The Cryogenian Period experienced two long lived global glaciations known as Snowball Earths. While these events were dramatic, eukaryotic life persisted through them, and fossil evidence shows that eukaryotes thrived during the c. 30‐million‐year interlude between the glaciations. Carbonate successions have become an important taphonomic window for this interval. One of the most notable examples is the c. 662–635 Ma Taishir Formation (Tsagaan Olom Group, Zavkhan Terrane, Mongolia) which has yielded a number of eukaryotic fossil taxa. Here, we examine more closely the morphology and taxonomic affinity of some of these Taishir fossils previously interpreted as remains of ciliate tintinnid loricae (purportedly the oldest fossil ciliates). New morphological and ultrastructural analyses indicate that these fossils are not ciliate tintinnids. Instead, we propose a new interpretation: that they are algal reproductive structures related to coeval macroscopic organic warty sheets described as putative red algae. We report the first occurrence of these fossils in the earliest Ediacaran Ol Formation, indicating that this taxon persisted through the Marinoan Snowball Earth. A new interpretation of these fossils as putative red algal spores has broad implications for our understanding of biodiversity in the Neoproterozoic Era, specifically during the Cryogenian Period, and for the antiquity of ciliates.

中文翻译：

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低温冰期间断中最古老的化石纤毛虫被重新解释为可能的红藻孢子

低温时代经历了两次被称为雪球地球的长期全球冰川。尽管这些事件是戏剧性的，但真核生物仍通过它们持续存在，化石证据表明，真核生物在c期间蓬勃发展。冰川之间存在3000万年的时间间隔。对于该间隔，碳酸盐岩演替已成为重要的层析窗口。最著名的例子之一是c。662–635 Ma Taishir组（蒙古扎夫汗特拉山的Tsagaan Olom集团），产生了许多真核生物化石类群。在这里，我们更仔细地研究了一些这些Taishir化石的形态和分类学亲和力，这些化石以前被解释为纤毛锡丁腈水藻（据称是最古老的纤毛虫化石）的遗迹。新的形态学和超微结构分析表明，这些化石不是纤毛状的丁丁橡胶。取而代之的是，我们提出了一种新的解释：它们是与被称为推定的红藻的近代宏观有机疣表有关的藻繁殖结构。我们报告这些化石最早出现在最早的Ediacaran Ol组中，这表明该分类群在整个Marinoan Snowball Earth中一直存在。