Tuatara and their Living Fossil Label

Abstract

The tuatara is often referred to as a ‘living fossil’ - which can be defined as a species that does not seem to have changed since the time its (extinct) ancestors were alive. I have reviewed literature that shows tuatara can neither be interpreted as identical to their Mesozoic relatives, nor in a state of ‘evolutionary stasis’ as is often assumed. While the description ‘living fossil’ may at first glance seem harmless, and even helpful for the tuatara’s public profile - it evokes an aura of respect for the animal - the term and the assumptions that go with it have been confusing. Tuatara are the last surviving members of an order of reptiles called Rhynchocephalia, and retain characteristics in their morphology that are very similar to those seen in fossils up to 225 million years old. Yet they also have many features that scientists argue are specialised adaptations to their current environment. Assuming tuatara are primitive, or at a standstill in evolution, has led to inaccurate scientific reasoning. In a wider context, the term ‘living fossil’ groups an inexact number and kind of extremely different organisms, in an undefined way, in the already inexact science of evolution. In the 150 years since Darwin coined the term, the seeming persistence of ‘living fossil’ species has puzzled scientists and has fuelled debates of evolutionary theory. Using the term in science communication has been of both negative and positive consequence. The aesthetic concept of ‘living fossils’ has aroused keen interest in a selected number of species, and may have benefit for the conservation of those that are rare.