The oldest known fossil tadpole was a big baby

Tadpoles have been wriggling within the arena’s ponds for no lower than 161 million years.

A newly detailed fossil finding pushes the record for earliest known tadpoles back an extra 30 million years, researchers report October 30 in Nature. The petrified pollywog shows that the fresh filter-feeding, puddle-dwelling characteristics of tadpoles had already evolved in a lot of the earliest frogs.

In 2020, a team of scientists from Argentina and China went to Argentinian Patagonia attempting to in finding dinosaur fossils, but as a replacement found hundreds of fossilized frogs of the extinct species Notobatrachus degiustoi. Among them was a tadpole fossil in a sandstone slab.

Evolutionary biologist Mariana Chuliver at the Félix de Azara Natural History Foundation in Buenos Aires and her colleagues identified the fossil as the same species as the adult frogs caused by shared features of its vertebrae. The tadpole was a ways along in its development, and a lot of its hind legs and forelegs had formed. It was also remarkably well-preserved, says Chuliver, with soft tissues, including eyes and nerves, set within the stone.

The N. degiustoi tadpole lived between about 168 million and 161 million years ago, within the guts of the Jurassic Period. While that’s about 20 million years after the primary frog within the fossil record, the findings out of Patagonia represent “the oldest tadpole found to this point,” says Chuliver. Before now, the oldest known tadpoles belonged to Shomronella jordanica, a frog that lived in Israel about 130 million years ago, at some stage within the Cretaceous Period. Other fossilized amphibian larvae date back even in the same fashion, but none bear the characteristics of tadpoles, which struggle through a uniquely extreme metamorphosis.

The amphibian wasn’t just ancient; it was huge, measuring about sixteen centimeters from snout to tail tip. This day, many species’ tadpoles are a pair centimeters or less in length. Such giant tadpoles aren’t common today, says Chuliver, and when they do occur, they normally grow into relatively small adults when put next with other frog species. As a substitute, N. degiustoi was big all through its life, an awful lot just like the fresh American bullfrog (Lithobates catesbeianus).

The fossil tadpole also appears to have fed like fresh tadpoles do, sucking and straining food particles out of the water. The tadpole fossil’s throat skeleton was preserved, showing it had the same vital filter-feeding apparatus as its fresh counterparts (SN: 9/25/17). This implies that filter-feeding tadpoles have been a winning evolutionary strategy for a extremely very long time, says Chuliver.