Fossil Factfile: Kronosaurus


John Pickrell


John Pickrell

John Pickrell is the editor of Australian Geographic. He is a science writer, author, nature lover and self-confessed geek. Blog posts range over Southern Hemisphere palaeontology, dinosaurs, megafauna, archaeology, palaeoanthropology and a smattering of other topics.
By John Pickrell January 28, 2016
Reading Time: 3 Minutes Print this page
This apex carnivore of Australia’s prehistoric Eromanga Sea is one of the world’s largest known marine reptiles.

When: Early Cretaceous, 125-100 million years ago
Where: Central Australia’s Eromanga Sea
Name: Kronosaurus queenslandicus
Size: 10m long; 11 tonnes in weight
Described: Heber Longman at the Queensland Museum in 1924
Fossils: Hughenden, Richmond and Boulia, Queensland

HAD YOU BEEN AROUND in outback Australia 100 million years ago, you would not have wanted to go for a swim in the Eromanga Sea. Today we are right to be wary of saltwater crocodiles at Top End swimming spots, but during the Early Cretaceous the shadowy form lurking underneath you might have been a massive Kronosaurus on the lookout for a snack.

With a 2.3m skull in the largest adults, this menacing pliosaur was one of the top carnivores of the Eromanga Sea. It may have been an ambush predator, lying in wait before attacking from below.

Kronosaurus had teeth up to 30cm long and it used them for tearing chunks off prey such as huge fish, squid, ammonites – and even other marine reptiles including ichthyosaurs and turtles. Possible bite marks from this beast are found on the one known skull of the long-necked elasmosaur, Eromangasaurus.

Kronosaurus used its four 2m-long flippers to rapidly propel itself through the water.

Australia was a wet and wild place in the Cretaceous Period. It was closer to the South Pole, but a warmer world meant temperate regions stretched further south than today. The Eromanga Sea covered much of Queensland; this body of water was so vast at one point that it extended into South Australia, splitting the continent. While dinosaurs held sway on the land, exotic reptiles flourished in the inland sea.

Four major groups dominated. Ichthyosaurs were dolphin-like predators with four flippers and a vertical tail fin. Sea turtles were represented by four known species, one of which was a 4m giant. Plesiosaurs had four flippers, but two different body types: large-headed, small-necked forms (pliosaurs); and small-headed, long-necked forms. Mosasaurs, which didn’t appear until about the time that ichthyosaurs became extinct and the Eromanga Sea retreated, were long-bodied predators related to snakes and monitor lizards.  


The Kronosaurus specimen collected from Army Down in 1932 and now housed at Harvard University. Today experts believe it was reconstructed incorrectly at 12m in length and has too many vertebrae. (Source: Wikimedia/ Tim Sackton)

The first specimen of Kronosaurus was found by Andrew Crombie near Hughenden in 1899 and this jaw was sent to the Queensland Museum and described by the director Heber Longman in 1924. A 1932 Harvard University expedition resulted in the discovery of a large and complete specimen at Army Downs, near Hughenden, which was taken to the US for preparation and display and can still be seen today at the university’s Museum of Comparative Zoology.

A 1.6m-long lower jaw or mandible was found by Robert Hacon in January 2015 on his cattle station Euraba, near Julia Creek. It is now on display at the Kronosaurus Korner museum, where palaeontologists say it is the most complete Kronosaurus jaw ever found, and that it has revealed an accurate picture of what its jaw looked like.

Based on this, they have been able to estimate that Kronosaurus had around twice as much bite force as a saltwater crocodile today. Definitely not the kind of animal you’d be wanted to splash about in the water with…


The end of the Kronosaurus jaw found by Queensland grazier Robert Hacon in 2015. A 50c piece is used for scale. (Source: Kronosaurus Korner)

John Pickrell is the author of Flying Dinosaurs: How fearsome reptiles became birds, published by NewSouth Books. Follow him on Twitter @john_pickrell.

Source: Text partially adapted from an article in AG 105