least for the first three layers.
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In addition, many cave bear skeletal elements were found in anatomical connection (fig. 4) in all quadrants and at each level – fully articulated foreleg (scapula, humerus, radius and ulna), hind leg (femur, patella, tibia and calcaneus), skulls and mandibles, manus, pes, etc., having different preservation degrees depending on depth. This evidence too suggests a low hydraulic gradient for the underground river and comes in agreement with the analysis of bone orientation. The assessment of the bones preservation degree may be an indicator of the genesis of the cave bear assemblage and for the depositional regime of cave sediments. The first sediment layer has bones with a very good preservation degree; the bones have a yellow-reddish color and are very resistant to mechanical action, indicating a quick flood event. On the contrary, within the third sediment layer the cave bear bones are very weathered, probably due to the long exposure of fossil remains before being flooded. The color of the fossil bones ranges from whiteyellow to black. The second and especially the third bone layers contain numerous black cave bear bones, sometimes contrasting with other bones found at the same depth. Within the deepest bone layer, so far, all the bones are black and strongly mineralized, apparently due to the deposition of a manganese coating. For the cave bear fossil remains found in the first three layers, a rough evaluation of Minimum Number of Individuals (MNI) was done using the right and left M1 and M2. The material studied thus so far revealed a minimum number of 24 adult individuals. The cave bear material obtained from the deeper sediment (>125 cm) of the excavation is still under examination.
Fig. 4: Skeletal elements in anatomical connection found in the excavation area at Urşilor Cave, Scientific Reserve. a) Foreleg (scapula, humerus, radius and ulna); b) Pelvis and femur; c) Skull and mandible; d) Pes; e) Skull and mandible; f) Radius and ulna. Fig. 4: Éléments du squelette en connexion anatomique dans la zone fouillée, Grotte Urşilor, Réserve Scientifique. a) Patte (scapula, humérus, radius et ulna) ; b) Bassin et fémur ; c) Crâne et mandibule ; d) Pes ; e) Crâne et mandibule ; f) Radius et ulna.
3.2 - MAGNETIC SUSCEPTIBILITY The anisotropy of magnetic susceptibility (AMS) ellipsoid is oblate and well defined magnetic foliation is observed with the minimum susceptibility axis nearly vertical and the maximum and intermediate susceptibility axes scattered in the horizontal plane. This type of AMS is characteristic for the primary fabric of underformed clay sediments deposited in a moderate current (Tauxe, 2002). The low frequency magnetic susceptibility ranges between 2.8–4.2×10-7 m3kg-1. The frequency dependence of magnetic susceptibility calculated from the values measured at 976 Hz and 15616 Hz is between 9.2 % and 12.8 %. The amplitude of magnetic susceptibility has the highest values in the clay intervals. These values correlate well with high values of frequency dependence of magnetic susceptibility. 3.3 - BIOCHRONOLOGY The dominant P/4 morphotypes encountered are D1 (protoconid, paraconid, metaconid and two small accessory cusps), C1 (protoconid, paraconid and metaconid), C2 (C1 + hipoconid), and E2 (protoconid, paraconid, metaconid, hypoconid, metalophid + small accessory cusps) (tab.1), while the P4 morphotype is D (protoconulus, metaconulus, hypoconulus, metalophulus + small accessory cusps). The P/4 index for the first three bone layers from the Urşilor Cave is 201.08 and the P4 index is
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P/4 Morphotype B1-C1 B2-C2 C1 C2 C1-C2 C2-C3 D1 D2 D3 D1-D2 E2 E2-E3 Total
Amount 2 1 3 3 2 1 3 1 2 1 3 1 23
Factor 0.75 1.75 1 2 1.5 2.5 1.5 2.5 3.5 2 3 3.5
Product 1.5 1.75 3 6 3 2.5 4.5 2.5 7 2 9 3.5 46.25
Frequency 8.69% 4.34% 13.04% 13.04% 8.69% 4.34% 13.04% 4.34% 8.69% 4.34% 13.04% 4.34% 100
Amount 2 1 1 1 1 1 8 1 2 1 19
Factor 1 1.5 1 1.5 1.5 2 2 3.5 3 3.5
Product 2 1.5 1 1.5 1.5 2 16 3.5 6 3.5 38.5
Frequency 10.52% 5.26% 5.26% 5.26% 5.26% 5.26% 42.10% 5.26% 10.52% 5.26% 99.96%
P4 Morphotype A/D A/D-D B B-C B-D C D D/F-F E E-F Total
Tab. 1: The P/4 and P4 cave bear morphotypes from the Urşilor Cave. Tab.1 : Les morphotypes du P/4 et P4 d’ours des cavernes de la Grotte Urşilor.
