Argentine scientists have discovered the world's oldest tadpole, which lived alongside dinosaurs in the Middle Jurassic period some 161 million years ago, a key paleontological find for understanding the evolution of frogs and toads.

The excellent state of preservation of the fossil found in Argentina's vast southern Patagonian region during a dinosaur dig led researchers to conclude the living form of tadpoles has remained almost unchanged over the past 160 million years.

"It's not only the oldest tadpole in the world and amazingly preserved, but it also tells us about the size of one of the few frog species known from that time," said Mariana Chuliver, researcher at regional conservation group Azara Foundation.

Chuliver, lead author of a study on the tadpole published on Wednesday in the journal Nature, added that the level of preservation of the specimen was extremely rare, since tadpoles, with their soft bodies, have little chance of fossilizing.

"This is very important because it allows us to know the diet and lifestyle of these organisms." Scientists discovered the fossil, which measured 16 centimeters, on a ranch in the province of Santa Cruz, about 2,300 kilometers (1429.15 miles) south of capital Buenos Aires, in January 2020 while searching for dinosaur remains.

The expert, who led work carried out by the Azara Foundation, the Museum of Natural Sciences and the Chinese Academy of Sciences, said the specimen belongs to Notobatrachus degiustoi, a species that is the ancestor of modern Anurans, a group that includes frogs, toads and toads.

(Production: Miguel Lo Bianco, Anna Portella)