According to today’s Times sex has been around for at least 350 million years. The fossilised remains of a pregnant fish, Incisoscutum ritchiei, have provided the earliest known evidence of copulation and live births in the animal kingdom. Until the evolution of the armoured fish, sex is thought to have been limited to external fertilisation techniques in which sperm and eggs were squirted into the water to mix.
The species, 350-380 million years old, is the same age as another closely related fossilised fish, Materpiscis attenboroughi, which was found last year with a newly born offspring still attached by the umbilical cord.
Researchers said the discovery of two types of fish living at the same time shows copulation among vertebrates was a common means of reproduction some 200 million years earlier than had been thought. “Seen in one fossil, it could have been a one-off. With our new discovery we are beginning to think sex is characteristic,” said Dr Zerina Johanson, of the Natural History Museum in London. “We now have to rethink how animals reproduced way back then. We would have expected before this, that this very primitive fish had an external form of fertilisation. We are having to rethink that now. It’s challenging how we think about reproduction at this early evolutionary stage... Sex started a lot sooner than we thought.”
The embryo found inside I. ritchiei was originally thought to have been the mother fish’s last meal but was reassessed after the discovery of M. attenboroughi. Both species were found in Western Australia’s Gogo formation which is thought to be the remnants of a reef in tropical inland sea.
The two species of copulating animals were examples of placoderms which were a class of fish that had armoured plates on their heads and thorax and dominated the seas during the Devonian. They are the most primitive form of jawed vertebrates yet found and most were predators. Placoderm fossils have been found in Europe, North America, North Africa, Australasia and Antarctica.
Hmm it looks like Philip Larkin was a few million years out when he wrote in his poem Annus Mirabilis that:
Sexual intercourse began
In nineteen sixty-three
(which was rather late for me) -
Between the end of the Chatterley ban
And the Beatles' first LP.
Then again he was a poet and not a scientist,,,