It's pretty hard to find a fossil of something that's completely squishy and tiny. Without bones or exoskeletons, there's not a lot from many microorganisms that gets preserved. But a 200-million year old cocoon has shown us a glimpse at an ancient microorganism that looks incredibly similar to some modern examples.
At Timber Peak in Antarctica, a layer of well preserved plant fossils was discovered, and in amongst the plant materials was a cocoon, possibly from a Triassic leech. But what was special was what was inside the cocoon: a well preserved example of a soft body microorganism — something which rarely survives the ravages of time. Intriguingly, the fossil looks incredibly similar to a modern protozoa, the Vorticella campanula bell animal. The ancient fossil is thought to be a "ciliate protozoan of the family Vorticellidae", and the modern relatives of this microorganism are incredibly common, and found in waterways around the world. This ancient example may have become trapped in the walls of the discarded cocoon as it solidified, anchoring in its walls, and then dying.
Not only does this microfossil give us a glimpse into the waterways and microscopic biomes of hundreds of millions of years ago, but it also hints that this might be a very useful way to keep looking for tiny remains. As the researchers conclude:
The preservation of microorganisms inside fossil clitellate cocoons appears to be surprisingly common; in addition to the Triassic bell animal and the Cretaceous nematode Captivonema, trilete spores and other unicellular organisms also have been reported encased in these microscopic conservation traps. We anticipate that a deliberate search for microinclusions in fossil clitellate cocoons may open up an invaluable source of information on ancient soft-bodied microorganisms and the past ecosystems in which they lived.