Researchers at the University of New South Wales discovered world's oldest fossilised giant sperm in a tiny shrimp that lived 17 million years ago.

The researchers said that the length of the fossil sperm is about 1.3 mm, which might be about the same length or slightly longer than the male itself. It was found tightly coiled up inside the organism's sexual organs.  

"The animal that produced this giant sperm belongs to the class Ostracoda or mussel shrimp," said lead author Renate Matzke-Karasz, a paleontologist at the Ludwig-Maximiliian University and Geo-Bio Center, Discovery News reports.

"This is the oldest fossilised sperm ever found in the geological record," said Professor Mike Archer, of the School of Biological, Earth and Environmental Sciences, in a press release. "... the discovery of fossil sperm, complete with sperm nuclei, was totally unexpected."

Researchers first collected the fossil specimen from Bitesantennary Site at Riversleigh in 1988 and then dispatched it to John Neil, a specialist Ostracod researcher at the La Trobe University. Neil discovered that the specimen contained soft tissue.

A microscopic analysis found that the 17 million-year-old preserved giant sperm had internal organs intact including its sexual organs. These organs further showed almost perfectly preserved giant sperm cells and within which, was the nuclei that once would have contained the creature's chromosomes and DNA.

Besides its sexual organs, researchers also found muscular pumps called Zenker organs in the specimen. The organs are used to transfer the sperms into the female.

"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," said Archer.

UNSW's Associate Professor Suzanne Hand said that bats could have played a key role in the conservation of the organism's sperm cells. The "poo" from several bats in the cave would have resulted in higher amounts of phosphorous in the water that could have in turn helped in the mineralisation of the soft tissues.

 "So the key to eternal preservation of soft tissues may indeed be some magic ingredient in bat droppings," Hand said.

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