terça-feira, 14 de setembro de 2010

Mother fish

29 May, 2008

Source: Museum Victoria"> Click here to view larger image.
Placoderm gives birth.
Source: Museum Victoria

380 million year old fishes found with unborn embryos.

In 2005 Museum Victoria’s expedition to the Gogo fossil sites in north Western Australia, lead 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.

Today the team announced its latest discovery: a remarkable 380 million year old fossil placoderm fish with intact embryo and mineralised umbilical cord.

The discovery, published in Nature and one of the most significant ever made by Australian scientists, 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.

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’.

References
Long, J.A., Trinajstic, K., Young, G.C. & Senden, T. 2008. Live Birth in the Devonian. Nature 453, 650-652.

Long, J.A., Young, G.C.,Holland, T., Senden, T.J. & Fitzgerald, E.M.G. 2006. An exceptional Devonian fish from Australia sheds light on tetrapod origins. Nature 444, 199-202.

Trinajstic, K., Marshall, E., Long, J. & Bifield, K. 2007. Exceptional preservation of nerve and muscle. Biology Letters 3, 197-200.

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