This 161-Million-Year-Old Tadpole Fossil Was Unearthed In Argentina
While searching for dinosaur fossils in Argentina, paleontologists accidentally discovered the fossil of a giant ancient tadpole instead.
It was found in the La Matilde Formation in Patagonia and could help clarify the timeline of frog evolution. The fossil is about a half-foot long and well-preserved, with several of its features clearly imprinted in a slab of sandstone.
Parts of the tadpole’s skull and backbone, along with impressions of its eyes, gills, and nerves, can be seen. The tadpole is from the frog species Notobatrachus degiustoi.
The specimen dates back around 161 million years ago, during the middle Jurassic period. It is the oldest-known fossil of a giant tadpole, surpassing the previous record holder by approximately 20 million years.
Researchers know that frogs existed as far back as 217 million years ago, but it is unclear when exactly the tadpole stage of frog development evolved.
Tadpole fossils are rare because they usually die in water, which also makes them easy targets for scavengers. Additionally, tadpoles are primarily made of cartilage and soft tissue. Those materials do not fossilize as well as hard bones, which tadpoles do not have until they reach adulthood.
“Luckily, this tadpole is in an advanced stage of development,” said Mariana Chuliver, the first author of the study and an evolutionary biologist at Maimónides University in Buenos Aires.
The vertebrae of the tadpole had just started to form, allowing the research team to see the bumps and ridges of the spine.
These unique features helped them determine what species it belonged to and connect it to its adult counterpart, a now-extinct giant frog.
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The tadpole was about six inches in length. Surprisingly, the adult frog was just as big. According to Chuliver, it is difficult to find a creature in nature today that is giant in both the juvenile and adult stages.
But back then, Jurassic ponds had plenty of resources, so the tadpoles were able to take longer to develop. Other than its size, the N. degiustoi tadpole is incredibly similar to the tadpoles of today.
It had spiny projections on its gills that resembled a gill scaffold system that modern tadpoles use to filter plankton, algae, and residue from water.
This means that ancient tadpoles likely ate the same way modern tadpoles do. Their survival strategy has stayed the same for millions of years, helping them withstand multiple mass extinction events.
It’s safe to say that tadpoles may have been around for just as long as adult frogs since the complex filter-feeding system already evolved in tadpoles 161 million years ago.
The research team hopes to receive more funding so they can return to the La Matilde Formation to search for more tadpole fossils.
The details of their findings were published in the journal Nature.
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