Anurans 的特点是双相生命周期，水生幼虫（蝌蚪）阶段和成虫（青蛙）阶段，这两个阶段都通过期联系在一起，在这个阶段发生剧烈的形态和生理变化1。现存的蝌蚪表现出极大的形态多样性和生态相关性2，但它们在前白垩纪化石记录（超过 1.45 亿年）中的缺失使它们的起源和早期进化变得神秘。这与可追溯到早侏罗世的后变质无头龙化石记录以及晚三叠世（约 217-2.13 亿年前 （马））的密切相关物种形成鲜明对比3。在这里，我们报道了来自巴塔哥尼亚中侏罗世（约 168-161 马）的茎 anuran Notobatrachus degiustoi 的晚期蝌蚪。这一发现具有双重重要性，因为它代表了已知最古老的蝌蚪，而且据我们所知，它是第一个茎无蚪幼虫。其精美的保存，包括软组织，显示出与现存蝌蚪的滤食机制特征相关的特征4,5。值得注意的是，N. degiustoi 蝌蚪和成虫都达到了较大的尺寸，这表明蝌蚪巨人症发生在茎无蝌中。这项新发现揭示了双相生命周期，其中滤食蝌蚪栖息在水生短暂环境中，已经存在于 stem-anurans 的早期进化历史中，并且至少保持稳定 1.61 亿年。

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The oldest tadpole reveals evolutionary stability of the anuran life cycle

Anurans are characterized by a biphasic life cycle, with an aquatic larval (tadpole) stage followed by an adult (frog) stage, both connected through the metamorphic period in which drastic morphological and physiological changes occur1. Extant tadpoles exhibit great morphological diversity and ecological relevance2, but their absence in the pre-Cretaceous fossil record (older than 145 million years) makes their origins and early evolution enigmatic. This contrasts with the postmetamorphic anuran fossil record that dates back to the Early Jurassic and with closely related species in the Late Triassic (around 217–213 million years ago (Ma))3. Here we report a late-stage tadpole of the stem-anuran Notobatrachus degiustoi from the Middle Jurassic of Patagonia (around 168–161 Ma). This finding has dual importance because it represents the oldest-known tadpole and, to our knowledge, the first stem-anuran larva. Its exquisite preservation, including soft tissues, shows features associated with the filter-feeding mechanism characteristic of extant tadpoles4,5. Notably, both N. degiustoi tadpole and adult reached a large size, demonstrating that tadpole gigantism occurred among stem-anurans. This new discovery reveals that a biphasic life cycle, with filter-feeding tadpoles inhabiting aquatic ephemeral environments, was already present in the early evolutionary history of stem-anurans and has remained stable for at least 161 million years.