fossilshk
(Lung)
管理員
 
UID 1
精華
22
積分 4509
帖子 2705
閱讀權限 200
註冊 2006-7-14
來自 中國/香港
狀態 離線
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[廣告]:
澳洲3.75億年前母魚化石連胚胎 活產紀錄回推2億年(中英/圖)
The stunning fossil of a fish giving birth that proves animals had 'sex for fun' 375 million years ago
Sex for pleasure is a lot older than we thought, according to a stunning new fossil find announced by scientists yesterday.A fossil of an ancient, extinct Australian fish which died just before giving birth to a live baby is, according to the scientist who made the discovery, 'the earliest evidence of vertebrates having sex by copulation – not just spawning in water, but sex that was fun'.
These are the fossil remains of the 375-million fish - the oldest vertebrate mother ever discovered
The find, revealed in the journal Nature, is by far the oldest 'viviparous', or live, birth yet found by scientists.
The fish, one of a primitive extinct group called the 'Placoderms', lived in the seas of Devonian Earth and has been dated to 380 million years old.
The fossil, discovered by Professor John Long at Museum Victoria in Melbourne, shows the bones of the tiny baby fish, still attached by its umbilical cord. It is thought the mother fish was about to give birth to maybe three or four babies just before she was killed.
“When I first saw the embryo inside the mother fish my jaw dropped, I was silent, stunned like a mullet. I realised that in my hands was the oldest known vertebrate embryo.”
The embryo can clearly be seen in this image of the fossil - even, amazingly, the umbilical cord
The find was made in the Gogo rock formation east of the remote town of Fitzroy Crossing, Western Australia, and pushes back the record for a live birth by 200 million years.
The fish, a new species, has been named Materpiscis attenboroughi, 'Attenborough's mother-fish' in honour of Sir David, who featured the extraordinary fossil beds at Gogo in his 1979 TV series Life on Earth.
“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 Long.
“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.
Dr John Long points out the umbilical cord on the fossil, the fossilised remains of the oldest mother ever discovered
The fossilised fish has been named in honour of Sir David Attenborough
The vertebrates consist of the fishes, amphibians, reptiles, birds and mammals. Only birds, among these, are exclusively egg-laying but live births among fishes were thought to be confined to the sharks and rays.
Like the sharks, this species of Placoderm possessed a pair of bony graspers with which the male grasped the female while fertilising her with his sperm. “It might have been fun, for the male at least,” said Dr Long.
Placoderms were fearsome looking creatures, with powerful nutcracker jaws, clad in bony armour plating and thought to be efficient predators. The fossil is of a specimen about the size of a mackerel but some placoderms grew to a length of nearly 20ft, and the group as a whole formed the dominant vertebrates of the Devonian era, a time when other species of fish were starting to crawl out onto the land and evolving into the first four-legged animals.
It is thought the placoderms became extinct as a result of climate change at the end of the Devonian; their place in the pecking order was taken by a new group of fishes to have evolved: the sharks.
The announcement of the finding was made at the grand opening of the refurbished Royal Institution in London yesterday, at which the Queen and the Duke of Edinburgh were present at the press conference.
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