Around 100 million years ago, it seems an ocean-dwelling ichthyosaur’s final meal was an unexpected creature – a pterosaur that ruled the skies. Soon after, the ichthyosaur met its own demise, being ripped apart by a massive pliosaur.
That’s the story a rare fossil found in Australia’s outback tells, according to palaeontologists, and it provides the first ever evidence that ichthyosaurs, large marine reptiles, consumed pterosaurs, the earliest known vertebrates to evolve powered flight.
Recreational fossil hunters discovered some of the ichthyosaur’s fossilised bones at a designated public site near the town of Richmond, in a semi-arid area of Queensland’s outback in 2019.
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Thousands of fossils have been found across the region, including those of ancient giant marine and flying reptiles, sharks and turtles. During the Early Cretaceous, between 120 and 95 million years ago, the area was part of the Eromanga Sea, a shallow inland sea that covered over one-third of the Australian continent.
When palaeontologists went back to excavate the site three years later, they uncovered a huge, partially articulated ichthyosaur. Identified as Platypterygius australis, it was almost 7 metres long, the size of an adult killer whale.
“What startled me was not only the size of the animal, but the way its skeleton had been damaged,” says at the University of New England, Australia, who led the investigation. He explains that the vertebrae were split, ribs were missing and numerous bones displayed large crushing bite marks, reminiscent of how existing crocodiles eat prey.
The only explanation, the team concluded, was that a powerful and deadly predator had chewed and dismembered the ichthyosaur, before its carcass dropped to the seafloor to eventually be preserved in stone.
“The only predator known from the Eromanga Sea capable of producing injuries of this magnitude is the giant pliosaur Kronosaurus queenslandicus,” says White.
The team also found strange globular masses near the ichthyosaur’s skull. Careful mechanical removal of rock around the fossil and 3D imaging revealed that one of these globules contained fragments of fish, squid-like cephalopods, and, remarkably, two pterosaur bones including a jaw fragment. The researchers think this was the ichthyosaur’s gut contents, which probably fossilised near the skull due to its digestive tract spilling out.
“It is almost certainly a case of predation or scavenging, and the first ever example of a pterosaur consumed by an ichthyosaur,” says at the University of Leicester, UK. He says the jaw fragment gives him “little doubt” it belonged to a pterosaur.
Given the size of the pterosaur jaw fragment, Unwin suggests the animal was about the size of the largest living albatrosses, which can have 4-metre wingspans. He says it’s plausible that the pterosaur swooped close to the water’s surface to catch fish and was snatched by the ichthyosaur. However, he thinks it is more likely that the ichthyosaur scavenged it after finding it dead and floating in the water.
“The impressively varied stomach contents of the ichthyosaur suggest that it was a super-scavenger of the seas, not fussy about what it ate and happily hoovering up the dead, the dying and the decaying, including pterosaurs,” says Unwin.
“This exceedingly rare fossil provides direct evidence of behaviour and predator-prey interactions from the ancient Eromanga Sea,” says at the University of Manchester in the UK. “The behavioural interaction observed in this specimen is unique and offers a window into ancient food webs – a three-tiered fossil food chain – which are very rarely preserved.”
Gondwana Research
