Science isn’t always pretty. It is rare for scientist to find samples of fossilized soft tissue, however researchers working at a site in Australia report that they have found the oldest known sample of semen. They believe that soft tissue fossil from the Riversleigh World Heritage Fossil Site was preserved by large quantities of bat dung.

The Riversleigh fossil deposits in remote northwestern Queensland, Australia is a treasure trove of fossil remains. The area has previously produced remains of a variety of creatures including a carnivorous kangaroo and a platypus with teeth. The discovery of preserved semen, however, has taken researchers by surprise.

“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 UNSW School of Biological, Earth and Environmental Sciences in a statement.

The giant sperm came from a a tiny shrimp, the ostracod, which lived in a pool within the cave.

“About 17 million years ago, Bitesantennary Site was a cave in the middle of a vast biologically diverse rainforest. Tiny ostracods thrived in a pool of water in the cave that was continually enriched by the droppings of thousands of bats,” says Professor Archer.

It is believed that the bat poo produced high levels of phosphorous in the water, which helped to preserve the soft tissue. The same site has turned up perfectly preserved leaf cells and soft tissue from the eyes of extinct marsupials.

Perhaps the most curious thing about the discovery is that the sperm are thought to have been longer than the body of the male from which it came, 1.3 millimetres, but were tightly coiled within the body of the animal. The Zenker organs, which acted as pumps to transfer the sperm to the female were also found.

The findings of Archer and his colleagues can be found in the journal Proceedings of the Royal Society B.