The fossilized sperm fragment was spotted by German-born scientist Benjamin Bomfleur, 35, and a team of international colleagues as they used a high-tech microscope to examine the inner service of a cocoon fossil discovered on Seymour Island, off the Antarctic Peninsula, by an Argentinian expedition.
It is believed to have been preserved for 50 million years and should help researchers find out more about the evolution of earth worms and how cocoon fossils have the potential to trap microrganisms.
After being published in scientific journal Biology Letters on Wednesday, news of the find went global on Thursday, with Bomfleur telling The Local that international press requests had been "coming in like an avalanche".
"To find a sperm was a weird surprise...about as bizarre as you can get," he said.
"We know it's because we found a sperm rather than something else that we've caught so much attention, but we don't mind, it is still good news to get our work in the media," he added.
"I got woken up by the Washington Post, I've had calls from the New York Times and high ranked scientific magazines...but not so much attention here in Sweden. Everyone here is on holiday, even the press office at the museum, so the wheels didn't really get into action if you know what I mean!"
Sperm cells are incredibly delicate and are rarely found in fossils. According to Nature
magazine, the oldest animal sperm previously discovered came from springtails trapped in amber, and was thought to be 40 million years old. However much older plant sperm fossils have been unearthed in Scotland, with some dating back 400 million years.
Bomfleur told The Local that the sperm discovered in the Antarctic fossil had been able to survive for so long thanks to the secretions of an ancient worm, which formed a cocoon of mucus that then hardened and locked in biological material - including sperm - along its walls.
"We don't know yet what kind of worm this was and we hope our research can give us some more information on the kind of animal that produced the cocoon," he said.
"There is a scientific significance to our findings because as well as simply finding such an old sperm, we know know more about these cocoon fossils and their potential to trap microorganisms...ancient microorganisms are very rarely preserved in a fossil," he said.
The paleontologist has been living in Stockholm for two years having previously worked as a researcher in the US. His global team on the project included another German, an Italian, an Argentinian and an Australian.