Regional geomorphology and palaeoenvironments
To evaluate the terminal Pleistocene and early Holocene environments of the region, trenches were excavated at four playas in the vicinity of the archaeological sites, two of which contained sufficient sediment for palaeoenvironmental analysis and luminescence dating: ARN (Site 1) and JMI (Site 4), (Fig. 1; Supplementary Note 5 and Supplementary Fig. 42). As local centres of deposition, and areas where water accumulated in the past, these playas provide archives of hydroclimate. Gravels found at the base of both 2 m deep trenches were poorly sorted, containing pebbles of up to 5 cm, and were interpreted as alluvial fan deposits. A luminescence age of 68.8 ± 5.0 ka (MIS-B-1) from JMI indicates that these sediments were deposited at the Marine Isotope Stage 5a to 4 transition (Table 1). Palaeohydrological activation at this time is consistent with both broader regional records28 and a surface find of a Middle Palaeolithic Levallois core from JMI (Supplementary Fig. 32).
Table 1 Luminescence ages from archaeological sites and playa deposits Full size table
At both excavated paleoenvironmental sites, the overlying sediments consist of a thin interval of alternating much finer-grained and well-sorted aeolian sands and playa deposits. These are followed by a prolonged sequence of playa deposits consisting of quartz sand, clays (illite and kaolinite), and calcite, indicating more humid conditions with increased water accumulation in these local depressions. We interpret the onset of playa sediment accretion as representing the change in the balance between aeolian erosion and fluvial sedimentation. During the LGM, the hyper-arid environment meant that any fine-grained sediments deposited in ephemeral floods were subsequently eroded by the wind. As the climate became less arid, fluvial sedimentation increased, becoming greater than the aeolian erosion rate and sediments started to accumulate. However, the subordinate carbonate concentration and the absence of root traces and organic-rich layers suggest that conditions remained too dry for the establishment of more permanent water bodies, indicating that a dryland environment persisted around these ephemeral, and probably seasonal, lakes. Luminescence ages constrain the onset of surface water to between 17.1 ± 1.7 ka (MIS-B-3) and 15.5 ± 1.5 ka (MIS-B-2) at JMI (Site 4) and to 12.7 ± 2.1 ka (SAH-L3-1) at ARN (Site 1) (Table 1). The onset of sedimentation after a long hiatus, coupled with an increase in calcite noted in both sedimentary records, indicates that local conditions gradually became more humid after ~16 ka at JMI to ~13 ka at ARN, with these site-specific differences in timing likely due to differences in catchment hydrology (Table 1). These sites thus represent the earliest evidence from northern Arabia of increased humidity following the hyper-arid LGM. However, the lakes were ephemeral, indicating an arid or semi-arid climate prevailed in the region.
Monumental rock art
Surveys at ARN and JMI identified previously unknown rock art landscapes with life-sized depictions of wild mammals and human figures, and an individual panel at MLH. Across the three areas 62 rock art panels were recorded, containing 176 engravings. Of these, 130 were life-sized and naturalistic engravings depicting camels (90), ibex (17), equids (15), gazelles (7), and aurochs (1), with individual representations frequently measuring up to 2.5–3.0 m in length and 1.8–2.2 m in height. In addition, we identified 2 camel footprints, 15 smaller scale naturalistic depictions of camels, 19 human figures, 4 human faces or masks, and 6 unidentified, partial engravings (Supplementary Data 1). Most of the recorded engravings show camels in a detailed and naturalistic style that echoes the reliefs of the Camel Site to the north of the Nefud desert. This includes the frequent depiction of a bulging neckline, indicating they represent male camels in rut29,30 (Fig. 2A, B).
