Evrim Yazgin
Cosmos science journalist
A fossil of a tree frog is Australia’s oldest, dating to 55 million years ago, challenging previous genetic studies on when Australian species split from their South American cousins.
The newly described species, Litoria tylerantiqua, was found at Murgon in southeastern Queensland, on the traditional lands of the Waka Waka people. The species is described in a paper published in the Journal of Vertebrate Palaeontology.
L. tylerantiqua is the earliest known member of the pelodryadid family of tree frogs. This group persists today, native to Australia, New Guinea and Pacific Islands. The smallest modern species belonging to the Litoria genus, the javelin frog (L. microbelos), is just 1.6cm long, while the giant tree frog (L. infrafrenata) can reach 14cm.
The oldest Australian tree frog fossils found had dated to the Late Oligocene period (about 26 million years ago) and Early Miocene (about 23 mya). Palaeontologists had previously believed these species had split from South American tree frogs about 33 mya, based on molecular clock studies which look at the genetic similarity of modern species.
“Our research indicates that that date is at least 22 million years too young,” says lead author of the new study, Roy Farman from the University of New South Wales (UNSW).
“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,” Farman adds.
Farman’s team used cutting-edge scanning technology to study a pelvic bone fossil and comparing it with modern pickled species from museum collections.
“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,” Farman says.
“Museums understandably want to ensure these often unique or rare pickled specimens remain intact for molecular studies because DNA can be obtained from their soft tissues. This meant that instead of skeletonising these specimens, we needed instead to make CT scans of them, enabling us to create 3D models of their otherwise invisible skeletons.”
L. tylerantiqua joins another frog found at Murgon, the ground-dwelling Platyplectrum casca, as the oldest Australian frogs. Both have living relatives, highlighting the resilience of these frog groups over time.
“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,” Farman says.
“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. This could provide clues about how we might be able to help by translocating some threatened frogs into more future-secure habitats.”
