More than 160 million years old, a newly discovered amphibian fossil has set a new record for the oldest known tadpole. And it’s a doozy, spanning almost 16 centimeters (or 6 inches) in length.

The print depicts the only known example of the larva of an ancient frog called Notobatrachus degiustoi . Since aIf adults of the species were found of similar size, it is speculated that the large pollywog could have been close to its metamorphosis phase.

It is therefore unlikely that the individual suffered from a rare condition, such as a problematic thyroid, which would have made him larger than his siblings. It is fair to assume that all tadpoles of this species grew to an impressive length before maturing.

We already know from the fossil record that frogs have been around since at least the late Triassic. 217 to 213 million years ago, but what was happening with tadpoles that long ago is, at least for now, a mystery.

Scientists suspected that key evolutionary features of tadpoles arose at a time when stems the anurans – the evolutionary ancestors of modern frogs and toads – diversified rapidly, at the start of the Triassic and Jurassic periods.

But that estimate was based on living frogs and toads rather than fossil evidence, because, as the study authors say emphasize“Fossil tadpoles are completely absent from the Triassic and Jurassic fossil record.”

So far, that’s the case.

Before this discovery, the oldest recorded tadpoles were around 145 million years old. This new discovery therefore pushes back the irrefutable evidence for this extreme type of metamorphosis by an additional 15 million years.

“This discovery has a double importance because it represents the oldest known tadpole and, to our knowledge, the first rod anuran larva,” explain the authors. to write.

“Its exquisite preservation, including soft tissue, exhibits features associated with the filter-feeding mechanism characteristic of extant tadpoles. Notably, both N. degiustoi both the tadpole and adult reached a large size, demonstrating that tadpole gigantism occurred in stem anurans. “

The tadpole fossil was discovered preserved in Jurassic rock within the La Matilde training in Argentina. Analyzing it closely, a team of researchers led by evolutionary biologist Mariana Chuliver from Maimonides University in Argentina mapped his body in incredible detail.

They could clearly see the little man’s head, as well as the large dark spot in his eye; most of his body; some nerves; part of its tail; and even a forelimb which helps confirm that the metamorphosis was on track before dying prematurely.

This unprecedented snapshot of prehistoric tadpole anatomy revealed that several key features of modern tadpoles – their filter-feeding system, known to scientists as the hyobranchial apparatus, a kind of skeletal tongue, not to mention those clumsy little paws – were an integral part of their lives. the childhood of anurans for at least 161 million years.

“The exquisite preservation of the new specimen, including most of the hyobranchial apparatus and soft tissues, allows us to infer the lifestyle and dietary habits of the N. degiustoi tadpole”, Chuliver and colleagues to write.

“This discovery significantly improves our knowledge of the origins and early evolution of the anuran biphasic life cycle.”

This research was published in Nature.

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