Gigantic sperm have been found in 17-million-year-old fossilized mussel shrimp. The specimens, collected in Queensland, Australia, carry the oldest petrified sex cells on record.
Using high-intensity X-rays, scientists were able to identify the ancient sperm in one male and three female Heterocypris collaris species and one female Newnhamia mckenziana. While the length of the petrified sperm cannot be calculated from the specimens, modern mussel shrimp from the same class can have sperm up to 10 millimeters long even though their bodies are only a millimeter or two in size, the team notes. For comparison, human sperm is roughly .055 millimeters long.
The researchers also note that the tightly filled semen receptacles found in the female N. mckenziana specimen suggest that the animal mated right before it died. The results appear May 14 in the Proceedings of the Royal Society B.