TF阅读真题第778篇The Evolution of Reptiles and Therapsids

The Evolution of Reptiles and Therapsids

 

The oldest known reptiles are found in deposits dating from the Upper Carboniferous (324-290 million years ago). Most of the skeletal differences between the earliest reptiles and their amphibian ancestors were minor. The most important way in which reptiles differ from amphibians-cold-blooded, partly aquatic vertebrates-is in their mode of reproduction. The key feature in the origin of the reptiles was the amniote egg, which is also employed by modern reptiles and birds. This egg provides the embryo with a nutritious yolk and two sacs: one (the amnion) to contain the embryo and the other to collect waste products. A durable outer shell protects the developing embryo. The amniote egg allowed vertebrates for the first time to live and reproduce away from bodies of water. The amniote egg apparently developed in Carboniferous time, when reptiles evolved.  

Because the amniote egg was in essence a self-contained pond, it eliminated the need for the young animal to live in water and thus enabled reptiles to exploit the land more fully. There is an interesting parallel here with the evolution of the seed in plants. Spore plants, like amphibians, require environmental moisture during part of their life cycle. The origin of the more advanced groups-the seed plants and reptiles-represented a transition to a fully terrestrial existence.

Later reptiles developed yet another feature of great importance: an advanced jaw structure that could apply heavy pressure upon closing and could slice food by means of bladelike teeth. Carboniferous amphibians and early reptiles had jaws that could snap closed quickly but could apply little pressure. Moreover, they had pointed teeth that could kill prey by puncturing it but that could not slice or tear food apart, so these animals were forced to swallow their meals whole.

Despite the origin of reptiles in Late Carboniferous time, amphibians continued to prosper into Early Permian time. During the Permian Period (290-251 million years ago), however, reptiles diversified and apparently began to replace amphibians in various ecologic roles, probably because the reptiles had more advanced jaws and teeth as well as greater speed and agility. Permian rocks of Texas have yielded large faunas of amphibians and reptiles that reveal this pattern. By Early Permian time, the pelycosaurs, fin- backed reptiles and their relatives, had become the top carnivores of widespread ecosystems. Their occurrence in the geological record suggests that many lived in swamps and that some may have been semiaquatic. Dimetrodon, one such carnivore, was about the size of a jaguar and had sharp, serrated teeth. Whereas even the Permian carnivorous amphibians, such as the alligator-like Eryops, were forced to swallow prey whole, Dimetrodon could tear large animals to pieces.

Dimetrodon and other pelycosaurs had a skull structure that in some ways resembled that of mammals, which evolved from them. Their descendants, the therapsids, were especially similar to mammals. Therapsids’ legs were positioned more vertically beneath their bodies than were the sprawling legs of primitive reptiles or even pelycosaurs. In addition, the jaws of therapsids were complex and powerful, and the teeth of many species were differentiated into frontal incisors for nipping, large lateral fangs for puncturing and tearing, and molars for shearing and chopping food.

Many experts believe that the therapsids were endothermic, or warm-blooded: by virtue of a high metabolic rate, they maintained their body temperatures at relatively constant levels that were usually above those of their surroundings. Hair similar to that of modern mammals may have insulated therapsids’ bodies. Even if they were endothermic, however, therapsids may not have kept their body temperatures at levels as constant as those of mammals. In any case, the upright postures and complex chewing apparatuses of advanced Permian therapsids show that these active animals approached the mammalian level of evolution in anatomy and behavior.

The endothermic condition allows animals to maintain a sustained level of activity-to hunt prey or to flee from predators with considerable endurance. Ectothermic (or cold-blooded) reptiles, in contrast, must rest frequently in order to soak up heat from their environment. Endothermic metabolism, along with advanced jaws, teeth, and limbs, may account not only for the success of the therapsids during Permian time but also for the decline of the pelycosaurs, which were probably ectothermic.

 

 

 

 

 

 

1

The oldest known reptiles are found in deposits dating from the Upper Carboniferous (324-290 million years ago). Most of the skeletal differences between the earliest reptiles and their amphibian ancestors were minor. The most important way in which reptiles differ from amphibians-cold-blooded, partly aquatic vertebrates-is in their mode of reproduction. The key feature in the origin of the reptiles was the amniote egg, which is also employed by modern reptiles and birds. This egg provides the embryo with a nutritious yolk and two sacs: one (the amnion) to contain the embryo and the other to collect waste products. A durable outer shell protects the developing embryo. The amniote egg allowed vertebrates for the first time to live and reproduce away from bodies of water. The amniote egg apparently developed in Carboniferous time, when reptiles evolved.  

