Giant Sperm Cells Belonging to 17 Million Year Old Shrimp Are the Oldest Ever Found

The sperm were longer than the male shrimp’s entire body

The sperm cells were found in Riversleigh, a remote spot in northwestern Australia that was once a teeming rainforest. Photo: Huygens

Researchers working in northwest Australia just announced the discovery of the world's oldest sperm. The sperm are approximately 17 million years old and belonged to creatures called ostracods—tiny freshwater shrimp. The fossilized specimen, found within the reproductive tract of several females and within a male, also revealed that the ostracods' ancient sperm were relatively massive. At about 1.3 mm, they stretched at least the length of the males' bodies, if not more. To manage them, the males produced the sperm in tightly wound bundles. 

The fossils were actually discovered back in 1988, but it took a while for researchers to realize they contained the remains of fossilized soft tissue, the team explains. In addition to the giant sperm cells themselves, the team also found the remains of structures called Zenker organs, which acted as biological pumps for transferring sperm from males to females. 

Bats, the researchers point out, probably receive the credit for preserving the amazing shrimp specimens. Today, the site where the researchers found the fossils appears dry and barren, but 17 million years ago it was a bustling rainforest ecosystem. Bats roosted above the ostracod's jungle pool, and the nutrients from their droppings likely helped preserve the shrimp. "So the key to eternal preservation of soft tissues may indeed be some magic ingredient in bat droppings," the researchers joked in a release. 

Get the latest stories in your inbox every weekday.