Question

【题目】Paleontologists(古生物专家) at the University of Alberta have developed a new theory to explain why the ancient ancestors of dinosaurs stopped moving about on all fours and rose up on just their two back legs.

Bipedalism(双腿直立行走) in dinosaurs was inherited from ancient and much smaller proto-dinosaurs. “The tails of proto-dinosaurs had big, leg-powering muscles,” says Persons. Having this muscle mass provided the strength and power required for early dinosaurs to stand on and move with their two back feet.

Over time, proto-dinosaurs developed to run faster and for longer distances. Adaptations like longer back legs allowed ancient dinosaurs to run faster, while smaller front legs helped to reduce body weight and improve balance. Eventually, some proto-dinosaurs gave up walking on fours altogether.

The research, conducted by Persons and Phil Currie, paleontologist and Canada Research Chair, also debunks(揭穿真相) theories that early proto-dinosaurs stood on two legs for the only purpose of free their hands for use in catching food. “Those explanations don’t stand up,”says Persons. It is more likely they seized their meals with their powerful jaws.

If it is true that bipedalism can develop to help animals run fast, why aren’t mammals like horses bipedal? “Largely because mammals don’t have those big tail-based leg muscles”, Persons explains. “Looking across the fossil record, we can trace when our proto-mammal ancestors actually lost those muscles. It seems to have happened back in the Permian period, over 252 million years ago.”

The researchers also claim that living in caves may have helped our ancestors to survive a mass extinction that occurred at the end of the Permian. But when proto-mammals came out from their caves, and some eventually developed to be fast runners, they lacked the tail muscles that would have helped them towards bipedalism.

【1】What helped dinosaurs walk with two back legs actually?

A. Big tail-based leg muscles.

B. Strong and powerful jaws.

C. The ability of improving balance.

D. Four legs with leg-powering muscles.

【2】Which of the following would Persons and Phil Currie agree with?

A. Our ancestors always had big tail-based leg muscles.

B. Ancient dinosaurs’ back legs helped to reduce body weight.

C. Many kinds of animals may have died out in the Permian period.

D. Most animals could stand on two legs with tail-based leg muscles.

【3】What’s the main idea of the text?

A. What bipedalism really means to mammals.

B. What caused dinosaurs to become movable.

C. How ancient dinosaurs actually lived in caves.

D. How dinosaurs learned to stand on their own two feet.

Answer 1

【答案】

【1】A

【2】C

【3】D

【解析】

文章主要介绍了古生物学家的一项新理论：他们提出了原始恐龙放弃爬行而进化为双腿行进的原因。

【1】A 推理判断题。根据文章第二段第二、三句可知，原始恐龙的尾巴具有强大的可支撑双腿的肌肉，这可帮助它们直立行走。再根据倒数第二段第二句中的… those big tail-based leg muscles信息可知，A项符合题意。

【2】C 推理判断题。根据最后一段 “… may have helped our ancestors to survive a mass extinction that occurred at the end of the Permian” 中a mass extinction…可以推出：在Permian period末期，发生了大量物种灭绝事件，故C项正确。

【3】D 主旨大意题。本文主要讲述了一些古生物学家的一项新的理论，他们提出了原始恐龙放弃爬行而进化为双腿行进的原因, 故选D项。