The accidental unearthing in 1994 of an outstanding set of human fossils gave rise to the archeological excavation and multidisciplinary study of the site (11). As a result, a significant archeopaleontological record is being recovered, largely composed of Neandertal remains. The karstic site of El Sidrón is located in the region of Asturias, Spain, (43°23'01''N, 5°19' 44''W) (Fig. 1). Geologically, the site is found in the so-called "Surco Oviedo-Infiesto" (11), a strip of Mesozoic and Cenozoic sediments limited by Paleozoic relief to the north and south. The cavity is a pression tube of 600 m long, with a central stretch of 200 m oriented nearly west–east ("Galería del Río"). This tube shows on its southern bank transverse galleries in a NE–SW to N–S direction, generally of a restricted nature. The fossil site is located in one of these transverse galleries, the Osario Gallery, of 28 m long and 12 m at its widest part (Fig. 1). All of the remains are recovered from a surface 6 m2 within stratum III of the sedimentary sequence. Sediments accumulated in the Osario Gallery constitute a relatively thin deposit, so far prospected at a maximum thickness of 227 cm.
The archeological assemblage recovered at the site is in secondary position, and it certainly comes from a close exterior location. Ex hypothesis, the original deposit was located outside the cavity, possibly in a doline close to the vertical of the site. A collapse of nearby fissures produced the sudden entry of the archeological material in a single event. Several taphonomic signals help to clarify the scenario. Refitting of several bone fragments and 53 stone tools indicates a limited displacement as well as synchrony of the assemblage. Preservation of osteological surfaces is excellent with very limited trampling and erosion. There are no toothmarks of large carnivores on the bones, with marginal action of rodents and a small carnivore (e.g., fox) on a few nonhuman remains. A few bones have hydraulic abrasion but no weathering. In short, the data point to a limited exposure of bones outside the cavity; a mass displacement moved the archeological deposit into the cave secondarily, with very little movement after final deposition.
Dating. Three human specimens were 14C accelerator mass spectrometer-dated: SD-500 (tooth), 40,840 ± 1,200 14C B.P. (Beta 192065); SD-599a (bone), 37,300 ± 830 14C B.P. (Beta 192066); and SD-763a (tooth), 38,240 ± 890 14C B.P. (Beta 192067). Calibrated with CalPal (www.calpal.de), the dates become 44,310 ± 978, 42,320 ± 367, and 42,757 ± 464 cal B.P., respectively, the average calibrated age being 43,129 ± 129 cal B.P. (7). A similar age was obtained from preliminary of amino acid razemization (11), both from gastropods (39,000 ± 7,000) and human fossils 32,000 ± 11,000).
Paleontological Sample. A series of 1,323 human remains has been recovered at El Sidrón (Table 1). The collection has been divided into the 140 specimens unprofessionally unearthed (labeled SDR) (11–14)n and the systematically recovered sample (labeled SD) (11). Refitting of bones and stone tools derived from both sets largely testifies to a single archeological deposit. All of the skeletal parts are represented in the sample, and at least eight individuals have been identified: one infant, one juvenile, two adolescents, and four young adults. Nonhuman bones are very scarce (Table 1), with the presence of Cervus elaphus, a large bovid, very few small mammals and gastropods.
Ancient DNA. Mitochondrial DNA (mtDNA) sequences have been retrieved so far from two El Sidrón samples (10): a right I2 (SD-441) and a femur fragment (SD-1252; SI2 in ref. 9). The first sample yielded a 48-bp sequence (between positions 16,230 and 16,278 of the mtDNA reference sequence), and the second yielded an almost complete mtDNA hypervariable region 1 (302-nt sequence, between positions 16,076 and 16,378). The sequences are identical in the overlapping 48-bp segment, and thus it cannot be discarded from the genetic data that they belong to the same individual.
Lithics. A total of 333 lithic artifacts have been recovered, including side scrapers, denticulates, a hand axe, and several Levallois points. The raw material comes from the immediate cave environment, and it is mostly chert, and quartzite in a lesser proportion. The lithic assemblage is largely flake-based, with a few laminar products and some Levallois supports. Also, up to 17 flakes, some of them retouched, have been refitted on a core fragment, reflecting knapping at the primary location of the assemblage.