ancient copulation
October 20, 2014

Researchers Discover The Origins Of Sex In The Primordial World

Brett Smith for redOrbit.com - Your Universe Online

At some point in our primordial past, life on Earth began to reproduce sexually – leading to greater and greater genetic diversity.

According to a new study in the journal Nature, a team of international researchers has found the earliest-known organism to reproduce by sexual intercourse, a small bony fish known as Microbrachius dicki.

Also known as placoderms, these tiny armored fish grew to just over 3 inches and lived around 385 million years ago in the lakes around modern-day Scotland. The study team found that placoderms used their L-shaped genital limbs to hold onto each other while the male transferred his sperm to the female.

The discovery identifies when sexual intercourse came into existence, as opposed to reproduction by spawning, when a female fish lays eggs that are then later fertilized by sperm from a male.

[ Watch the Video: Professor John Long’s Discovery Of The Origins Of Sex ]

“Microbrachius means little arms but scientists have been baffled for centuries by what these bony paired arms were actually there for,” study author John Long, a paleontologist at Flinders University in Australia, said in a statement. “We’ve solved this great mystery because they were there for mating, so that the male could position his claspers into the female genital area.”

The study team reached their conclusion after studying placoderm fossils from collections across Europe. They speculated, based on an anatomical analysis, the bony fish probably reproduced in a sideways position.

"They couldn't have done it in a 'missionary position'," Long told BBC News Science Correspondent Rebecca Morelle. "The very first act of copulation was done sideways, square-dance style."

[ Watch the Video: HD Animation Showing The Earliest Known Copulation ]

He added that the males’ genital arms and complimentary plates on females allowed the two sexes to lock together while mating, probably increasing the rate of fertilization.

"They act like Velcro, locking the male organ into position to transfer sperm,” Long said.

Study author Brian Choo, a postdoctoral researcher at Flinders, said the discovery represent the first time in history that the two sexes showed differences in their physiology.

“Until this point in evolution, the skeletons of jawed vertebrates couldn’t be distinguished because males and females had the same skeletal structures,” Choo said. “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 in for mating.”

The new study builds on previous research from Long and many of the other same researchers.

“Our earlier discoveries published in Nature in 2008 and 2009 of live birth and copulation in placoderms concerned more advanced placoderm groups,” he said. “Our new discovery now pushes the origin of copulation back even further down the evolutionary ladder, to the most basal of all jawed animals.”

“Placoderms were once thought to be a dead-end group with no live relatives but recent studies show that our own evolution is deeply rooted in placoderms, and that many of the features we have, such as jaws, teeth and paired limbs, first originated with this group of fishes,” Long continued. “Now, we reveal they gave us the intimate act of sexual intercourse as well.”

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