112 bear metapodials are presented in Table 2. Two ratio diagrams were drawn for these parameters (fig. 5 and 6) and indicate that the Urşilor Cave bear population was overall smaller dimensionally than at the cave bear sites of Gamsulzen (Austria), Potočka zijalka (Slovenia) (Withalm, 2004), and Nerubajskoe (Ukraine) (Nagel et al., 2005), except for the first metacarpal length and the fifth metacarpal smallest breadth – the highest for this comparison. Two bar-charts (fig. 7) show the index of plumpness and the K-index, respectively, and a third ratio diagram (fig. 8) shows a comparison of the K-index for all metapodials with respect to the above mentioned sites. Although the K-index values for Urşilor Cave are well beneath the other three cave bear sites (except for the
202.63. After the standardization (with Gamsulzen Cave, Austria) (Rabeder, 1999), P/4 standardardized index was 101.45 % and the P4 standardized index was 79.30 %. Therefore, the ImP4/4 standardized for the first three bone layers from Urşilor Cave is 90.38 %. Assuming a good correlation between the P4/4 index and the radiometric scale, the age of the first three cave bear bone layers appears to correspond roughly to the Marine Isotope Stage (MIS) 3. 3.4 - OSTEOMETRY The results of the measurements of the greatest length and the smallest breath of the diaphysis (DT) of cave
Fig. 6: Ratio diagram of the smallest breath of the diaphysis (Dtdia. min.) of the cave bear metapodials from the Urşilor Cave (PU) and other cave bear sites: GS - Gamsulzen, PZ - Potočka zijalka, NB Nerubajskoe. Fig. 6 : Diagramme du rapport entre le plus petit diamètre transversal de la diaphyse (Dtdia. min.) des métapodes d’ours des cavernes de la Grotte Urşilor (PU) et d’autres sites (GS - Gamsulzen, PZ - Potočka zijalka, NB - Nerubajskoe).
Fig. 5: Ratio diagram of the greatest length of the cave bear metapodials (Mt) from the Urşilor Cave (PU) and other cave bear sites: GS - Gamsulzen, PZ - Potočka zijalka, NB – Nerubajskoe. Fig. 5 : Le diagramme du rapport de la plus grande longueur de métapodes (Mt) d’ours des cavernes de la Grotte Urşilor (PU) et provenant d’autres sites: GS - Gamsulzen, PZ - Potočka zijalka, NB - Nerubajskoe.
Tab. 2: The greatest length and the smallest breath of the diaphysis (DT) of the cave bear metapodials from the Urşilor Cave (PU) and other cave bear sites: GS – Gamsulzen, PZ - Potočka zijalka, NB – Nerubajskoe. Tab. 2 : La plus grande longueur et le diamètre transversal de la diaphyse (DT) des métapodes d’ours des cavernes de la Grotte Urşilor (PU) et d’autres sites d’ours des cavernes : GS - Gamsulzen, PZ - Potočka zijalka, NB - Nerubajskoe.
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113 respectively. The scatterplots on cave bear canines emphasize the sexual dimorphism for this species and are usually considered a good tool for the assessment of the sex ratio. The two scatterplots on canine measurements show two distinct clouds, the largest one belonging to females. The sex ratio for the cave bears from the first three bone layers in our excavation is 3:1, the majority belonging to females.
4 - DISCUSSION 4.1 - BONE TAPHONOMY
Fig. 7: (a) Index of plumpness of the cave bear metapodials from the Urşilor Cave. (b) K-index of the cave bear metapodials from the Urşilor Cave. Fig. 7: (a) Indice de la rondeur des métapodes de l’ours des cavernes de la Grotte Urşilor. (b) K-indice des métapodes de l’ours des cavernes de la Grotte Urşilor.
