Although belemnites form a major clade of extinct cephalopods, the early stage of their diversification remains poorly known in time and space. Here we investigate the first diversification episodes of belemnites (order Belemnitida) using a new species‐level database encompassing the Hettangian–Aalenian interval (Early Jurassic – earliest Middle Jurassic) and covering the Western Tethys. Rarefied richness shows a four‐fold increase from the Planorbis chronozone to the Ibex chronozone, a strong decrease between the Margaritatus and Spinatum chronozones, followed by a drop in the Spinatum–Serpentinum interval that is coeval with the second‐order Toarcian biological crisis. The Bifrons chronozone records a high richness that departs significantly from those of the surrounding chronozones. A last richness peak in the Dispansum chronozone precedes a decrease towards the Aalenian. Biogeographical analyses do not reveal any clear large‐scale provincialism for belemnites, in sharp contrast with ammonoids. Such a long‐term homogeneous spatial distribution of belemnites is probably due to: (1) the relatively poorly‐documented fossil record of belemnites, especially in Mediterranean localities; and (2) contrasted dispersal abilities of belemnites compared to ammonoids over the studied time interval.

中文翻译：

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西特提斯侏罗纪早期贝母石多样性的起伏

尽管Belemnites是绝种的头足类动物的主要进化枝，但其多样化的早期阶段在时间和空间上仍然鲜为人知。在这里，我们使用新的物种水平数据库（包括侏罗纪至阿里尼亚期（早侏罗纪至最早的中侏罗纪）并覆盖西特提斯），调查了贝伦尼特人的第一个多样化事件（阶贝母目）。稀疏的丰富度显示，从Planorbis年代带到Ibex年代带增加了四倍，在Margaritatus和Spinatum年代带之间急剧下降，其次是Spinatum-Serpentinum间隔的下降，这与二阶Toarcian生物危机同时出现。Bifrons chronozone记录了丰富的丰富度，与周围的chronozones明显不同。Dispansum chronozone中的最后一个富集峰在朝Aalenian减小之前出现。生物地理学分析没有显示出任何明显的大规模省地方主义贝伦尼特体，与氨烃类形成鲜明对比。长期以来，贝类动物的均匀空间分布可能是由于：（1）贝类动物化石记录的文献记录相对较少，尤其是在地中海地区；（2）在所研究的时间间隔内，与甜菜碱相比，甜菜碱的分散能力有所不同。