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.化石标本仅能从裸露区域被便捷采集，因此相较于常用的露头（outcrop，即测绘）面积，岩石裸露面积理应是岩石可获取性更合适的替代指标（proxy）。通过遥感与地理信息系统（GIS）收集的数据表明，不同区域的测绘面积与岩石裸露面积并不始终存在相关性。岩石裸露率在地理分布上并不恒定，且受诸多独立于露头面积的变量影响，包括距海岸的距离、海拔、基岩年代、土地利用方式与岩性。这些变量对岩石裸露率的影响似乎并非相互独立，且其影响效应在各大洲之间并不一致。露头面积与岩石裸露面积之间相关性的不一致性，以及不同因素对岩石裸露率影响的变异性，表明将露头面积作为采样替代指标的合理性支撑不足。由于与岩石裸露面积缺乏相关性，露头面积作为采样替代指标的缺陷凸显出来，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（paleodiversity）曲线的结论为时尚早。因此更适宜在区域尺度开展研究，将区域化石采集数据与代表采样各维度的多项替代指标进行对比。露头面积与岩石裸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合理的解释，且地质宏偏差（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深远。