An international team of researchers says a primitive bony fish called Microbrachius dicki is the first-known animal to stop reproducing by spawning and instead mate by having sex.
BBC News reports that the fish lived in ancient lakes about 385 million years ago in what is now Scotland. The lead author, Professor John Long, from Flinders University in Australia, said, “We have defined the very point in evolution where the origin of internal fertilisation in all animals began.”
“That is a really big step.”
The discovery was actually made somewhat on accident. The professor says he was simply looking through a box of ancient fish fossils when he noticed something unusual. The professor says he noticed that one of the M. dicki specimens had an odd L-shaped appendage. When he investigated the strange appendage further, he realized there was a difference between the two sexes and the appendage was actually the male fish’s genitals.
The female fish, on the other hand, was void of the L-shaped appendage and instead had a small bony structure at their rear that locked the male organ into place. Sadly it appears the ancient fish’s way of copulation wasn’t very effective. Fish returned to their act of spawning, and it wasn’t until a few million years later that larger species such as sharks began the act again.
The Sydney Morning Herald notes that the Long was excited about the find because it shows the time that “sex first became fun.”
“This is not just about bony structures on these fish, it’s about the evolution of behaviour, of when sex first became fun. Why would something develop these big bony clasper things and place them inside a female unless they enjoyed the act.”
One should note that before fish developed gender-specific sex organs, both males and females shed their gametes in open water to fertilize, so something evolutionary happened where these fish evolved to interact with one another in this specific way. Long also noted that the sex of the ancient yesteryear was nothing like it is today. In fact, it looked more like a square dance move than copulation.
The way the organs were located on the body meant the fish would have to have sex side-by-side with their arms clasped. The picture below shows exactly how these ancient fish would have had to perform their mating act.
Professor Long did note that “it is very remarkable that we haven’t noticed this before.”