The above is a picture of (as near as I can tell) the fruit or seed of a type of green algae called charophytes. They are 400 million year old microfossils that scientists have recently found a new and important way to study.
Researchers at the ESRF have presented the possibilities that microtomography offers by showing the steps of a 3D non-destructive investigation by X-ray synchrotron microtomography on a gyrogonite from Late Cretaceous (Mesozoic) period, originating from the South of France. This charophyte doesn’t belong to the Sycidiales, but shows the possibilities of X-ray synchrotron microtomography on small fossils. The first step is a high resolution microradiograph (pixel size of 1.4 microns) showing the spirals twisted from base to apex. From a complete set of microradiographs taken during a half rotation, virtual slices are reconstructed (step 2). From all the slices, we obtain a 3D representation of the sample (step 3) showing its external morphology. Step 4 presents the internal cavity after the “virtual” removal of a part of the gyrogonite wall. Using these 3D data, the team reconstructed a virtual mould inside the gyrogonite (step 5). On this virtual oospore (step 6), numerous details are visible, such as the sutures, the apex, or the basal plate. Image number 7 is an observation with a polarizing microscope of a slide in an equivalent sample.
The applications of this new technique are, to say the least, extremely wide and varied:
The use of X-ray synchrotron microtomography for this pioneering study on fossil algae opens new doors to paleontology. Indeed, charophytes represent only one group among numerous others of very small fossils. This kind of investigation should hence become a reference for non-destructive three-dimensional approach of small fossils.
Incidentally, researchers found two types of structures in their study. The first, which you can see above, were a series of ridges in a spiral pattern. The second was a vertical pattern of ridges. An additional surprising find was of a uticule:
An utricule is a supplementary protective layer believed to protect the zygote (reproductive cell) against desiccation. The fact that such a structure was acquired during the evolution of these very old algae means that they probably lived in a harsh environment. This structure could be interpreted as an adaptation to strong seasonality with dry summers leading to ephemeral aquatic environments.
Amazing, the things science can do these days!