"It was a clasper, a sex organ, and it was the oldest and the most primitive one yet found on the planet," Long told The Guardian, noting that fossils without the appendages had two plates in about the same position. Those were the lady antiarchs.
"When these ancient fish called antiarchs first evolved, they were the first creatures to have jaws, the first creatures to have hind-paired limbs," Long told Vox. "Now we know that [fish] also invented copulation."
Given the particular arrangement of these organs, the researchers could then determine the way in which they came together - that is to say, the world's first sexual position. And like many firsts in this realm tend to be, it was rather awkward.
"The very first act of copulation was done sideways, square-dance style," says Long.
"The male can get his large L-shaped sexual organ into the right position to dock with the female genital plates, which are like cheese graters – very rough – so they act like Velcro, locking the male organ into position to transfer sperm."