New Zealand's native tuatara chews its food like no other land animal, using a "steak-knife sawing motion", British researchers have discovered.
Researchers were able to make a computer model of the tuatara's jaw after filming them munching their food at Chester Zoo in the UK.
The modelling showed that the tuatara's unique chewing motion allows it to "slice up" food that is too big for its mouth.
In a paper published in the journal The Anatomical Record, the researchers describe how the teeth of the tuatara's lower jaw close between two upper rows of teeth "before sliding forward to slice food apart like a draw-cut saw".
Lead researcher Marc Jones from University College London told BBC Nature this was unlike any living lizard or snake, which used "more of a simple opening and closing" motion.
He said the tuatara's "slicing jaws" allowed it to eat a wide range of prey like beetles, spiders, crickets and small lizards.
Dr Jones said the research may also help explain some gruesome discoveries in the tuatara's habitat, including seabirds with their heads sawn off.
"Tuatara will tend to go for hatchlings if they can, but as far as I can make out [they] do sometimes take small adults," he said.
"[We think] they change their diet seasonally - eating lots more seabirds during the summer."
The closest relatives of the lizard-like reptile died out more than 200 million years ago.
Tuatara are found in the wild on 37 offshore islands.
It is thought they may have a life span of over 100 years.