The Early–Middle Pleistocene palaeoenvironmental change based on the squamate reptile and amphibian proxies at the Gran Dolina site, Atapuerca, Spain

Abstract

Although still ongoing, the archaeological and palaeontological excavations in the Gran Dolina cave (Sierra de Atapuerca, Burgos) every year since 1976 have already revealed a long, culturally and palaeontologically rich sequence dated by biostratigraphy, ESR, U-series, and the palaeomagnetic record at between roughly 1 my and 250 ky. Gran Dolina has one of the longest and most continuous vertical profiles. The section, 19 m thick, divided into 11 stratigraphic levels, represents a time span of nearly 700,000 years. The Gran Dolina sequence was partially excavated during a preliminary evaluation of its archaeological and palaeontological richness. This excavation, known as the “Gran Dolina Sondeo South”, lasted from 1993 to 1999. Hominin remains were unearthed in 1994 from level 6 of Gran Dolina, and level 6 was dated to somewhat more than 780 ky based on palaeomagnetic and microfaunal evidence, making these the oldest known hominins in Europe. Given the importance of this discovery, every effort is being made to reconstruct the landscapes where these hominins once thrived. The Gran Dolina Sondeo South (TDS) has furnished a great number of microvertebrate remains, and of these around 40,000 bones are attributed to amphibians and squamates. The faunal list of the squamates and amphibians of the TDS comprises at least 22 species, a diversity similar to what exists nowadays in Spain: Triturus sp., Alytes obstetricans, Pelobates cultripes, Pelodytes punctatus, Bufo bufo, Bufo calamita, Hyla arborea, Rana temporaria, Rana cf. dalmatina, Rana cf. iberica, Pelophylax ( ridibunda) sp., Blanus cinereus, Lacerta s.l., small-sized indeterminate lacertids, Anguis fragilis, Natrix natrix, Natrix maura, Coronella austriaca, Coronella cf. girondica, Rhinechis scalaris, Vipera cf. aspis and Vipera cf. latasti. These ectotherm vertebrates show variations in their taxonomic diversity throughout the sequence. Although they do not differ specifically from the extant herpetofauna of the Iberian Peninsula, they do so in the composition of their taxonomic assemblage. When the squamates and amphibians of TDS are grouped by habitat categories (the habitat weightings method), and studied in terms of their vertical evolution throughout the sequence, it is possible to follow environmental changes across the Early–Middle Pleistocene transition. Results from the squamate and amphibian studies indicate that the landscape had open habitats in the vicinity of the Atapuerca caves throughout the sequence, with wet points in the surrounding area. Open-dry microhabitats were more developed during warm periods, whereas during cold periods the environment was slightly more humid and wooded. These results are compared with studies in small mammals, pollen analysis and geomorphology, giving a scenario for the palaeoclimatic and palaeoenvironmental changes that occurred during the Early to Middle Pleistocene boundary in Atapuerca, and hence a scenario for the hominins that once lived in the Sierra de Atapuerca.