Cross-section of fossilized ostracod sperm. The nuclei in each sperm (dark spot) are indicated by arrows (R. Matzke-Karasz)
Cross-section of fossilized ostracod sperm. The nuclei in each sperm (dark spot) are indicated by arrows (R. Matzke-Karasz)R. Matzke-Karasz

World's oldest known sperm cells have been discovered by scientists. The sperms, termed "giant" by scientists, are about 16–17 million years old and were found fossilized in rock.

The fossilized sperms were found at Riversleigh World Heritage Fossil Site in Northwest Queensland, Australia. The cells were found in the reproductive tract of a small female crustacean, called seed shrimp or ostracod.

The Riversleigh fossil deposits in remote northwestern Queensland have been the site of the discovery of many prehistoric Australian animals.

"But the discovery of fossil sperm, complete with sperm nuclei, was totally unexpected. It now makes us wonder what other types of extraordinary preservation await discovery in these deposits," said Mike Archer, of the University of New South Wales, School of Biological, Earth and Environmental Sciences.

"We can distinguish the typical helical organization of the organelles in the sperm cell, which makes its surface look like a hawser or cable. But the most astounding aspect of our findings is that it strongly suggests that the mode of reproduction in these tiny crustaceans has remained virtually unchanged to this day," Live Science quoted study researcher Renate Matzke-Karasz, from Ludwig Maximilian University of Munich, Germany.

The cells are believed to be some of the oldest fossilized sperms found till date.

Though the ostracod looks small, it produces giant sperms that are about four times longer than shrimp itself. Seed shrimps measure about only a few millimeters long but their sperm reaches over 0.4 inches, which is 1 centimeter in length. Some insects, including some moths and flies, also produce giant sperm, the purpose of which is still unclear.

Mussel shrimps display a large variety of strange sexual practices. Many of them have two sets of reproductive organs and both take part during mating. Some species even have three genders: males, females and females that do not undergo intercourse with males.