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


Credit: Hany Mahmoud, Author supplied

The pig-nosed turtle, an endangered freshwater turtle native to the Northern Territory and southern New Guinea, is exclusive in lots of respects. Unlike most freshwater turtles, it’s nearly fully 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 can be 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.

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A 5-million-year-old fossil from Museums Victoria’s collections has now fully rewritten this story. Discovered at Beaumaris, 20km southeast of Melbourne, this fossil lay unidentified in Melbourne Museum’s assortment for nearly 100 years till our crew 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 as we speak within the journal Papers in Palaeontology. Although the fossil is only a fragment, we had been fortunate that it was from a really diagnostic space of the shell.

The fossil reveals that carettochelyid turtles have been dwelling in Australia for thousands and thousands of years. But what was a pig-nosed turtle doing in Beaumaris 5 million years in the past, hundreds of kilometers from their fashionable vary?

Rare fossil reveals prehistoric Melbourne was once a paradise for tropical pig-nosed turtles
Artist’s impression of the pig-nosed turtle swimming in an historic river. Credit: Jaime Bran

Well, prior to now, Melbourne’s climate was loads hotter and wetter that it’s now. It was extra akin to the tropical conditions through which these turtles reside as we speak.

In reality, this is not the primary prehistoric tropical species found right here: monk seals, which as we speak reside in Hawaii and the Mediterranean, and dugongs additionally as soon as lived in what’s now Beaumaris.

A tropical Melbourne?

Millions of years in the past, Australia’s jap seaboard was a tropical turtle hotspot. The hotter and wetter atmosphere would have been good for supporting a better variety of turtles prior to now. This is in stark distinction to fashionable instances; as we speak, Australia is generally house to the side-necked turtles.

Tropical turtles would have needed to cross hundreds of kilometers of ocean to get right here. But this isn’t uncommon—small animals typically cross the ocean by hitching a ride on vegetation rafts.

  • Rare fossil reveals prehistoric Melbourne was once a paradise for tropical pig-nosed turtles
    The 5-million-year-old pig-nosed turtle fossil, in life place on the shell of a contemporary pig-nosed turtle. Credit: Erich Fitzgerald
  • Rare fossil reveals prehistoric Melbourne was once a paradise for tropical pig-nosed turtles
    Distribution of Australia’s freshwater turtles as we speak, and the placement of the pig-nosed turtle fossil. Star reveals the place the brand new fossil was discovered at Beaumaris. Credit: Author supplied, turtle silhouette by Aline M. Ghilardi

So the place are these turtles now? Why is the fashionable pig-nosed turtle the final remaining species of the carettochelyids? Well, similar to as we speak, animals prior to now had been threatened by climate change. When Australasia’s local weather grew to become cooler and drier after the ice ages, all of the tropical turtles went extinct, apart from the pig-nosed turtle within the Northern Territory and New Guinea.

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

This is true of quite a lot of Australia’s native animals and vegetation. In reptile species reminiscent of turtles and crocodiles, intercourse may be decided by the temperature at which eggs are incubated. This is yet one more issue that would put these species in danger because the local weather modifications.

The treasure trove of fossils from Beaumaris reveals simply how vital Australia’s beforehand tropical atmosphere was for historic animals. Southern Australia was house to many tropical species that now have rather more restricted ranges.

Just final 12 months, the invention of tropical monk seals fossils from Beaumaris fully modified how scientists thought seals advanced. This reveals simply how a lot we nonetheless should study Australia’s prehistoric previous, when it was so totally different from the sunburnt nation we all know as we speak.

Rare pig-nosed turtles once called Melbourne home

More data:
James P. Rule et al, Turtles all the best way down: Neogene pig‐nosed turtle fossil from southern Australia reveals cryptic freshwater turtle invasions and extinctions, Papers in Palaeontology (2021). DOI: 10.1002/spp2.1414

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Rare fossil reveals prehistoric Melbourne was as soon as a paradise for tropical pig-nosed turtles (2021, December 11)
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