QUEENSLAND’S remarkable Riversleigh World Heritage Fossil Site has produced another amazing world first — giant sperm.

The sperm came from tiny shrimps that lived at least 17 million years ago.

Thought to have been longer than the male’s entire body, the sperm are tightly coiled up inside the sexual organs of the fossilised freshwater crustaceans, which are known as ostracods.

And perhaps the weirdest thing about the find is that it likely took a steady rain of disgusting bat poo into a rainforest pond to preserve the cells.

Mike Archer, of the UNSW school of biological, earth and environmental Sciences, who has been excavating Riversleigh for 38 years, said they were the oldest fossilised sperm ever found.

``The discovery of fossil sperm, complete with sperm nuclei, was totally unexpected,’’ Professor Archer said. ``It now makes us wonder what other types of extraordinary preservation await discovery in these deposits.

``It’s one thing to find cells but to find internal structure in cells like the nucleus is staggering. It’s mind blowing.’’.

Riversleigh in remote northwest Queensland has seen the discovery of many extraordinary prehistoric animals, like giant, toothed platypuses and flesh-eating kangaroos.

``We have become used to delightfully unexpected surprises in what turns up there,’’ he said.

A UNSW research team led by Professor Archer, Suzanne Hand and Henk Godthelp collected the ostracods from an area known as the Bitesantennary Site at Riversleigh in 1988.

They were sent to John Neil, a specialist ostracod researcher at La Trobe University, who realised they contained fossilised soft tissues.

He showed them to European specialists, including Renate Matzke-Karasz from Ludwig Maximilian University of Munich, Germany, who examined the specimens with Paul Tafforeau at the European Synchrotron Radiation Facility in Grenoble, France.

The microscopic study revealed the fossils contain preserved internal organs. Within these are almost perfectly preserved giant sperm cells, and within them, the nuclei that once contained the animals’ chromosomes and DNA.

Also preserved are the Zenker organs — chitinous-muscular pumps used to transfer the giant sperm to the female. The researchers estimate the fossil sperm are about 1.3 millimetres long, about the same length or slightly longer than the ostracod itself.

Professor Archer said the animals lived in water in a cave in the middle of a vast rainforest.

``Tiny ostracods thrived in a pool of water in the cave that was continually enriched by the droppings of thousands of bats,” Prrofessor Archer said.

UNSW’s Suzanne Hand, a specialist in extinct bats and their ecological role at Riversleigh, said the bats could have played a role in the preservation of the sperm cells.

The steady rain of poo from thousands of bats in the cave would have led to high levels of phosphorous in the water, which could have aided mineralisation of soft tissues.

``This amazing discovery … is echoed by a few examples of soft-tissue preservation in fossil bat-rich deposits in France,’’ Associate Professor Hand said.

``So the key to eternal preservation of soft tissues may indeed be some magic ingredient in bat droppings.’’

Perfectly preserved cells of leaves have been found, as well as the preserved soft tissue of eyeballs in the eye sockets of extinct marsupials.

The study is published in the journal Proceedings of the Royal Society B.