The first act of sex took place about 385 million years ago in ancient lakes in Scotland. Scientists have discovered that an ancient fish called Microbrachius dicki is the first known-animal to have sexual intercourse. Before that, these fish reproduced by spawning, where the female releases eggs and the male releases sperms in the water to fertilize.

Ancient Fish Sex

Placoderms gave rise to all vertebrates with jaws

Scientists led by John Long of the Flinders University in Adelaide, Australia said the primitive bony fish was only about 8cm long. These antiarch placoderms, the armor-plated creatures, were the first to develop specific female and male genitalia. Placoderms are known to have given rise to all modern vertebrates with jaws. Findings of the study appeared Sunday in the journal Nature.

Microbrachius dicki fossils are quite common. But nobody ever noticed their sexual organs until now. Professor Long discovered it while looking through a box of ancient fish fossils. He noticed an odd L-shaped appendage in the M. dicki specimens. Further analysis revealed that these appendages were “claspers,” the male fish’s genitals. On the other hand, the female fish had a small bony structure at the rear end, which locked the claspers into place.

Intercourse of the ancient fish was constrained by their anatomy

Antiarch placoderms are closest to the root of the animal family tree. So, it indicates that all placoderms reproduced using claspers. But the ancient fish’s intercourse was constrained by their anatomy. They had to copulate side by side. Prof Long said the male and female fish would stay in position with the help of their arm-like fins.

Ancient Fish In Scottish Lake Were First To Have Sex: Scientists

But the bony fish that followed placoderms in the evolutionary tree show no evidence of internal fertilization. It suggests that the first attempt of internal reproduction wasn’t around for long. As the ancient fish evolved, they reverted to external fertilization, i.e., spawning. It took their descendants another few years to “re-invent” organs for sexual intercourse. Previously, scientists believed that such a reversion was evolutionary improbable.

Prof Long said the reversion from internal to external fertilization was totally unexpected. But their research showed that it’s the way it happened.