World’s Oldest Fossilized Sperm Discovered in Australia

Australian researchers have discovered the world's oldest sperm belonging to tiny shrimps.

Researchers from the University of New South Wales, Australia,  discovered the giant sperm that thrived at least 17 million years ago at the Riversleigh World Heritage Fossil Site. The giant sperm along with well preserved internal reproductive organs is that of an ostracod, a mussel shrimp.

The team found four fossilized female mussel shrimps and one male mussel shrimp with sperm in an ancient cave deposit.  And what preserved these ostracod sperm cells are bat droppings.

"These are the oldest fossilised sperm ever found in the geological record," Professor Mike Archer, who has been excavating at Riversleigh for more than 35 years, said in a statement. "The Riversleigh fossil deposits in remote northwestern Queensland have been the site of the discovery of many extraordinary prehistoric Australian animals, such as giant, toothed platypuses and flesh-eating kangaroos. So we have become used to delightfully unexpected surprises in what turns up there. 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."

The enormous sperm was believed to be longer than the male's entire body and was found coiled up within the sexual organ of the ostracod.  These fossilized ostracods were collected in 1988. It was John Neil, a specialist ostracod researcher at La Trobe University, who confirmed that the samples had fossilized soft tissues.

Microscopic studies showed the well preserved internal organs of the ostracods including their  sexual organs.  It was within this that the fossil sperm was present, which measured 1.3 millimeters long, equal to the length of the ostracod.

Professor Archer explains that over 17 million years ago the Bitesantennary site was a cave located in the middle of a rainforest. The pool water had the tiny ostracods, which were fossilized and preserved under the bat droppings; the steady rain of bat poo upped the levels of phosphorous in the water that helped mineralization of the soft tissue. 

"This amazing discovery at Riversleigh is echoed by a few examples of soft-tissue preservation in fossil bat-rich deposits in France. So the key to eternal preservation of soft tissues may indeed be some magic ingredient in bat droppings," said UNSW's associate professor, Suzanne Hand.

The finding was documented in the journal Proceedings of the Royal Society B.