In 2005, Museum Victoria’s expedition to the Gogo fossil sites in north Western Australia, led by Dr John Long, made a swag of spectacular fossil discoveries, including that of a complete fish, Gogonasus, showing unexpected features similar to early land animals.
Now the same team has made a new discovery: a remarkable 380-million-year-old fossil placoderm fish with intact embryo and mineralised umbilical cord.
The discovery, published in Nature, makes the fossil the world’s oldest known vertebrate mother. It also provides the earliest evidence of vertebrate sexual reproduction, wherein the males (which possessed clasping organs similar to modern sharks and rays) internally fertilised females.
“The discovery is certainly one of the most extraordinary fossil finds 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,” said Dr John Long, Head, Sciences, Museum Victoria.
“The existence of the embryo and umbilical cord within the specimen provides scientists with the first ever example of internal fertilisation - i.e sex - confirming that some placoderms had remarkably advanced reproductive biology. This discovery changes our understanding of the evolution of vertebrates,” he added.
This fossil has been named Materpiscis attenboroughi, meaning ‘mother fish’, in honour of Sir David Attenborough, who first drew attention to the significance of the Gogo sites in his 1979 series Life on Earth.
Armour-plated shark-like fishes with no modern relatives, a second placoderm specimen containing three embryos was found earlier in 1986 and only recently recognised. These embryos also provided the first data on their developmental biology, indicating the early sequence of bone formation in the placoderm’s growth stages.
Studied using an ultra-fine CT scanner at the Australian National University in Canberra, such extraordinary preservation in such an old fossil is unprecedented. The team had also previously announced the first 3-D preserved muscle, nerve and circulatory tissues in a Devonian age (380 million year old) fish in 2007 paper in Biology Letters.
This research project was funded by Australian Research Council Grant DP0772138 ‘Old Brains, New Data’.
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