London: Sexual intercourse was invented 385 million years ago in Scotland by fish from an extinct group called placoderms, which are among the earliest vertebrate ancestors of humans, according to a new study.
Scientists have long been puzzled by the purpose of bony protrusions in placoderms that resembled a surplus pair of fins or limbs just in front of the tail.
A new study, to be published in the journal Nature, has found that the protrusions were in fact used by the fish to cling together as they mated, 'The Sunday Times' reported.
The 6 inch fish appear to have been the first in the fossil record to develop such appendages, suggesting it was the originator of the mating practices used by humans and most other vertebrates today.
Placoderm fossils have been found in Orkney and northern Scotland around John o' Groats.
The research was led by John Long, of Flinders University in Australia, with colleagues including Zerina Johanson, the curator of fossil fish at London's Natural History Museum.
Placoderms were a large group of mostly armoured fish that emerged about 450 million years ago, evolving into a range of species that included large marine predators 33ft long.
They were wiped out 360 million years ago in a mass extinction event but their 90 million years of dominance saw them evolve some of the key features of modern vertebrates.
Long and his colleagues travelled the world studying fossils in museum collections and collecting new ones for clues.
In 2009, Johanson and Long announced the discovery of a 365 million-year-old fossil fish from Australia that appeared to have been pregnant when it died, implying that fertilisation of eggs inside the body was already happening.
The fish involved in the new discovery is 20 million years older and comes from a far more primitive group of placoderms, called the antiarchs, researchers said.