Abstract The evolution of the calcareous nannofossil Eiffellithus turriseiffelii – E. eximius lineage in the Turonian from the western tropical Atlantic and Indian Ocean indicates identical eiffellithid forms with morphological change in the rotation of the crossbar, relative to the longitudinal axis, from an “x” (E. turriseiffelii) to a “+” (E. eximius). Within these indistinguishable eiffellithid assemblages, neither the size nor shape show significant change during the morphological transition of the crossbar orientation. The rotation of the crossbar toward an axial alignment results in two shifts in the mean angle values. Prior to the first shift, the mean angles of the eiffellithid assemblage have values between 35o and 45o with no forms with crossbar angles of

中文翻译：

---

Eiffellithus eximius 物种复合体的生物特征分析及其生物地层学意义

摘要 钙质纳米化石 Eiffellithus turriseiffelii - E. eximius 谱系的进化表明来自西热带大西洋和印度洋的 Turonian 具有相同的 eiffellithid 形式，横杆相对于纵轴的旋转形态发生变化，从“x” (E. turriseiffelii) 到“+” (E. eximius)。在这些难以区分的 eiffellithid 组合中，在横杆方向的形态转变过程中，大小和形状都没有显示出显着的变化。横杆朝向轴向对齐的旋转导致平均角度值的两次偏移。在第一次转变之前，eiffellithid 组合的平均角度值在 35o 和 45o 之间，没有横杆角度为