Considering how short-lived sperm is, the discovery of fossilized worm sperm dating back to 50 million years ago is a surprising gold mine for the scientific community.
During an expedition on the Seymour Island, just off the Antarctic Peninsula, Benjamin Bomfleur and Argentinian fellow researchers stumbled upon an uncommon fossilized item: cocooned worm sperm dated to 50 million years ago.
Bomfleur, who is the lead author of the study detailing the team’s finding and works at the Swedish Museum of Natural History declared:
“It was a big surprise and almost pure chance.”
A pure chance that made the paleontologists’ beam with excitement. Such fossilized preserved cells are hard to come by. Thanks to the cocoon, the worm sperm was perfectly preserved over the course of millions of years:
“Because sperm cells are so short-lived and fragile, they are vanishingly rare in the fossil record”,
added Benjamin Bomfleur.
What species of worm could the sperm belong to is still unknown. After thorough electron microscope analysis, the worm sperm was identified as resembling that of modern crayfish worms.
Yet, the location where the fossilized cocoon containing the ancient worm sperm suggested that whatever the worm species, it certainly had a wider geographic span that the modern crayfish worm.
The annelid cocoon is specific to earthworms or leeches, as well as others related and is particularly hard on the outside to preserve and protect the sperm or eggs released inside. In the case of the fossilized cocoon, the worm sperm possibly got entangled in the wall material before the cocoon fossilized.
Benjamin Bomfleur and Stephen McLoughlin had also found a fossil in Antarctica before: a leech cocoon dated back to the Triassic. Fossilized cocoons as such are now deemed to be the next treasure chest for the scientific community. One annelid cocoon alone is the ideal place to look for trapped micro-organism that provide a window to the past.
In the case of this fossilized cocoon found to contain worm sperm, many aspects are still pending analysis. Such as the geographical span. If the worms were similar to crayfish worms, it is a wonder that they could have thrived in Antarctica when they are now found exclusively in the Northern Hemisphere.
Certainly more studies will be looking into the fossilized cocoon, as well as others that haven’t been given sufficient attention so far. According to Benjamin Bomfleur, doing so would yield a wealth of information regarding the fossil record of a group that barely registered any fossils before.
The finding is detailed in the Royal Society journal Biology Letters.
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