Oldest Known Male Fossil Is Discovered

British researchers have discovered the oldest known fossil that is unequivocally male, a tiny, shrimp-like creature that lived 425 million years ago in the Silurian period when the first land plants emerged and fish moved into fresh water.

Researchers have long observed even older differences within species that represent sexual dimorphism -- differences in size and shape between males and females. But in these cases, it has not been clear which individual is which gender because soft tissues are generally not preserved in fossils.

That’s not the case with the new fossil, an ostracode that was buried by volcanic ash in a rock bed in Herefordshire. The 0.2-inch fossil was so intact that paleontologist David Siveter and his colleagues at the University of Leicester were able to observe eyes, gills, a circulatory system, an anus and, most crucially, a penis.

The team reported in the current issue of the journal Science that they named the creature Colymbosathon ecplecticos, meaning “astounding swimmer with a large penis.”

To view the ostracode, the team sliced the rock fossil into very thin pieces, photographed them and stored the information in a computer. They were then able to reconstruct a three- dimensional image of the ani- mal.

Ostracodes have a two-part shell and exist today in ponds, lakes, rivers and seas, living as scavengers and predators. Surprisingly, they have changed very little over the last 425 million years. Most things that lived in the Silurian period are now extinct and don’t have any living relatives, experts said.