The sperm, described in the Royal Society journal Biology Letters, is so old that it predates the prior record-holder (fossilized sperm from a mussel shrimp) by over 30 million years.
The discovery “was a big surprise and almost pure chance,” lead author Benjamin Bomfleur of the Swedish Museum of Natural History told Discovery News. Almost, because he and senior author Stephen McLoughlin had previously found another super ancient item — a fossilized tiny protozoan animal — inside of a Triassic leech cocoon, also from Antarctica.
Bomfleur explained that earthworms, leeches and their relatives produce incredibly sturdy cocoons into which their eggs and sperm are released.
In this case, a scanning electron microscope at very high magnification revealed that sperm cells had become entrapped in the segmented worm’s cocoon wall material before it completely fossilized. Similar to bugs and plant bits trapped in amber, the sperm and its surrounding material later hardened and preserved over millions of years.
Based on the fossils, the sperm looked like that of a modern worm species.
The head of the sperm, which resembles drill bits, “(appears) strikingly similar to those of this one peculiar group of leech-like worms that is today only found living symbiotically on crayfish in the Northern Hemisphere,” Bomfleur said. “Quite perplexing!”
It could be that the worms had a much greater geographic range 50 million years ago than they do today. If that’s verified, and the reasons for the range shifts are determined, the information could shed future light not only on the early worm populations, but also on those of their shellfish hosts and other creatures in their ecosystem.
At the time of the prehistoric worm’s existence, the researchers believe what’s now Antarctica would have been much warmer, with a climate similar to that found today in southern Chile.
It appears to have been a mini paradise teeming with flora and fauna.
“The seas were brimming with sea life, with nautiloids (a mollusk group), sea urchins, clams and mussels, and a wide variety of sharks and other fish; on land, there was a diverse mammal fauna, ranging from small marsupials to large ungulates and sloths, as well as large cursorial (running) birds,” Bomfleur said.
He continued, “Isolated seeds of water lilies and lotus plants are common in the deposit where the cocoon was found, so we can expect that there were at that time also vegetated lakes or swamp areas.”
Read more at Discovery News
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