Oldest Sperm Ever to be Discovered Found in Antarctica at 50 Million Years Old

First Posted: Jul 15, 2015 08:22 AM EDT

Scientists have uncovered the oldest sperm to ever be found-by accident. They've discovered the remains of long, thin cells preserved inside the 50-million-year-old fossilized cocoon of a worm species that once lived in Antarctica.

The researchers actually spotted the sperm fragments when they used an electron microscope to examine the inner surface of the cocoon fossil. This finding, though, is particularly rare. Because they're delicate, sperm cells are rarely found in fossils. The previous oldest animal sperm was from springtails preserved in Baltic amber, about 40 million years old.

Cocoons are secreted by some worms, including earthworks and leeches, which deposit sperm and eggs inside. Each cocoon then hardens to form a protective case for the developing embryos.

The researchers aren't sure exactly what kind of worm left the sperm. Yet scanning electron microscopes reveal helical structures resembling drill-bits and beaded tails, which are characteristic of sperm produced by crayfish worms, leech-like creatures that live on freshwater lobsters.

There's no extractable DNA left in the sperm fragments. This is because the chemical makeup of the organic material would have changed from its original composition over such a long time. However, the sperm cells don't just retain their outer casts, but also retain their inner structure.

The findings could actually provide important insights into the evolution of the kinds of worms that secrete cocoons.

"I think we might have a really interesting system here that can be sort of a hidden window to the past," said Jakob Vinther, one of the researchers, in a news release. "There could be a lot of potential hidden gems inside those cocoons."

The findings are published in the journal Biology Letters.

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TagsFossil, Evolution, Antarctica, sperm