This farmer got a whole lot more than he was expecting.

The Blaze – A farmer in Australia was killing weeds on his property when he noticed what he thought were fossilized mussels.

Apparently thinking those were not very interesting at the time, he told the Brisbane Times that he continued on about his business. But a few minutes later, he thought he’d better get another look.

“I was out poisoning prickly Acacia and saw some objects shining in the distance,” Robert Hacon, who lives in Queensland, told the newspaper. “At first glance I thought they were fossilized mussel shells so I drove away. Ten minutes later my curiosity got the better of me and I turned back.”

What he discovered was actually the jaw of a prehistoric sea monster known as Kronosaurus queenslandicus. The jaw itself was more than five feet long, originally belonging to an animal that reached up to 36 feet and lived up to 115 million years ago in what was then an inland sea, the Times reported.

Read more: The Blaze