Fig 1.
Examples of major (by frequency) monument types from Dhofar.
Clockwise from upper left: Platform D028-001, meter scale visible in excavation trench near closest section; HCT D033-001, 20 cm scale visible at mid height; Boat graves D100-001 with meter scale at upper left; a trilith (unsurveyed) with uprights 40-50 cm height. Photo credits clockwise from upper left: Joy McCorriston, Jennifer Everhart, Wael AbuAzizeh, and Michael Harrower.
Fig 2.
Timeline of major monument types based on multiple radiocarbon determinations from excavated monuments in Hadramawt, Yemen and in Dhofar, Oman.
Top register compiles precipitation proxy record from Qunf Cave, Dhofar [51] with Holocene Humid Period proxy records (silt terraces) in Hadramawt [38]. For Dhofar, platforms (n = 26, 14C = 4,) are black, HCTs (n = 135, 14C = 10) are fuschia, triliths (n = 165, 14C = 2) are blue, and boat graves (n = 22, 14C = 2) are represented in dark purple, with other (infrequent) monument types (yellow, green, pink). Taq denotes “terminus ante quem,” which indicates a stratigraphic position of sample that constrains the dated event to an earlier time; tpq denotes “terminus post quem,” or an event dated after the radiocarbon determination. These priors define eras of monument construction and use. For example, Dhofar platforms appear after 7500 cal yr. BP. Samples here are only from Dhofar [14,52]; radiocarbon calibrations generally match the Bayesian posteriors (horizontal lines) established with comparable data from Hadramawt, Yemen [12,16,38] and observations within the broader literature of Arabian prehistory. (See Supporting S1-Table, S2 Table, S3 Table for details). The long dotted line for HCT reflects stratigraphic evidence of re-use centuries and millennia after primary interments. Image by Shane Scaggs and Joy McCorriston.
Table 1.
The independent environmental variables used in the analysis.
Fig 3.
The locations of monuments, survey transects, primary roads and springs in Dhofar.
Fig 4.
a. Variable importance from the bootstrap aggregating (Left); 4b. Partial dependence plots, with deciles for data points, show the relationship between environmental variables and the predicted probability of monument occurrence (Right).
Fig 5.
The regularized multinomial logistic regression model coefficients show the relationship between the environmental variables and the monument types.
Standard errors cannot be accurately estimated in regularized logistic regression. A positive coefficient indicates that the monument type is associated with higher values of that variable, whilst a negative coefficient shows that the monument type is associated with lower values of that variable.
Fig 6.
The mean center and standard distance (1 SD) of the monument types.
The mean center is shown as a labelled colored point with the corresponding circle showing standard distance. Platforms (green), Scabs (orange), HCTs (blue), Triliths (purple) and Boat graves (red).
Table 2.
The results of the collocation analysis.
Fig 7.
Boxplots comparing total stone volumes across several monument groupings. Groupings include the five monument types, the two categories of technological requirement, and whether or not one or more large stones (>0.75 m) were present. We also compare the latter for all monuments, within monument types, and the two categories of technological requirement. The letters show the results of Tukey HSD post hoc pairwise comparisons following ANOVA tests. Monument types with letters in common indicate no statistically significant differences, while different letters indicate statistically significant differences.