The unique way tuatara chew their food challenges a widespread perception that complex chewing ability is closely linked to high metabolism, English researchers say.
Scientists from University College London (UCL) and the University of Hull used a sophisticated computer model to demonstrate that tuatara slice their food in the way a steak knife would.
The way it chewed was unlike any other animal on the planet, UCL said.
The tuatara is the only survivor of a group that was globally widespread at the time of the dinosaurs.
They eat beetles, spiders, crickets, small lizards, and occasionally seabirds.
The scientists describe the highly specialised jaws of the tuatara in a paper published in The Anatomical Record.
When tuatara chew, the lower jaw closes between two rows of upper teeth.
Once closed, the lower jaw slides forward a few millimetres to cut food between sharp edges on the teeth, sawing food apart.
Lead author Dr Marc Jones, from UCL Cell and Developmental Biology, said chewing had been linked to high metabolism because mammals showed the most sophisticated form of chewing.
"However, the tuatara chews food in a relatively complex way, but its metabolism is no higher than that of other reptiles with simpler oral food processing abilities.
"Therefore the relationship between extensive food processing and high metabolism has perhaps been overstated."
The shape of the tuatara jaw joint meant that as its jaws slide forwards they also rotate slightly about their long axes.
That made the shearing action more effective and demonstrated that the left and right lower jaws were not fused together at the front as they were in humans.
The tuatara provided an example in which specialisation of the feeding mechanism appeared to allow a broader diet.
Although the tuatara-like chewing mechanism was rare today, fossils from Europe and Mexico showed that during the time of the dinosaurs, about 160 million years ago, some relatives of the tuatara used a similar system and it was much more widespread, Dr Jones said.
The computer model used by the researchers was developed at the University of Hull.
It allowed complex moving structures to be studied in 3D and from all angles.
Co-author Dr Neil Curtis, from Hull University's engineering department, said the virtual model was developed using software that was widely used in the analysis of complex engineering systems.
It was the most detailed musculoskeletal model of a skull ever developed.
"It allows us to investigate movements within skulls that would be impossible to monitor in a live animal without using harmful x-rays which is not an option for protected species like the tuatara."
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