Ancient amphibian was Triassic frog

Tiny fossils reveal one of the oldest amphibian species ever found. Andrew Masterson reports.

A concept rendering of a Chinle frog, inside the jaw of a phitosaur.

Andrey Atuchin/Virginia Tech

A collection of tiny bone fragments have enabled palaeontologists to identify a 216-million-year-old relative of frogs.

The fragments, recovered from rocks from an area in the US state of Arizona called the Chinle Formation, are each smaller than a fingernail clipping and come from several different individuals. The researchers estimate the animal, when alive, was no more than a couple of centimetres in length.

A team led by Michelle Stocker from Virginia Tech, US, concluded that the fossil species was the earliest frog-like creature so far found, dating from the Late Triassic period.

“The Chinle frog could fit on the end of your finger,” Stocker says.

Writing in the journal Biology Letters, the scientists say the animal was a member of the salientian clade, which includes modern frogs and some closely-related groups. However, it was not a direct ancestor of today’s frogs, but part of a divergent lineage that went extinct.

“This new find highlights just how much there is still to learn about the Late Triassic ecosystem, and how much we find when we just look a little closer,” notes Stocker.

She adds that the find demonstrates the importance of searching for the fossils of small animals, as well as larger, more attention-grabbing creatures.

Co-author Sterling Nesbitt says that the Chinle discovery redefines the timing of the emergence of amphibians and other complex animals, and sets new goals for investigation.

"Now we know that tiny frogs were present approximately 215 million years ago from North America,” he says, “we may be able to find other members of the modern vertebrate communities in the Triassic Period.”

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