Australians find a mother of a fossil
The world's oldest mother and her baby have been found fossilised in north-western Australia, pushing the known record of live birth back by about 200 million years.
The fossil, discovered by Australian scientists, appears in today's edition of Nature.
The placoderm fish fossil shows the embryo attached to its mother by an umbilical cord, and is estimated to be up to 380 million years old.
"It is not only the first time ever that a fossil embryo has been found with an umbilical cord, but it is also the oldest known example of any creature giving birth to live young," says team leader Professor John Long, Museum Victoria's head of science.
And according to colleague Dr Kate Trinajstic, of the University of Western Australia's School of Earth and Geographical Sciences it is hoped the specimen might yet yield genetic material and biomolecules.
The 25-centimetre specimen, preserved in three dimensions, was found at the world-famous Gogo fossil site, near Fitzroy Crossing in the Kimberley, which was once an ancient barrier reef teeming with fish.
It has been named Materpiscis attenboroughi after the naturalist Sir David Attenborough, who first drew attention to the Gogo fish sites in the 1979 Life on Earth television series.
The team says the new specimen is "exceptional in revealing a small partial skeleton located within the upper body cavity of a pregnant adult female".
"The small internal individual must be an embryo, rather than an ingested prey item, because the delicate bones show no breakage or etching from stomach acids," the paper says.
"Our new example extends the definite record of vertebrate viviparity (giving birth to live young) back by some 200 million years."
Young, an adjunct professor with the Australian National University, says high-resolution computer tomography scanning of Materpiscis shows details of the umbilical cord including the path of a major vessel and possibly the recrystallised yolk sac.
After identifying the embryo, Trinajstic re-examined another Gogo specimen found in 1986, which had what were originally thought to be three back scales.
Instead scans revealed there were three small embryos in the adult female Austroptyctodus gardineri, another species of placoderm.
Trinajstic says the embryos are the first fossilised evidence of sexual reproduction.
"It shows that very early on with jawed vertebrates they were having internal fertilisation and giving birth to live young," she says.
"We always thought these ancient fish would have laid eggs."
Placoderms were the dominant vertebrate on the planet during the Middle Palaeozic era between 420 to 350 million years ago.
The ancient jawed fish is known as the "dinosaur of the sea" and was the ruler of the world's seas for almost 70 million years.
Long who has been working in the Gogo area for the past 22 years says he instantly knew he had found something special.
"It was one of those great Eureka moments in science when after 20 years you suddenly find something you're holding and the penny drops that you've got something unique sitting in your hands," he says.
"Not only is it the world's oldest mother, it gives us a window into vertebrate sex."
There is no other evidence yet recovered of internal fertilisation by vertebrates as far back as Materpiscis.
The researchers' work is also being presented to the Queen via a videolink to the Royal Institution of Great Britain.