Data from: Inferring skeletal production from time-averaged assemblages: skeletal loss pulls the timing of production pulses towards the modern period

Age-frequency distributions of dead skeletal material on the landscape or seabed – information on the time that has elapsed since the death of individuals – provide decadal- to millennial-scale perspectives on the history of production and on the processes that lead to skeletal disintegration and burial. So far, however, models quantifying the dynamics of skeletal loss have assumed that skeletal production is constant during time-averaged accumulation. Here, to improve inferences in conservation paleobiology and historical ecology, we evaluate the joint effects of temporally variable production and skeletal loss on postmortem age-frequency distributions (AFDs) to determine how to detect fluctuations in production over the recent past from AFDs. We show that, relative to the true timing of past production pulses, the modes of AFDs will be shifted to younger age cohorts, causing the true age of past pulses to be underestimated. This shift in the apparent timing of a past production pulse will be stronger where loss rates are high and/or the rate of decline in production is slow; also, single pulses coupled with declining loss rates can, under some circumstances, generate bimodal distributions. We apply these models to death assemblages of the bivalve Nuculana taphria from the Southern California continental shelf, finding that (1) an onshore-offshore gradient in time averaging is dominated by a gradient in the timing of production, reflecting the tracking of shallow-water habitats under a sea-level rise, rather than by gradients in disintegration and sequestration rates, which remain constant with water depth, and (2) loss-corrected model estimates of the timing of past production are in good agreement with likely past changes in local production based on an independent sea-level curve.