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14: The Holocene Herpetofauna of El Mirón Cave
- University of New Mexico Press
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| 250 | T he excavations directed by M. González Morales and L.G. Straus in El Mirón Cave yieldedrelativelyfewremainsofamphibiansandreptilesfromtheHolocenedeposits . These are the subject of the present zooarchaeological analysis, complementing the studies of other zoological groups reported upon in this monograph. González Morales and Straus (2000a, b; Straus et al. 2001) provide the relevant details about the site and its stratigraphy, archaeology, and chronology. methods Taxonomic Identification The taxonomic nomenclature used here follows Salvador (1998) and Frost (2010). The morphological traits used for identification are based on the criteria developed by Bailon (1999) and Böhme (1977) for the anurans and Szyndlar (1984) for the ophidians, as well as on direct comparisons with material in the collections of the Museo Nacional de Ciencias Naturales (CSIC) in Madrid. Archaeozoological Criteria The calculation of minimum numbers of individuals (MNI) is based on the most numerous single skeletal element per species from each stratigraphic level, taking into account side as well as sex in cases of clear sexual dimorphism. Biological Information The information that we provide on ecological aspects of the species (periods of activity, predators, etc.) is taken from works by Barbadillo et al. (1999), Salvador (1998), Salvador and García-París (2001), and Salvador and Pleguezuelos (2002). All the species represented in the early to mid-Holocene levels of El Mirón are found today in Europe. For their ChAPter Fourteen The holocene herpetofauna of el mirón Cave Borja Sanchiz, Jorge M. Lobo, and Salvador Bailon Translated by Lawrence Guy Straus Holocene Herpetofauna | 251 | This methodology is an alternative to the climatic inferences exclusively based on the observed occurrences of a species, as recently done for the Pleistocene (e.g., Blain, Bailon, and Cuenca-Bescós 2008; Blain et al. 2009) and tries to skip the nonrandom prospection in the making of herpetological distribution atlases. The variables selected for making paleoclimatic inferences are: (1) annual average temperature (o C), (2) annual precipitation (mm), (3) annual insolation (hours ofsunlight),and(4)altitude(m).Thelastvariable,whose value obviously has not changed for the site during the Holocene, acts in fact in zoogeography as a resultant factor that incorporates several occult populational variables , such as longevity or growth rate (see, e.g., Esteban and Sanchiz 2000). The species selected for biogeographic analysis were Anguis fragilis, Bufo bufo, and Rana temporaria, in two different combinations representative of the herpetofaunas from most of the levels. The remains of other species are sporadic, and their absences from some of the levels are not statistically significant. The environmental conditions of the grids showing the joint presence of a selected group of species are compared with those for which these species have not been cited. We also compare the environmental values for those zones with high and low probability of presence of the abovementioned species groups, according to their predictive models of habitat suitability. These calculations were done with Statistica 6.1 software (StatSoft Inc. 2003). material The Holocene herpetological material is stored in the Museo de Prehistoria y Arqueología de Cantabria, Santander.Itconsistsof356bonefragments,ofwhich331 could be identified to species or genus level. The distribution of the finds by taxa and levels is presented in table 14.1. All remains seem to belong to adult individuals. results Paleontological Analysis and Ecological and Taphonomic Observations UTM grid cell VN69, where El Mirón Cave is located, hasbeenatpresentrelativelylittlesurveyedforherpetofauna (only 6–10 citations, according to Pérez-Mellado continental distributions, one can consult Gasc et al. (1997). The syntheses of Holman (1998) and Martín and Sanchiz (2010) provide data on the presence of these taxa in other European Quaternary sites. Biogeographical Criteria Information on modern species’s geographical ranges is taken from the recent herpetological atlas of Spain (Pleguezuelos, Márquez, and Lizana 2002), which was done on a UTM projection with a resolution of 10 × 10 km cells. We selected as our study area those 100 km2 cells within the Iberian northern Atlantic climatic zone (with the exclusion of small portions of northern Portugal, for which adequate information is lacking). The geographic analysis was done using the IdRISI 32 GIS software (Eastman 2001). For each 100 km2 grid we included the following information: (1) climatic data (average annual temperature, total annual precipitation , and annual insolation) as provided by the Spanish Instituto Nacional de Meteorología, (2) altitudinal data (average elevation) according to a digital terrain model (Clark Labs 2000) with a resolution of 1 km, (3) data on groundcover and land use (woods, brush or heathlands...