Cosmopolitanism occurred recurrently during the geologic past, especially after mass extinctions, but the underlying mechanisms remain poorly known. Three theoretical models, not mutually exclusive, can lead to cosmopolitanism: (1) selective extinction in endemic taxa, (2) endemic taxa becoming cosmopolitan after the extinction and (3) an increase in the number of newly originated cosmopolitan taxa after extinction. We analyzed an updated occurrence dataset including 831 middle Permian to Middle Triassic ammonoid genera and used two network methods to distinguish major episodes of ammonoid cosmopolitanism during this time interval. Then, we tested the three proposed models in these case studies. Our results confirm that at least two remarkable cosmopolitanism events occurred after the Permian–Triassic and late Smithian (Early Triassic) extinctions, respectively. Partitioned analyses of survivors and newcomers revealed that the immediate cosmopolitanism event (Griesbachian) after the Permian–Triassic event can be attributed to endemic genera becoming cosmopolitan (model 2) and an increase in the number of newly originated cosmopolitan genera after the extinction (model 3). Late Smithian cosmopolitanism is caused by selective extinction in endemic taxa (model 1) and an increase in the number of newly originated cosmopolitan genera (model 3). We found that the survivors of the Permian–Triassic mass extinction did not show a wider geographic range, suggesting that this mass extinction is nonselective among the biogeographic ranges, while late Smithian survivors exhibit a wide geographic range, indicating selective survivorship among cosmopolitan genera. These successive cosmopolitanism events during severe extinctions are associated with marked environmental upheavals such as rapid climate changes and oceanic anoxic events, suggesting that environmental fluctuations play a significant role in cosmopolitanism.

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深入理解世界主义：以二叠纪中二叠纪至三叠纪中叶菊石为例

世界主义在地质历史时期反复发生，特别是在大灭绝之后，但其潜在机制仍然鲜为人知。三个不相互排斥的理论模型可以导致世界主义：（1）地方性分类群的选择性灭绝，（2）灭绝后地方性分类群成为世界性的，（3）灭绝后新起源的世界性分类群的数量增加。我们分析了一个更新的发生数据集，包括 831 个中二叠纪到中三叠纪菊石属，并使用两种网络方法来区分该时间间隔内菊石世界主义的主要事件。然后，我们在这些案例研究中测试了三个提出的模型。我们的研究结果证实，在二叠纪-三叠纪和史密斯纪晚期（早三叠纪）灭绝之后，至少发生了两次显着的世界主义事件，分别。对幸存者和新来者的分区分析表明，二叠纪-三叠纪事件后立即发生的世界主义事件（格里斯巴赫）可归因于地方性属变得世界性（模型2）和灭绝后新起源的世界性属数量的增加（模型3） ）。晚期史密斯世界主义是由地方性分类群的选择性灭绝（模型 1）和新起源的世界性属的数量增加（模型 3）引起的。我们发现二叠纪-三叠纪大灭绝的幸存者没有表现出更广泛的地理范围，这表明这种大灭绝在生物地理范围中是非选择性的，而晚期史密斯幸存者表现出广泛的地理范围，表明在世界性属中选择性幸存。