The oldest tadpole in history was a Jurassic giant

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While searching for dinosaur fossils in Argentina, paleontologists made a chance discovery: the oldest tadpole ever found.

A fossil discovered in the La Matilde Formation in Patagonia may finally end the debate about frog evolution, scientists reported Wednesday (October 30) in the journal Nature.

The fossil is a fantastically preserved specimen of a species of frog. Notobatrachus degiustoiComplete with imprints of soft tissues including the animal’s eyeballs, gills and nerves, according to the study.

The sample dates back to approximately 161 million years ago, during the Middle Jurassic. next oldest tadpole was dated early Cretaceous period145–100 million years ago. The newfound fossil is also the first ancient tadpole to be matched to its adult counterpart in the fossil record. This may end the debate over when the frog’s tadpole stage of development arose.

“Some researchers argue that probably the most (ancient) frogs did not have a tadpole stage,” he said. Mariana Chuliverevolutionary biologist at the University of Maimonides in Buenos Aires and first author of the paper. That’s because the oldest frog fossil dates to the Late Triassic (about 217 million years ago), tens of millions of years earlier than the oldest known tadpole fossils. But by finding this fossil, “we have demonstrated that this is not true,” she said.

Connected: Dinosaur-era frog found fossilized with belly full of eggs and likely killed during mating

Fossils of tadpoles are generally difficult to find because young swimmers usually die while still in the water. Because scavengers are willing to feast on dead animals, water can sometimes be a bad place for petrification. Additionally, tadpoles are composed primarily of cartilage and soft tissue; they do not form hard bones, which are more easily fossilized into adulthood.

“Fortunately, this tadpole is at an advanced stage of development,” Chuliver told Live Science. The tadpole’s vertebrae began to ossify, allowing the researchers to see ridges and spine ridges that helped them identify the species and associate the tadpole with its adult counterpart.

“The most amazing thing to me is the preservation of such fragile structures,” Chuliver said, “which are really hard to find in the fossil record.” The size of the specimen also helped identify the species, she said. The tadpole was about 6 inches (16 cm) long—like a baseball with a 3-inch (7.6 cm) tail. The adult frog is just as large, which surprised the researchers.

“Giant stages (juvenile and adult) are very difficult to find in nature today,” Chuliver said. But for N. degiustoiIn her opinion, the Jurassic ponds had sufficient resources, and the tadpoles could afford a longer development time.

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However, in addition to size, the body N. degiustoi the tadpole is very similar to the modern tadpole. The imprints of the spines on the gills indicated that the tadpole probably even fed similarly to modern tadpoles, with a filter feeding system that allowed it to suck up plankton, algae and detritus from the water around it. The researchers suggested that, given that these complex systems had already evolved in tadpoles 161 million years ago, tadpoles likely existed as long as adult frogs.

Chuliver hopes to gain more funding to return to the La Matilda Formation in search of more tadpoles to expand the fossil record.