The oldest tadpole fossil known to science dates back 161 million years.

The beautifully preserved fossilized tadpoles are the oldest discovered by science, dating back 161 million years, and their anatomy is strikingly similar to some of today’s species. I am.

Paleontologists discovered the fossil in January 2020 while searching for feathered dinosaurs in Argentina’s Santa Cruz province.

“They missed the mark,” says Mariana Churivar of Universidad Maimonides in Buenos Aires, Argentina. “But after many days of digging, one of our team members discovered a stone with a special signature: a fossilized tadpole.”

Chubar and her colleagues have now identified this tadpole as belonging to an extinct frog species. Notobatrachus degiustoiwas deciphered from hundreds of adult specimens discovered in the same fossil deposit since 1957.

Until now, scientists had never unearthed tadpole fossils from before the Cretaceous Period, which began about 145 million years ago. This specimen is also the first ever fossilized tadpole from an early frog lineage known as stalk anurans, which is older than modern species known as crown anurans.

This fossil is very well preserved, with eyes and nerves visible in the head, forelimbs, and part of the tail. The researchers estimate that it was about 16 centimeters long, comparable to the largest tadpole in existence today.

The part of the skeleton that supports the gills suggests that the specialized filter-feeding anatomy of modern tadpoles had already evolved in this fossilized tadpole, Chubar said.

The similarities between ancient and modern tadpoles are so great that the researchers were even able to determine the developmental stage in the fossils, concluding that they were just about to undergo metamorphosis into frogs.

Earth’s warm, humid climate in the past, coupled with the lack of competition and predation from other frog species and fish, may have made it easier for tadpoles to grow large, Chubar said.

Jodi Rowley from the Australian Museum in Sydney said the discovery of the oldest known tadpole “confirms how successful and stable the ‘typical’ frog life cycle we all learn about in school is.” states.

The size of the tadpoles tells us a lot about the habitat in which frogs evolved more than 160 million years ago, a water-rich environment with few predators or competitors, she says. “This is something modern frog species can only dream of.”