Iconic New Zealand reptile shows chewing is not just for mammals

Using a sophisticated computer model, scientists from UCL and the University of Hull demonstrate how the tuatara is able to slice its food like a “steak knife”. The tuatara's complex chewing technique raises doubts about the supposed link between chewing and high metabolism in mammals.

The New Zealand tuatara (Sphenodon) is a lizard-like reptile that is the only survivor of a group that was globally widespread at the time of the dinosaurs. It lives on 35 islands scattered around the coast of New Zealand and was recently reintroduced to the mainland. Its diet consists of beetles, spiders, crickets, small lizards and, occasionally, sea birds.

In a paper published in The Anatomical Record, scientists describe the highly specialised jaws of the tuatara. When the reptile chews, the lower jaw closes between two rows of upper teeth. Once closed, the lower jaw slides forward a few millimeters to cut food between sharp edges on the teeth, sawing food apart.

Lead author Dr Marc Jones, UCL Cell and Developmental Biology, said: “Some reptiles such as snakes are able to swallow their food whole but many others use repeated bites to break food down. The tuatara also slices up its food, much like a steak knife.”

“Because mammals show the most sophisticated form of chewing, chewing has been linked to high metabolism. 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 team report that due to the shape of the jaw joint, as the jaws slide forwards they also rotate slightly about their long axes. This makes the shearing action more effective and demonstrates that the left and right lower jaws are not fused together at the front as they are in humans.

The tuatara provides an example in which specialisation of the feeding mechanism appears to allow a broader diet.

Dr Jones said: “The slicing jaws of the tuatara allow it to eat a wide range of prey including beetles, spiders, crickets, and small lizards. There are also several grizzly reports of sea birds being found decapitated following predation by tuatara.”

“Although the tuatara-like chewing mechanism is rare today, fossils from Europe and Mexico show us that during the time of the dinosaurs (about 160 million years ago) some fossil relatives of the tuatara used a similar system and it was much more widespread.”

The team used a computer model developed at the University of Hull which provides a novel way of investigating the evolution and biodiversity of reptiles, allowing complex moving structures to be studied in 3D and from all angles.

Co-author Dr Neil Curtis from the University of Hull's Department of Engineering said: “We developed this virtual model using software that is widely used in the analysis of complex engineering systems. It is the most detailed musculoskeletal model of a skull ever developed and demonstrates the huge potential of this type of computer modelling in biology.

“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.”

The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and The Palaeontological Association.

About UCL (University College London)

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. We are among the world's top universities, as reflected by performance in a range of international rankings and tables. UCL currently has 24,000 students from almost 140 countries, and more than 9,500 employees. Our annual income is over £800 million.

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About the University of Hull

The University of Hull is an institution with a long heritage of academic excellence and is rich in tradition. Established in 1927 as England's fourteenth university, it received a Royal Charter in 1954 and has campuses in Hull and Scarborough.

The University has an illustrious history which includes pioneering developments in science and engineering, health, business, humanities and social sciences as well as performing arts. The University today is a vibrant and future-oriented institution, recognised for excellence in learning and teaching as well as a commitment to research, enterprise and engagement. The University is known for its friendliness and high student satisfaction as well as the employability of its graduates.

The University regularly features in the top bracket of national teaching quality league tables and has consistently performed impressively in the National Student Survey, reflecting the high premium the University places on the quality of student experience. Staff and students frequently win prestigious national and international awards and accolades. Hull is currently placed among the top 350 in the Times Higher Education (THE) World University Rankings.

Research and enterprise are core academic activities of the University. Amongst its most well known achievements are the discovery of liquid crystal displays and the bone density scanner which revolutionised the detection of osteoporosis, both of which were featured in Eureka UK's list of '100 discoveries and developments in UK universities that have changed the world'. The most recent Research Assessment Exercise revealed that 80% of the University's submitted research is of international standard in terms of originality, significance and rigour.