From Water to Land

 

Fish were the earliest vertebrates (animals with backbones), able to live only in water. During the Devonian period (416-358 million years ago), a group of lobe-finned fish started a transition from water to land that ultimately led to the evolution of tetrapods-four-limbed animals including amphibians, reptiles, birds, and mammals (some tetrapods, like snakes, have later evolved to be limbless). Unlike ray-finned fish-the most common types of fish found today-lobe-finned fish have bones supporting some of their fins. This arrangement made it possible for fins to evolve into primitive limbs. It is likely that the main anatomical transition from fins to limbs was completed in an aquatic environment, where the limbs did not have to support the entire weight of the body due to the water’s buoyancy (the upward force of water on a submerged object). The primitive fin-limbs probably first developed flexible joints, helping them to bend and push the fish forward as it crawled along in the shallows or negotiated thick waterweeds. The fin-limbs grew stronger as they developed simple knee, ankle, elbow, and wrist joints. Eventually, the primitive fish-tetrapod would have been able to crawl out of the water, where the lack of buoyancy would drive the evolution of limbs to support the weight of the animal’s body. In turn, this would favor a stronger internal skeleton.

 

One such skeletal adaptation was the development of a rigid backbone, with sliding and overlapping processes to link adjacent vertebrae, while providing the necessary overall flexibility. In addition to securing support for the body, the hind limbs became the actual driving force for tetrapod locomotion. This required strong hip bones to anchor these rear limbs to the backbone. The fore limbs became the steering force, and so shoulder bones- which attach to the skull in fish-became detached in tetrapods, providing them with a flexible neck. Muscular changes accompanied these skeletal adaptations, promoting strong limb function and linking the hip and shoulder bones to the backbone.

Another requirement for the evolution of tetrapods, together with legs that work on land, is the ability to breathe air on land. Primitive air sacs existed in ray- finned and lobe-finned fish long before the first tetrapods appeared. In ray-finned fish, these air sacs were used as swim bladders to maintain buoyancy. In lobe-finned fish of the Devonian period, however, the air sacs had already evolved into air-breathing lungs. Lobe- finned fish, such as living lungfish, breathe by gulping air into their mouths at the surface of the water. When they subsequently dive, the increasing water pressure bearing onto them forces the air in the mouth down into the lungs. The process reverses as the fish rises to the surface again, forcing stale air out of the lungs and mouth as the fish gulps in a fresh mouthful. Since this basic mechanism for respiration already existed in Devonian lobe-fins, the earliest tetrapods were already well on their way to the evolutionary stage of breathing on land.

The transition from fins to limbs was only one part of the evolutionary journey for terrestrial tetrapods. Many other anatomical changes must have taken place to help early tetrapods cope with life on the land. For example, the evolutionary change that resulted in a flexible neck increased the mobility of the head, helping them pick up food instead of grabbing items that passed by in the water. No one knows exactly which evolutionary forces prompted the transition from fins to limbs. The first tetrapods were probably still fully aquatic animals that lived in shallow waters. Some experts think they may have used their primitive limbs to stalk prey through the dense vegetation that lined the bottom of rivers and swamps. Others believe that environmental pressures, such as an increasingly dry climate, prompted the transition from watel to land. As the heat dried up the shallow waters, primitive limbs may have helped the earliest tetrapods crawl between pools of water. Yet another hypothesis is that they were chased out of the water by bigger predatory fish. Any tetrapod that could survive out of water would have found itself in a new paradise, with an abundance of plant and insect foods and a notable absence of dangerous predators.

 

 

1

Fish were the earliest vertebrates (animals with backbones), able to live only in water. During the Devonian period (416-358 million years ago), a group of lobe-finned fish started a transition from water to land that ultimately led to the evolution of tetrapods-four-limbed animals including amphibians, reptiles, birds, and mammals (some tetrapods, like snakes, have later evolved to be limbless). Unlike ray-finned fish-the most common types of fish found today-lobe-finned fish have bones supporting some of their fins. This arrangement made it possible for fins to evolve into primitive limbs. It is likely that the main anatomical transition from fins to limbs was completed in an aquatic environment, where the limbs did not have to support the entire weight of the body due to the water’s buoyancy (the upward force of water on a submerged object). The primitive fin-limbs probably first developed flexible joints, helping them to bend and push the fish forward as it crawled along in the shallows or negotiated thick waterweeds. The fin-limbs grew stronger as they developed simple knee, ankle, elbow, and wrist joints. Eventually, the primitive fish-tetrapod would have been able to crawl out of the water, where the lack of buoyancy would drive the evolution of limbs to support the weight of the animal’s body. In turn, this would favor a stronger internal skeleton.

According to paragraph 1, which of the following enabled lobe-finned fish to evolve into tetrapods?

AThey had larger backbones than other fish.

