The upper Miocene to lower Pliocene fossil from Beaumaris in Victoria, south-eastern Australia, completely rewrites the evolution of pig-nosed turtles.
The living pig-nosed turtle (Carettochelys insculpta), persisting in far northern Australia and southern New Guinea, is the last surviving member of the family Carettochelyidae.
Despite having a global fossil record dating to the Cretaceous period, the absence of pig-nosed turtle fossils from Australia has implied a relatively recent colonization of this landmass.
“Almost the entire evolutionary history of pig-nosed turtles occurred in the northern hemisphere, with their present limited occurrence on the northern margin of Australia,” said Dr. James Rule, a researcher in the School of Biological Sciences at Monash University.
“The discovery of a 5-million-year-old pig-nosed turtle fossil in Beaumaris changes this picture entirely.”
“We are so lucky in Melbourne to have such fossils right here in our own backyard,” said Dr. Erich Fitzgerald, a senior curator of vertebrate paleontology at Museums Victoria.
“The fossils at Beaumaris still have so much to teach us about our past, present and future.”
The specimen points to a broader pattern of turtles migrating across entire oceans in the ancient past to reach the once tropical waters of southern Australia.
“This one fossil specimen reveals a previously unknown evolutionary history of tropical turtles in Australia, and suggests we still have much to learn about the endangered pig-nosed turtle,” Dr. Rule said.
Five million years ago, the climate in Melbourne was far warmer and was home to turtles found only in the tropics today.
“Climate change in the last few million years eliminated these tropical habitats, leaving the northern Australasian pig-nosed turtles as sole survivors,” Dr. Rule said.
“Our discovery provides key insights into ancient climate change shaping modern species distribution.”
A paper on the findings appears today in the journal Papers in Palaeontology.
James P. Rule et al. Turtles all the way down: Neogene pig-nosed turtle fossil from southern Australia reveals cryptic freshwater turtle invasions and extinctions. Papers in Palaeontology, published online December 7, 2021; doi: 10.1002/spp2.1414
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