Tuatara reptile slices food with 'steak-knife teeth'
New Zealand's tuatara has a unique way of chewing its food, say scientists who have studied its jaws in detail.
This beak-headed reptile uses a "steak-knife sawing motion" as it chews.
This could help explain how the species has continued to adapt to a changing world - and changes in available prey - over more than 200 million years.
A computer model of the tuatara, recreating its jaws as it munched on prey, has revealed that it chews like no other land animal.
This seems to allow it to "slice up" food that is too big for its mouth.
In their paper 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".
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Lead researcher Marc Jones from University College London said this was very unlike any living lizard or snake, which used "more of a simple opening and closing" motion.
The UK-based researchers were able to observe and film chewing tuataras at Chester Zoo.
Dr Jones and his colleagues from the universities of Hull and York then used this footage to accurately digitise and simulate the creature's characteristic chomp.
Dr Jones said that the "slicing jaws" of the tuatara allowed it to eat a wide range of prey including beetles, spiders, crickets and small lizards.
But he added that this study helped to explain some rather gruesome discoveries in the reptile's habitat.
"People have described finding seabirds with their heads sawn off," he told BBC Nature.
"Tuatara will tend to go for hatchlings if they can, but as far as I can make out [they] do sometimes take small adults.
"[We think] they change their diet seasonally - eating lots more seabirds during the summer."Close relatives?
Although the tuatara looks very much like a lizard, it actually belongs to a group of animals commonly known as beak heads, or Rhynchocephalia in the formal terminology.
The reptile, found wild only in New Zealand, is the last surviving species of its group. Its relatives died out more than 200 million years ago.
At that time, the creatures were spread throughout the globe; scientists have found some the fossilised remains of the tuatara's extinct relatives in the UK.
It is not entirely clear how and why the rest of these ancient reptiles became extinct, but the tuatara's ability to saw up its food could be a secret to its continued survival.