Palaeontologists at Seymour Island
© FEDERICO DEGRANGE, CENTRO DE INVESTIGACIONES EN CIENCIAS DE LA TIERRA AND JONAS HAGSTRÖM, SWEDISH MUSEUM OF NATURAL HISTORYPalaeontologists at the fossil site on Seymour Island.
The discovery of the earliest known modern amphibians in Antarctica provides further evidence of a warm and temperate climate in the Antarctic Peninsula before its separation from the southern supercontinent Gondwana.

The fossils, which belong to the family of helmeted frogs, are described in a paper in the journal Scientific Reports by researchers from Sweden, Argentina and Switzerland.

They discovered the remains of a hip bone and ornamented skull bone during expeditions to Seymour Island between 2011 and 2013. The specimens are about 40 million years old, from the Eocene period. Both belong to the Calyptocephalellidae family.

No traces of cold-blooded amphibians or reptiles from families still in existence had previously been found in Antarctica.

"Among Recent amphibians, the frogs (Anura) have the widest distribution, covering all continents except Antarctica, where the conditions have been uninhabitable for over tens of millions of years," the researchers write.

Reconstruction of Eocene helmeted frog
© ARTWORK POLLYANNA VON KNORRING. PHOTOS SIMON PIERRE BARRETTE, JOSÉ GRAU DE PUERTO MONTT, MATS WEDINReconstruction of Eocene helmeted frog on the Antarctic Peninsula.
"Contrary to all other continents, no traces of any extant amphibian group, all of which belong to the lissamphibian clade, have been documented from Antarctica. This paper presents the first record of a lissamphibian in Antarctica..."

The family Calyptocephalellidae is exclusively known from South America, the researchers say. The five extant species are restricted to the Chilenean Andes while most fossil representatives are known from Argentine Patagonia.

Previous evidence suggests that ice sheets formed across the Antarctic Peninsula before the final break-up of the southern supercontinent Gondwana into continents of the present-day Southern Hemisphere, including South America and Antarctica.

The researchers say their discovery suggests that the climatic conditions of the Antarctic Peninsula during the late middle Eocene may have been comparable with the humid and temperate climate in the forests of South America today.

As such the forests of South America may be a modern analogue of the Antarctic climate just prior to the glaciation of the southern continent and may now be home to species originally found across the Antarctic Peninsula.