Aragonite bias, and lack of bias, in the fossil record: lithological, environmental, and ecological controls
Aragonite bias, and lack of bias, in the fossil record: lithological, environmental, and ecological controls
复制标题
化石记录中文石偏差和缺乏偏差：岩性、环境和生态控制
作者：
M. Foote;J. Crampton;A. Beu;C. Nelson
抽象的。
宏观进化和宏观生态研究必须考虑化石记录中的偏差，特别是在涉及保存和采样潜力不同的类群的相对丰度和多样性的问题时。使用来自温带环境(新西兰)的新生代海洋软体动物，我们发现腹足类与双壳类发生的长期时间变化很大程度上与文石与钙质分类群的阶段水平采样概率有关。钙质物种的平均采样概率较高，但这种对比是以一种可预测的方式随时间变化的，集中在广泛的碳酸盐沉积阶段。为了完全理解这些结果，我们将它们与单个点引用级别的分析链接起来。这样做表明，陆源碎屑沉积物中实际上没有文石偏向。相比之下，在石灰岩中，钙质物种的采样几率至少是文石物种的两倍。这一结果在碳酸盐沉积广泛的时期最为明显，在那里，采样物种的每次采集几率的差异是8倍。在碳酸盐富集期，碎屑岩中的钙质分类群也有较高的采样几率。乍一看，这一结果可能暗示了对文石的简单保存偏见。然而，用绝对采样率比较文石和钙质样品的相对几率表明，富碳酸盐时代的正方解石偏向反映了钙质分类群的平均出现率高于平均出现率(而不是文石类群的出现率较低)，而石灰岩中的文石偏负反映了文石类群的出现率低于文石类群的平均出现率(而不是钙质类群的出现率较高)。因此，我们的结果表明了两个主要因素的时间变化的相互作用：(1)碳酸盐沉积物中文石物种的挖掘损失，在陆源碎屑中没有实质性的偏向；(2)无论岩性本身如何，钙质类群对具有普遍碳酸盐沉积时期特征的环境具有生态偏好。
Abstract.
Macroevolutionary and macroecological studies must account for biases in the fossil record, especially when questions concern the relative abundance and diversity of taxa that differ in preservation and sampling potential. Using Cenozoic marine mollusks from a temperate setting (New Zealand), we find that much of the long-term temporal variation in gastropod versus bivalve occurrences is correlated with the stage-level sampling probabilities of aragonitic versus calcitic taxa. Average sampling probabilities are higher for calcitic species, but this contrast is time-varying in a predictable way, being concentrated in stages with widespread carbonate deposition. To understand these results fully, we link them with analyses at the level of individual point occurrences. Doing so reveals that aragonite bias is effectively absent in terrigenous clastic sediments. In limestones, by contrast, calcitic species have at least twice the odds of sampling as aragonitic species. This result is most pronounced during times of widespread carbonate deposition, where the difference in the per-collection odds of sampling species is a factor of eight. During carbonate-rich intervals, calcitic taxa also have higher odds of sampling in clastics. At first glance this result may suggest simple preservational bias against aragonite. However, comparing relative odds of aragonitic versus calcitic sampling with absolute sampling rates shows that the positive calcite bias during carbonate-rich times reflects higher than average occurrence rates for calcitic taxa (rather than lower rates for aragonitic taxa) and that the negative aragonite bias in limestones reflects lower than average occurrence rates for aragonitic taxa (rather than higher rates for calcitic taxa). Our results therefore indicate a time-varying interplay of twomain factors: (1) taphonomic loss of aragonitic species in carbonate sediments, with no substantial bias in terrigenous clastics; and (2) an ecological preference of calcitic taxa for environments characteristic of periods with pervasive carbonate deposition, irrespective of lithology per se.