Fig 1.
Location of the sites mentioned in the text.
1. Gruta do Caldeirão. 2. Abrigo do Lagar Velho; 3. Lapa do Anecrial; 4. Lapa do Picareiro; 5. Gruta da Oliveira; 6. Gato Preto; 7. Gruta Nova da Columbeira; 8. Cardina/Salto do Boi; 9. Pego do Diabo; 10. Cova de Malladetes; 11. Cueva Antón; 12. Fica Doña Martina and Abrigo de La Boja (Rambla Perea). 13. Cueva Bajondillo. Relief map: Global Multi-Resolution Topography Synthesis (https://www.gmrt.org/GMRTMapTool/). Reproduced from [5] under a CC BY 4.0 license.
Fig 2.
A. Overview of the small limestone escarpment where Gruta do Caldeirão is located, taken with a zoom lens from the town of Pedreira, 765 m to SSE (1986). B. The cave entrance at the time of discovery (1980). C. The Entrance trench at the end of the 1979–88 fieldwork. D. The Entrance trench during excavation (1987). E. Excavation of the Upper Solutrean deposit in the Corridor area (1985). F. The Back Chamber towards the end of the excavation (1987); the staining of the wall at the bottom end of the chamber denotes the elevation reached by layer ABC-D, the thick black earth deposit of recent Holocene age that originally capped the stratigraphic succession.
Fig 3.
Plan of the cave at the elevation of the sedimentary infill prior to excavation, and one-square-meter grid used during the 1979–88 field seasons. The excavated grid units are highlighted; the darker shading indicates those where the Early Upper and Middle Palaeolithic levels were reached.
Fig 4.
Stratigraphy and disturbance (features and agents).
A. The P>Q14-11 profile at the end of the excavation, seen from the angle between Corridor and Back Chamber. B. Zenithal view of the stepped base of the Back Chamber trench at the end of the excavation; the long-dash lines mark the contour of the cave wall; the stratigraphic depth reached in each grid unit is indicated. C. The P11>10 profile; the short-dash lines denote the stratigraphic succession’s two major discontinuities. D-E. The large, c. 50 cm-deep burrows penetrating layers Fa-Ja in squares Q-R/12-13 and L-N/13-15; elevations are in cm below datum. F. The base of the P11>10 profile seen in oblique view taken from the opposite edge of grid unit P11; note how, along the south and west walls of the trench, layer O formed a thick, hard crust. G. Meles meles (badger) left mandible (P12-194/sc358, layer Fa). H. Sample of the large concentration of hyaena coprolites retrieved in the NE corner of square P11 (P11sc907, layer M). I. Crocuta crocuta (spotted hyaena), right mandible (P11-865, layer L).
Fig 5.
Illustration (original field record, hand-drawn at 1:10; elevations in cm below datum) and geological description of the P>O11 (North) profile of square P11 extant at the end of the 1979–88 excavations (completed with observations made in P11>10 and P>Q11-13).
Fig 6.
A. Magnetic susceptibility curve (log scale) [2, 29]. B. Orthorectified photo mosaic and stratigraphic interpretation of the P11>10 profile (based on an original field record drawn at 1:10; elevations are below datum); the colour bands indicate the position of the magnetic susceptibility sampling columns.
Fig 7.
Solutrean diagnostic artefacts.
1–3. Shouldered points with impact fractures from layer ABC-D (N15sc22; Franco-Cantabrian subtype; upwardly displaced) and basal layer Eb of the Corridor area (O14sc160 and N13sc118; Mediterranean subtype; Solutreogravettian?). 4. Parpallò point with impact fracture, layer Fa (L14-60; in burrowed area); 5. Broken laurel-leaf modified into perforator, layer H (P12-459); 6. Endscraper on ventrally thinned blank, layer I (P12-518). 7. Vale Comprido point with distal impact fracture, layer Ja (O12-125). 8. Dufour bladelet (mesial fragment), with zoom-in views of its direct (left side) and inverse (right side) retouch, layer Ja (P11sc978).
Table 1.
Solutrean diagnostics.
Fig 8.
Quartzite cores from layers Jb-L.
1. P11-811, layer K. 2. P12-739, layer K (possibly also used or re-used as a hammerstone). 3. P11-831, layer L. 4. P11-796, layer K.
Fig 9.
