暴龍的祖先 五彩冠龍暴龍的祖先 五彩冠龍 有冠恐龍化石,可能是暴龍的祖先。中國和美國的古生物學家在新疆準噶爾盆地發現生活在一億六千萬年前侏羅紀後期的有冠恐龍化石,可能是暴龍的祖先。美國喬治華盛頓大學古生物學家James M. Clark和中國科學院古脊椎動物與古人類研究所的徐星等人在新疆準噶爾盆地發現大小兩隻恐龍的化石。牠們全身的骨骼都很完整,頭部有冠狀突起物,加上發現化石的地層有五種顏色,因此將之命名為「五彩冠龍」(Guanglong wucaii)。他們在2002年發現化石,分別將其編號為IVPPV14531和IVPPV14532。他們發現的兩隻恐龍距離很近,比較大的五彩冠龍V14531特徵最明顯,頭部有冠,身長 三公尺 ,死亡的時候是12歲,已經成年,較小的五彩冠龍V14532則是七歲。暴龍的祖先 五彩冠seo龍 ,根據這兩隻恐龍牙齒、頭骨、骨盤的結構,可以確定牠們是新種暴龍。他們表示,根據這兩隻恐龍牙齒、頭骨、骨盤的結構,可以確定牠們是新種暴龍。在電影《侏羅紀公園》中,暴龍被描述成侏羅紀最兇猛的肉食恐龍。但實際上,科學家此前發現的體型巨大的暴龍,大部分生活在八千多萬年前比侏羅紀晚的白堊紀。因此五彩冠龍若不是最古老的暴龍,就是暴龍的始祖。較大的五彩冠龍V14531頭上的冠長約卅公分,高約 十公分 ,厚僅 零點一五公分 。這個骨質冠薄且脆弱,因此他們推測它沒有爭鬥等實用功能,很可能是求偶或識別同類的標志。這一骨質冠與現代許多鳥類頭部的求偶標志非常相似,是鳥類與獸腳目恐龍起源於同一祖先的證據之一。五彩冠龍大概只有 三米 長,站立起來不到 一米 ,和白堊紀長十多米房屋貸款、高達 四米 以上的暴龍完全不能相比。但牠的形貌與暴龍非常相似,擁有強壯的後肢、類似鳥一般的頭部和銳利的牙齒,表明它是一種兇猛的肉食恐龍。已知最古老的暴龍是一億三千萬年前的奇異帝龍(Dilong paradoxus),身上還帶有羽毛,為中國和美國古生物學家兩年前宣布發現。這兩隻恐龍的化石看不出來身上有羽毛,但五彩冠龍的近親被認為有羽毛,五彩冠龍可能也有羽毛覆蓋。Clark表示,他們完全沒想到會發現這種有冠的恐龍,這說明早期的暴龍顯然還有很多地方有待發掘。參與這項研究的紐約美國自然史博物館古生物學家Mark A. Norell說,發現這種古老的暴龍,令人對暴龍這個族群及其祖先的多樣性大開眼界。Norell指出,這兩隻恐龍的骸骨有幾個原始特徵,如前臂短,有三指。暴龍前臂變得更短,指剩婚禮佈置下兩個,前肢幾乎沒什麼功能,而且身材變大,身長為冠龍兩三倍。Before the Tyrannosaurus, Guanlong Roamed China Chinese and American scientists have discovered what appears to have been the granddaddy of all tyrannosaurs, a primitive crested dinosaur that lived 160 million years ago in northwestern China. The scientists announced yesterday that an analysis of two fossil specimens suggested that they were either remains of the most primitive tyrannosaur known or the first branch on the family tree leading to Tyrannosaurus rex, the symbol of tooth and claw predation in the age of reptiles. James M. Clark, a paleontologist at George 褐藻醣膠Washington University , said the discovery "shows us how ancestors of tyrannosaurus took the first step that led to the giant T. rex almost 100 million years later." The research team, led by Dr. Clark and Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing , named the new species Guanlong wucaii. The first, or generic, name is derived from the Mandarin word for "crowned dragon," a reference to its large, fragile crest. The second, or species, name refers to the rich colors of the Junggar Basin , the remote discovery site north of the Tian Shan range. The discovery, made in 2002, is described in detail 酒店打工in today's issue of the journal Nature. Dr. Clark and other team members discussed the ancestral tyrannosaur yesterday at a news conference in Washington . Two specimens of the new species were uncovered near one another. The most revealing one, the scientists said, was a nine-foot-long, 12year-old adult with the crested head believed to be typical of the species. The other was a smaller, 7-year-old juvenile. Almost immediately, Dr. Clark said, "we knew we had something fairly rare." The clearest evidence of an ancestral link to tyrannosaurs were the teeth and pelvic structure of the two skeletons. Closer examination, Dr. Clark said, 房屋二胎dispelled any lingering skepticism and showed a definite relationship with later tyrannosaurs. Mark A. Norell, a paleontologist at the American Museum of Natural History in New York and a team member, said, "The discovery of this basal tyrannosaur is giving us a much broader picture of the diversity of this group and its ancestors." Dr. Norell noted several primitive traces in the skeletons, including the presence of long forearms and three-fingered hands. The well-known T. rex, which lived about 70 million years ago, toward the end of the Cretaceous period of geologic time, evolved short forearms that were virtually nonfunctional seotwo-fingered hands, and a mammoth body two or three times the length of these early ancestors. The differences suggest that the newfound animals were an intermediate step in evolution between primitive coelurosaurs, a group of birdlike dinosaurs, and tyrannosaurs. The skeletons were found in sediments from the late Jurassic period, when the site in the desert basin was a warm land of lakes and marshes. The region of the discovery, near China 's borders with Mongolia and Kazakhstan , was previously explored by a Chinese-Canadian fossil hunting expedition in the 1980's. Other paleontologists said they were not surprised that the 室內設計region had yielded more discoveries from earlier epochs in the time of dinosaurs. Only a few scraps of dinosaur fossils were previously uncovered in the Jurassic deposits, but Dr. Clark said the age of the Guanlong specimen was "about where we would expect the oldest tyrannosaurs to be." The earliest previously known tyrannosaur was a 130-million-year-old feathered specimen, Dilong paradoxus, which American and Chinese scientists reported two years ago. No signs of feathers were found on the two Guanlong specimens. The presence of a crest on the Guanlong adult's head was a complete surprise, Dr. Clark said, showing that there was 關鍵字排名"clearly still much more to be learned about early tyrannosaurs." The research team said the crest was about as thin as a tortilla and only two and a half inches high. It appeared to be filled with air sacs and reminded the paleontologist of the ornamental features found on some living birds, like cassowaries and hornbills. Dr. Norell said the crest was too thin to have provided much protection, or to have been used in butting heads in combat. More likely, he said, the crest of these "crowned dragons" had something to do with attracting mates or identifying fellow species members. Source: 租屋http://www.nytimes.com/2006/02/09/science/09dino.html 其他相關新聞:

nq56nqhotj 發表在 痞客邦 PIXNET 留言(0) 人氣()