What the live birth of prehistoric fish might have looked like (Museum Victoria)
A fossil fish uncovered in Australia is the oldest-known example of a mother giving birth to live young, scientists have reported in the journal Nature.
The 380 million-year-old specimen has been preserved with an embryo still attached by its umbilical cord.
The find, reported in Nature, pushes back the emergence of this reproductive strategy by some 200 million years.
Until now, scientists thought creatures from these times were only able to develop their young inside eggs.
When I looked at it, my jaw dropped. I said we are onto something big here
Prof John Lane, Museum Victoria
Before this find, the earliest evidence for this form of reproduction came from reptile fossils dating to the Mesozoic Era (248 to 65 million years ago)
The team said the latest discovery had a remarkably advanced reproductive biology, similar to modern sharks and rays.
The extremely well-preserved fossil represents a new species of "placoderm" fish.
The placoderms were an incredibly diverse group and are thought to be the most primitive known vertebrates with jaws.
These armoured fish dominated seas, rivers and lakes throughout the Devonian Period (420-360 million years ago).
This latest placoderm specimen, which measures about 25cm (10in) in length, was found in the Gogo area of Western Australia in 2005 by a team led by John Long from Museum Victoria.
The fossil was found in Western Australia
Close examination revealed that the team had unearthed something unusual.
Professor Lane said: "When I looked at it, my jaw dropped. I said: 'we are onto something big here'."
The team found an embryo and an umbilical cord, which had been exquisitely preserved along with the female fish.
The scientists have named it Materpiscis attenboroughi, in honour of the naturalist Sir David Attenborough, who first drew attention to the Gogo fish fossil sites in the 1970s.
Sir David told the team that he was "very very flattered" to have had his name given to such an "astonishing creature".
The discovery prompted the researchers to return to another fossil that they had unearthed in 1986.
Close investigation revealed that this too contained evidence of live births - it contained three embryos.
Professor Lane said: "After we saw this, we realised we had totally nailed it, everyone was convinced that this creature bore live young."
Until the latest fossil find, scientists thought life forms that existed during these times had only evolved to reproduce using externally fertilised eggs - a primitive version of the way fish spawn today.
Now, however, the team believes this ancient species bore live young through internal fertilisation (viviparity).
Dr Long commented: "This 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.
"The existence of the embryo and umbilical cord within the specimen provides scientists with the first ever example of internal fertilisation - or sex - confirming that some placoderms had remarkably advanced reproductive biology.
He added: "This is a world first fossil find, and it opens up a window into the developmental biology of an entire extinct class of organisms."
Commenting on the paper, Zerina Johanson, a palaeontologist at London's Natural History Museum, said: "It is extremely rare to find preservation like this in the fossil record. This new discovery extends the record of viviparity back almost 200 million years in the fossil record.
"Placoderms represent the most primitive group of jawed vertebrates, so this work shows that the capacity for internal fertilisation and giving birth to live young evolved very early during vertebrate history."
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