Argentina discovers world's oldest dinosaur tadpole fossil

Based on phylogenetic analysis of modern amphibian larvae, the fossils helped identify Notobatrachus tadpoles as very close to the group that includes all living frogs and toads.

On October 30, the National Council for Scientific and Technical Research of Argentina (CONICET) announced that an archaeologist had discovered a 16cm long dinosaur tadpole fossil , dating back about 165 million years, in the southern province of Santa Cruz.

The specimen was found to belong to the species Notobatrachus degustoi - an ancestor of today's frogs and toads. This is the oldest fossil specimen of tadpoles discovered in the world, dating back to the mid-Jurassic period in Patagonia, Argentina.

 The specimen found belongs to the species Notobatrachus degustoi - the ancestor of today's frogs and toads. (Photo: phys.org).

Dr. Matías Motta of CONICET said he discovered the fossil by chance while on an expedition organized by scientists from the Museo Naturale Scientifique Argentin a 'Bernardino Rivadavia' and the Chinese Academy of Sciences to search for dinosaur fossils at the La Matilde farm in Santa Cruz. He picked up a rock during his lunch break and noticed bones and imprints on the rock.

The tadpoles have been known since 1957, when scientists discovered skeletons at the farm, which preserved 'primitive' features not found in frogs and toads today. The discovery of this well-preserved dinosaur tadpole will allow scientists to understand the evolution of frogs and toads.

Some researchers have said that most ancient toads probably did not go through a tadpole stage, but this discovery shows that this assumption is incorrect, said biologist Mariana Chuliver of the Félix Azara Natural History Foundation, the first expert to participate in this archaeological work.

Research team member Federico Agnolín, an expert at the Argentine Museum of Natural Sciences 'Bernardino Rivadavia' of CONICET, stressed that the scarcity of tadpole fossils makes the origin and early evolution of the larval stage a mystery.

Adult frogs are present in the fossil record from the Late Triassic period (about 217–213 million years ago), but tadpoles have not been recorded before the Cretaceous period (about 145 million years ago).

According to CONICET, based on phylogenetic analysis of modern amphibian larvae, the fossil has helped identify the Notobatrachus tadpole very closely to the group that includes all current frogs and toads. The head, most of the body and part of the tail as well as the eyes, nerves and forelimbs of the fossil can all be observed. This proves that the tadpole was in the final stage of evolution to become an adult amphibian.

Scientists believe that the evolution of the larval stage has undergone little change in 160 million years, and that primitive tadpoles fed in much the same way as tadpoles do today.