A newly discovered fossil amphibian more than 160 million years old has set a new record for the oldest known tadpole. And it really is a huge tadpole, reaching almost 16 centimeters (or 6 inches) long.

The cast is the only known example of the larva of an ancient frog called Notobatrachus degiustoi. Considering that the adults of this species are of similar size, it can be thought that the chunky kumka may be close to the metamorphosis stage.

This rules out the possibility that this individual suffers from a rare disease such as a thyroid problem that causes him to be larger than his siblings. It is fair to assume that all tadpoles of this species may have reached a considerable length before maturation.

We already know from the fossil record that frogs have existed since at least the Late Triassic period, about 217-213 million years ago, but what happened to tadpoles in that ancient period remains a matter of conjecture, at least for now.

Scientists suspected that the key features of tadpole evolution emerged at the boundary between the Triassic and Jurassic periods, a time when stem anurans (the evolutionary ancestors of modern frogs and toads) were rapidly diversifying. However, this estimate was based on living frogs and toads, not fossil remains; because, as the authors of the study note, “Fossil tadpoles are completely absent in Triassic and Jurassic fossils.”

So far it is.

Before this discovery, the oldest known tadpoles were dated to about 145 million years ago; Therefore, this new finding pushes concrete evidence of this extreme type of metamorphosis back another 15 million years.

“This finding is doubly significant as it represents the earliest known tadpole and, to our knowledge, the first trunk-like anuran larva,” the authors write.

“The excellent preservation, including of soft tissues, is evidence of features related to the filter-feeding mechanism that are characteristic of tadpoles to this day. It is noteworthy that both the tadpole and the adult N. degiustoi reach large sizes, demonstrating the gigantism of tadpoles among stem anurans.”

The tadpole fossil was found in Jurassic rock in the La Matilda Formation in Argentina. A team of researchers led by evolutionary biologist Mariana Chuliver from Maimonides University in Argentina produced an incredibly detailed map of his body after careful analysis.

They were able to clearly see the baby’s head, its large dark eye spot, most of its body, some of its nerves, part of its tail, and even its front legs; This helps confirm that metamorphosis was in full swing before the tadpole died an untimely death.

This unprecedented snapshot of prehistoric tadpole anatomy reveals that many key features of modern tadpoles—a filter-feeding system known to scientists as the hyobranchial apparatus, a distinctive skeletal tongue, and not to mention clumsy little legs—were a normal part of anuran childhood. took it out. at least 161 million years.

“The excellent preservation of the new specimen, including most of the hyobranchial apparatus and soft tissues, allows us to infer the lifestyle and feeding habits of the tadpole N. degiustoi,” Chuliver and colleagues write. “This finding significantly expands our knowledge of the origin and early evolution of the two-phase life cycle of anurans.” This research was published in the journal Nature.