A team of paleontologists led by Federico Agnolín discovered the oldest tadpole documented so far, approximately 161-168 million years old, in Estancia La Matilde, Santa Cruz, Argentina. This discovery was serendipitous, as the team was looking for dinosaur fossils in the quarry, but instead found frog fossils of extinct species. Notobatrachus degiustoi. The preservation of the fossil is remarkable because it allows us to observe details such as the gills, eyes and nerves of the tadpole, which reveal crucial aspects of its biology and evolution.
The fossil shows that frogs had a tadpole phase for millions of years, something many experts already suspected. According to herpetologist Alexander Haas, of the Leibniz Institute in Germany, “this is a nice confirmation of what many experts suspected.” This discovery is important because it demonstrates that tadpoles represent an established and long-lasting evolutionary phase in the frog life cycle since the Jurassic period, about 30 million years ago longer than previously believed.
For the analysis of the fossil, Agnolín enlisted the help of biologist Mariana Chuliver, who observed that the gill cartilage of this ancient tadpole is surprisingly similar to that of modern tadpoles. This suggests that the feeding behavior of the tadpoles of No degiustoi It was similar to that of some modern species. Like modern tadpoles, they probably fed on microorganisms in the water and grew considerably before completing metamorphosis.
However, these fossil tadpoles were remarkably large, which is unusual since most extant frogs reach their maximum size in the adult stage. Zoologist Marissa Fabrezi expresses her surprise at “the exceptional conservation of this tadpole” and believes that this gigantic size is important for understanding its evolution. It is hypothesized that this giant species could grow large in the tadpole stage because it lived in temporary ponds, where the lack of predators allowed it to remain in this stage longer.
🟢CONICET scientists have found remains of the oldest tadpole ever recorded in Patagonia. The study of the fossil, 165 million years old, allows us to better understand the evolution of the peculiar life cycle of toads and frogs.⬇️ pic.twitter.com/rFsyd8eCxN
— CONICET Dialoga (@CONICETDialoga) October 31, 2024
Chuliver notes that the fossil shows a tadpole close to metamorphosis, so it probably didn’t grow much when it became an adult. Duckling frogs (Pseudis paradoxa), which inhabit similar environments, also grow significantly into the tadpole stage, which may be an adaptation to temporary environments in which they exploit resources before transitioning to terrestrial life.
Ultimately, Agnolín considers this discovery proof of the evolutionary success of frogs, but also highlights their current vulnerability. Because they depend on aquatic and terrestrial habitats, frogs face significant threats from alteration of their natural environments, making them more prone to extinction. As Agnolín reflects, “the same metamorphosis that made them successful now makes them more prone to extinction.”
Time.news Editor (TNE): Welcome, Dr. Agnolín! It’s a pleasure to have you here to discuss your remarkable discovery in Santa Cruz, Argentina. Your team’s finding of the oldest documented tadpole is truly groundbreaking. Can you tell us what it felt like to unearth such a significant fossil?
Federico Agnolín (FA): Thank you for having me! It was an incredible moment, to be honest. We were initially focused on searching for dinosaur fossils, so when we stumbled upon what turned out to be the oldest tadpole—dating back 161-168 million years—it was quite unexpected. It felt like the Earth was revealing a long-kept secret!
TNE: It sounds like a stroke of luck! What were some of the characteristics of this fossil that made it so special?
FA: The preservation of the fossil is indeed extraordinary. We could observe fine details such as the gills, eyes, and nerve structures. It provides us with crucial insights into the biology and evolutionary history of frogs. The clarity of these features is what sets this fossil apart from others we’ve discovered.
TNE: Herpetologist Alexander Haas noted that this finding confirms the long-established tadpole phase in frogs. How does this change the narrative around frog evolution, especially concerning their lifecycle?
FA: It changes quite a bit! The discovery reinforces that tadpoles have been an essential and enduring phase in the frog lifecycle since at least the Jurassic period. It extends the timeline of this developmental stage by about 30 million years more than we previously thought, suggesting that tadpoles were not just temporary but crucial to their survival and evolution.
TNE: Fascinating! Mariana Chuliver highlighted the similarities between the gill cartilage of Notobatrachus degiustoi and modern tadpoles. What implications does this have for our understanding of tadpole behavior over millions of years?
FA: It implies that not only did the tadpole phase exist, but that their feeding behavior has been consistent throughout history. Like their modern counterparts, N. degiustoi probably consumed microorganisms in the water. This continuity in behavior suggests a successful evolutionary strategy that has persisted for millions of years.
TNE: Zoologist Marissa Fabrezi expressed surprise at the size of this ancient tadpole, noting it was remarkably large. Could you elaborate on how size plays a role in its evolutionary significance?
FA: Absolutely! The large size of this tadpole is unusual since most frogs tend to maximize their size in adulthood. It’s likely that N. degiustoi thrived in temporary ponds where fewer predators existed, allowing them to remain in the tadpole stage longer. This could indicate a different adaptive strategy in their environment, which is crucial for understanding how these organisms evolved.
TNE: It seems this discovery could reshape our understanding of amphibian evolution quite significantly. What’s next for your research team? Are there more fossils to uncover?
FA: We certainly hope to uncover more fossils and gather additional data! Understanding the ecosystem dynamics of the time and discovering how other amphibians may have existed alongside these ancient tadpoles is a priority. Each fossil has a story that can teach us more about our planet’s biological history.
TNE: That sounds like an exciting journey ahead! Thank you, Dr. Agnolín, for sharing your insights on this significant discovery. We look forward to hearing more about your team’s future findings.
FA: Thank you! It’s been a pleasure discussing our work. I’m excited about what lies ahead in paleontology and the secrets we still have to uncover!