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Fossilised fish uncover more secrets

11 March 2009

Monash alumnus, artist Peter Trusler has recreated the likeness of the placoderms, an extinct group of fish from the Middle Palaeozic era.

New research by Monash University honorary researcher Dr John Long of the School of Geosciences, reveals that vertebrates have been having sex for more than 375 million years – making sexual intercourse more ancient than scientists first thought.

The evidence of the first vertebrate sex has been confirmed in a fossilised fish, which was named last year after the British naturalist David Attenborough.

Dr Long said the latest revelation proves that the sexual activity of the first vertebrates involved copulation, shifting the evolutionary origin of this mode of reproduction further back in time.

"Further investigation of the fossilised remains of the placoderm, or armoured jawed fish, have revealed they had pelvic fins with structures similar to claspers, as in modern sharks, confirming the way they had sex involved internal fertilisation," Dr Long said.

The findings were made using the same fossil that last year made world-wide headlines and became known as world's oldest mother, Materpiscis attenboroughi, a placoderm fish with embryo and umbilical cord attached.

"The discovery of Materpiscis attenboroughi confirmed animals were reproducing 375 million years ago, but we didn't know how this was happening. Our study of the fossil shows that reproduction was achieved through intercourse," Dr Long said.

The placoderms are an extinct group of jawed fish that were the dominant group of vertebrates through the Middle Palaeozic era. The placoderms, often referred to as the 'dinosaurs of the seas', were the rulers of the world's lakes and seas for almost 70 million years.

Dr Long is renowned as one of the world's leading palaeontologists and is Head of Sciences at Museum Victoria. His latest research was conducted in partnership with Dr Kate Trinajstic from the University of Western Australia and Dr Zerina Johanson from London's Natural History Museum.