Oldest mother ever discovered

Australian researchers have discovered the fossil of a new species of placoderm - primitive jawed fish - carrying an embryo connected by an umbilical cord.

It is the oldest record of a live-bearing vertebrate ever discovered and extends the known record of viviparity by 200 million years.

Materpiscis attenboroughi was discovered in 2005 during a Museum Victoria expedition to the Gogo Formation in the Kimberley region of WA. It has been named after David Attenborough, who used the site to demonstrate the evolution of fish in his 1979 television series Life on Earth.

Museum Victoria's head of science, Dr John Long, who along with colleagues from the University of Western Australia and ANU made the discovery and is lead author of a paper published in today's issue of Nature, said it is one of the most important discoveries he had ever made.

"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," he said.

Long is the leading expert on the Gogo Formation, a Late Devonian shale reef that has provided a remarkably preserved catalogue of three-dimensional placoderms. One of his most important findings was the so-called Gogo Fish, Mcnamaraspis kaprios, which provides a link between early fish ancestors and tetrapods, or four-legged land animals.

Materpiscis, or "mother fish", was a ptyctodont, one of the seven orders of placoderm, and featured heavy, crushing tooth-plates with which it ground up clams and shells. It was carrying a fully formed embryo attached to an umbilical cord and what is thought to be a yolk sac.

Long and his team used a standard acid etching technique to uncover the very delicate bones of the embryo.

"Our first thought was, was this something the creature ate," Long said. "But these things have highly specialised durophagous (shell-crushing) diets so they wouldn't have been predatory on other fish. Then we looked at the position of the embryo and there are several bits of evidence.

"One is that the embryo is located close to the axial skeleton, where the ovaries would have been, not down in the gut region. And it is an exact miniature of the adult in every respect; even the tooth-plates, which are highly characteristic of each species, show that it is the same species.

"And even more importantly we have the first ever - preserved in any fossil known - maternal feeding structure, a mineralised umbilical cord."

The realisation that what he was looking at was an embryo sparked a further discovery, this time that the tiny clusters of bones he had found in another fossil, Austroptyctodus gardineri, on his very first trip to Gogo in 1986, were the fossils of three embryos.

"It had what I thought were a series of scales along the body and that's what I labelled them in the paper I wrote," Long said. "I had a photo of this specimen that I blew up on the computer, and I could see immediately that these weren't scales - they were little clusters of bones and each one was an embryo.

"My collaborator Kate Trinajstic, who is one of my ex-PhD students, had a look at the specimen in Perth and rang me back that day and confirmed that it was a mother with three embryos inside her. They are from the same fossil bed so they are the same age."

Long said the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to some of today's sharks and rays.

The fossil will go on public display at Museum Victoria today.