首页
登录
职称英语
Birds evolved during the great reptilian radiation of the Mesozoic era, A
Birds evolved during the great reptilian radiation of the Mesozoic era, A
游客
2024-08-09
5
管理
问题
Birds evolved during the great reptilian radiation of the Mesozoic era, Amniotic eggs and scales on the legs are just two of the reptilian features we see in birds.But modem birds look quite different from modem reptiles because of their feathers and other distinctive flight equipment.
Almost every part of a typical bird’s anatomy is modified in some way that enhances flight.The bones have an internal structure that is honeycombed, making them strong but light.The skeleton of a frigate bird, for instance, has a wingspan of more than 2 meters but weighs only about 113 grams.Another adaptation reducing the weight of birds is the absence of some organs.Females, for instance, have only one ovary.Also, modem birds are toothless, an adaptation that trims the weight of the head.Food is not chewed in the mouth but ground in the gizzard, a digestive organ near the stomach.Crocodiles also have gizzards, as did some dinosaurs.The bird’ s beak, made of keratin, has proven to be very adaptable during avian evolution, taking on a great variety of shapes suitable for different diets.
Flying requires a great expenditure of energy from an active metabolism.Birds are endothermic: they use their own metabolic heat to maintain a warm, constant body temperature.Feathers and, in some species, layers of fat provide insulation that enables birds to retain their metabolically generated heat.An efficient respiratory system and a circulatory system with a four-chambered heart keep tissues well supplied with oxygen and nutrients, supporting a high rate of heat and reduce the density of the body metabolism.The lungs have tiny tubes leading to and from elastic air sacs that help dissipate.
For safe flight, senses, especially vision, must be acute.Birds have excellent eyes, perhaps the best of all the vertebrates.The visual areas of the brains are well developed, as are the motor areas: flight also requires excellent coordination.
With brains proportionately larger than those of reptiles and amphibians, birds generally display very complex behavior.Avian behavior is particularly intricate during breeding season, when birds engage in elaborate rituals of courtship.Because eggs are shelled when laid, fertilization must be internal.After eggs are laid, the avian embryo must be kept warm through brooding by the mother, father, or both, depending on the species.
A bird’s most obvious adaptation for flight is its wings.Bird wings are airfoils that illustrate the same principles of aerodynamics as the wings of an airplane.Providing power for flight, birds flap their wings by contractions of large pectoral (breast) muscles anchored to a keel on the sternum (breast-bone).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 continuously to stay aloft.In either case, it is the shape and arrangement of the feathers that form the wings into an airfoil.The fastest birds are the appropriately named swifts, which can fly 170 km/hr.
In being both extremely light and strong, feathers are among the most remarkable of vertebrate adaptation.Feathers are made of keratin, the same protein that forms our hair and fingernails and the scales of reptiles.Feathers may have functioned first as insulation during the evolution of endotherm, only later being so-opted as flight equipment.
Analyses of fossilized skeletons support the hypothesis that the closest reptilian relatives of birds were the theropods, a group of relatively small, bipedal carnivorous dinosaurs.Most researchers agree that the ancestor of birds was a feathered theropod.However, some scientists place the origin of birds much earlier, from an ancestor common to both birds and dinosaur.The intense current interest in the origin of birds will undoubtedly bring us closer to understanding how these masters of the sky evolved from non-flying reptiles.
In describing the characteristics of birds, almost every part of a typical bird’s anatomy is made different in some way that enhances【A1】________.Modem birds do not have 【A2】________, an adaptation that reduces the weight of the head.Birds use their own【A3】________to maintain the body temperature.Because birds’ eggs are shelled when laid, fertilization must be【A4】________.Most researchers believe that the 【A5】________was a feathered theropod that was a small, bipedal carnivorous dinosaur. [br] 【A5】
选项
答案
ancestor of birds
解析
文章最后一段第二句提到,鸟类的祖先被大数研究者视为是一种有羽毛的兽脚亚目恐龙。因此,填入ancestor of birds。
转载请注明原文地址:https://tihaiku.com/zcyy/3712641.html
相关试题推荐
______becameliterarycurrentduringtheperiodofthesuccessfulIndustrialRev
We,thepeople,stillbelievethatenduringsecurityandlastingpeacedonotre
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
ContextDefinition:Ourenvironment,particularlyitssignificanceduring【D1】___
Ifyourcar______anyattentionduringthefirst12months,takeittoanauthori
Ifyourcar______anyattentionduringthefirst12months,takeittoanauthori
随机试题
Accordingtothenewsitem,manyCanadiansgatheredinMontreal______.[origina
布达拉宫(PotalaPalace)是一座举世闻名的建筑群。它是世界上最高的古代宫殿,最高点达到3700米。布达拉宫占地总面积为36万平方米,主楼高1
从1990年至2003年,浙江第三产业占GDP比重上升了几个百分点?A.2
直流电源直流配电屏交流输入主回路松动,造成充电模块交流输入失电;或直流供电主回路
有些类型的生态环境一经破坏就不能再恢复,实行预防性( )几乎是唯一的措施。A.
一位研究者考察被试的简单听觉反应时,经测量得25名被试的反应时平方和(SS)为7
公积金个人住房贷款的资金来自于()A:银行自有的信贷资金B:公积金管理部门归集
电压互感器采用三相星形接线的方式,若要满足二次侧线电压为100V的仪表的工作要求
40岁女性,G4P2,3年前普查时发现子宫肌瘤,定期检查。月经周期规则,量中等,
常见阴道出血的原因有A.内分泌功能失调 B.以上都是 C.损伤 D.妊娠相
最新回复
(
0
)