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標題: 最新研究! 孔子鳥研究或助了解恐龍雌雄  
 
Edmond
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最新研究! 孔子鳥研究或助了解恐龍雌雄

恐龍近親孔子鳥的研究有突破,古生物學家首次憑化石分辨這種史前動物的性別。今次發現有重大意義,可能有助了解恐龍的雌雄之別。
孔子鳥就是活在一億二千萬年前的一種遠古鳥類,牠的學名竟然出自「孔子」的英文名,這個當然不是巧合,這種雀鳥的正式學名真的名為「孔子鳥」,因為牠的第一批化石在一九九三年的遼寧出土,當時的中國專家希望新品種的名字有中國元素,所以以象徵中國文化的孔子命名。
孔子鳥對古生物學別具意義。因為演化論有一個說法,認為現代鳥類是由恐龍演化而來。起初發現始祖鳥,被視為是兩者之間的過渡性物種。至於孔子鳥的身體特徵又剛好介乎始祖鳥與現代鳥類之間,填補這片空白,進一步鞏固演化論。
孔子鳥外觀是憑化石推斷而來,顏色自然靠畫家各自想象。不過有一點十分客觀,就是過往發現的化石都顯示孔子鳥有兩種,一種是有兩條長尾毛,另一種就沒有。牠們應該代表兩種性別,但哪一種是雌性,哪一種是雄性一直無定論。
不過,最近的研究終於解答這個問題,有專家在某隻無長尾的孔子鳥化石上發現髓骨組織,功能是為鳥類製造蛋殼,是雌性才有。所以孔子鳥與孔雀一樣,外表較平實的是雌性,比較花枝招展的為雄性。
這次是靠化石分辨遠古鳥類性別的首例。類似的方法,將來或者在恐龍研究上都能運用。因為孔子鳥亦是恐龍的近親,但對於恐龍的雌雄分別其實一直知得不多。

英文報導
http://nanopatentsandinnovations ... and-early-bird.html

Sex And The Early Bird
International team of paleontologists discovers way to identify gender of ancient avian species

In a paper published in Nature Communications on January 22, 2013, a team of paleontologists including Dr. Luis Chiappe, Director of the Natural History Museum of Los Angeles County's (NHM) Dinosaur Institute, has discovered a way to determine the sex of an avian dinosaur species.

Confuciusornis sanctus, a 125-million-year-old Mesozoic bird, had remarkable differences in plumage — some had long, almost body length ornamental tail feathers, others had none — features that have been interpreted as the earliest example of avian courtship. However, the idea that male Confuciusornis birds had ornamental plumage, and females did not, has not been proven until now. Chiappe and the team studied hundreds of Confuciusornis fossils unearthed from rocks deposited at the bottom of ancient lakes in what is today northeastern China and found undisputed evidence of the gender difference: medullary bone.

Chiappe conducted the study with Anusuya Chinsamy of the Department of Biological Sciences, University of Cape Town, South Africa; Jesús Marugán-Lobón of Madrid's Universidad Autonóma, Cantoblanco; Gao Chunling and Zhang Fengjiao of the Dalian Natural History Museum in China.

"Our discovery provides the first case of sex identification in an ancient bird, an animal closely related to dinosaurs, such as the famous Velociraptor," said Chiappe. "When people visit dinosaur exhibits, they often want to know if the skeletons are male or female. We have nicknames like Thomas and Sue, but of all the thousands of skeletons of dinosaurs or early birds found around the world, only the sex of a few has been determined."

According to Chinsamy, the bone histologist on the team, "Just like modern hens, female Confuciusornis birds that lived 125 million years ago deposited this special bone inside their long bones, and then used it to make the calcium-rich eggshells." Finding such tissue — present during a short period of time in reproductively active females — in a specimen that lacked long feathers proved that those birds without ornamental plumage are females.

"This now permits us to assess gender differences in growth and development of this Mesozoic bird," she said.

But while this discovery offers evidence that both early and modern female avian species were essentially using the same physiological strategy to reproduce, it also spotlights an important difference in when they sexually matured.

"In human terms, knowing the sex of these specimens sheds light on when these early birds begin puberty," said Chiappe, "Now we know that early birds began reproducing way before they were full grown, a pattern that contrasts with what we know of living birds, which typically begin reproducing after they reach full body size." In that way, ancient birds produced offspring like dinosaurs, which also began to reproduce before they were fully grown.

The specimens, housed at the Dalian Natural History Museum in northeastern China, had been excavated from rocks formed at the bottom of ancient lakes in a forested environment surrounded by volcanoes. Ancient catastrophes, presumably related to volcanic eruptions, killed large numbers of birds and other animals, whose bodies were buried deep in the lake mud that helped minimize decay and preserving the organs, skeletons, and plumage. "This discovery is part of the big picture of understanding the early evolution of birds,'' Chiappe said, "and how living birds became what they are."

The Dinosaur Institute

The Dinosaur Institute was founded in 2005 with a mission to make the Natural History Museum the dinosaur hub of the West Coast. Housed within the Museum, it conducts national and international research on dinosaurs and other animals that lived with them during the Mesozoic Era. It also manages an aggressive field program aimed to substantially increase the Museum's holdings of these fossils.


圖片附件: [雄性孔子鳥] Confuchisornis_sanctus.JPG (2013-1-24 10:15 AM, 143.74 K)



圖片附件: [雌性孔子鳥] 556px-Confuciusornis_sanctus_fossil.jpg (2013-1-24 10:15 AM, 85.21 K)

2013-1-24 10:15 AM#1
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達爾文 (香港版)
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其實雄性動物身上具突出的特徵來吸引異性,於動物世界已找到很多,但恐龍是否一樣可以用這種觀念去區分,最後隨時可能會相反



有進化的
2013-1-24 05:22 PM#2
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Edmond
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也許科學家認為某些恐龍跟鳥類關係很接近, 所以從此早期鳥類去推論兩性特徵, 而且, 現生動物(包括很多鳥類)有很多具突出的特徵, 估計當時也有一定的恐龍品種具有明顯的雄性特徵, 就是說,這些特徵是很早經已演化出來。

這個發現至少找到一些線索, 還有更多的證據等待被發現
2013-1-24 10:04 PM#3
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