One of the finalists in the European Geosciences Union General Assembly 2011 Photo Competition was an image from Russell Garwood. This image was not a traditional photograph but a 3D reconstruction of a 312 million year old arachnid Eophrynus prestvicii, from a CT scan of the fossil. The image itself will be the feature for the Imaggeo Mondays post on 16th May. However, due to the different nature of the image Russell has put together a brief description of the image and how it was created.
Russell Garwood is a invertebrate palaeontologist who is currently based at the Natural History Museum in London. He has a personal research webpage. He presented work on Tomographic reconstruction in palaeontology at the EGU General Assembly 2011.
Many Carboniferous fossils, such as this specimen of Eophrynus prestvicii, are found as three-dimensional voids within siderite (iron carbonate) concretions. This means that traditional palaeontological techniques – for example, splitting the rock open and inspecting the surface revealed – result in incomplete data recovery. Such limitations can be overcome with the aid of x-ray micro-tomography (XMT), a high-resolution form of CT scanning. This remarkably complete specimen of Eophrynus prestvicii was first described in 1871, and was used three years ago to test the applicability of XMT to siderite-hosted fossils, resulting in this image. The XMT provided a slice-based (tomographic) dataset. Custom software (called SPIERS) was used to threshold and clean each slice, and then define regions of interest. This allowed the limbs to be rendered separately and coloured. The image you see was then created by outputting a finished ‘virtual fossil’ as a mesh, and using the open source ray-tracer Blender to model it under user-defined lighting conditions. The reconstruction reveals an arachnid with heavy armour – presumably a defensive adaptation – and also showed, for the first time, the mouthparts (or chelicerae) of the species. Representatives of the order to which this species belongs, the Trigonotarbida, were amongst the earliest terrestrial predators. While this Carboniferous (~311 million year old) specimen postdates these early examples of the order by many millions of years, it too was a predator, probably running down its prey with its long limbs. The same techniques has now been applied to a wide range of the arthropods living in these Carboniferous coal forests. The image first appeared in the publication Garwood et al. (2009). A more comprehensive introduction to these techniques can be found in the publication Garwood et al. (2010).
Garwood, R.J., Dunlop, J.A. & Sutton, M.D. 2009. High-fidelity X-ray micro-tomography reconstruction of siderite-hosted Carboniferous arachnids. Biology Letters, 5(6):841-844. doi: 10.1098/rsbl.2009.0464 link, , requires subscription for full article]
Garwood, R.J., Rahman, I.A. & Sutton, M.D. 2010. From clergymen to computers – the advent of virtual palaeontology. Geology Today, 26(3):96-100.
doi: 10.1111/j.1365-2451.2010.00753.x link, requires subscription for full article