Non-chert débitage from layers Jb-L.
1. Cortical flake, quartz (P13-483, layer L). 2. Flake with distal-marginal micro-denticulation of the edges (use-wear?), quartzite (P12-720, layer K). 3. Levallois flake, distal fragment, quartz (P11-766, layer K). 4. Flake, quartzite (P11-790, layer K). 5. Flake, quartzite (P12-742, layer K).
Fig 10.
1. Unilaterally retouched, naturally backed blade (P13-401, top of layer K). 2. Dufour bladelet, mesial fragment (P11sc980, top of layer L).
Fig 11.
1. Sidescraper (bilateral, inverse retouch; O13-361, surface of layer L). 2. Sidescraper (bilateral, alternate retouch; P11sc852-3, base of layer K).
Table 2.
Back chamber stone tools (layers Jb-P).
Table 3.
Back chamber lithic typology (layers Jb-P).
Fig 12.
Personal ornaments in layers Jb-K and their radiocarbon ages.
1. Perforated Aporrhais pespellacani shell. 2. Broken Littorina obtusata shell. 3. Worn-down Sparus auratus tooth (undated) and SEM image of the natural wear of the occlusal surface. 4. Eroded Semicassis saburon shell (leftmost ventral view taken after removal of the infill, showing the characteristic coarse sand/small pebble matrix of its layer of provenance). Nos. 1 and 2 are from layer Jb, nos. 3 and 4 are from layer K.
Fig 13.
1. Levallois flake (P11-853). 2. Regular flake (P11-850).
Fig 14.
Back chamber’s upper and middle palaeolithic bone samples submitted for radiocarbon dating.
A. Human mandibular fragment with dm2. B. Horse tooth (mandibular M1 or M2). C. Unfused red deer first phalange. D-G. Non-plotted shaft fragments (the items that yielded enough collagen are associated with age result plus inventory and lab numbers; the fragment indicated by the dotted rectangle in G is illustrated in F): spit L1 of layer L (D); spit L3 of layer L (E); spit M1 of layer M (F, G).
Fig 15.
Stratigraphic provenance and significance of the back chamber’s pleistocene dating samples.
OSL samples were taken from the P>Q13-11 profile at the indicated positions (except for the layer O sample, which was taken from the P11>12 profile at x = 30 and is herein represented as a projection). All twenty-five single-item, AMS-dated radiocarbon samples are projected using their y- and z-axis coordinates (five non-plotted items are assigned to the centroid of their square/spit provenience). The colour codes reflect the significance attached to radiocarbon results in terms of accuracy and site formation process (MAMS-33905 and MAMS-41871 are not coded because their interpretation remains open). The lab numbers are associated with the 95.4% probability intervals of the samples’ calendar ages. The original field record was hand-drawn at 1:10. Elevations are in cm below datum.
Table 4.
AMS radiocarbon dating of the Pleistocene deposit in back chamber, corridor, and entrance: Samples.
Table 5.
AMS radiocarbon dating of the pleistocene deposit in back chamber and corridor: Results.
Table 6.
Single-grain OSL dating results.
Fig 16.
Radial plots showing the OSL samples’ single-grain De distributions.
The grey bar is centred on the age model that provides the optimum statistical fit for each distribution (bold values in S1D Table in S1 File).
Fig 17.
Entrance trench: Stratigraphy and dating.
A. Orthorectified photo of the S-Q20>19 profile, and stratigraphic interpretation (the dark pocket reaching the base of unit 4 is a disturbance feature); the 95.4% probability intervals of the calendar ages (ka BP) for units 5 and 6 in Tables 7 and 8 are indicated; elevations are in cm below datum. B, C. Non-plotted shaft fragments from spits F10 of unit 5 (B) and F16 of unit 6 (C); the specimens that yielded enough collagen are associated with age result plus inventory and lab numbers.
Table 7.
AMS radiocarbon dating in the entrance trench: samples.
Table 8.
AMS radiocarbon dating in the entrance trench: Results.
Fig 18.
Entrance trench: Upper Palaeolithic artefacts.
1. Bifacial preform fragment, chert (P21-21, Unit 2). 2. Carinated scraper/core, quartzite (R20-43, Unit 4).
Fig 19.
Entrance trench: Middle Palaeolithic debitage.
