The authors have essentially performed a CAT scan of these tiny fossils, except they use energies high enough to fry human tissues. This is sufficient to reveal subtle internal features, including what appears to be a nucleus inside many of the cells, as shown above. The authors argue that this isn't not just a matter of similar appearance. The object has a consistent location within the cells, takes up a consistent fraction of the cell's volume, and only appears once per cell, all of which are features of a nucleus.Source and full story: http://arstechnica.com/science/news/2011/12/precambrian-fossils-once-thought-to-be-embryos-reinterpreted-as-somethign-else.ars
Mass Extinctions have long been an area of interest to me, so I find this deeply interesting. As much for the advances of Technology in Paleontology/Paleobiology, as for the actual fossils being discussed.