The pig-nosed tortoise, an endangered freshwater turtle native to the Northern Territory and southern New Guinea, is unique in many ways. Unlike most freshwater turtles, it is almost completely adapted to life under water. Sea turtles have paddle-like flippers, a snorkel-like “pig nose” that helps them breathe when submerged in water, and eggs that only come into contact with water during the rainy season.
It is also the last living species of a group of tropical tortoises called calatocerids that once lived in the Northern Hemisphere. Scientists used to believe that pig-nosed tortoises arrived in Australia within the last few thousand years, because fossils of pig-nosed tortoises had never been found here.
A 5 million year old fossil from the Museum Victoria collection has completely rewritten this story. Discovered at Beaumaris, 20 km south-east of Melbourne, the fossil was unknown in the Melbourne Museum collection for nearly 100 years before our team encountered it.
As reported in the journal Today, the fossil has been identified as a small portion of the front of the shell of a pig-nosed turtle. paleontology paper.. the fossil is just one piece, but I was lucky it came from a very clinical area of the shell.
Fossils show that caratochelid tortoises have been living in Australia for millions of years. But what was the pig-nosed tortoise doing in Beaumaris, thousands of kilometers from its modern range, five million years ago?
Well, in the past, the weather in Melbourne was much hotter and rainier than it is now. It was more similar tropical conditions these turtles live in today.
In fact, it is not the first prehistoric tropical species found here. Monk seals that live in what is today Hawaii and the Mediterranean Sea, and dugongs, which lived in what is now Beaumaris.
Millions of years ago, the east coast of Australia was a hotspot for tropical tortoises. The warm and moist environment was perfect for supporting the diversity of turtles of the past. This is the exact opposite of modern times. Today, Australia is primarily home to lateral neck turtles.
Tropical tortoises have to cross thousands of kilometers to reach here. But it is not unusual. Small animals often cross the ocean. Hitchhiker on a vegetable raft..
So where are these turtles now? Why is the modern pig-nosed tortoise the last remaining species of Culet cerido? Well, like today, animals of the past climate change.. When Australia’s climate was cold and dry after the Ice Age, all tropical tortoises became extinct except for the northern region and the pig-nosed tortoise in New Guinea.
It also suggests that the already endangered modern pig-nosed tortoise is under threat from human climate change. These turtles are very sensitive to the environment and their eggs cannot hatch without rain.
This is true for many native flora and fauna in Australia. As with reptile species such as turtle crocodiles, sex can be determined by the temperature at which eggs are laid. This is yet another factor that could endanger these species in the face of climate change.
A wealth of fossils from Beaumaris shows how important Australia’s past tropical environment was to ancient animals. South Australia was once home to several tropical races. Now there is a much more limited range.
Just last year, the discovery of fossil tropical seals from Beaumaris completely changed the way scientists think about how seals evolved. This shows how much we still have to learn about Australia’s prehistoric past, which was very different from the restricted nations of today.
A rare pig-nosed tortoise once called Melbourne’s home
for more information:
James P. Rule et al, Turtles all down: Neogene pig-nosed turtle fossils in southern Australia reveal the invasion and extinction of mysterious freshwater turtles. paleontology paper (2021). DOI: 10.1002/spp2.1414
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Rare fossils show that prehistoric Melbourne was once a tropical pig-nosed paradise
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