A fossil fish from Australia was one of the earliest known vertebrates to reproduce by fertilising eggs inside the female, a study suggests.
Nature journal says the ancient fish was carrying a 5cm-long embryo.
The fertilisation of eggs by sperm outside the mother's body - external fertilisation - is thought to have evolved before copulation.
The fossil suggests the fertilisation of eggs inside the female's body evolved sooner than previously thought.
"These (fish) show some of the earliest evidence for internal reproduction," Zerina Johanson, curator of fossil fish at London's Natural History Museum (NHM), told BBC News.
"We expected that these early fishes would show a more primitive type of reproduction, where sperm and eggs combine in the water and embryos develop outside the fish."
According to Dr Johanson, the 365 million-year-old specimen shows that "the type of advanced fertilisation, taking place inside the mother, was more common among early fishes than previously thought.
"This discovery is incredibly important because evidence of reproductive biology is extremely rare in the fossil record," she said.
Dating to the Upper Devonian Period, the specimen has been bestowed with the scientific name Incisoscutum ritchiei.
It belongs to a group of early fish known as placoderms, which were covered in tough armour.
Full article with video and pictures at: http://news.bbc.co.uk/1/hi/sci/tech/7909984.stm
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