Synchrotron X-ray tomographic microscopy of fossil embryos

The inside story on microfossils Fossils of exquisitely preserved half-a-billion year old animal embryos impregnated and encrusted with calcium phosphate have created great excitement as they may contain precious information on developmental processes at a crucial period of animal evolution. Their small size makes them hard to study, but a newly developed technique can recover previously inaccessible detail. The new method, which involves submicrometre-scale tomographic analysis using a synchrotron X-ray light source, has been used to resolve some problems at the extreme limits of fossilization. Remarkable data on the internal anatomy of microscopic fossils of the earliest known bilaterian embryos, Markuelia and Pseudooides, clear up some questions about the phylogeny of the former and reveal a previously unknown model of development in the latter. The cover shows a series of virtual slices through a Markuelia embryo, demonstrating both embryonic and post-mortem features.