首页
登录
职称英语
In prehistoric times brachiopods were one of the most abundant and diverse f
In prehistoric times brachiopods were one of the most abundant and diverse f
游客
2025-04-22
17
管理
问题
In prehistoric times brachiopods were one of the most abundant and diverse forms of life on Earth: more than 30,000 species of this chainlike creature have been cataloged from fossil records. Today brachiopods are not as numerous, and existing species are not well studied, partly because neither tile animal’ s fleshy inner tissue flor its shell has any commercial value. Moreover, in contrast to the greater diversity of the extinct species, the approximately 300 known surviving species are relatively, uniform in appearance. Many zoologists have interpreted this as a sign that the animal has been unable to compete successfully with other marine organisms in the evolutionary struggle.
Several things, however, suggest that the conventional view needs revising. For example, the genus Lingula has an unbroken fossil record extending over more than half a billion years to the present. Thus, if longevity is any measure, brachiopods are the moat successful organisms extant. Further, recent studies suggest that diversity among species is a less important measure of evolutionary success than is the ability to withstand environmental change, such as when a layer of clay replaces sand on the ocean bottom. The relatively greater uniformity among the existing brachiopod species may offer greater protection from environmental change and hence may reflect highly successful adaptive behavior.
The adaptive advantages of uniformity for brachiopods can be seen by considering specialization, a process that occurs as a result of prolonged colonization of a uniform substrate. Those that can survive on many surfaces are called generalists, while those that can survive on a limited range of substrates are called specialists. One specialist species, for example, has valves weighted at the base, a characteristic that assures that the organism is properly positioned for feeding in mud and similar substrates; other species secrete glue allowing them to survive on the face of underwater cliffs. The fossil record demonstrates that most brachiopod lineages have followed a trend toward increased specialization. However, during periods of environmental instability, when a particular substrate to which a specialist species has adapted is no longer available, the species quickly dies out. Generalist, on the other hand are not dependent on a particular substrate, and are thus less vulnerable to environmental change. One study of the fossil record revealed a mass extinction of brachiopods following a change in sedimentation from chalk to clay. Of the 35 brachiopod species found in the chalk, only 6 survived in the clay, all of them generalists.
As long as enough generalist species are maintained, and studies of arctic and subarctic seas suggest that generalists are often dominant members of the marine communities there, it seems unlikely that the phylum is close to extinction. [br] The second paragraph makes use of which of the following?
选项
A、Specific examples.
B、Analogy.
C、Metaphor.
D、Quotation.
答案
A
解析
第二段中作者以brachiopods为例来具体说明,故选A。
转载请注明原文地址:https://tihaiku.com/zcyy/4049272.html
相关试题推荐
Inprehistorictimesbrachiopodswereoneofthemostabundantanddiversef
Inprehistorictimesbrachiopodswereoneofthemostabundantanddiversef
Inprehistorictimesbrachiopodswereoneofthemostabundantanddiversef
Althoughdiverse,Africanmusichascertaindistinctivetraits,oneofwhichis
Inpromisingtofusemediaasdiverseastelevision,telephonecommunication
Inpromisingtofusemediaasdiverseastelevision,telephonecommunication
Inpromisingtofusemediaasdiverseastelevision,telephonecommunication
Biotechnologyinoneformoranotherhasflourishedsinceprehistorictimes.
Biotechnologyinoneformoranotherhasflourishedsinceprehistorictimes.
Biotechnologyinoneformoranotherhasflourishedsinceprehistorictimes.
随机试题
Ineedtoreadsomepapers.Turnoffthetelevision,______?A、doyouB、willyou
[originaltext]Thayer:Well,Ithinkthat..,probably,the..,uh...speaking
AlltherecentnewsonAIDSisbad.ThedeathofRockRudsonlastyearraise
【B1】[br]【B4】A、boughtB、bornC、gottenD、seenA语义衔接题。property的意思是“财产”,这句指出“非洲裔美国
Duringthetraditionalweddingceremony,thebridalcouplepromiseseachothe
[audioFiles]audio_ehbm_j44001(20082)[/audioFiles]A、About50pages.B、Itisvery
Theteacherstoodwithhisbacktothe(11)onawintermorning.Hedecided
为流浪乞讨人员提供全天候救助的地点是()。A.派出所 B.救助站 C.救助
根据有关税收优惠政革,天使投资个人在试点地区投资多个初创科技型企业的,对其中办理
(2016真题)在对可燃纤维织物加工车间配置灭火器时,除水基型灭火器外,下列灭火
最新回复
(
0
)