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Tuatara skeleton

Sophie Regnault

Download this image from Wellcome Collection.

Micro-computed tomography (micro-CT) scan of the skull and front legs of a tuatara. The tuatara of New Zealand are all that remain of a group of animals that used to share the earth with dinosaurs. Their name comes from the spines along their neck, back and tail; Tuatara is a Maori word meaning ‘spiny back’. Virtual X-ray ‘slices’ of a preserved specimen of this rare reptile were taken and used to create a digital 3D model. The digital model can be virtually cut and rotated without damaging the precious original sample. In this way, the sesamoid bones (tiny bones within tendons in the limbs) can be easily visualised and studied. The width of the image is 150 mm.

Why are tuatara so important?

Tuatara are the last surviving member of an ancient order of diverse reptiles (Rhynchocephalia), which lived all over the world as far back as 245 million years ago. Some refer to tuatara as ‘living fossils’, but this is misleading because they have continued to evolve and aren’t the same today as their ancestors were millions of years ago. Despite looking similar to lizards, they are only very distantly related to them and belong to a separate lineage. Tuatara and lizards are being studied to look at how certain characteristics have evolved in these two groups; for example, studying the evolution of sesamoid bones (small bones within tendons in the limbs) will help us to understand more about how these bones affect animal movement. These tiny bones are often covered in soft tissue, which can make them difficult to find in dissection, but using micro-computed tomography (micro-CT) to create a 3D model makes them much easier to visualise. They can be seen here as small circular fragments near the top of each ‘finger’ digit in the lower centre of the image.