A fresh mystery may have been hatched after a surgical plate was found in the stomach of a large crocodile in Queensland, Australia.

The Koorana Crocodile Farm announced one of its larger reptiles named MJ had passed away on Wednesday and in an attempt to find the cause of his death, an autopsy had revealed the surgical instrument in his gut – as well as a number of stones known as gastroliths crocodiles swallow to help grind up food.

In a Facebook post, the farm mused: “So what has MJ been up to? He was a wild caught croc from Queensland that we purchased from another farm years ago. No staff and no pets are missing here! So for now, it’s a mystery… Regardless, he should have eaten something with more nutritional value!”

MJ, who measured 4.7 metres from snout to tail, had suffered injuries in a fight with another crocodile on the farm named Big Joe a year ago and deteriorated since then.

Farm owner John Lever told ABC News: “Obviously whatever bone he’d taken in that had had the operation performed on it, had been eaten away by the crocodile’s stomach juices and just left the stainless steel plate with the six screws in it.”

“Being subjected to the high-acidic content of a crocodile’s stomach, I’m surprised it was in such good order as it was – [it is] good stainless steel that’s for sure.”

He told the channel he has contacted a company in the UK to find the manufacturer of the plate to help identify it and clarify if it is one commonly used in the veterinary or medical industry.

Once the results are back, Lever said he would offer the plate to police for further investigations if necessary.