Chuliver Mariana, Agnolín Federico L, Scanferla Agustín, Aranciaga Rolando Mauro, Ezcurra Martín D, Novas Fernando E, Xu Xing
Fundación de Historia Natural "Félix de Azara", Centro de Ciencias Naturales, Ambientales y Antropológicas, Universidad Maimónides, Ciudad Autónoma de Buenos Aires, Argentina.
Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, CONICET-Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Ciudad Autónoma de Buenos Aires, Argentina.
Nature. 2024 Dec;636(8041):138-142. doi: 10.1038/s41586-024-08055-y. Epub 2024 Oct 30.
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 occur. Extant tadpoles exhibit great morphological diversity and ecological relevance, 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)). 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 tadpoles. 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.
无尾目动物的特点是具有双相生命周期，即水生幼体（蝌蚪）阶段之后是成体（蛙）阶段，两者通过变态期相连，在变态期会发生剧烈的形态和生理变化。现存的蝌蚪表现出极大的形态多样性和生态相关性，但在白垩纪之前的化石记录（超过1.45亿年）中没有它们的身影，这使得它们的起源和早期进化成谜。这与可追溯到早侏罗世的变态后无尾目化石记录以及晚三叠世（约2.17 - 2.13亿年前）的近缘物种形成对比。在这里，我们报告了来自巴塔哥尼亚中侏罗世（约1.68 - 1.61亿年前）的基干无尾目动物德氏诺托蟾的晚期蝌蚪。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，据我们所知，也是首个基干无尾目幼虫。它保存精美，包括软组织，显示出与现存蝌蚪特有的滤食机制相关的特征。值得注意的是，德氏诺托蟾的蝌蚪和成体都体型巨大，这表明蝌蚪巨型化现象在基干无尾目中就已出现。这一新发现揭示，具有滤食性蝌蚪栖息于临时性水生环境的双相生命周期，在基干无尾目的早期进化历史中就已存在，并且至少保持了1.61亿年的稳定。
