Paleontologists have unearthed the oldest known tadpole fossil, dating back at least 161 million years.

The discovery, made in January 2020 and published in *Nature* on October 30, 2024, was accidental.

The research team, while engaged in another project, stumbled upon the remarkable fossil embedded in sandstone.

The exceptionally well-preserved fossil includes portions of the tadpole’s skull and spine, along with imprints of its eyes and nerves.

Study author Mariana Chuliver, a biologist at Buenos Aires’ Maimonides University, described it as “not only the oldest tadpole known, but also the most exquisitely preserved.”

Ben Kligman, a paleontologist at the Smithsonian (who wasn’t involved in the research), noted the find helps refine the timeline of frog life-cycle evolution.

The fossil belongs to the Jurassic species *Notobatrachus degiustoi* and offers insights into frog evolution.

The fossil exhibits features similar to modern tadpoles, including a filter-feeding mechanism.

The exceptionally large fossil measures approximately six inches in length.

While modern frog sizes vary greatly—the Goliath frog being the largest extant species—their tadpoles are generally comparable in size, although Goliath frog tadpoles can reach a remarkable 12.5 inches and weigh up to 7.2 pounds.

The fossil’s identification as a tadpole was immediate, but further examination revealed its exceptional preservation and age.

“When I first saw the fossil, I said, ‘Okay, it is a tadpole, there is no doubt,'” Chuliver stated. “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.”