This specimen is the earliest example of this stage of the frog life cycle in amphibian evolution.
In September 2023, a fascinating chance encounter occurred during the Burning Man festival in Nevada. The rains that fell during the event uncovered something remarkable: a “dinosaur shrimp” found in the middle of the desert. A year later, another group of scientists has stumbled upon an equally historic discovery.
A very “old” tadpole. While searching for dinosaur tracks, a team of researchers in Argentina’s Patagonia found a very ancient tadpole fossil dating back an astounding 161 million years. This makes it the oldest specimen of this frog life cycle in amphibian development.
The fossil belongs to the species Notobatrachus. It was discovered in a quarry in Santa Cruz, Argentina. Notably, it measures just over 6 inches in length, comparable to that of an adult frog.
Evolution and life cycle. Researchers said that the fossil provides unique insights into the development of metamorphosis in frog ancestors. Until now, fossil records of adult frogs dated back to the Triassic period, around 217 million years ago. In addition, the oldest known tadpole fossils were from the Cretaceous period, around 140 million years ago.
The recent Patagonia finding helps the science community to fill an important gap in the timeline of amphibian evolution. It also suggests that the process of metamorphosis was already a characteristic feature of amphibians from the very beginning of their evolution.
Tadpole characteristics. The specimen found includes the head, body, and tail and anatomical details such as eyes, mouth, nerves, and limbs. This combination of features allowed researchers to determine that the tadpole was in an advanced stage of development, just about to begin its metamorphosis into adulthood.
As mentioned earlier, the research team identified the fossil as a Notobatrachus species. This identification was primarily based on the similarities in vertebrae with other adult fossils found in the same location and the absence of other frog species in that geographic area of Argentina.
Ecological and evolutionary significance. A notable feature of the tadpole is its gill system, which allowed it to filter food particles from the water, similar to modern tadpoles. Scientists believe that this feeding system has been present since the early days and continues to be a vital mechanism in thousands of frog species today.
Regarding the tadpole’s unusually large size, researchers suggest that it may have resulted from a lack of competition for food in the temporary ponds where they lived.
Implications for metamorphosis. In conclusion, researchers emphasize that discovering a large tadpole from the Jurassic period supports the theory that metamorphosis was already present in early frogs. They add that their metamorphosis had evolved much earlier than previously believed. In other words, this research work provides “solid and beautiful evidence” for the antiquity of this process in the ancestors of modern frogs, according to Kim Roelants, a frog biology expert at the Vrije Universiteit Brussel in Belgium.
Ultimately, this fascinating finding in Argentina helps the scientific community better understand amphibians’ evolution and early adaptations. It confirms that the larval stages of these creatures were established much earlier in geological history than previously thought.
Image | Chuliver et. al., Journal (2024)
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