Evrim Yazgin
Cosmos science journalist
A whopping 16-centimetre-long tadpole fossil has been found – dating to the heyday of the dinosaurs.
The find, described in a paper published in Nature today, represents the oldest tadpole in the world, adding to our understanding of the evolution of frogs and toads. It dates to 161–168 million years ago – the middle of the Jurassic period (201–145 million years ago).
The tadpole belongs to the known ancient frog species Notobatrachus degiustoi. Adult fossils have been found measuring 9–15cm in length.
It is not uncommon for tadpoles to be larger than adults. Pseudis paradoxa, for example, is a South American frog which lives today. Its 27cm tadpoles can be 3–4 times larger than adults. This has earned it the common names: paradoxical frog or shrinking frog.
The tadpole specimen shows that many key features of the tadpole body present today had already evolved by the Middle Jurassic. It shows that the two-stage life cycle of anurans was already present more than 160 million years ago.
Both N. degiustoi tadpole and adult reaching large sizes also shows that gigantism occurred among the earliest anurans.
Gigantism evolved several times in anuran history.
The largest ever frog, Beelzebufo ampinga, lived 65–70 million years ago and could reach 41cm and 4.5kg. The biggest frog today is the west African goliath frog. It can be 35cm long and weigh 3.3kg.
The N. degiustoi tadpole fossil was also found in South America. The specimen was uncovered at the La Matilde Formation in Argentina’s Santa Cruz Province. The formation is in the southern part of Patagonia, near the icy southern tip of the continent.
Unsurprisingly, the giant tadpole lived in a land of giants. Fossil footprints from the La Matilde Formation include those of predatory therapod dinosaurs.
About 500km north, in the similarly-aged Cañadón Asfalto Formation, dinosaur bones have been found from large carnivores Eoabelisaurus and Asfaltovenator, 15-metre-long sauropod Patagosaurus, and the small herbivore Manidens.
Patagonia is where the largest dinosaurs ever lived, about 80 million years after N. degiustoi.
Fossils of anurans – the family which includes frogs and toads – are sparse earlier than the beginning of the Cretaceous period 145 million years ago, which makes studying their evolution difficult.