Fig. 2: Rock art panels at Jebel Arnaan. Tracings highlight the layering of engravings, showing phase 1 in green, phase 2 in yellow, phase 3 in white and phase 4 in shades of blue. Rock art scale is 10 cm wide. A Panel ARN21A: Several small, stylised depictions of women (phase 1, traced in green), superimposed with a large human figure (phase 2, traced in yellow). Large, kneeling camel engraved over the top (phase 3, traced in white). B Panel ARN22A : naturalistic camel (phase 3, traced in white), superimposed by a camel with stylised, rounded eye and standardised outline (phase 4, traced in blue); original and unfinished camel head (traced in dark blue); three gazelle engravings were added during a later part of phase 4 (traced in light blue). Additional examples are provided in Supplementary Fig. 4. C Panel ARN3B : ibex with cartoon-like eye and horn (phase 4, traced in blue), superimposed with life-sized aurochs (phase 4, traced in lighter blue). D Panel ARN 39 : equid with cartoon-like eye, and with a young (phase 4, traced in blue). Untraced photos are provided in Supplementary Figs. 2 and 3. Full size image
The depictions span multiple engraving phases, with images often overlapping on rock surfaces. Sometimes this was done to update an existing representation (Fig. 2B) or to depict a different animal species (Fig. 2C). We distinguish four phases here. Two early rock art phases: small, stylised depictions of women (phase 1, traced in green), followed by large human figures in frontal view (phase 2, traced in yellow). These human figures were always noted to be older than, i.e. underneath, the recorded life-sized animal representations (Fig. 2A), and they make up a much smaller proportion of motifs. The third phase shows detailed, extremely naturalistic representations of animals, where each depiction has individual characteristics (traced in white) (Fig. 2A, B). A later, fourth phase (traced in blue) shows more stylised depictions of animals with cartoonish features, including rounded eyes and horn ridges, and more standardised, near-identical depictions of animals (Figs. 2C, D and 3C).
Fig. 3: Monumental rock art panel at Jebel Misma (JMI18). A Location of the panels at 34 m and 39 m height, and trenches JMI7 and JMI8 (project vehicle for scale). An OSL date of 12.0 ± 1.8 was obtained from JMI8 (Table 1: JMI8-T1-4). Excavated playa deposits are located directly behind this spur (see also Figs. 1 and 8). B narrow, downward sloping ledges in front of the panel viewed from above. C orthophoto generated via a high-resolution 3D model of the panel, with tracings showing 19 life-sized camels and 3 equids (one further camel was documented on a collapsed fragment left of the image). Naturalistic animals belonging to phase 3 traced in white. More stylised and standardised depictions of phase 4 traced in blue, including two engravings of equids traced in dark blue, and superimposed stylised camels traced in light blue. Unidentified lines traced in black. White traced camels: 1.7–1.9 m length, blue camels: 2.15–2.6 m length. A human figure was added on the far left for scale (1.7 m). Full size image
Unlike the SAU site, where many of the engravings were found inside narrow gaps between boulders27, engravings at ARN and JMI were found on prominent locations on boulders or cliff surfaces, facing into the landscape (Supplementary Figs. 1 and 7). Some of these panels were etched onto cliff surfaces in inaccessible but highly visible locations (Fig. 3). The difficulty in getting to and engraving these rock surfaces, and their enhanced visibility by height were clearly attractive for the engravers. The precarious nature of the engraving process is particularly evident in the largest recorded panel. On the ground, panel JMI18 is today only visible in optimal light conditions for about 1.5 h in the morning, due to its elevated location and the varnish build-up on the engravings. This panel would have been accessed by climbing up a cliff and then engraved while standing on a downward sloping ledge, only ~30–50 cm in width (Fig. 3B). Today the sandstone is too degraded to reach the ledge safely, and the panel was documented using a drone. The friable nature of the substrate and the slope of the narrow ledges suggest the engravers likely risked their lives to create this art. Engraving at close range would have required them to use direct percussion, while also preventing them from being able to see the complete image. Twenty-three life-sized camels and equids, each with an individual length of ~1.7–2.6 m were engraved on this surface (Fig. 3C), with the engravings stretching ~23 m across two cliff surfaces at a height of 34 m and 39 m (Fig. 3A), giving this rock art a monumental scale.
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