A team of researchers from the University of Bristol studying the ''living fossil'' Sphenodon - or tuatara - have identified a new way to measure the evolutionary rate of these enigmatic creatures, giving credence to Darwin's theory of ''living fossils''.
The tuatara is a relatively large lizard-like animal that once lived on the main islands of New Zealand but has been pushed to smaller, offshore islands by human activity. Tuataras are not lizards, although they share a common ancestor from about 240 million years ago, and have survived as an independent evolutionary line for all that time.
In the study, researchers measured jaw bones from all fossil relatives of the living tuatara, and compared these as evidence of dietary adaptation. They also examined rates of morphological evolution in the living tuatara and its extinct fossil relatives.
The study confirms two key points: the tuatara has shown very slow evolution, as expected, and importantly, its anatomy is very conservative.
Lead author, Jorge Herrera-Flores, said: 'The fossil relatives of the tuatara included plant eaters and even aquatic forms, and were much more diverse than today. We found the living tuatara shares most in common with its oldest relatives from the Triassic.'
When Charles Darwin invented the term 'living fossils' in 1859, he was thinking of living species that look just like their ancestors of millions of years ago. His explanation was they occupied small parts of the world, escaping competition, and therefore did not change.
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