Gigantic Sperm Belonging To Tiny Prehistoric Shrimp Discovered

By Shweta Iyer on May 15, 2014 9:52 AM EDT

giant sperm
This is an artist's impression of Bitesantennary Site 17 million years ago. The cave was in the middle of a vast biologically diverse rainforest in an area that is now part of the Riversleigh World Heritage Fossil Site in northwestern Queensland, Australia. (Photo: Dorothy Dunphy.)

Millions of years ago, tiny shrimp similar to modern day ones lived in pools of water and like the modern ones had huge sperm coiled up within their testes. This was confirmed with the discovery of enormous fossilized sperms belonging to shrimps at the Riversleigh World Heritage Fossil Site by a team including UNSW (University of New South Wales) Australia researchers. Their study is published in the journal Proceedings of the Royal Society B, according to a press release Wednesday.

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The fossilized sperm belonged to freshwater crustaceans known as ostracods. Ostracods are small, typically 1 mm in size but their sperms can be up to six times the length of the male ostracod itself. In the fossils, the sperms were found tightly wound inside the sexual organ of the male.

"These are the oldest fossilised sperm ever found in the geological record," says Professor Mike Archer, of the UNSW School of Biological, Earth and Environmental Sciences, who has been excavating at Riversleigh for more than 35 years.

"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."

Following its collection from the Bitesantennary Site at Riversleigh in 1988 by the UNSW research team led by Professor Archer, Associate Professor Suzanne Hand, and Henk Godthelp, the fossil ostracods were examined by John Neil, a specialist ostracod researcher at La Trobe University, who realised they contained fossilised soft tissues.

He was then aided by Dr. Renate Matzke-Karasz, from Ludwig Maximilian University of Munich, Germany and Dr. Paul Tafforeau, in examining the fossils at the European Synchrotron Radiation Facility in Grenoble, France. Microscopic studies revealed all kinds of perfectly preserved internal organs including sexual organs. Within these are the almost perfectly preserved giant sperm cells, and within them, the nuclei that once contained the genetic material of the organism. Studies also revealed well-preserved "zenker organs" that are used to transfer the sperms 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. But what preserved these ostracods for so long? Bat poo according to Professor Archer. Along with ostracods there were also a huge number of now extinct bat species that populated the site.

"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," he said. Bat droppings would have led to phosphorization of the water, which would have preserved the soft tissues and the sperms.

UNSW's Associate Professor Suzanne Hand says, "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."

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