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Data from: Breaking down the lithification bias: the effect of preferential sampling of larger specimens on the estimate of species richness, evenness, and average specimen size

Citation

Hawkins, Andrew D.; Kowalewski, Michal; Xiao, Shuhai (2017), Data from: Breaking down the lithification bias: the effect of preferential sampling of larger specimens on the estimate of species richness, evenness, and average specimen size, Dryad, Dataset, https://doi.org/10.5061/dryad.p85q4

Abstract

Lithification, the transition of unconsolidated sediments to fully indurated rocks, can potentially bias estimates of species richness, evenness, and body size distribution derived from fossil assemblages. Fossil collections made from well-indurated rocks consistently exhibit lower species richness, lower evenness, and a specimen size distribution skewed towards larger specimens relative to collections made from unconsolidated sediments, even when collections are drawn from the same assemblage. This phenomenon is known as the lithification bias. While the bias itself has been demonstrated empirically, much less attention has been paid to its causes. Proposed causes include taphonomic processes (e.g., destruction of small specimens during early diagenesis) or methodological differences (e.g., sieving vs. counting specimens on outcrops, bedding surfaces, or mechanically split surfaces). Here we investigate the potential effects of preferential intersection that could also result in a methodologically related bias: the preferential sampling of larger specimens relative to smaller ones when fossils are counted on rock surfaces. We used an analog model to simulate preferential intersection (fossil collection via splitting fossiliferous rock) and compare the results to a random draw model that approximates the effects of sieving. The model was parameterized using nine different combinations of species abundance and species size distributions. The results show that, with rare exceptions, species richness is 5–23% lower, evenness 5-25% lower, and average specimen size 24–150% higher in preferential intersection than in random draw simulations. We conclude that preferential intersection can impose a significant bias independent of other mechanisms (e.g., preferential destruction of smaller specimens during diagenetic or sampling processes), that the magnitude of this bias is partially dependent on the species abundance and size distributions, and that this bias alone does not fully account for empirically observed lithification bias on species richness (i.e., other sources of bias are also at work).

Usage Notes

Funding

National Science Foundation, Award: NSF EAR-1528553; NASA Exobiology and Evolutionary Biology Program NNX15AL27G