Australia’s Winter Amphibian, Koolasuchus

What do Madagascar and Australia have in common?

If you said amphibians that ate dinosaurs, you’d be correct!

Nowhere is the difference between past and present more apparent than in Australia. During the Early Cretaceous period 125 million years ago, Australia was located at a much more southern latitude and was within the Antarctic circle. This meant that Australia had a much colder climate, with some regions experiencing long winter seasons that could go up to six weeks without experiencing any sunlight. Instead of sprawling deserts, Cretaceous Australia was home to temperate forests littered with ferns, conifers, and ginkgoes. The temperate forests within a polar climate have no modern equivalent, making Cretaceous Australia a unique environment.

Dinosaurs were common in this polar environment. Most dinosaurs were small plant-eaters, though some species (such as the carnivorous Australovenator and the herbivorous Muttaburrasaurus) weighed over a tonne. Mammal fossils are also well known from the region, while those of reptiles, including pterosaurs, are rare. Living amongst the dinosaurs and mammals, a much stranger type of prehistoric creature lay below the waters of the region’s floodplains. While this animal, named Koolasuchus cleelandi, may have been a type of ancient amphibian, it’s unlike any alive today.

To say Koolasuchus looked alien may be an understatement. With tiny limbs, a fish-like tail, and a massive skull, the entire body of Koolasuchus is awkward. The wide and flat head is particularly strange and appears to be too wide for the streamlined body of Koolasuchus. The disproportionate features seem out of place, that is until the size and behaviours of Koolasuchus are considered.

With an estimated size of five meters long, Koolasuchus wasn’t just one of the biggest amphibians ever, it was also the same size as the largest crocodiles alive today! Koolasuchus likely behaved like crocodiles too. The powerful and robust tail would have allowed for short bursts of power, making ambushing prey a probable tactic. The tail, alongside wide jaws lined with dozens of sharp teeth, would have made Koolasuchus a fearsome ambush predator. With such an abundance of small dinosaurs, it isn’t difficult to assume that dinosaurs may have been on the menu.

Koolasuchus was a member of the Temnospondyl order, a massive lineage of ancient amphibians. With almost 300 species found globally, Temnospondyls are one of the most diverse orders of extinct animals. The Temnospondyls evolved 330 million years ago and underwent rapid speciation over the next 130 million years. Following the Triassic-Jurassic extinction event 201 million years ago, Temnospondyls experienced a massive decline in their numbers.  They seemingly went extinct during the late Jurassic period, 155 million years ago. Despite this, Koolasuchus was able to survive for over 30 million years following the extinction of its relatives.

How was this possible? As it turns out, the frigid climates of Cretaceous Australia may provide the answer. In Australia, where average annual temperatures ranged between 0-8° Celsius, cold-blooded predators like crocodiles were unable to survive. While crocodiles outcompeted Temnospondyls across the world, they couldn’t survive in polar Australia. Like modern amphibians, Koolasuchus may have been able to hibernate during the long winter months, allowing it to endure the long periods of darkness that crocodilian competition simply couldn’t.

Koolasuchus was a relic of an era with giant crocodile-like amphibians. In the cold climates of polar Australia, it carved out a niche gobbling up unlucky dinosaurs and other small animals that wandered to the shorelines. Its considerable success in Cretaceous Australia wouldn’t last, however. After 125 million years ago, Australia’s climate underwent gradual warming, allowing crocodiles to colonize the continent. With their arrival, Koolasuchus would be outcompeted and soon go extinct. With their demise, amphibians would never again grow so large nor so fearsome again.

Have a merry Christmas everyone!

Works Cited

I do not take credit for any images found in this article.

Header image courtesy of Arioch paleoart, found here

Koolasuchus in the fall courtesy of unknown, found here

Koolasuchus attack courtesy of PaleoGuy, found at his devinatart here

Koolasuchus and girl courtesy of Dewlap, found here

Temnospondyl family tree courtesy of Gabriel Ugueto, found at his twitter here

Fortuny, Josep, and J.-Sébastien Steyer. “New Insights into the Evolution of Temnospondyls.” Journal of Iberian Geology, vol. 45, no. 2, 2019, pp. 247–250., https://doi.org/10.1007/s41513-019-00104-0.

Vickers-Rich, Patricia, and Thomas Hewitt Rich. “Dinosaurs of Polar Australia.” Scientific American, 2014, pp. 46–53.