Eukaryogenesis—the process by which the eukaryotic cell emerged—has long puzzled scientists. It has been assumed that the fossil record has little to say about this process, in part because important characters such as the nucleus and mitochondria are rarely preserved, and in part because the prevailing model of early eukaryotes implies that eukaryogenesis occurred before the appearance of the first eukaryotes recognized in the fossil record. Here, I propose a different scenario for early eukaryote evolution than is widely assumed. Rather than crown group eukaryotes originating in the late Paleoproterozoic and remaining ecologically minor components for more than half a billion years in a prokaryote-dominated world, I argue for a late Mesoproterozoic origin of the eukaryotic crown group, implying that eukaryogenesis can be studied using the fossil record. I review the proxy records of four crown group characters: the capacity to form cysts as evidenced by the presence of excystment structures; a complex cytoskeleton as evidenced by spines or pylomes; sterol synthesis as evidenced by steranes; and aerobic respiration—and therefore mitochondria—as evidenced by eukaryotes living in oxic environments, and argue that it might be possible to use these proxy records to infer the order in which these characters evolved. The records indicate that both cyst formation and a complex cytoskeleton appeared by late Paleoproterozoic time, and sterol synthesis appeared in the late Mesoproterozioc or early Neoproterozoic. The origin of aerobic respiration cannot as easily be pinned down, but current evidence permits the possibility that it evolved sometime in the Mesoproterozoic.

真核细胞发生的过程——真核细胞出现的过程——长期以来一直困扰着科学家们。人们假设化石记录几乎没有说明这个过程，部分原因是细胞核和线粒体等重要特征很少被保存，部分原因是早期真核生物的普遍模型暗示真核发生发生在在化石记录中发现的第一个真核生物。在这里，我为早期真核生物进化提出了一种不同于普遍假设的情景。与其说冠群真核生物起源于晚古元古代并在原核生物主导的世界中保留了超过 50 亿年的生态次要成分，我认为真核冠群起源于中元古代晚期，这意味着可以使用化石记录研究真核发生。我回顾了四个冠组特征的代理记录：形成囊肿的能力，如脱囊结构的存在所证明的；由棘或幽门证明的复杂细胞骨架；甾醇合成由甾烷证明；和有氧呼吸——以及线粒体——由生活在有氧环境中的真核生物所证明，并认为有可能使用这些替代记录来推断这些特征的进化顺序。记录表明，囊肿形成和复杂的细胞骨架均出现在古元古代晚期，甾醇合成出现在中元古代晚期或新元古代早期。有氧呼吸的起源不容易确定，