Monday, 24 September 2012

Palaeontology is a Real Science Part 2: Using CT Scans

This week, we'll continue on with our theme of "palaeontology is a real science" by talking about how palaeontologists use computed tomography (CT) to view and analyse fossils. Many of you have probably heard of CT scans in terms of medicine. The basis of this technique is that it uses x-rays to produce cross-sectional tomographic images ('slices') of the area of the body in question. These slices can then be studied for abnormalities such as tumours, as it can show some soft tissue as well. If several x-rays are taken around an axis of rotation, the slices can be put together to form a 3-dimensional model of the structure in question, showing the internal and external structure. 
Example of CT slices from the base of the skull (top left) to the top of the head (top right)
In palaeontology, CT scans can be very useful. First of all, they allow analysis of a bone if it is still in the rock. In some cases, a bone cannot be completely removed from the rock because of preservation, or in cases where the original geometry of the rock needs to be retained like an egg or several specimens in a single section that show interesting behaviour. In these cases, CT can be very useful to see the full structure of the bone, and what else is in the rock. 
Example of a dinosaur egg as a whole, and showing the internal structure after CT scanning (Balanoff et al. 2008)
In addition to allowing you to see the full external structure, it also allows visualisation of the internal structure of the bone. One especially cool aspect of CT scans is that it allows for the reconstruction of soft tissue, such as the brain. Because brains are incased in a braincase of bone, CT scans of the braincase can show the shape and structure of brains from extinct animals. This has been done in a number of fossils, including dinosaurs (e.g. Spinophorosaurus) and pterosaurs (e.g. Anhanguera). There is a palaeontology lab in the USA run by Dr. Larry Witmer that does many of these studies, and has produced endocasts (the casts made from the braincase) for several extinct animals. 
Example of a braincase from the sauropod dinosaur Spinophorosaurus  from Knoll et al. 2012. To see a 3D animation, go here
Related to reconstructing brain cases, CT scans can allow us to see structures within the bones like replacement teeth, or the roots of teeth. This can help to determine things like tooth replacement patterns in extinct animals. 
Example of the teeth and bone from the right dentary (lower jaw) of the small dinosaur Fruitadens from Butler et al. 2012
The third main way that CT scans are used in palaeontology is to create a 3D model of the skull or bones, often using a relatively new strategy of analysing fossils called Finite Element Analysis (FEA). Now for any engineers out there, you will know that FEA has been around for a long time. It's used by engineers to determine areas of high stress and strain in things like bridges and buildings. This method can also be used in fossils to see where the areas of high stress and strain in a dinosaur's skull might be. This method was used by Arbour and Currie (2012) to determine different taphonomic (what happens to an animal after it dies and becomes fossilised) pressures necessary to cause the deformation seen in an anylosaur dinosaur. The models created from CT scans can also be used to determine muscle attachment points and therefore aid in muscle reconstruction (see our previous post on muscle reconstruction in fossils). 
Finite Element Analysis on the skull of the ankylosaur dinosaur Minotaurasaurus showing areas of low (blue) and high (red/white) stress (Arbour and Currie 2012).
Hopefully you now understand a very useful piece of technology for palaeontologists, and how we can better understand fossils using CT scans. 

If you're interested in learning more about CT scans and palaeontology, check out the University of Bristol page on CT in palaeontology.
For more cool stuff from the Witmer Lab, check out their website, especially looking at projects and 3D visualization.

Open Access (freely accessible) References:
Arbour, V. M., and Currie, P. J. (2012) Analyzing taphonomic deformation of ankylosaur skulls using retrodeformation and Finite Element Analysis. PloS One e39323.
Butler, R. J. et al. (2012) Anatomy and cranial functional morphology of the small-bodied dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA. PloS One e31556.
Knoll, F., et al. (2012) The braincase of the basal sauropod dinosaur Spinophorosaurus and 3D reconstructions of the cranial endocast and inner ear. PloS One e30060.

References (not Open Access):
Balanoff A. M., et al. (2008) Digital preparation of a probable neoceratopsian preserved within an egg, with comments on microstructural anatomy of ornithischian eggshells. Naturwissenschaften 95: 493-500.

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