首页
登录
职称英语
"The Evolution of Birds" The Origin of Birds Analysis of birds and of rept
"The Evolution of Birds" The Origin of Birds Analysis of birds and of rept
游客
2024-01-03
37
管理
问题
"The Evolution of Birds"
The Origin of Birds
Analysis of birds and of reptilian fossils indicate that birds belong to the group called therapods. Several species of dinosaurs closely related to birds had feathers with vanes, and a wider range of species had filamentous feathers. Such findings imply that feathers evolved long before powered flight.
Among the possible functions of these early feathers were insulation, camouflage, and courtship display.
Derived Characteristics of Birds
Many of the characteristics of birds are adaptations that facilitate flight, including weight-saving modifications that make flying more efficient. For example, birds lack a urinary bladder, and the females of most species have only one ovary. Living birds are also toothless, an adaptation that trims the weight of the head.
A bird’s most obvious adaptations for flight are its wings and feathers. Feathers are made of the protein B-keratin, which is also found in the scales of other reptiles. The shape and arrangement of the feathers form the wings into airfoils, and they illustrate some of the same principles of aerodynamics as the wings of an airplane. Power for flapping the wings comes from contractions of large pectoral (breast) muscles anchored to a keel on the sternum (breastbone). Some birds, such as eagles and hawks, have wings adapted for soaring on air currents and flap their wings only occasionally; other birds, including hummingbirds, must flap their wings continuously to stay aloft. Among the fastest birds are the appropriately named swifts, which can fly up to 170 km/hr.
A Flight provides numerous benefits. B It enhances hunting and scavenging; many birds consume flying insects, an abundant, highly nutritious food resource. C Flight also provides ready escape from earthbound predators and enables some birds to migrate great distances to exploit different food resources and seasonal breeding areas. D
Flying requires a great expenditure of energy from an active metabolism. Birds are endothermic; they use their own metabolic heat to maintain a high, constant body temperature. Feathers, and in some species layers of fat, provide insulation that enables birds to retain their body heat. The lungs have tiny tubes leading to and from elastic air sacs that improve airflow and oxygen uptake. This efficient respiratory system with a four-chambered heart keep tissues well supplied with oxygen and nutrients, supporting a high rate of metabolism.
Flight also requires both acute vision and fine muscle control. Birds have excellent eyesight. The visual and motor areas of the brain are well developed, and the brain is proportionately larger than those of amphibians and nonbird reptiles. Birds generally display very complex behaviors, particularly during breeding season, when they engage in elaborate courtship rituals.
How did flight evolve in the therapods? In one scenario, feathers may have enabled the small, running dinosaurs chasing prey or escaping predators to gain extra lift as they jumped up into the air. Or, small dinosaurs could have gained traction as they ran up hills by flapping their feathered forelimbs—a behavior seen in birds today. In a third scenario, some dinosaurs could have climbed trees and glided, aided by feathers. Whether birds took to the air from the ground up or from the trees down, an essential question being studied by scientists ranging from paleontologists to engineers is how their efficient flight stroke evolved.
By 150 million years ago, feathered therapods had evolved into birds. Archaeopteryx, which was discovered in a German limestone quarry in 1861, remains the earliest known bird. It had feathered wings but retained ancestral characteristics such as teeth, clawed digits in its wings, and a long tail. Archaeopteryx flew well at high speeds, but unlike a present-day bird, it could not take off from a standing position. Fossils of later birds from the
Cretaceous
show a gradual loss of certain ancestral dinosaur features, such as teeth and clawed forelimbs, as well as the acquisition of innovations found in extant birds, including a short tail covered by a fan of feathers.
Glossary
Cretaceous: a time period, 144-65 million years ago [br] The word elaborate in the passage is opposite in meaning to
选项
A、simple
B、quiet
C、sad
D、short
答案
A
解析
In this passage, simple is an antonym for "elaborate." Context comes from the references to "complex" in the previous sentence.
转载请注明原文地址:https://tihaiku.com/zcyy/3329617.html
相关试题推荐
WhyisMatthewconsideringastudentworkplacement?[br][originaltext]Narrato
WhyisMatthewconsideringastudentworkplacement?[br][originaltext]Narrato
WhyisMatthewconsideringastudentworkplacement?[br][originaltext]Narrato
WhyisMatthewconsideringastudentworkplacement?[br][originaltext]Narrato
TheTreloarValleypassengerferry[br][originaltext]Narrator:Youwillhearp
TheTreloarValleypassengerferry[originaltext]Narrator:Youwillhearpartof
Choosethecorrectletter,A,BorC.[br]WhatwillKathydonext?[originaltex
Choosethecorrectletter,A,BorC.[br]Auniversityis[originaltext]GEOFFRE
Choosethecorrectletter,A,BorC.[br]Itisdangerousto[originaltext]GEOF
Choosethecorrectletter,A,BorC.[br]Thelecturewasorganisedby[origina
随机试题
Indepartmentstoresandclosetsallovertheworld,theyarewaiting.Their
【S1】[br]【S4】F)。空格处单词位于动词不定式符号to之后,代词it之前,需要填入动词。该句意思为:美国人一回到家里,就以极大的热情尽力改善自己的居
在网络安全防御中,密码类扫描技术的目的是检测系统和网络存在的弱口令,然后建立起针
理财师处理客户投诉的正确的方法和技巧包括()。A.告知客户投诉处理的流程,减
根据《中华人民共和国招标投标法》,依法必须进行招标的项目,自招标文件开始发出之日
近年来,我国石墨烯行业的发展态势喜人。但在________发展的背后,石墨烯行业
顾客对产品的满意程度来自于使用过程的体验,通常是在过去多次购买和使用中逐渐形成
岩溶形态是水的溶蚀能力与可溶岩的抗蚀能力在空间和时间上相互作用的结果,可定性地表
上表各省(市)中,2015年土地购置费超过1000亿元的有( )个。A
有学者认为,技术文本和政治文献的机器翻译替代人工翻译在未来几年就可能实现,机器翻
最新回复
(
0
)