首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Tiktaalik rosae is considered to be an evolutionary ______ . 【36】
Tiktaalik rosae is considered to be an evolutionary ______ . 【36】
admin
2009-05-13
54
问题
Tiktaalik rosae is considered to be an evolutionary ______ .
【36】
Welcome everybody. My name is Derek Fisher and I’ll be taking you through this talk on a truly amazing discovery made by my team of researchers last year. As I’m sure you know, we discovered Tiktaalik rosae, a so-called "missing link" in the evolutionary process--a fish that walked on land. We made this extraordinary discovery in the Canadian Arctic. I should emphasise fight at the beginning that I do not have any evidence to suggest that this was the only such fish to make the leap from the sea to the land. I think that further discoveries may await researchers.
Anyway, the fossil discovery illuminates a chapter in the history of life on Earth that was essential to the ultimate emergence of human beings. This is an impression of Tiktaalik roseae, which, we believe, lived about 375 million years ago. As you can see, it has features that blur the distinction between fish and terrestrial limbed creatures. The fossils that we found on Ellesmere Island, 600 miles from the North Pole, are a fine example of evolution in action. They have allowed us to freeze-frame a process of adaptation to land that took tens of millions of years, and which made possible the development of all the mammals, birds, reptiles and amphibians that have existed since.
Without creatures such as Tiktaalik there would have been no dinosaurs, no primitive mammals and none of the hominids such as Australopithecus africanus and Homo erectus that started the human family tree. This animal represents the transition from water to land--the part of history that includes ourselves. It’s as much a part of our history as, say, Australopithecus africanus. Now, you can see those teeth. From that, it is clear to us that Tiktaalik roseae was a predator with sharp teeth and a head shaped like a crocodile’s that grew to between four feet and nine feet--that’s between 1.2 metres and 2.7 metres long for those of you using the metric system! We named it after consultation with elders from the Inuit people, who are native to the region, who suggested their word for "large shallow-water fish". The second part of the name honours the person who funded our research, but wishes to remain anonymous.
It had several remarkable anatomical features that show it was capable not only of wading in shallow water, like slightly earlier fish on the cusp of the move to land, but also of supporting itself outside the water in the manner of four-limbed animals or tetrapods. This is where Tiktaalik truly blurs the boundary between fish and land animals. This animal is both fish and tetrapod. At first, we jokingly call it a "fishapod". Unlike fish, it had a clearly defined neck and a strong ribcage that would have enabled it to stand outside water. Its pectoral fins had a wrist joint, which enabled it to crawl on the ground. This wrist is sufficiently similar to that of later animals, including human beings, to suggest that Tiktaalik or something very like it was an ancestor of all subsequent land animals. However, we cannot be sure of that. When we tall about the fish’s wrist, we’re talking about the origin of parts of our own wrist. It is absolutely clear from Tiktaalik’s skeleton that it could support itself in shallow water or on land. This is why it represents a critical early phase in the evolution of all limbed animals, including humans.
We found the Tiktaalik fossils in 2004 after a five-year search of a rock formation on Ellesmere Island, one of the large islands that comprise the north of Canada. This site was chosen because it was--or more exactly the rocks were--laid down during the late Devonian period, between 380 million and 365 million years ago, when the transition of fish from sea creatures to creatures that could survive on land is known to have taken place. It may surprise you to know that although the rocks are now within the Arctic Circle, in the late Devonian they lay close to the Equator. We, as individual humans, don’t notice plate movements because dramatic changes can only be seen over millions of years, but the continents as we know them today have moved considerably and will continue to do so. This exciting discovery is providing a much deeper understanding of this evolutionary milestone. Previous fossils representing this evolutionary event have really been fish with a few land characteristics, or land vertebrates with a few residual fish characteristics. These fossils show an animal that sits bang in the middle.
Now, let’s move on to...
选项
答案
clearly defined
解析
转载请注明原文地址:https://kaotiyun.com/show/fnAO777K
本试题收录于:
雅思听力题库雅思(IELTS)分类
0
雅思听力
雅思(IELTS)
相关试题推荐
Traditionalcriticalscholarshiphasconsideredaliteraryworktheproductofonefocusedmind,alongwithitssocialinfluence
Thousands,perhapsevenmillions,ofpeoplearoundtheworldareafflictedwithaneurologicalconditioncalledsynesthesia.The
WhetherthelanguagesoftheancientAmericanpeopleswereusedforexpressingabstractuniversalconceptscanbeclearlyanswer
Thelifestyleofmodern-dancepioneerIsadoraDuncanwasconsidered______,sinceitwasmarkedbyunconventionalbehaviorandat
BessieColeman,theworld’sfirstlicensedBlackaviator,wasconsidered______becausesheregularlyperformedriskyflyingstun
Becauseoftheirspare,whiteappearance,ancientGreekstatuesinmodernmuseumsareoftenconsidered(i)______;yetnewlyunea
Thefewfemalephysicianspracticingattheendofthenineteenthcenturymightbeconsidered______becausetheyconstitutedave
Guestsatthepartyfoundthegeneralmerrimentinfectiousandwerewonoverbytheparty’s______.
Unlikethewildturkey,whichcansuccessfullyflyforshortdistances,thedomesticatedturkeyiscompletely______flight.
随机试题
A.少海B.血海C.照海D.小海E.气海
A.支气管哮喘B.喘息型慢性支气管炎C.支气管肺癌D.肺炎支原体肺炎E.克雷伯杆菌肺炎常于秋季发病,儿童和青年人多见,起病缓慢。阵发性干咳、发热、肌痛,胸片示下叶间质性肺炎改变
奸党罪
()主要是指将组织的目标与成员的个人目标相结合,在更深远的层次上激发成员潜能的活动。
下列会计电算化梢案安全和保密措施不正确的是()。
关于会计记录文字论述,下列说{击中错误的是()。
转授权金额不得大于原授权,但在某些特定业务品种上可以突破。()
全陪在接团前准备阶段的工作主要包括()等内容。
定义两种运算:,则函数的奇偶性为________。
选项四个图形中,只有一个是由题干四个图形拼合而成的,请选出来。
最新回复
(
0
)