In August 2019, four amateur fossil hunters came across a scatter of large bones near Richmond, in outback Queensland. The site is open to the public, who may dig there with a licence. They donated the find to the nearby Kronosaurus Korner museum, where staff nicknamed it B.O.B., short for bag of bones. It turned out to contain something palaeontologists had never documented before: a food chain with three links, preserved in one animal.
Three years after the original find, the museum's curator, Kevin Petersen, went back to the site and unearthed the rest of the skeleton. Staff and volunteers then spent more than 600 hours excavating and preparing it. What emerged was a partially articulated ichthyosaur of the species Platypterygius australis. The animal was close to seven metres long and swam the inland Eromanga Sea more than 100 million years ago.
The decisive material was not the skeleton but several dense lumps of rock sitting just behind the skull. The team, led by Matt White of the University of New England, did not split them open. Instead they sent the concretions to the Australian Nuclear Science and Technology Organisation. There Joseph Bevitt used neutron imaging to look inside without touching them.
What the scans showed
The concretions held fish remains, squid-like cephalopods and fragments of the lower jaw of a pterosaur. Their position directly behind the skull, together with the mix of prey, points to fossilised gut contents. It is the first recorded case of an ichthyosaur eating a pterosaur, or part of one.
The animal's own remains told the next part. Vertebrae were split, ribs were missing, and bones carried large crushing bite marks. One vertebra still had a rib jammed against a broken surface. "What startled me was not only the size of the animal, but the way its skeleton had been damaged," White said. The bite pattern points to Kronosaurus queenslandicus, a short-necked pliosaur that reached around 12 metres. It was a predator large enough to treat a seven-metre ichthyosaur as prey.
The study appeared on 27 July in the journal Gondwana Research. "It's one of the clearest examples ever discovered of a three-tier predator interaction and offers an unprecedented snapshot of behaviour in Australia's Cretaceous seas," said palaeontologist Dean Lomax, who reviewed the paper.
Two details are worth holding onto. Fossils normally record anatomy, not behaviour. This one records who ate whom, twice over. And the chain of custody runs from four hobbyists through a small regional museum and 600 hours of volunteer labour to a neutron beamline. Palaeontology still depends on people who simply went looking.