The first cache containing prehistoric sperm preserved in both sexes has been found in a large batch of prehistoric tiny crustaceans called ostracods in Romania’s Southern Carpathian Mountains.
The ostracods are only about 14,400 to 10,000 years old, in the Late Glacial and Holocene periods, making them barely prehistoric. What makes them remarkable is the discovery of the sperm cache with both male and female ostracods—specifically Cypria ophtalmica, a freshwater species still in existence today. The shrimp-like crustaceans occupy niches in both fresh and saltwater habitats worldwide, and feature segmented bodies that typically are surrounded by a hinged, tough outer shell.
Between 5% and 10% of the ostracods in the study sample contained sperm. “This record represents the oldest and richest direct evidence of virtually morphologically unaltered animal spermatozoa preserved in females after mating,” a team of four Romanian researchers led by Sanda Iepure, Ph.D., of Romania’s Babes-Bolyai University concluded in an article detailing their discovery in the journal Die Naturwissenschaften (The Science of Nature).
In most of the specimens, the sperm bundles appeared to be neatly arranged in the position expected for the male reproductive organs, while in the remainder, the sperm bunches were located in a different place and dislocated from each other. Based on observations of living ostracods, Dr. Iepure and her colleagues posited that the former ostracods were males, and the latter, females.
The fossilized sperm is easy to spot by their size, since ostracods have the second longest sperm in relation to their body size, after some fly species. While ostracods are just one millimeter long, they can produce sperm up to 10 times longer, or one centimeter in length. Dr. Iepure and co-authors note that the prehistoric specimens are consistent with what researchers have observed among living ostracods.
However, it’s not the first discovery of ancient sperm. Previous studies have found such cells among roughly 5,000 year old ostracods from the U.K., while spermatophores have been found preserved in 40 million year-old amber with an insect called a springtail. Also, the essential seminal and receptacle organs have been found in Brazil by paleontologists studying ostracods believed to be 100 million years old.