Brussels, 10 Aug 2006
Researchers have obtained detailed, three-dimensional images of the internal structures of fossilised embryos over half a billion years old. What they have seen alters our understanding of the evolution of insects and crustaceans.
Due to their extremely small size and fragility, fossilised embryos are extremely rare. Yet despite this, fossilised embryos have been found in a number of sites around the world. Until now, traditional, non-destructive methods have allowed researchers to analyse exposed surfaces with relative ease. Obtaining views of the interior however was only possible with destructive methods which resulted in just a single, two-dimensional view of the interior.
Now a team of researchers has used synchrotron-radiation X-ray tomographic microscopy (SRXTM) to obtain high resolution, three dimensional images of the insides of embryos, and resolution rivals that obtained by destructive methods. Their findings are reported in the journal Nature.
'Because of their tiny size and precarious preservation, embryos are the rarest of all fossils. They are just gelatinous balls of cells that rot away within hours,' explained Phil Donoghue of the University of Bristol, who led the research. 'But these fossils are the most precious of all because they contain information about the evolutionary changes that have occurred in embryos over the past 500 million years. We are looking at the dawn of life.'
Their research looked at embryos from a range of species at various stages of embryonic development. Among other things, the details revealed by the images have allowed the scientists to determine the structure of the embryos and clarify the relationships between these ancient animals.
Significantly, the images of fossilised arthropod (insect and crustacean) embryos reveal them to be very similar to modern arthropod embryos. According to the scientists, this means that arthropod evolutionary history may have to be pushed further back in time than previously thought.
These internal images have also helped the scientists to answer outstanding questions about the evolutionary relationships between various species.
Ultimately, the researchers believe that using the SRXTM has wide applicability in the study of fossilised microscopic structures. '[It] may thus bring about a revolution in palaeontology on a par with that once brought about by the scanning electron microscope,' they write.