Data from: Problems with using rock outcrop area as a paleontological sampling proxy: rock outcrop and exposure area compared with coastal proximity, topography, land use, and lithology.

Fossil specimens can be recovered easily only from exposed localities, so rock exposure area should represent a better proxy for rock availability than the frequently used outcrop (i.e., map) area. Data collected via remote sensing and GIS show that map area does not consistently correlate with exposure area in different regions. Proportional rock exposure is not geographically consistent and is influenced by a number of variables that are independent of outcrop area, including proximity to the coast, elevation, bedrock age, land use and lithology. These variables appear to be non-independent in their influence on rock exposure, and are not consistent in their effects across continents. The inconsistency in the correlation between outcrop and exposure area, and the variability in the influence of different factors on rock exposure, suggests that using outcrop area as a sampling proxy is poorly supported. The weaknesses in using outcrop area as a sampling proxy, highlighted by the lack of correlation with exposure area, suggest that a single accurate global sampling proxy may never be attained and it is premature to assume that paleodiversity curves can be corrected using such proxies. It is therefore preferable to work on a regional scale, comparing regional fossil collection data with a number of proxies representing all aspects of sampling. The lack of correlation between outcrop and exposure area suggests that the covariance detected between outcrop area and paleodiversity might be better explained by a common-cause model, and that geological megabiases may not have had as profound an effect on paleodiversity curves as previously thought.

化石标本仅能从出露地点轻松采集，因此相较于当前广泛使用的露头面积（outcrop area，即绘图面积），岩石出露面积（rock exposure area）可作为岩石可获取性的更优采样替代指标（proxy）。通过遥感与地理信息系统（GIS）获取的数据表明，不同区域内的绘图面积与岩石出露面积并非始终存在相关性。岩石出露比例不存在地理一致性，且受诸多与露头面积无关的变量影响，包括距海岸的距离、海拔、基岩年代、土地利用类型与岩性。这些变量对岩石出露的影响并非相互独立，且其作用效果在各大洲之间亦存在差异。露头面积与岩石出露面积之间的相关性不一致，加之不同因素对岩石出露的影响存在变异，这表明以露头面积作为采样替代指标的合理性支撑不足。鉴于与岩石出露面积缺乏相关性，以露头面积作为采样替代指标的缺陷凸显，这意味着我们或许永远无法获得单一精准的全球采样替代指标，且假设可通过此类替代指标校正古生物多样性曲线（paleodiversity curves）的观点尚为时过早。因此，更适宜在区域尺度开展研究，将区域化石采集数据与覆盖采样各维度的多项替代指标进行对比分析。露头面积与岩石出露面积之间缺乏相关性，这表明露头面积与古生物多样性之间检测到的协方差或许可通过共同成因模型得到更优解释，且地质宏采样偏差（geological megabiases）对古生物多样性曲线的影响或许并不如此前所认为的那般显著。