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Sex started with fish at least 385 million years ago

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Sex was happening on Earth at least 35 million years earlier than we previously knew, according to a new study. Even though fish generally reproduce externally by releasing eggs and sperm outside the body, a group of researchers back in 2009 found that at least one type of fish had started using internal fertilization about 350 million years ago. That same group of researchers, led by John Long of Flinders University, has now found a different species that they say was having sex as early as 385 million years ago, presenting what's now the earliest-known example of an animal that reproduced through internal fertilization. The findings are described in a study published in Nature.

"They gave us the intimate act of sexual intercourse."

Called the Microbrachius dicki, the creature is one of many long-extinct armored fish. It lived in lakes around Scotland and was barely over 3-inches in length. While studying them, Long and his research group noticed that the fish's male fossils had small limbs called "claspers" that could be used to deliver sperm and that the female fossils had a pair of bones that could lock the claspers in place. "This is the first time in vertebrate evolution that males and females developed separate reproductive structures," Long says in a statement. Similar structures exist today on sharks.

Long says that a good number of features in modern humans came from the group of animals, called placoderms, that M. dicki is a part of. Those include jaws, teeth, and paired limbs, which are believed to have originated with them. "“Now," Long says, "we reveal they gave us the intimate act of sexual intercourse as well." What's still quite notable is that this development eventually went away in fish before returning again later. The BBC reports that it wasn't for another few million years, when sex appeared again in the ancestors of sharks and rays.