A first-of-its-kind "massive monster" prehistoric species of sea scorpion has been identified in a Queensland fossil after spending more than 10 years plaguing researchers.
The Queensland Museum said the sea scorpion Woodwardopterus freemanorum is the first fossil evidence of sea scorpion in the state.
Researchers say the animal was likely more than a metre long and the largest water predator in the area 252 million years ago.
The "tantalising" specimen is also the last of its kind in the world.
Nick Freeman, who formerly lived in the central Queensland town of Theodore, made the discovery on his family property near Theodore in the 1990s, but it was not brought to the museum for identification until 2013.
It has taken the museum until now to determine exactly what this tricky fossil was.
Queensland Museum Associate Professor Andrew Rozefelds said he believed Mr Freeman was "delighted" with the discovery.
His surname has been adapted for the name of the species.
"He gave it to us with the expectation we do something with it," he said.
"I kept on looking at it going 'what am I looking at?'
Last known sea scorpion fossil
Dr Rozefelds partnered with German researcher Markus Poschmann, an expert on this group of animals.
"The Theodore sea scorpion has been accurately dated as living 252 million years ago, and after extensive research this particular fossil turned out to be the last eurypterid known from anywhere in the world," Dr Poschmann said.
This dates the animal as existing just before the end of Permian extinction event, where about 96 per cent of species disappeared, including sea scorpions.
The museum said this particular sea scorpion would have been one of the largest predators in the lakes and rivers around Theodore at the time it existed.
Dr Rozefelds said museum closures during the 2020-2021 pandemic lockdowns allowed him to revisit the cold case.
"This particular fossil had always intrigued me."
