Abstract The biomarker distributions of mid-Neoproterozoic sediments (800–717 million yr, Ma) from various locations are characterized by the occurrence, besides cholestane isomers, of a novel series of C28 steranes, whereas classical C-24 alkylated steranes are absent. These unusual C28 steranes, termed cryostanes, seem to be restricted to pre-Snowball Earth sediments. We report their conclusive identification as 26-methyl cholestanes based on comparison of gas chromatographic (GC) behavior and mass spectrum of the last eluting cryostane isomer with those of a 26-methyl 5α(H),14α(H),17α(H),20R-cholestane standard obtained by way of synthesis. Sterols methylated at C-26 seem to be restricted to some demosponges and, based on molecular clock estimates, demosponges may have emerged in the time interval 800–700 Ma. A sponge origin of cryostanes is thereby conceivable, making cryostanes the oldest molecular markers for animals. However, other biological sources need to be explored, including the wide variety of eukaryotic protists.

中文翻译：

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中新元古代沉积物中26-甲基胆甾烷的合成及低温烷的鉴定

摘要 来自不同地点的中新元古代沉积物（800-7.17 亿年，Ma）的生物标志物分布特征在于，除了胆甾烷异构体外，还存在一系列新的 C28 甾烷，而没有经典的 C-24 烷基化甾烷。这些不寻常的 C28 甾烷，称为低温烷，似乎仅限于雪球地球之前的沉积物。根据最后洗脱的低温烷异构体的气相色谱 (GC) 行为和质谱与 26-甲基 5α(H),14α(H),17α(H) 的比较，我们报告了它们作为 26-甲基胆甾烷的结论性鉴定,20R-胆甾烷标准品通过合成的方式得到。在 C-26 处甲基化的甾醇似乎仅限于某些去海绵体，根据分子钟估计，去海绵体可能在 800-700 Ma 的时间间隔内出现。因此可以想象低温烷的海绵起源，使低温烷成为动物最古老的分子标记。然而，需要探索其他生物来源，包括种类繁多的真核原生生物。