Background and Aims Previous molecular dating studies revealed historical mass extinctions and recent radiations of extant cycads, but debates still exist between palaeobotanists and evolutionary biologists regarding the origin and evolution of Cycadaceae. Methods Using whole plastomic data, we revisited the phylogeny of this family and found the Palawan endemic Cycas clade was strongly related to all lineages from Southeast Eurasia, coinciding with a plate drift event occurring in the Early Oligocene. By integrating fossil and biogeographical calibrations as well as molecular data from protein-coding genes, we established different calibration schemes and tested competing evolutionary timelines of Cycadaceae. Key Results We found recent dispersal cannot explain the distribution of Palawan Cycas, yet the scenario including the tectonic calibration yielded a mean crown age of extant Cycadaceae of ~69–43 million years ago by different tree priors, consistent with multiple Palaeogene fossils assigned to this family. Biogeographical analyses incorporating fossil distributions revealed East Asia as the ancestral area of Cycadaceae. Conclusions Our findings challenge the previously proposed Middle–Late Miocene diversification of cycads and an Indochina origin for Cycadaceae and highlight the importance of combining phylogenetic clades, tectonic events and fossils for rebuilding the evolutionary history of lineages that have undergone massive extinctions.

中文翻译：

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不是那么年轻：结合质体系统发育、板块构造和化石证据表明苏铁科的古近纪多样化

背景和目的 以前的分子测年研究揭示了现存苏铁的历史性大规模灭绝和最近的辐射，但古植物学家和进化生物学家之间仍然存在关于苏铁科的起源和进化的争论。方法利用整个质体数据，我们重新审视了该科的系统发育，发现巴拉望地方性苏铁分支与欧亚大陆东南部的所有谱系密切相关，与早渐新世发生的板块漂移事件相吻合。通过整合化石和生物地理校准以及来自蛋白质编码基因的分子数据，我们建立了不同的校准方案并测试了苏铁科的竞争进化时间表。主要结果 我们发现最近的扩散无法解释巴拉望苏铁的分布，然而，包括构造校准在内的情景通过不同的树木先验产生了约 69-4300 万年前现存苏铁科的平均树冠年龄，这与分配给该科的多个古近纪化石一致。结合化石分布的生物地理分析表明，东亚是苏铁科的祖先地区。结论 我们的研究结果挑战了之前提出的中新世中新世中晚期苏铁的多样化和苏铁科的印度支那起源，并强调了结合系统发育进化枝、构造事件和化石对于重建经历了大规模灭绝的谱系进化历史的重要性。结合化石分布的生物地理分析表明，东亚是苏铁科的祖先地区。结论 我们的研究结果挑战了之前提出的中新世中新世中晚期苏铁的多样化和苏铁科的印度支那起源，并强调了结合系统发育进化枝、构造事件和化石对于重建经历了大规模灭绝的谱系进化历史的重要性。结合化石分布的生物地理分析表明，东亚是苏铁科的祖先地区。结论 我们的研究结果挑战了之前提出的中新世中新世中晚期苏铁的多样化和苏铁科的印度支那起源，并强调了结合系统发育进化枝、构造事件和化石对于重建经历了大规模灭绝的谱系进化历史的重要性。