1. Kombewa flake, silcrete (S20sc69). 2. Pseudo-Levallois point, silcrete (P20-16; excavation-damaged; the dashed line indicates the outline of the item’s original edge). 3. Laminar flake, silcrete (S20-61). 4. Levallois flake, quartz (S20-50). Nos. 1–2 are from Unit 5, nos. 3–4 from Unit 6.
Fig 20.
Entrance trench: Middle palaeolithic quartzite cores.
1. Centripetal Levallois core, exhausted (Unit 6, S20sc130). 2. Discoidal core, initial phase (set-up of the reduction surface) (Unit 5, P20-15).
Table 9.
Entrance lithics.
Fig 21.
Site formation process in the holocene.
Processes of sedimentary accumulation and post-depositional disturbance as inferred from stratigraphy, refitting, and spatial distributions (modified after Fig 3.11 of [1]).
Fig 22.
Back chamber artefact distributions illustrative of site formation process.
A. y- over z-axis (columns 10–15 and 17–18) and x- over z-axis (rows L-O) projection of piece-plotted Early Neolithic potsherds (N = 72), Solutrean diagnostics (N = 70; includes 29 sieve items assigned to the centroid of the square/spit field provenience), and upwardly displaced Solutrean horse tooth O13sc91. B. Refit unit REM-50 (quartzite flakes from layer K, P11-798 and P12-665). C. y- over z-axis projection of piece-plotted lithics from layers Ja-P. D. Density of quartz artefacts (total number per area unit of excavation, manuports excluded) across layers Ja-L. Elevations are in cm below datum.
Fig 23.
Chronology and palaeoenvironmental context of the transition at Gruta do Caldeirão (back chamber).
The bars indicate the 95.4% probability intervals of the calendar ages in Tables 5 and 6. OxA-37728 and OxA-37729 (which date intrusive human bone from the overlying Cardial context), OxA-5521, OxA-5541 and OxA-8670 (which reflect incomplete decontamination and are minimum ages only), and OxA-22301 (which is from a subfossil marine shell) have been excluded. Plotting of the NGRIP climate curve used CalPal (version 2017.5) [83]. The magnetic susceptibility curve is from Fig 6A, here sectioned into segments whose length has been adjusted to account for the hiatuses and the dating.
Fig 24.
Bayesian modelling (back chamber).
Model IV (cf. Table J for a summary of priors and likelihoods, and Table N for posteriors and statistical parameters). The prior age distributions for the dating determinations (likelihoods) are shown as light coloured probability density functions (PDFs): blue = radiocarbon determinations; green = single-grain OSL determinations. The modelled posterior distributions for the dating determinations and stratigraphic unit boundaries are shown as dark coloured and grey PDFs, respectively. Unmodelled and modelled ages are shown on a calendar year timescale, and both are expressed in years before AD1950. The white circles and associated error bars represent the mean ages and 1σ uncertainty ranges of the PDFs. The 68.3% and 95.4% ranges of the highest posterior probabilities are indicated by the horizontal bars underneath the PDFs.
Fig 25.
Bayesian modelling (back chamber and entrance).
Model V (cf. Table J for a summary of priors and likelihoods, and Table O for posteriors and statistical parameters). The prior age distributions for the dating determinations (likelihoods) are shown as light coloured probability density functions (PDFs): blue = radiocarbon determinations; green = single-grain OSL determinations. The modelled posterior distributions for the dating determinations and stratigraphic unit boundaries are shown as dark coloured and grey PDFs, respectively. Unmodelled and modelled ages are shown on a calendar year timescale, and both are expressed in years before AD1950. The white circles and associated error bars represent the mean ages and 1σ uncertainty ranges of the PDFs. The 68.3% and 95.4% ranges of the highest posterior probabilities are indicated by the horizontal bars underneath the PDFs.
Table 10.
Data for the estimation of rates of sedimentation and density of finds.
Fig 26.
Stratigraphic variation in the rate of accumulation of archaeological remains.
A. Per unit volume of excavated sediment. B. Per unit area of excavation and maximum duration based on Model V. C. Per unit area of excavation and maximum duration; maximum duration as in (B) for layers I-L but based on chronostratigraphic reasoning for layers Fa-Fc (half a millennium) and H (one millennium). The lines represent item counts (manuports excluded), and the columns represent weight counts. N = number of finds, pp = piece-plotted items.