Antarctica was not always a frozen rock at the bottom of the world. Earlier this month, analysis of a 100-foot-deep sediment core from the Antarctic ocean floor revealed the presence of ancient pollen, roots and other tell-tale signs of a rainforest that thrived there some 90 million years ago. Now, paleontologists have uncovered an even more recent sign of the frigid continent’s balmy past: a fossilized frog dating to roughly 40 million years ago, reports Maria Temming for Science News.
This fossil frog is the first ever discovered in Antarctica, according to the new research published in the journal Scientific Reports. Prior digs have unearthed the remains of less familiar-looking bygone amphibians, but none with such a direct evolutionary through-line to creatures that walk—or hop— the Earth today.
The ancient frog’s anatomy bears a close resemblance to a living family of frogs called helmeted frogs (Calyptocephalellidae) which inhabit damp, temperate forests in Chile.
"They looked like today's frogs. No different. Our frog was rather small but this is in the range of the living ones, although most of the living ones are bigger," Thomas Mörs, study co-author and a paleontologist at the Swedish Museum of Natural History, tells Katie Hunt of CNN.
During the life of this frog, Antarctica was replete with water lilies, mammals and even leeches—all of which have also been discovered on Seymour Island, the area that produced the frog fossil, Mörs tells CNN.
"My guess is that it [Antarctica] was a rich and diverse place. We have only found a percentage of what lived there," he tells CNN.
Paleontologists were able to make such a precise connection to living frogs because the fossil frog skeleton included a skull and a particularly useful hip bone called the ilium, reports Lucas Joel for the New York Times.
“The ilium is probably the most diagnostic part of a frog skeleton,” David Wake, a herpetologist at the University of California, Berkeley, who was not involved in the research tells the New York Times. “A frog paleontologist wants an ilium.”
The precious ilium gives reason to think the Antarctic climate of 40 million years ago was not unlike the one preferred by the helmeted frogs of Chile today. This climatic timestamp could help scientists pin down how quickly Antarctica developed frozen sheets of ice amid the crackup of the supercontinent Gondwana, reports Science News.
“The question is now, how cold was it, and what was living on the continent when these ice sheets started to form?” Mörs tells Science News. “This frog is one more indication that in [that] time, at least around the Peninsula, it was still a suitable habitat for cold-blooded animals like reptiles and amphibians.”
The new research estimates Antarctica’s highest monthly average temperatures 40 million years ago would have been roughly 56 degrees Fahrenheit. Not quite beach weather, but warm enough for these ancient frogs. Frogs in Antarctica may seem unfathomable, but humanity’s rampant use of fossil fuels is bringing the planet closer to this ancient climate than it has been in 3 million years. That’s the last time atmospheric carbon dioxide was as high as it is today (averaging around 407 parts per million), and, fossil evidence suggests, it was also the last time there were forests in Antarctica.
“They found fossil leaves of southern beech,” Jane Francis, director of the British Antarctic Survey, told Damian Carrington of the Guardian in 2019. “I call them the last forests of Antarctica. They were growing at 400ppm CO2, so this may be where we are going back to, with ice sheets melting at times, which may allow plants to colonize again.”