The World's Oldest Sperm was discovered in Antarctica: 50-million-year-old sperm cells from a worm.
Scientists have discovered 50-million-year-old sperm cells, which are the oldest known sperm cells yet found. The specimen comes from a species of extinct Antarctic worm and was found in a fossilized cocoon spun for sex.
The finding, detailed in the current issue of the journal Biology Letters, represents one of the very few instances in which fossil sperm cells have ever been found.
"Because sperm cells are so short-lived and fragile, they are vanishingly rare in the fossil record," says study first author Benjamin Bomfleur, a paleontologist at the Swedish Museum of Natural History (SMNH) in Stockholm.
One of Bomfleur's team members, Thomas Mörs, also at SMNH, accidentally discovered the fossil while sifting through rock samples from Antarctica in search of small animal remains. While sifting, Mörs found fossil worm cocoons, and a closer look using an electron microscope revealed the presence of numerous trapped sperm cells.
By comparing the fossil sperm's physical characteristics with that of living worms, the team concluded that they belonged to annelids, the group of animals that includes earthworms and leeches. In particular, the fossil sperm bore a close resemblance to the sperm of modern-day crayfish worm, tiny leech-like creatures that live on the shells of crayfish and feed on dead organic matter.
"Surprisingly, modern crayfish worms are only known from the Northern Hemisphere," says study-coauthor Steve McLoughlin, a senior curator at SMNH. "If our identification is correct then it implies that this group of animals had a much greater geographic range [50 million years ago] than they do today."