PICKED out the garden on Hanbury St for fish tank decorations, the last thing Janine and Wayne Weber expected was for two rocks to house fossils.
Blake McKay was 3 and playing with rocks while his grandparents cleaned out their fish tank when he bashed the two together, uncovering marine fossils inside.
Mrs Weber said her grandson thought he'd be in trouble for breaking them as he peered around the corner.
"We had no idea that they were in there," she said.
"I just picked the rocks out of the garden because I thought they would look good in the fish tank.
"I've only seen fossils in New South Wales before - we've never found anything like this before."
Blake said it was pretty cool to see what was inside and his mother said he was always trying to crack rocks open now.
"I smashed them together and they made a big crack," he said.
"And I saw a crab inside."
Blake's grandfather Wayne said part of the front of the creature looked like a Morten Bay bug.
"When you wet the fossils they really come up nice, almost shiny," Mrs Weber said.
"So that's why they are going back in the fish tank.
"People keep saying they are going to deteriorate in there, but they've lasted this long, I think they'll be fine."
She said while they didn't know what type of fossils they have, the Webers' neighbour took a photo and is trying to get in contact with a museum to determine the origin of the geo-discovery.
Last year a Bucca woman and her family found fossils believed to be 115 million years old in the garden.
A spokesman from the Queensland Museum Discovery Centre told the Bucca family they were fossil bivalves - a group of molluscs, including clams, oysters and scallops, that most likely come from a rock unit called the Maryborough Formation.