In 2008, I shared the story of the great longevity of the lizard-like tuatara of New Zealand. Today, Victoria Gill of the BBC’s Nature blog has reported on a study from researchers investigating what appears to be a unique chewing motion in tuatara. Based on computer simulation analysis programmed from video of feeding tuatara at the Chester Zoo, Marc Jones from University College London determined that tuatara slide the lower jaw forward when chewing, a more sophisticated motion than the simple up and down chomping that characterizes the jaw motion of other reptiles. Jones and his fellow researchers think that the sawing motion created by the tuataras’ sliding lower jaws might help them masticate a wide range of prey items – from insects, spiders, and lizards to nesting seabirds – and be important for the continued survival of this species for such a long time.
But hold on there. The whole point of an efficient chewing motion is that it might give a species an advantage in terms of processing a wider variety of prey items or in extracting a greater amount of energy from its food. Do tuatara have an advantage over other reptiles in New Zealand? I don’t see it: There are 43 geckos and 34 skinks in New Zealand, but the two species of tuatara have not fared well on the main islands and are now restricted to heavily managed sanctuaries on about 32 offshore islands. Losing the great majority of the species’ native distribution indicates to me that tuatara are ill-prepared to survive in a world populated by humans and their associated species, like rats. What about the varied diet? Well, skinks and geckos are much smaller than tuatara, so they can’t be expected to eat much in the way of other lizards and seabirds, but they do consume the same types of invertebrates that are the staple of tuatara diets. Lizards from the Australasian region that are more like tuatara in size seem to overlap in diet quite a bit, e.g., frilled lizards eat smaller lizards and small mammals in addition to arthropods, and monitors take a wide variety of invertebrate and small vertebrate prey items. Finally, tuatara don’t seem to derive more energy from their food than do other reptiles. If anything, they seem to extract less, maintaining a significantly lower body temperature and metabolism than other reptiles. So while tuatara might chew their food unlike other reptiles do, I would hold off on speculation that that has anything to do with the species’ survival.