From Cocoon to Lagerstatte?

There’s a recent bit of palaeo-news which really piqued my interest recently, yet I failed to blog about it when it was announced. So here it is…

The fossil is on the left, a vorticellid in the centre, and a leech cocoon on the right. Image credit: Hans Kerp et al / Muenster University

From deposits in Antarctica a fossilised cocoon, like those produced by the modern medicinal leech Hirudo medicinalis, has been found containing an exceptionally preserved microfossil. A cocoon would, in most cases, be a type of trace fossil, a remnant of ancient animal behaviour, but this one has become much more. Due to its mucous content it trapped a microorganism which had attached itself to the cocoon, becoming preserved along with it when the cocoon fossilised.

This is not the first example of such preservation, though few are known as they have not really been explored thus far. What makes this particular find grab the attention is that it easily fits into a modern group, one which has no fossil record due to its soft-bodied microscopic nature. It is what is nicknamed a “bell animal”, a member of the Vorticella family – single celled protozoa which use cilia for mobility.

What we have here is an ichnofossil (fancy word for trace fossil) which can function like a mini lagerstatte (another fancy term, for a site of exceptional preservation) though the term conservation trap is probably more appropriate (but less grand). Its preservational qualities are much like amber, but with a fossil record which extends further back than amber deposits, and are an untapped source. Similar finds in the future might expand our knowledge of ancient microbes, filling in gaps in the fossil record which we previously thought could not be filled. I personally find that exciting.

For more on the story, you can find press releases here, here and here, and the paper itself is here.

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