Data from: Graptoloid diversity and disparity became decoupled during the Ordovician mass extinction

The morphological study of extinct taxa allows for analysis of a diverse set of macroevolutionary hypotheses, including testing for change in the magnitude of morphological divergence, extinction selectivity on form, and the ecological context of radiations. Late Ordovician graptoloids experienced a phylogenetic bottleneck at the Hirnantian mass extinction (~445 Ma), when a major clade of graptoloids was driven to extinction while another clade simultaneously radiated. In this study, we developed a dataset of 49 ecologically-relevant characters for 183 species with which we tested two main hypotheses: (a) could the biased survival of one graptoloid clade over another have resulted from morphological selectivity alone and (b) are the temporal patterns of morphological disparity and innovation during the recovery consistent with an interpretation as an adaptive radiation resulting from ecological release? We find that a general model of morphological selectivity has a low probability of producing the observed pattern of taxonomic selectivity. Selectivity on non-morphological variation, such as geographic range or different physiological tolerances, is more likely the cause. Contrary to predictions from theory on adaptive radiations and ecological speciation, changes in disparity and species richness are uncoupled. We also find that the early recovery is unexpectedly characterized by relatively low morphological disparity and innovation, despite also being an interval of elevated speciation. As it is necessary to invoke factors other than ecology to explain the graptoloid recovery, more complex models may be needed to explain recovery dynamics after mass extinctions.

对灭绝类群的形态学研究，可为多样的宏演化假说提供分析框架，包括检验形态分化幅度的变化、基于形态的灭绝选择性，以及辐射演化的生态背景。奥陶纪晚期的笔石类（graptoloids）在赫南特纪生物大灭绝（Hirnantian mass extinction，约4.45亿年前，即~445 Ma）期间遭遇了系统发育瓶颈：一个主要的笔石演化支走向灭绝，而另一演化支同时发生辐射演化。本研究构建了涵盖183个物种的49个生态相关性状数据集，用以检验两项核心假说：（a）某一笔石演化支相较于另一类的偏倚幸存，是否仅由形态选择性所致；（b）复苏阶段内形态差异度（morphological disparity）与演化创新的时间模式，是否符合生态释放驱动的适应辐射这一解释？研究结果表明，通用形态选择性模型复刻观测到的分类选择性模式的概率极低，而非形态性状差异（如地理分布范围或不同生理耐受能力）相关的选择性，更可能是该现象的成因。与适应辐射及生态物种形成的理论预测相悖，本研究发现形态差异度与物种丰富度的变化并无关联。此外，尽管早复苏期存在较高的物种形成速率，其形态差异度与演化创新却意外地处于较低水平。由于需引入生态以外的因素来解释笔石类的复苏过程，未来或需构建更为复杂的模型，以阐释大灭绝后的复苏动力学。