100-million-year-old giant sperm trapped in amber is world’s oldest

Researchers have discovered the oldest known animal sperm sample, dating back 100 million years. A piece of amber caught dozens of small crustaceans called ostracods in a compromising position with their “soft parts” out, and weirder still their sperm is giant, measuring around a third of the animals’ body length.

Researchers have discovered the oldest known animal sperm sample, dating back 100 million years. A piece of amber caught dozens of small crustaceans called ostracods in a compromising position with their “soft parts” out, and weirder still their sperm is giant, measuring around a third of the animals’ body length.

Ostracods are some of the most commonly found fossil remains, stretching all the way from the Ordovician to the present – a span of over 480 million years. But normally it’s only the hard calcified shells that remain, with softer tissues proving very rare. That makes the new discovery pretty amazing. The one piece of amber captured 39 individual ostracods, including males, females and juveniles, preserving their privates in unprecedented detail.

The team used X-ray micro-CT scans to peer through the amber and create 3D models of their rarely-seen soft parts, to get a better understanding of how these critters get it on. Male ostracods, it turns out, have a fifth limb with hooks on it, which they use to grasp females while they guide their two penis-like organs into the female’s two vaginas. The giant sperm are then pushed up two long canals in the female into two storage sacs, where they wait for eggs to fertilize.

The amber actually preserved the creatures in such high detail that the researchers were able to see the sperm inside these sacs, indicating that the ostracods had only just wrapped up the act when they met their untimely end.

Interestingly, modern ostracods still mate in much the same way, meaning the mechanism has remained unchanged for over 100 million years. At that age, the team says that these are the oldest animal sperm samples ever found, around twice as old as the previous record holder.