BThey had bones that other fish lacked in some of their fins.

CTheir body weight was more evenly distributed than other fish.

DThey had a strong internal skeleton that other fish lacked.

 

2

One such skeletal adaptation was the development of a rigid backbone, with sliding and overlapping processes to link adjacent vertebrae, while providing the necessary overall flexibility. In addition to securing support for the body, the hind limbs became the actual driving force for tetrapod locomotion. This required strong hip bones to anchor these rear limbs to the backbone. The fore limbs became the steering force, and so shoulder bones- which attach to the skull in fish-became detached in tetrapods, providing them with a flexible neck. Muscular changes accompanied these skeletal adaptations, promoting strong limb function and linking the hip and shoulder bones to the backbone.

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

Aneighboring

Bseparate

Call

Ddifferent

 

3

One such skeletal adaptation was the development of a rigid backbone, with sliding and overlapping processes to link adjacent vertebrae, while providing the necessary overall flexibility. In addition to securing support for the body, the hind limbs became the actual driving force for tetrapod locomotion. This required strong hip bones to anchor these rear limbs to the backbone. The fore limbs became the steering force, and so shoulder bones- which attach to the skull in fish-became detached in tetrapods, providing them with a flexible neck. Muscular changes accompanied these skeletal adaptations, promoting strong limb function and linking the hip and shoulder bones to the backbone.

According to paragraph 2, all of the following helped tetrapods adapt to life on land EXCEPT

Aa backbone that was rigid but also flexible

Bhip bones that attached hind limbs to the backbone

Cshoulder bones that were connected to the skull

Dchanges to the muscles that connected some parts of the body

 

4

Another requirement for the evolution of tetrapods, together with legs that work on land, is the ability to breathe air on land. Primitive air sacs existed in ray- finned and lobe-finned fish long before the first tetrapods appeared. In ray-finned fish, these air sacs were used as swim bladders to maintain buoyancy. In lobe-finned fish of the Devonian period, however, the air sacs had already evolved into air-breathing lungs. Lobe- finned fish, such as living lungfish, breathe by gulping air into their mouths at the surface of the water. When they subsequently dive, the increasing water pressure bearing onto them forces the air in the mouth down into the lungs. The process reverses as the fish rises to the surface again, forcing stale air out of the lungs and mouth as the fish gulps in a fresh mouthful. Since this basic mechanism for respiration already existed in Devonian lobe-fins, the earliest tetrapods were already well on their way to the evolutionary stage of breathing on land.

According to paragraph 3, which of the following is true about how lungfish breathe?

AThey store air in air sacs that also function as swim bladders.

BThey need to dive down in order for air to reach their lungs.

CThey remain on the surface while taking in and forcing out air.

DThey force air out to reduce the water pressure as they dive below the surface.

 

5

Another requirement for the evolution of tetrapods, together with legs that work on land, is the ability to breathe air on land. Primitive air sacs existed in ray- finned and lobe-finned fish long before the first tetrapods appeared. In ray-finned fish, these air sacs were used as swim bladders to maintain buoyancy. In lobe-finned fish of the Devonian period, however, the air sacs had already evolved into air-breathing lungs. Lobe- finned fish, such as living lungfish, breathe by gulping air into their mouths at the surface of the water. When they subsequently dive, the increasing water pressure bearing onto them forces the air in the mouth down into the lungs. The process reverses as the fish rises to the surface again, forcing stale air out of the lungs and mouth as the fish gulps in a fresh mouthful. Since this basic mechanism for respiration already existed in Devonian lobe-fins, the earliest tetrapods were already well on their way to the evolutionary stage of breathing on land.

Paragraph 3 suggests which of the following about the evolution of lungs in lobe-finned fish?

ALungs in lobe-finned fish, first evolved as a breathing organ but eventually took on a role in maintaining buoyancy.

BAs lungs evolved in lobe-finned fish, the fish became less affected by changes in water pressure.

CWhile the lungs of lobe-finned fish allowed the fish to take in air above water during the Devonian period, the more evolved lungs of later lobe-finned fish allowed those fish to take in air underwater.

DThe lungs that lobe-finned fish developed in the Devonian period eventually evolved into the lungs of tetrapods.

 

6

The transition from fins to limbs was only one part of the evolutionary journey for terrestrial tetrapods. Many other anatomical changes must have taken place to help early tetrapods cope with life on the land. For example, the evolutionary change that resulted in a flexible neck increased the mobility of the head, helping them pick up food instead of grabbing items that passed by in the water. No one knows exactly which evolutionary forces prompted the transition from fins to limbs. The first tetrapods were probably still fully aquatic animals that lived in shallow waters. Some experts think they may have used their primitive limbs to stalk prey through the dense vegetation that lined the bottom of rivers and swamps. Others believe that environmental pressures, such as an increasingly dry climate, prompted the transition from watel to land. As the heat dried up the shallow waters, primitive limbs may have helped the earliest tetrapods crawl between pools of water. Yet another hypothesis is that they were chased out of the water by bigger predatory fish. Any tetrapod that could survive out of water would have found itself in a new paradise, with an abundance of plant and insect foods and a notable absence of dangerous predators.