The word “durable” in the passage is closest in meaning to

Alarge

Blong-lasting

Cheavy

Dsmooth

 

2

The oldest known reptiles are found in deposits dating from the Upper Carboniferous (324-290 million years ago). Most of the skeletal differences between the earliest reptiles and their amphibian ancestors were minor. The most important way in which reptiles differ from amphibians-cold-blooded, partly aquatic vertebrates-is in their mode of reproduction. The key feature in the origin of the reptiles was the amniote egg, which is also employed by modern reptiles and birds. This egg provides the embryo with a nutritious yolk and two sacs: one (the amnion) to contain the embryo and the other to collect waste products. A durable outer shell protects the developing embryo. The amniote egg allowed vertebrates for the first time to live and reproduce away from bodies of water. The amniote egg apparently developed in Carboniferous time, when reptiles evolved.  

The word “apparently” in the passage is closest in meaning to

Aseemingly

Boriginally

Cgradually

Dfully

 

3

Because the amniote egg was in essence a self-contained pond, it eliminated the need for the young animal to live in water and thus enabled reptiles to exploit the land more fully. There is an interesting parallel here with the evolution of the seed in plants. Spore plants, like amphibians, require environmental moisture during part of their life cycle. The origin of the more advanced groups-the seed plants and reptiles-represented a transition to a fully terrestrial existence.

In paragraph 2, why does the author discuss the parallel between the amniote egg in vertebrates and the seed in plants?

ATo explain why it is thought that reptiles and seed plants originated at about the same time

BTo identify a way in which reptiles and seed plants are more advanced than earlier animals and plants

CTo explain why reptiles came to depend on seed plants rather than on spore plants

DTo explain why reptiles and seed plants require more moisture than amphibians and spore plants do during reproduction

4

Later reptiles developed yet another feature of great importance: an advanced jaw structure that could apply heavy pressure upon closing and could slice food by means of bladelike teeth. Carboniferous amphibians and early reptiles had jaws that could snap closed quickly but could apply little pressure. Moreover, they had pointed teeth that could kill prey by puncturing it but that could not slice or tear food apart, so these animals were forced to swallow their meals whole.

According to paragraph 3, later reptiles differed from early reptiles in which of the following?

AThe ability to snap their jaws closed quickly

BThe ability to swallow food whole

CThe ability to puncture food with their pointed teeth

DThe ability to apply great pressure with their jaws

 

5

Despite the origin of reptiles in Late Carboniferous time, amphibians continued to prosper into Early Permian time. During the Permian Period (290-251 million years ago), however, reptiles diversified and apparently began to replace amphibians in various ecologic roles, probably because the reptiles had more advanced jaws and teeth as well as greater speed and agility. Permian rocks of Texas have yielded large faunas of amphibians and reptiles that reveal this pattern. By Early Permian time, the pelycosaurs, fin- backed reptiles and their relatives, had become the top carnivores of widespread ecosystems. Their occurrence in the geological record suggests that many lived in swamps and that some may have been semiaquatic. Dimetrodon, one such carnivore, was about the size of a jaguar and had sharp, serrated teeth. Whereas even the Permian carnivorous amphibians, such as the alligator-like Eryops, were forced to swallow prey whole, Dimetrodon could tear large animals to pieces.

According to paragraph 4, Permian rocks from Texas provide evidence that

Apelycosaurs and amphibians possessed a similar jaw structure and teeth

Bnew adaptations allowed reptiles to take over some of the ecological roles of amphibians

Cboth amphibian and reptile populations increased dramatically in the Permian Period

Dless advanced reptiles began to disappear during the Early Permian

 

6

Despite the origin of reptiles in Late Carboniferous time, amphibians continued to prosper into Early Permian time. During the Permian Period (290-251 million years ago), however, reptiles diversified and apparently began to replace amphibians in various ecologic roles, probably because the reptiles had more advanced jaws and teeth as well as greater speed and agility. Permian rocks of Texas have yielded large faunas of amphibians and reptiles that reveal this pattern. By Early Permian time, the pelycosaurs, fin- backed reptiles and their relatives, had become the top carnivores of widespread ecosystems. Their occurrence in the geological record suggests that many lived in swamps and that some may have been semiaquatic. Dimetrodon, one such carnivore, was about the size of a jaguar and had sharp, serrated teeth. Whereas even the Permian carnivorous amphibians, such as the alligator-like Eryops, were forced to swallow prey whole, Dimetrodon could tear large animals to pieces.

