Evolution

Uncommon fossil reveals prehistoric Melbourne was as soon as a paradise for tropical pig-nosed turtles


The pig-nosed turtle, an endangered freshwater turtle native to the Northern Territory and southern New Guinea, is exclusive in lots of respects. In contrast to most freshwater turtles, it’s nearly utterly tailored to life in water. It has paddle-like flippers much like sea turtles, a snorkel-like “pig-nose” to assist it breathe whereas staying submerged, and eggs that may solely hatch when uncovered to the waters of the moist season.

It’s also the final surviving species of a gaggle of tropical turtles known as the carettochelyids, which as soon as lived all through the northern hemisphere. Scientists thought pig-nosed turtles solely arrived at Australia throughout the previous few millennia, as no pig-nosed turtle fossils had ever been discovered right here – or so we thought.

Artist's impression of pig-nosed turtle.
Artist’s impression of the pig-nosed turtle swimming in an historical river.
Jaime Bran

A 5-million-year-old fossil from Museums Victoria’s collections has now utterly rewritten this story. Found at Beaumaris, 20km southeast of Melbourne, this fossil lay unidentified in Melbourne Museum’s assortment for nearly 100 years till our group got here throughout it.

We recognized the fossil as a small part of the entrance of a pig-nosed turtle’s shell, as we report immediately within the journal Papers in Palaeontology. Though the fossil is only a fragment, we have been fortunate that it was from a really diagnostic space of the shell.

Fossil held next to the shell of a modern pig-nosed turtle
The 5-million-year-old pig-nosed turtle fossil, in life place on the shell of a contemporary pig-nosed turtle.
Erich Fitzgerald

The fossil exhibits that carettochelyid turtles have been residing in Australia for tens of millions of years. However what was a pig-nosed turtle doing in Beaumaris 5 million years in the past, hundreds of kilometres from their trendy vary?

Nicely, prior to now, Melbourne’s climate was loads hotter and wetter that it’s now. It was extra akin to the tropical circumstances wherein these turtles reside immediately.

Actually, this isn’t the primary prehistoric tropical species found right here: monk seals, which immediately reside in Hawaii and the Mediterranean, and dugongs additionally as soon as lived in what’s now Beaumaris.




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Probably the most endangered seals on the planet as soon as known as Australia residence


A tropical Melbourne?

Thousands and thousands of years in the past, Australia’s japanese seaboard was a tropical turtle hotspot. The hotter and wetter atmosphere would have been excellent for supporting a better range of turtles prior to now. That is in stark distinction to trendy occasions; immediately, Australia is generally residence to the side-necked turtles.

Tropical turtles would have needed to cross hundreds of kilometres of ocean to get right here. However this isn’t uncommon – small animals typically cross the ocean by hitching a journey on vegetation rafts.

Map showing distribution of pig-nosed and side-necked turtles
Distribution of Australia’s freshwater turtles immediately, and the placement of the pig-nosed turtle fossil. Star exhibits the place the brand new fossil was discovered at Beaumaris.
Creator offered, turtle silhouette by Aline M. Ghilardi

So the place are these turtles now? Why is the trendy pig-nosed turtle the final remaining species of the carettochelyids? Nicely, similar to immediately, animals prior to now have been threatened by local weather change. When Australasia’s local weather turned cooler and drier after the ice ages, all of the tropical turtles went extinct, aside from the pig-nosed turtle within the Northern Territory and New Guinea.

Painting of tropical Australia
Australia wasn’t all the time dry and sunburnt. Thousands and thousands of years in the past, it was a tropical paradise crammed with weird animals.
Dorothy Dunphy/Riversleigh by Archer, Hand & Godthelp/Reed Books

This additionally means that the trendy pig-nosed turtle, already endangered, is underneath menace from human-driven local weather change. These turtles are very delicate to their atmosphere, and with out rain their eggs can’t hatch.

That is true of plenty of Australia’s native animals and vegetation. In reptile species reminiscent of turtles and crocodiles, intercourse might be decided by the temperature at which eggs are incubated. That is yet one more issue that might put these species in danger because the local weather adjustments.

Beaumaris at low tide, showing the red cliffs and rocky beach
Many superb fossils have been discovered on the seaside underneath the purple cliffs of Beaumaris.
Erich Fitzgerald

The treasure trove of fossils from Beaumaris exhibits simply how essential Australia’s beforehand tropical atmosphere was for historical animals. Southern Australia was once residence to many tropical species that now have rather more restricted ranges.

Simply final 12 months, the invention of tropical monk seals fossils from Beaumaris utterly modified how scientists thought seals developed. This exhibits simply how a lot we nonetheless need to find out about Australia’s prehistoric previous, when it was so completely different from the sunburnt nation we all know immediately.




Learn extra:
Scientists thought these seals developed within the north. 3-million-year-old fossils from New Zealand counsel in any other case


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