Paleontologists have discovered the well-preserved fossilized remains of a tadpole of the early anuran species Notobatrachus degiustoi at the locality of Estancia La Matilde in Patagonia, Argentina.
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Life reconstruction of tadpoles and adults of Notobatrachus degiustoi. Image credit: Gabriel Lio.
Frogs and toads belong to a group of tailless amphibians called the anurans.
They are characterized by a biphasic life cycle, with an aquatic larval (tadpole) stage followed by an adult (frog) stage
Adult anurans are represented in the fossil record back to the Late Triassic epoch (around 217-213 million years ago), but tadpoles are undocumented before the Cretaceous period (around 145 million years ago).
“Tadpoles are the free-living, non-reproductive aquatic larvae of anurans, which have to go through a metamorphic phase of profound morphological and ecological changes within a short period of time to reach the adult reproductive stage,” said Universidad Maimónides paleontologist Mariana Chuliver and her colleagues.
“This drastic type of metamorphosis of anurans is the most extreme among living tetrapods, and tadpoles represent a highly derived larval stage.”
The authors examined a well-preserved fossil tadpole of Notobatrachus degiustoi from the La Matilde Formation in Patagonia.
This giant anuran lived during the Middle Jurassic epoch, between 168 and 161 million years ago.
The species is also represented by a large number of superbly preserved adult specimens from the same locality.
Notobatrachus degiustoi tadpole. Image credit: Chuliver et al., doi: 10.1038/s41586-024-08055-y.
According to the team, the tadpole of Notobatrachus degiustoi was almost 16 cm (6.3 inches) in length.
The head, most of the body and part of the tail are visible, as are the eyes, nerves and a forelimb, which suggests the tadpole was in the late stages of metamorphosis.
Collectively, they show that key features of today’s tadpoles, such as their filter feeding system, had already evolved in early anurans around 161 million years ago.
“The tadpole’s exquisite preservation, including soft tissues, shows features associated with the filter-feeding mechanism characteristic of living tadpoles,” the researchers said.
“Notably, both Notobatrachus degiustoi tadpole and adult reached a large size, demonstrating that tadpole gigantism occurred among stem-anurans.”
“This new discovery reveals that a biphasic life cycle, with filter-feeding tadpoles inhabiting aquatic ephemeral environments, was already present in the early evolutionary history of stem-anurans and has remained stable for at least 161 million years.”
The findings were published this week in the journal Nature.
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M. Chuliver et al. The oldest tadpole reveals evolutionary stability of the anuran life cycle. Nature, published online October 30, 2024; doi: 10.1038/s41586-024-08055-y
