Its remarkable secret has finally been revealed after researchers discovered it contained one of the highest concentrations of dinosaur footprints ever documented in Australia.
The white clay boulder about the size of a small table features 66 fossilised footprints of small dinosaurs from 200 million years ago.
The three-toed footprints from 47 individual dinosaurs date back to the Early Jurassic period, University of Queensland researcher Anthony Romilio said.
They belong to the Anomoepus scambus, a dinosaur that moved on two 50cm long legs, with a short neck, chunky body and small head with a beak.
"It was a plant-eating dinosaur that wasn't particularly large by dinosaur standards," Dr Romilio told AAP.
The discovery sat unnoticed at Biloela State High School in central Queensland after being donated from Callide Mine 20 years ago.
"Significant fossils like this can sit unnoticed for years, even in plain sight," Dr Romilio said.
The footprints on the boulder were likely made by the dinosaurs passing over a patch of wet, white clay while walking along or crossing a waterway.
They would not have been travelling particularly fast, around 6km/h.
Dr Romilio was able to figure out what kind of dinosaur left the peculiar marks by matching the footprint with skeletal fossils from overseas.
He said the significant discovery would help scientists better understand what dinosaurs roamed Australia millions of years ago.
"It's an unprecedented snapshot of dinosaur abundance, movement and behaviour from a time when no fossilised dinosaur bones have been found in Australia," he said.
The school boulder is not the only unlikely source of dinosaur knowledge Dr Romilio has discovered lying around central Queensland.
He found a rock with footprints being used as a carpark entry marker at Callide Mine near Biloela.
The much larger boulder weighing about two tonnes featured two distinct footprints left by a bigger dinosaur walking on two 80cm tall legs."We have gained new insight into the ancient past in this region," Dr Romilio said.
The research is published in Historical Biology.
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