Fossils and flow, bringing extinct animals to life
A CFD model of fl ow over this graptolite, showing the pattern of water velocity. Flow in this instance is from bottom to top of the image. Warmer colours indicate more rapid flow.
Ms Emma Passmore and Dr Susan Rigby
University of Edinburgh
Novel engineering techniques are bringing new life to extinct organisms that lived on Earth over 350 million years ago. New images of a form of plankton known as graptolites, are uncovering how their structure influenced the way they moved and fed in oceans that have long since disappeared from Earth. 'The eerily beautiful images our techniques create reveal how water flows around graptolites and how the flow changes as the graptolite structure changes,' explains Sue Rigby a palaeontologist at the University of Edinburgh.
Fossils of graptolites show they were colonies of plankton with the individual members of the colony or zooids being part of an overall branching structure. 'Although graptolites could have eight or more branches the ones we are imaging are the single branched forms,' says Sue. As graptolites grew, more living space was added for further zooids with the branch or branches originating from a central point. The width of the branch, angle of the cone shapes containing the zooids and other structures would all affect the flow of water. 'It is striking how regular the forms became as graptolites evolved,' says Sue, 'this regularity could indicate some advantage in terms of feeding or movement in the oceans and this is what our work is trying to establish'.
Using computer aided design (CAD) the Edinburgh team design and build virtual graptolites. Computerized tomography (CT) scans where multiple x-rays are used at once are taken of model graptolites to provide further detail for the computer models. 'Currently we are experimenting with CT scans of real fossils,' says Sue, 'but the technique is still being perfected'. Once the virtual graptolites are constructed then the flow of fluids around them can be modelled using computational fluid dynamics. In this technique, the space around the shape of interest is divided into smaller and smaller units, in the case of the graptolites typically about 1.6 million units of space. The equations for the movement of fluids for each unit of space are then calculated which enables precise calculation of the overall flow around the object. Further computer software allows graphs or images of the flow for any part of the graptolite to be created. 'Previously we carried out this work by placing models of graptolites in wind tunnels but this method was less than ideal. Wind tunnels are built for racing cars and airplanes not biological things, and particularly not for biological things moving at such slow speeds,' explains Sue. The techniques now available to the team are enabling them to alter the shapes of their virtual graptolites and see how this influences water flow.
'The methods being used in Edinburgh are not limited to graptolites and could have applications for other extinct species. You could image air flow over a running velociraptor, for example, or water flow over an ammonite,' suggests Sue, 'by imaging and studying these ghosts from millions of years ago we gain an insight into an alternative series of ecosystems, allowing us to stand outside modern biology and see living systems from a different perspective'.