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A tadpole fossil found in Argentina, dating back at least 161 million years, is the oldest that has ever been discovered.
The fossil was found back in January 2020, with news of the discovery published on Oct. 30, 2024, in Nature.
The team was not necessarily in search of what they found and came upon their monumental discovery by accident.
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The team was actually on the hunt for dinosaur fossils, according to National Geographic.
What they ended up finding was the oldest-known fossil of a tadpole on a piece of sandstone, according to The Associated Press.
The fossil contained parts of the tadpole's skull and backbone, as well as impressions of eyes and nerves, according to the source.
"It’s not only the oldest tadpole known, but also the most exquisitely preserved," said study author Mariana Chuliver, a biologist at Buenos Aires’ Maimonides University, per AP.
"It’s starting to help narrow the timeframe in which a frog becomes a frog," said Ben Kligman, a paleontologist at the Smithsonian National Museum of Natural History who was not part of the research, according to the source.
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The tadpole discovered belongs to the Jurassic species Notobatrachus degiustoi, according to the published research, and provides a greater understanding of the evolution of the life cycle of a frog.
The fossil shared similar characteristics to a modern-day tadpole. Similarities include "the filter-feeding mechanism characteristic" that is present in tadpoles still in existence today, according to the research.
The exceptionally large tadpole fossil measured to be about six inches in length.
Modern frogs range greatly in size. The largest frog species surviving today is the Goliath frog.
Though the tadpoles belonging to these species generally fall in line with other frog species in terms of size, they can grow to be a whopping 12.5 inches, according to San Diego Zoo's website. These massive frogs can weigh up to 7.2 pounds, per the source.
As for the tadpole fossil recently studied, there was no doubting what it was upon discovery, but further investigation began to reveal more about the record-breaking find.
"When I first saw the fossil, I said, 'Okay, it is a tadpole, there is no doubt,'" Chuliver said, per NPR. "But then when I saw it under the binocular microscope, I said, 'Okay, this is the best tadpole ever!' Because up to now, there wasn't any other type of fossil tadpole with the gill skeleton preserved."