Paragraph 4 supports which of the following statements about certain animals’ habit of swallowing prey whole during the Permian period?

AIt presented these animals with an evolutionary disadvantage in relation to fin-backed reptiles such as the Dimetrodon

BIt had allowed one such animal, the alligator-like Eryops , to become the top carnivore in certain ecosystems.

CIt resulted in less speed and agility in these animals

DIt was a necessary adaptation to life in swamps and semiaquatic environments.

 

7

Dimetrodon and other pelycosaurs had a skull structure that in some ways resembled that of mammals, which evolved from them. Their descendants, the therapsids, were especially similar to mammals. Therapsids’ legs were positioned more vertically beneath their bodies than were the sprawling legs of primitive reptiles or even pelycosaurs. In addition, the jaws of therapsids were complex and powerful, and the teeth of many species were differentiated into frontal incisors for nipping, large lateral fangs for puncturing and tearing, and molars for shearing and chopping food.

According to paragraph 5, many therapsids resembled mammals in each of the following ways EXCEPT

Athe positioning of their legs

Bthe strength of their jaws

Cthe size of their bodies

Dthe differentiation of their teeth

 

8

Many experts believe that the therapsids were endothermic, or warm-blooded: by virtue of a high metabolic rate, they maintained their body temperatures at relatively constant levels that were usually above those of their surroundings. Hair similar to that of modern mammals may have insulated therapsids’ bodies. Even if they were endothermic, however, therapsids may not have kept their body temperatures at levels as constant as those of mammals. In any case, the upright postures and complex chewing apparatuses of advanced Permian therapsids show that these active animals approached the mammalian level of evolution in anatomy and behavior.

According to paragraph 6, many experts believe which of the following about Permian therapsids?

AThey may have had more hair than modern mammals have.

BTheir bodies were generally warmer than outside temperatures were.

CTheir bodies were significantly less advanced than those of mammals

DThe body temperature of individuals varied less than those of mammals do.

 

9

The oldest known reptiles are found in deposits dating from the Upper Carboniferous (324-290 million years ago). Most of the skeletal differences between the earliest reptiles and their amphibian ancestors were minor. [■]The most important way in which reptiles differ from amphibians-cold-blooded, partly aquatic vertebrates-is in their mode of reproduction. [■]The key feature in the origin of the reptiles was the amniote egg, which is also employed by modern reptiles and birds. [■]This egg provides the embryo with a nutritious yolk and two sacs: one (the amnion) to contain the embryo and the other to collect waste products. [■]A durable outer shell protects the developing embryo. The amniote egg allowed vertebrates for the first time to live and reproduce away from bodies of water. The amniote egg apparently developed in Carboniferous time, when reptiles evolved.  

Look at the four squaresthat indicate where the following sentence could be added to the passage

Amphibians had to return to water to lay their eggs, but a different solution developed in early reptiles.

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Based on archaeological evidence, the first reptiles likely appeared during the Carboniferous period.

AOne of the main features that distinguished early reptiles from amphibians was their skeletal structure, which differed greatly from that of amphibians.

BBecause amphibians were aquatic and even the earliest reptiles lived away from water, amphibians and reptiles rarely competed with one another.

CAs reptiles developed more advanced jaw structures and more agile bodies, they began to replace less-advanced amphibians.

DThe amniote egg was an important step in reptile evolution because it allowed reptiles to live and reproduce on land.

EThe earliest mammals appeared at the end of the Permian Period, though their skull and jaw structures were not as complex as those of reptiles.

FReptiles called therapsids shared certain features with mammals, such as an endothermic metabolism, that enabled them to be successful hunters and avoid predation.

 

答案：