As the underground stream is in the close vicinity of the excavation area, fluviatile transport of the fossil bones seems a reasonable hypothesis. In the excavation no pebbles or rock fragments were found embedded in-between the fossil bones and the clay sediment that could sustain a high-energy hydraulic activity. The overwhelming majority of the surveyed bones were parallel to a horizontal plane. In figure 3 one may see that no preferred pattern exists and therefore a high-energy fluviatile transport is unlikely. The remaining hypothesis is that the cave bear bone layers resulted chiefly from carcasses being accumulated upstream the current sump
Fig. 8: Ratio diagram of the K-index of the cave bear metapodials from the Urşilor Cave (PU) and other cave bear sites: GS Gamsulzen, PZ - Potočka zijalka, NB - Nerubajskoe. Fig. 8: Diagramme du rapport du K-indice des métapodes de l’ours des cavernes de la Grotte Urşilor (PU) et d’ours des cavernes provenant d’autres sites : GS - Gamsulzen, PZ - Potočka zijalka, NB - Nerubajskoe.
values measured for the first and the second metacarpal) it is worth noticing the same morphological trend for all the cave bear populations, especially when comparing the bears from Urşilor Cave with the Potočka zijalka site. For canine measurements two scatter plot diagrams are shown in figure 9 for the lower and the upper canines,
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Fig. 9: Scatter plot of the upper (a) and lower (b) cave bear canines from the excavation at Urşilor Cave. Fig. 9: Diagramme de dispersion des canines respectivement supérieures (a) et inférieures (b) d’ours des cavernes de la Grotte Urşilor.
114 with the possible (but hard to ascertain) addition of some animals falling down the shaft. The cave bear bone layers show a heterogeneous thickens in the excavation area, suggesting a random deposition of the assemblage having a larger thickness towards the right wall of the chamber, i.e. close to the former riverbed. For example, the D4 quadrant, located next to the left wall of the chamber, has only 40 cm of fossil bones, while the A1, B1, and C1 quadrants located closer to the right wall have at least 70 cm of fossils for the first three layers. Toots (1965a, 1965b) and Voorhies (1969) showed that the transport of skeletal elements is reflected not only by the preferential sorting but also by the patterned orientations of long bones. Moreover, Behrensmeyer’s (1990) and Kreutzer’s (1988) results pointed that in strong currents elongate bones generally orient parallel to the flow direction, with the heavier end upstream whereas in shallow water or weak current elongate bones may orient perpendicularly to the current. However, this seems not to be the case, at least for the three uppermost layers, where many cave bear skeletal parts were found articulated in every quadrant and at every level. This fact too suggests a very low hydraulic energy when the sediments and embedded bones were deposited. On the other hand, the claw marks observed at the upper part of the shaft suggest that occasionally this place may have been acted also as a natural trap where cave bears may have been falling. Finally, the combined sedimentology and magnetic susceptibility analyses suggest that the sediment transported in the cave derived mainly from soil erosion as shown by Evans & Heller (2003). Similar oscillations of the magnetic susceptibility were interpreted as an indication of a warm climate during the deposition of the cave sediments.
