Picture a frigid Scottish loch. Now inside this loch picture two gyrating armored prehistoric fish that would later be called M. Dicki. The fish, the most primitive jawed vertebrates, would never win any beauty contests. But in the amorous world of the aptly-but-coincidentally named M. Dicki, love was blind. Which was probably a good thing.
The planet’s first act of sex 385 million years ago, as documented in fresh research published in the journal Nature, wasn’t a gentle affair. It involved what Australian paleontologist John Long described in an interview as “a bone with a strange groove on it,” “plates that helped locked the male organ into place like Velcro,” and a strange jig that was sort of like square dancing. It wasn’t poetic. It wasn’t touching. It was the awkward origins of sex.
“We didn’t expect these little suckers to have reproductive organs,” said Long, the study’s lead author and a professor at Flinders University in Adelaide. “We thought they were like pelvic fins like a shark’s, and we never thought there would be anything like this.”
It’s been a big year for Australian researchers in the field of ancient sex. In May, Australian scientist Michael Archer discovered the world’s oldest sperm, which he told The Washington Post was “staggering,” gigantic, and involved something called a “zenker organ.”
Long knew the study well. “Oh, yeah!” he reminisced. “I wrote a column about that one!”
Long, in fact, has done a lot of writing on prehistoric sex and the reproductive practices of placoderms like M. Dicki, penning memorably named books such as “Hung Like an Argentine Duck.” Alternate title: “The Dawn of the Deed.” “We all know about the birds and the bees, but what about the ancient placoderm fishes and the dinosaurs?” the book asked. “The history of sex is as old as life itself — and as complicated and mysterious.”
Few instances of sexual activity are more mysterious than that of M. Dicki. The path to the discovery began in 2008. That was the year Long discovered a fossil of a placoderm that would become known as the “mother fish.” From 380 million years ago, it proved to be the oldest vertebrate embryo and first known instance of internal fertilization. “When I first saw the embryo inside the mother fish, my jaw dropped,” Long told Live Science that year. “It dawned on me after studying the specimen that this was the earliest evidence of vertebrates having sex by copulation — not just spawning in water, but sex that was fun.”
But it wouldn’t be the last. “Inspired by this incredible find, Long began a quest to uncover the paleontological and evolutionary history of copulation and insemination,” his book said.
That journey ultimately led Long to Tallinn, Estonia, last year. There, he came into contact with fossils of Microbrachius Dicki, named after Robert Dick, who found the fossils in northern Scotland in the late 19th century. The name “microbrachius” means “little arms,” and the creature, eight centimeters (three inches) long, populated the island’s rivers and lakes, the Conversation, an academic news Web site, reported.
But M. Dicki had one arm Long didn’t understand. “I at first couldn’t figure out that this was a male sexual organ,” Long said. “It was made of bone and not soft tissue, and this was why we thought it would have been strange to mate with it.” But Long said the discovery’s “clincher” arrived several months later when he analyzed a complete female and male. He found that the female had “small paired bones” that could lock the male in.
“Until this point in evolution, the skeletons of jawed vertebrates couldn’t be distinguished because males and females had the same skeletal structures,” fellow author Brian Choo said in a press release from the university. “This is the first time in vertebrate evolution that males and females developed separate reproductive structures, with males developing claspers, and females developing fixed plates to lock the claspers for mating.”
Still, one question remained: How did the “clasping” work? Long said the two fish probably copulated in a sideways position, bony arms locking every which way. “This enabled the males to maneuver their genital organs into the right position,” Long said.
He said it wasn’t dissimilar to square dancing. And this realization was around when the jokes started. “Oh, we made lots of jokes about these fish — especially with a name like ‘Dicki,'” Long said. “We didn’t name it ‘Dicki.’ It was just coincidental that a fish named that happens to reveal the origins of sex.”