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 ______ . How long had the researchers been looking when they found the Tikt
Tiktaalik rosae is considered to be an evolutionary ______ . How long had the researchers been looking when they found the Tikt
admin
2009-05-13
71
问题
Tiktaalik rosae is considered to be an evolutionary ______ .
How long had the researchers been looking when they found the Tiktaalik remains?
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
5/five years
解析
转载请注明原文地址:https://kaotiyun.com/show/AnAO777K
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
Areresponsestoodorsacquiredasafunctionoftheemotionalcontextinwhichtheyareinitiallyperceived?Researchers
DuringaEuropeanbroadcastin2002,televisionviewerswere(i)______byabordercollie’sabilitytocorrectlyretrievespecifi
Becauseofhis______,Brian’sguestsfeltverywelcomeandcomfortablestayingathishousefortheweekend.
Forgenerations,NativeAmericansusedmythsandlegendstoexplainthemysteriousworldaroundthem.Onesuchetiologicalmyth
Forgenerations,NativeAmericansusedmythsandlegendstoexplainthemysteriousworldaroundthem.Onesuchetiologicalmyth
Inarecentstudy,DavidCressyexaminestwocentralquestionsconcerningEnglishimmigrationtoNewEnglandinthe1630s:what
Inhumans,thepilomotorreflexleadstotheresponsecommonlyknownasgoosebumps,andthisresponseiswidelyconsideredtob
Indireneedof______,thetravelersfortifiedthemselveswithfoodanddrinkinordertocompletetheirjourney.
随机试题
损伤后出现外无肿形,自觉疼痛范围痛无定处,体表无明显压痛点,属于
屈原创作的《离骚》与《诗经》并称“______”,对后世诗歌产生了深远影响。
关于Hp感染,下列哪些说法正确
A、γ-羟丁酸B、西地那非C、麦角酸D、吗啡阿托品注射液E、阿普唑仑根据《麻醉药品和精神药品品种目录(2007年版)》属于第一类精神药品的是
中药说明书格式中的"主要成分"是指
某金融机构2008年第三季度业务情况如下:(1)发放贷款取得利息收入3000万元,其中包括用自有资金发放贷款取得的利息120万元,用储蓄存款发放贷款取得利息收入1800万元;(2)为市人事考试中心代收考试费用200万元,取得手续费3万元;(3)转让某种债
苹果几乎将消费文化表现得________。有人为了一台苹果手机去卖肾,也有人为了得到新发布的iPad彻夜排队。这种事不分种族不分国家发生在整个地球上,地球人被苹果打造的消费帝国迷得________。依次填入画横线部分最恰当的一项是()。
若a,b为实数,且的值是______。
1997年修改后的《刑法》赋予公民对某些犯罪采取绝对防卫而不受限度限制的权利,即对正在进行()以及其他严重危及人身安全的暴力犯罪采取防卫行为,造成不法侵害人伤亡的,不属于防卫过当,不负刑事责任。
.假设内存管理采用可变式分区分配方式,系统中有五个进程P1一P5,且某一时刻内存使用情况如下图所示(图中空白处表示未使用分区)。此时,若P5进程运行完并释放期占有的空间,则释放后系统的空闲区数应(1);造成这种情况的原因是(2)。
最新回复
(
0
)