Scientists say the largest ever rodent probably used its huge front teeth like tusks, defending itself and digging with them instead of just biting food.
The bull-sized cousin to the guinea pig died out around two million years ago.
Based on a CT scan of its skull and subsequent computer simulations, its bite was as strong as a tiger – but its front teeth were built to withstand forces nearly three times larger.
This suggests that its 30cm incisors were much more than eating implements.
Researchers from York in the UK and Montevideo in Uruguay published the work in the Journal of Anatomy.
Only a single fossilised skull has been found belonging to this 1,000kg South American rodent, known as Josephoartigasia monesi. Unearthed in Uruguay in 2007, the animal lived in the Pliocene period – a warm era when large mammals were relatively abundant, including the first mammoths.
It remains the largest rodent ever discovered.
To study the mechanics of the skull, the team performed a CT scan of the skull and used it to reconstruct a computer model – including its missing lower jaw, which they copied from a related species.