4.2 - BIOCHRONOLOGY Quilès (2003) has shown that defining evolutionary trends based on morphological observations requires standardization as a mean of comparing the results with a reference unit. Following the studies of Rabeder & Tsoukala (1990), Rabeder & Nagel (1997) and Rabeder (1999), the reference set is the arithmetic mean of the fourth premolar morphodynamic indices, the P4/4. Rabeder (1999) demonstrated that within the biochronological framework, P4 is highly correlated with the absolute chronology, thus offering a chance for a broad estimate of a cave bear population. The method was used for numerous cave bear sites from Europe and offers information about the average age of cave occupation by cave bear population. Pacher & Stuart (2009) stated the cave bear extinction chronology at c. 27800 cal. yr BP for the Alps and the adjacent areas, which is approximately coincident with the start of the Greenland Stadial 3, c. 27500 cal. yr BP. In the absence of conclusive data about the extinction of cave bears from the Carpathians we adopted the same extinction limit as in the Alps. Therefore, assuming the maximum error of ± 27 ky of the morphodynamic analysis of P4/4 index (for the Salzofen Cave, Austria), the cave bear assemblage from the first three bone layers from the Urşilor Cave excavation ranges from c. 27.8 cal. ky BP to c. 56.5 cal. ky BP, which falls roughly within the MIS 3 (fig.10). 4.3 - OSTEOMETRY As Withalm (2004) suggests, the morphometric analysis of cave bear metapodials indicates the evolutionary level of a population and the K-index of the 2nd metatarsal bone is a good indicator for biochronological estimation. The low values of the K-index when comparing
Fig.10: Biochronological estimation for the first three cave bear bone layers from the Urşilor Cave (PU). Fig. 10 : Estimation biochronologique pour les trois premières couches de la Grotte Urşilor Cave (PU). Sites/Sites : Bad - Badalucco; Bas - Basura; C-na - Cioclovina Uscata; CU - Conturines; Faa - Fate arhaic; Fat - Fate typique; GS - Gamsulzen; Gb Grotte Blanche; HD1 - Herdengel; HD2 - Herdengel 360-380; HD3 - Herdengel 330-360; HD4-6 - Herdengel 200-330; Ho - Hortus; NL - Nixloch; Oa - Oase Cave; RK - Ramesch; SO - Salzofen; SW - Schwabenreith; To - Tournal. (Source: Rabeder, 1999; Quiles, 2004; Quiles et al., 2006; Petrea, 2009).
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115 the Urşilor Cave with other European cave bear sites could be explained considering the sex ratio: the females outnumber the males three times, therefore a false low evolutionary level emerge. Withalm’s results suggested that, when tracing the evolution of the K-index of the 2nd metatarsal bone, this parameter may be correlated to the P4/4 index and thus to the absolute age of a cave bear population. In the case of Urşilor Cave where P4/4 index has high values but the K-index is low (due to sex ratio i.e. sexual dimorphism) we found a weak correlation, in contrast with the sites where the cave bear males are dominant. Therefore, at least in the case of the Urşilor Cave population, a link between the morphodynamic analysis on P4/4 and the K-index could not be established.
5 - CONCLUSIONS The genesis of the first three cave bear bone layers in the Excavation Chamber from the Urşilor Cave is related to a slow sedimentation of lacustrine-like origin, with sediments having a soil derived source. Considering the morphology of the cave in this sector, the chamber is considered to have been partially filled by the water of a back-sump “dam lake” that favored the accumulation of bear carcasses. The skeletal elements found in anatomical connection, the analysis of the long bones orientation, the gradient of bone preservation indicate that the resulting bone bed was covered by lacustrine sediments during at least three flooding episodes. The anisotropy of the magnetic susceptibility revealed the presence of underformed clay sediments deposited in moderate currents. The morphodynamic analysis of fourth cave bear premolars from the first three layers indicates MIS 3 ages, ranging from c. 27.8 cal. ky BP to c. 56.5 cal. ky BP. The correspondence between the P4/4 and K-index is low and we believe that this approach should be considered with caution due to some factors that may bias the results. The K-Index may lose relevance when sex ratio is not properly evaluated or when the fourth metacarpal of other species of Ursidae (i.e. Ursus arctos) are considered together with the fourth metatarsal derived from cave bear.
ACKNOWLEDGMENTS This study is part of KARSTHIVES Project – Climate archives in karst funded by CNCS – UEFISCDI Grant IDEI 31/2010. The authors are indebted to Professor Gernot Rabeder and dr. Emanoil Ştiucă for providing useful data and suggestions on the cave bear morphodynamic analysis on teeth and to Dr. Gerhard Withalm for suggestions concerning metapodial analysis. We thank Raluca Ioana Băncilă and Rodica Plăiaşu for drawing the ratio diagrams. The insightful reviews of Dr. Claude Guérin and Dr. Jean-Luc Guadelli were helpful in improving this paper.
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