06:Why does the author state that “primitive limbs may have helped the earliest tetrapods crawl between pools of water”?

ATo challenge the theory that early tetrapods were fully aquatic animals living in shallow waters

BTo support the theory that primitive limbs helped tetrapods to stalk prey and to avoid predators

CTo illustrate how specific environmental pressures could have encouraged the evolution of fins into limbs

DTo provide evidence for the idea that climate change significantly reduced the habitat of early tetrapods

 

7

The transition from fins to limbs was only one part of the evolutionary journey for terrestrial tetrapods. Many other anatomical changes must have taken place to help early tetrapods cope with life on the land. For example, the evolutionary change that resulted in a flexible neck increased the mobility of the head, helping them pick up food instead of grabbing items that passed by in the water. No one knows exactly which evolutionary forces prompted the transition from fins to limbs. The first tetrapods were probably still fully aquatic animals that lived in shallow waters. Some experts think they may have used their primitive limbs to stalk prey through the dense vegetation that lined the bottom of rivers and swamps. Others believe that environmental pressures, such as an increasingly dry climate, prompted the transition from watel to land. As the heat dried up the shallow waters, primitive limbs may have helped the earliest tetrapods crawl between pools of water. Yet another hypothesis is that they were chased out of the water by bigger predatory fish. Any tetrapod that could survive out of water would have found itself in a new paradise, with an abundance of plant and insect foods and a notable absence of dangerous predators.

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

Aremarkable

Bfavorable

Ctotal

Dunexpected

 

8

The transition from fins to limbs was only one part of the evolutionary journey for terrestrial tetrapods. Many other anatomical changes must have taken place to help early tetrapods cope with life on the land. For example, the evolutionary change that resulted in a flexible neck increased the mobility of the head, helping them pick up food instead of grabbing items that passed by in the water. No one knows exactly which evolutionary forces prompted the transition from fins to limbs. The first tetrapods were probably still fully aquatic animals that lived in shallow waters. Some experts think they may have used their primitive limbs to stalk prey through the dense vegetation that lined the bottom of rivers and swamps. Others believe that environmental pressures, such as an increasingly dry climate, prompted the transition from watel to land. As the heat dried up the shallow waters, primitive limbs may have helped the earliest tetrapods crawl between pools of water. Yet another hypothesis is that they were chased out of the water by bigger predatory fish. Any tetrapod that could survive out of water would have found itself in a new paradise, with an abundance of plant and insect foods and a notable absence of dangerous predators.

Paragraph 4 mentions all of the following as possible advantages of the transition from fins to limbs EXCEPT

Aimproved ability to move along the bottom surfaces of water environments

Bavailability of warmer habitats

Creduced pressure from predators

Deasier access to food sources

 

9

Fish were the earliest vertebrates (animals with backbones), able to live only in water. During the Devonian period (416-358 million years ago), a group of lobe-finned fish started a transition from water to land that ultimately led to the evolution of tetrapods-four-limbed animals including amphibians, reptiles, birds, and mammals (some tetrapods, like snakes, have later evolved to be limbless). Unlike ray-finned fish-the most common types of fish found today-lobe-finned fish have bones supporting some of their fins. This arrangement made it possible for fins to evolve into primitive limbs. It is likely that the main anatomical transition from fins to limbs was completed in an aquatic environment, where the limbs did not have to support the entire weight of the body due to the water’s buoyancy (the upward force of water on a submerged object). The primitive fin-limbs probably first developed flexible joints, helping them to bend and push the fish forward as it crawled along in the shallows or negotiated thick

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

The emergence of each of those new structures allowed greater mobility.

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

10

Tetrapods are vertebrates that have evolved to live on land.

AThe process of the evolution of tetrapods likely started with lobe-finned fish in the Devonian period, which already had air-breathing lungs.

BFish-tetrapods first evolved hind limbs strong enough to push the body forward on land before they developed lungs that were adapted to breathing on land.

COne challenge facing early tetrapods was making the transition from feeding on aquatic plants to feeding on land plants, which required additional adaptations in the mouth and neck.

DFish fins evolved into limbs, which eventually became strong enough to support the body weight of the animal without the buoyancy of water.

EThe transition from water to land required improved flexibility and mobility, which was accompanied by a series of changes in joints, skeleton, and muscles.

FAfter tetrapods moved onto land, those that later returned to live in aquatic environments had difficulty maintaining features like flexible necks and strong hip bones.

 

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