Researchers Find World's Oldest, Giant Sperm in Ancient Shrimp

Researchers discovered world's oldest fossilised sperm in an ancient kind of tiny shrimp that lived in the Australian outback some 17 million years ago. The sperm is a giant, almost as long as the male itself.

The team, which included researchers from University of New South Wales, found the sperm at the Riversleigh World Heritage Fossil Site. It was found in freshwater crustaceans called Ostracods. The sperm was tightly coiled inside the organism's sexual organs.

"These are the oldest fossilised sperms ever found in the geological record," said Professor Mike Archer, of the UNSW School of Biological, Earth and Environmental Sciences.

Ostracods are by far the most extensively studied crustaceans under micropalaeontology. These organisms are ancient relatives of crabs and lobsters. Today, Ostracods have over 8000 living species, making them one of the most successful crustacean groups. These organisms can range from anywhere between 0.1 and 32 mm in length.

The fossils used in the study were first discovered in Bitesantennary Site at Riversleigh in 1988. The samples were sent to John Neil, a specialist ostracod researcher at La Trobe University. Neil realized that the specimen had soft tissue. Analysis of the tissue revealed that it contained the internal organs of the creature, including its sexual organs.

Microscopic study of the sexual organs showed that it had almost perfectly preserved giant sperm cells and within them, the nuclei, which once would have had contained the genetic material of the organism, a news release said.

According to the researchers, the fossil sperm is about 1.3 millimetres long, which is about the same length or slightly longer than the creature. Researchers also found muscular pumps called Zenker organs in the ostracod. Zenker organs are used to transfer the sperm 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. The phosphorous from the bat droppings mineralized the soft tissues of the osctracods.

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

Australian Research Council, UNSW CREATE Fund, Queensland Museum and others support the research at Riversleigh.