The Evalution Of Birds

Birds Began as Feathered Reptiles

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 modern birds look quite different from modern reptiles because of their features and other distinctive flight equipment.

Characteristics of Birds

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, modern birds are toothless, an adaptation that trims the weight of the head. Food is not chewed in the moouth but ground in the gizzard, a digestive organ near the stomach. (Crocodiles also have gizzards, as did some dinosours.) 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 requiers a great expenditure of energy from an active metabolism. Birds are endothemic: they use their own medabolic 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 metabolism.

The lungs have tiny tubes leading to and form elastic air sacs that help dissipate heat and reduce the density of the body.

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 excelent 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 eloborate rituals of courtship. Because eggs are shelled when laid, fertilization must be internal. Copulation involves contact between the mates’ vents, the openings to their coloacas. After eggs are laid, the avian emtryo must be kept warm through brooding by the mother, father, or both, depending on the species.

A bird’s most obcious 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 their case, it is the shape and arrangement of the feathers that form the wings into and airfoil. The fastest birds are the appropriately named switfs, which can fly 170 km/hr.ther

In being both extremely light and strong, feathers are among the most remarkable of vertebrate adaptations. Feathers are made of keratin, the same protein that forms our hair and fingernais and the scales of reptiles. Feathers may have functioned first as insulation during the evolution of endothermy, only later being so-opted as flight equipment.

The evolution of flight required radical alteration in body form, but flight provides many benefits. It enhances hunting and scavenging: many birds exploit flying insects, an anbundant, highly nutritious food resource. Flight also provides ready escape from earthbound predators and enables some birds migrate great distances to utilize different food resources and seasonal breeding areas. The bird that travels farthest in its annual migration is the arctic tern, which flies round-trip between the North Pole and South Pole each year.

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.

1. According to paragraph 2, how did birds adapt to efficient flight?A. They developed a skeleton with fewer bones.B. Their organs became smaller overtime.C. Most of their weight was distributed in their heads.D. Teeth were replaced by a beak made of keratin.

2. The word modified in the passage is closest in meaning toA. Made differentB. Made betterC. Made smallerD. Made modern

3. The word their in the passage refers toA. FeathersB. SpeciesC. LayersD. Birds

4. The word elaborate in the passage is opposite in meaning to

A. Simple B. Quiet

C. Sad D. Short

5. According to paragraph 6, which of the following is true about the wings of birds?A. All birds flap their wings constantly by using breast muscles.B. Eagles and hawks have wings that propel them at 170 km/hr.C. The airfoils of birds function like the wings on airplanes.D. Wings are attached to airfoils in the bird’s skeletal structure.

6. In paragraph7, the author explains the term keratin by.A . identifying it in hair and fingernailsB. comparing it to bird feathersC. providing a definition in the textD. describing the way it looks

7. The word radical in the passage is closest in meaning to.

A. very clear

B. very wide

C. very fast

D. very new 8. According to paragraph 9, what can be inferred about research on the evolution

on the births?

A.They research is not very resent

B.The subject is popular

C.Many researcher are working on it

D.There are some definitive conclusions

9. According to the passage, which characteristic do birds share withreptiles?

A.They defend themselves with claws

B.They reproduce by laying eggs

C.They have a similar skeletal structure

D.They utilize a two-chambered heart

10. Which of the sentences below best expresses the information in the highlighted

statement in the passage? The other choices change the meaning or leave out

important information.

A. Very early birds appeared after the dinosaurs.B. Birds and dinosaurs may share the same ancestor .C. Birds and dinosaurs were probably very common.D. The origin of birds and dinosaurs is very early.

11. All of the following are mentioned as adaptations to the bird’s anatomy to

accommodate flight EXCEPT

A. a covering of feathers B. relatively large brains C. very sharp eyesD. small legs and feet

Listening

Section 1

1. Why does the student go to see the professor?A. To tell the professor that he is getting marriedB. To find out when the research project is dueC. To ask the professor to do him a favorD. To explain why he was late turning in the paper

2. What excuse does the student use?A. He is getting married.B. He has an important family event to attend.C. The due date for the project is too soon.D. The project is much harder than he had expected.

3. How does the professor seem to feel about the student’s request? (click two answer)A. Missing a few days of class for the wedding is OK.B. Missing a few days of class for the wedding is not OK.C. Delaying the research project is OK.D. Delaying the research project is not OK.

4. Listen again to part of the conversation by playing Track 3. Then answer the question. Which of the following might the professor say?

A. “You have plenty of time to complete the project before the wedding”B. “Maybe the wedding could be postponed.”C. “It seems like a good reason to delay the project.”D. “I can’t believe that the wedding is so soon.”

5. Listen again to part of the conversation by playing Track 4. Then answer the question.What does the professor mean?

A. I’m not really doing you a big favor, but I’m telling you it is.B. I’m sure you don’t believe this because you never believe what I say.C. It certainly seems like a big favor, but it’s not.D. You may not like my suggestion now, but you will later.

Lecture 1

6. What made the bald eagle the national bird of the USA?A. It’s a symbol of strength and courage. B. It’s a symbol of power and independence.C. It’s a symbol of competence and courage.D. It’s a symbol of strength and confidence.

7. What happened to bald eagles?A. The polluted fish killed 3,000 of them.B. Insects poisoned so many of them.C. Pollution greatly reduced their number.

D. Pesticides made them extinct.8. What is true about the bald eagle?

A. The bird is not adored any more.B. The bird does not eat the poisonous fish.C. The bird begins to lay fewer and fewer eggs.D. Measures are being taken to save the bird.

9. What happened in Missouri?A. The bird was eliminated.B. The bird migrated here from all over America.C. The number of the bird increased by 2000 per year.D. Missouri is noticed for the large increase of the bird.

10. How did the pollution affect the existence of the bald eagle?A. The polluted earth poisoned the birds.B. The poisoned eggs cannot be hatched because its thin shell.C. The pesticide killed birds directly.D. Eagles cannot lay eggs because of the pollution.

11. Listen again to part of the lecture by playing Track 5 then answer the question.What does the professor mean by saying this?

A. Bald eagles were considered as the symbol of strength until 1782.B. Bald eagles have been Americans’ favorite birds when they were chosen as the

symbol.C. Bald eagles was not Americans’ favorite birds until they were chosen as the

symbol.D. Bald eagles was not Americans’ favorite birds although then have always been

the symbol.