Frogs have existed for a long time. The oldest fossil remains of the animals date from two hundred and seventeen million years ago. This is early in the era of the dinosaurs. Paleontologists—biologists who study the fossilized remains of past life—wondered whether those early frogs had a life cycle like the one we are familiar with for some common species of modern frogs.
This cycle begins when the animals hatch from eggs into fishlike tadpoles with long tail fins. Tadpoles eat pond vegetation, and as they grow, they eventually sprout four legs. Their finned tails shrink and vanish as they undergo the metamorphic change into adult frogs. In this second stage of their life cycle, they can leave their pond and venture onto land. Soon they find mates, lay eggs, and the cycle begins again. Researchers didn’t know how long this cycle has existed because no early fossils of tadpoles had ever been found.
In 2024 a team of paleontologists reported their discovery of the oldest tadpole fossil. They found it in Argentinian Patagonia while searching for dinosaur bones. The tadpole lived about one hundred and sixty million years ago, during the Jurassic era—a time famous for its dinosaurs. The fossil remains were remarkably well preserved and showed many of the same anatomical features as tadpoles do today. The animal was about the size of a modern bullfrog tadpole. When it died, it was well along in development, and had begun to sprout legs. The findings show that the most familiar sort of frog life cycle has existed since the time of the dinosaurs.
A special thanks goes to Rayna C. Bell, California Academy of Sciences, for reviewing today's episode!
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Sources
The oldest known fossil tadpole was a big baby, Science News
161 million year old fossil is the oldest known tadpole, Sci-News
Oldest tadpole known to science dates back 161 million years, New Scientist
Chuliver et al. 2024 The oldest tadpole reveals evolutionary stability of the anuran lifestyle, Nature
