Fish with Gigantic Genitals Were the First Species to Get Laid

A recreation of the ancient fish sex

Sex is an ancient act, but it hasn't been around forever. From the beginning of time to about 430 million years ago, life forms reproduced by spawning. But sometime between then and 385 million years back, a kind of armored fish known as a placoderm developed things like arms, legs, jaws, and genitals that—if you squinted real hard—made it resemble a human being. And sometime during that window, two of those placoderms threw their inhibitions out the window and got down to fuckin’. These findings, published in Nature on Sunday, are the result of paleontologist John Long's 30-years’ worth of research into placoderms and, more narrowly, fish sex.

The story began in 2008, when Long, who works in Australia, discovered the fossil of a 380-million-year-old fish with an intact embryo inside it. The find was huge because it provided evidence that placoderms might have had claspers, the organs that sharks and rays use to reproduce today. That suspicion was confirmed late last year when Long was digging through a box of microbrachius dicki fossils and came across one with an extending one-inch-long bone that he couldn't identify.

“What I found was that these ancient bony fishes were the first to develop copulation,” he told me. “It's a major thing to discover the origin of a major sexual development in the history of evolution.” A group of private collectors allowed Long to access their placoderm fossils, and eventually donated them to the Natural History Museum in London, which allowed him to expand on his theory that the first cum shot was fired in a Scottish lake between a couple of two-legged fish.

The placoderms developed advanced brain structure and teeth very rapidly around the time they started doing it, something that Long theorizes came from the sudden doubling of chromosomes. “Vertebrates hit a huge cascade of mutations all at once,” he says. “It's a really vital part of our evolution, and it's now only starting to be explored.”

But the genesis of our history as copulating beings isn’t as sexy as you might imagine. Long describes a bony L-shaped mass that the male would stick into the female's sexual organ, which resembled a cheese-grater. “The only way they could fit the two together was sideways,” he says. “We've been calling it square-dance style.” They could only do it sideways because the males had humongous genitals that were nearly as long as their bodies. Long says they could fit “just the tip” into the cloaca of the female to deposit the sperm.

This new method served an evolutionary purpose. By keeping the embryo cloistered away in a female's stomach, it was more likely to survive. An egg left floating in the water was free game for predators. As a result, the placoderm population expanded from the UK to China to Estonia, and eventually all over the world. “Whatever they were doing, they were suddenly everywhere,” Long tells me. “All living fishes and all living animals evolved from placoderms, although there's nothing alive like them today.”

Long says their tiny little arms were the key to their success. The placoderms used the arms to hold each other during sex and to keep from disconnecting. But for whatever reason this type of reproduction fell out of evolutionary favor before its eventual comeback. As the Guardian notes, these findings prove that “sex with internal fertilization evolved early on in the history of vertebrates but was then lost, with fish reverting back to spawning in water, and then evolved again in a different way. Modern sharks and rays have claspers that they use to deposit sperm into females, but instead of being attached to their whole bodies as in antiarchs, the organs grow along the inner part of their pelvic fins.”

Long told me about another theory concerning shark sex that he hasn’t fully fleshed out. A male shark will often bite his mate to keep her from escaping before he can impregnate her with his claspers. But now that we know this method of sexual reproduction evolved in tandem with jaws and teeth, it's perhaps worth considering that this is no accident. “I have another wacky idea that [these things] evolved to assist with copulation,” he says. “But that's a whole other theory.”

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