Reproduction is a key aspect of evolution, but the process is rarely preserved in the fossil record. Organisms fortuitously preserved undergoing reproduction provide an exceptional window illuminating the biology of extinct taxa, especially those with unknown phylogenetic position. Here we report exceptional specimens of chitinozoans (enigmatic Paleozoic organic-walled microfossils) preserved as “test-in-test” morphology, which have previously been interpreted as teratological forms. Application of advanced imaging techniques on newly recovered and reexamined Ordovician materials enabled documentation of critical morphological details of the test’s inner ultrastructure for the first time. The results show that the newly observed spongy material and dendritic structure on or inside the chitinozoan test as well as the test wall itself are all made of clustered rounded spherical particles. Morphological details suggest that those specimens represent key stages of new asexual reproductive strategies, hitherto undescribed, which produce either one or several offspring at a time. This observation challenges the prevailing hypothesis that chitinozoans are eggs of cryptic extinct marine metazoans. Instead, it is more plausible that they represent a new isolated group of protists.

中文翻译：

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僵化的生殖方式揭示了几丁质的千足虫亲和力

繁殖是进化的关键方面，但这一过程很少保存在化石记录中。幸运地保存下来并正在繁殖的生物提供了一个特殊的窗口，阐明了灭绝的分类单元的生物学，特别是那些系统发育位置不明的生物。在这里，我们报告了奇特类动物（神秘的古生代有机壁微化石）的特殊标本，这些标本保存为“测试中”的形态，以前被解释为致畸形式。先进的成像技术在新近恢复和重新检查的奥陶纪材料上的应用首次使该文件的内部超微结构的关键形态细节得以记录。结果表明，新观察到的海绵状物质和在甲壳动物试验中或内部的树突结构以及试验壁本身均由簇状的圆形球形颗粒组成。形态学细节表明，这些标本代表了迄今未描述的新的无性繁殖策略的关键阶段，这些策略一次产生一个或多个后代。这一发现挑战了一个普遍的假设，即甲壳动物是隐性灭绝的海洋后生动物的卵。取而代之的是，他们代表了一个新的孤立的原生生物群体。这一发现挑战了一个普遍的假设，即甲壳动物是隐性灭绝的海洋后生动物的卵。取而代之的是，他们代表了一个新的孤立的原生生物群体。这一发现挑战了一个普遍的假设，即甲壳动物是隐性灭绝的海洋后生动物的卵。取而代之的是，他们代表了一个新的孤立的原生生物群体。