Data from: Abundance and extinction in Ordovician-Silurian brachiopods, Cincinnati Arch, Ohio and Kentucky

A basic hypothesis in extinction theory predicts that more abundant taxa have an evolutionary advantage over less abundant taxa, which should manifest as increased survivorship during major extinction events and longer fossil-record durations. Despite this, various paleontologic studies have found conflicting patterns, indicating a more complex relationship between abundance and extinction in the geologic past. This study tests the relationship between abundance and extinction among brachiopod genera within seven third-order depositional sequences spanning the Late Ordovician to Early Silurian (Katian-Aeronian) of the Cincinnati Arch, USA. Contrary to predictions, abundance is not positively correlated with duration in this study. Abundance and duration range from strongly negatively correlated to uncorrelated depending on the spatial scale of analysis and the geologic intervals included, but never indicate that abundance is an evolutionary advantage. In contrast, abundance was an advantageous trait prior to the Ordovician/Silurian extinction, and brachiopods with higher abundances were more likely to survive the event than less abundant brachiopods. While this result is in keeping with common models of extinction, it has not been observed previously at a mass extinction boundary. This may be further evidence that the Ordovician/Silurian extinction was not accompanied by a shift in the macroevolutionary selectivity regime.

灭绝理论中的一项基本假说指出，丰度更高的类群相较于丰度较低的类群拥有演化优势，这一优势应体现为在大灭绝事件中更高的存活率，以及更长的化石记录存续时长。尽管存在这一假说，但诸多古生物学研究却发现了相悖的模式，表明地质历史中丰度与灭绝之间的关系更为复杂。本研究针对美国辛辛那提隆起晚奥陶世至早志留世（凯迪期-阿伦尼克期）的7套三级沉积层序（third-order depositional sequences）中的腕足动物（brachiopod）属，检验了丰度与灭绝之间的关系。与假说预测相悖的是，本研究中丰度与存续时长并未呈现正相关关系。根据分析的空间尺度与所纳入的地质间隔的不同，丰度与存续时长的相关性从显著负相关到无相关不等，但从未表明丰度是一项演化优势。与之形成对比的是，在奥陶纪-志留纪灭绝事件发生之前，丰度是一项有利性状，丰度更高的腕足动物相较于丰度较低的类群更有可能在该事件中存活下来。尽管这一结果符合主流的灭绝模型，但此前在大规模灭绝界线处从未观测到此类现象。这或许进一步表明，奥陶纪-志留纪灭绝事件并未伴随宏观演化选择性机制的转变。