The oldest sperm cells that have ever been found in the geological record were reported by Professor Mike Archer of the University of New South Wales School of Biological, Earth and Environmental Sciences and colleagues in the May 13, 2014, edition of the journal Proceedings of the Royal Society B. The sperm cells originally came from ostracod fossils. The sperm cells are 17 million years old.
The fossil ostracods were originally discovered at the Bitesantennary Site at the Riversleigh fossil deposits in northwestern Queensland in 1988. Ostracods are an ancient species of shrimp that has about 8,000 species living today. Only recently did the researchers discover that the fossil shrimp contained soft tissue.
The soft tissue included ostracod sexual organs and gigantic sperm cells. The sperm cells were 1.3 millimeters long. The shrimp were about the same order of size. The Zenker organs were also preserved as soft tissue. The sperm cells included a complete nucleus and all the DNA of the ancient shrimp.
The researchers propose that the Bitesantennary Site was a tropical rainforest 17 million years ago. The ostracods lived in small pools of water in the rainforest. The location where the fossils were originally found was a cave. The scientists propose that a continuous deposit of bat guano over 17 million years provided an environment that preserved the soft tissue of the shrimp. Phosphorous in the bat guano provided the chemical environment that was responsible for the preservation of the ostracod fossils and the preservation of extremely ancient soft-tissues.
The preservation of soft tissues or even the mineralization of soft tissues from ancient animals is extremely rare. The Riversleigh fossil deposits have provided several other soft tissue samples over the years. It is possible that the soft-tissues of a female ostracod from the same time period may be found. The potential to create an ancient species from ancient DNA preserved for millions of years may be possible.