An ancient fossil that is 161 million years old is the oldest known tadpole.An ancient fossil that is 161 million years old is the oldest known tadpole.


At the location of Estancia La Matilde in Patagonia, Argentina, paleontologists have found the well-preserved fossilized remains of a tadpole belonging to the early anuran species Notobatrachus degiustoi.


Toads and frogs are members of the anurans, a class of small amphibians.

Their life cycle is biphasic, consisting of an aquatic larval (tadpole) stage and an adult (frog) stage.

Tadpoles are unknown prior to the Cretaceous period (about 145 million years ago), although adult anurans are attested in the fossil record as far back as the Late Triassic epoch (around 217–213 million years ago).

According to Mariana Chuliver, a paleontologist at Universidad Maimónides, and her colleagues, "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."

"Tadpoles represent a highly derived larval stage, and this drastic type of metamorphosis of anurans is the most extreme among living tetrapods."

A well-preserved fossilized Notobatrachus degiustoi tadpole from Patagonia's La Matilde Formation was studied by the authors.

Between 168 and 161 million years ago, during the Middle Jurassic epoch, this enormous anuran was alive.

Numerous excellently preserved adult specimens from the same region also serve as representatives of the species.


The team estimated that the Notobatrachus degiustoi tadpole measured over 16 cm (6.3 inches) in length.

It appears that the tadpole was in the final stages of metamorphosis because the head, the majority of the body, and a portion of the tail are visible, along with the eyes, nerves, and a forelimb.

When taken as a whole, they demonstrate how important traits of modern tadpoles, such their filter feeding mechanism, had already developed in early anurans some 161 million years ago.

According to the researchers, "the tadpole's amazing preservation, including its soft tissues, exhibits features associated with the filter-feeding mechanism characteristic of living tadpoles."

"Notably, both the adult and tadpole of Notobatrachus degiustoi grew to a large size, indicating that tadpole gigantism occurred among stem-anurans."

With filter-feeding tadpoles living in aquatic ephemeral habitats, this new discovery shows that a biphasic life cycle was already present in the early evolutionary history of stem-anurans and has remained stable for at least 161 million years.

Source sci.news

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