Fossil discovery pushes tree frog origins back 55 million years

Ancient fossils are challenging what we thought we knew about the evolution of tree frogs in the Southern Hemisphere. The tiny creature, unearthed from southeastern Queensland, is changing the estimated timeline by tens of millions of years.

Scientists at UNSW Sydney have identified Litoria tylerantiqua as Australia’s earliest known tree frog, pushing the family’s history back to around 55 million years ago.

This is far earlier than the previously accepted date of 33 million years for when Australian and South American tree frogs were believed to have split on the evolutionary tree.

Rewriting tree frog history

Back when Litoria tylerantiqua was alive, Australia, Antarctica, and South America were still connected by the remnants of the ancient supercontinent Gondwana. The world was warmer. Forests stretched between continents, giving animals room to spread across vast, green corridors.

Until now, the earliest known Australian tree frogs came from the Late Oligocene (about 26 million years ago) and the Early Miocene (around 23 million years ago).

Fossils found at Kangaroo Well in the Northern Territory, Lake Palankarinna in South Australia, and the Riversleigh World Heritage Area in Queensland supported this timeline.

But the Murgon fossils – discovered on the traditional lands of the Waka Waka people – tell a different story. They show that these frogs were hopping around Australia 30 million years earlier than previously thought.

“Our research indicates that that date is at least 22 million years too young,” said Dr. Roy Farman.

“While molecular studies are important for understanding the evolutionary relationships of different groups of animals, these studies should be calibrated using knowledge from the fossil record and in this case the fossil record provides a more accurate time for separation of the southern world’s tree frogs.”

Naming the tree frog with honor

The new species was named Litoria tylerantiqua to honor the late Michael Tyler, one of the first experts to study frog fossils in the country.

“It is only fitting to name Australia’s earliest tree frog in honor of a man who was a giant in Australian frog research and in particular the first to explore the fossil record for Australian frogs,” said Dr. Farman.

To figure out where this ancient frog fits in evolution, the researchers had to overcome a major hurdle. The frog’s pelvic bones, key to identifying species, were not visible in preserved specimens.

“We had a real problem at the start of this study because the pelvic bones of most living frogs were invisible inside whole pickled frogs rather than available for study as skeletons,” noted Dr. Farman.

Models of museum specimens

Most museums want to keep specimens intact for DNA studies, which meant the team couldn’t just remove and study the bones. Instead, they turned to technology.

Using CT scans, the experts created 3D models of museum specimens, revealing hidden skeletons without harming the frogs.

“Using these cutting-edge investigative methods, we were able to determine from the shape of the fossil ilia – one of three bones that make up each side of the pelvis – that this new Murgon species of frog is more closely related to the Australian tree frogs (pelodryadids) than the South American tree frogs (phyllomedusids),” said Dr. Farman.

Lessons from the past

Litoria tylerantiqua now joins Platyplectrum casca (formerly Lechriodus casca), another Murgon fossil, as one of the oldest frogs ever found in Australia. Both have modern relatives still living today in Australia and New Guinea.

“Despite their delicate nature, frogs have been surprisingly successful at surviving several mass extinction events since their origins about 250 million years ago, including the mass extinction 66 million years ago that took out the non-flying dinosaurs,” said Dr. Farman.

Today, many frogs face serious threats. Climate change, habitat loss, and diseases like chytrid fungus are wiping out populations. But understanding how frogs adapted and survived in the past might help scientists protect them now.

Understanding how trees frogs survived

“Although global extinction events triggered by human activities – such as rapid climate change and the spread of chytrid fungus – may be among the worst challenges frogs have had to face, the fossil record could reveal how some frog groups overcame previous challenges, perhaps by adapting to new, less-threatening habitats,” said Dr. Farman.

“This could provide clues about how we might be able to help by translocating some threatened frogs into more future-secure habitats.”

One example is the southern corroboree frog, now struggling in its current environment. If fossil records show similar frogs once thrived in different settings, scientists may be able to relocate modern frogs to safer places.

The full study was published in the journal Journal of Vertebrate Paleontology.

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