How aquatic vertebrates evolved into land vertebrates has been difficu

How aquatic vertebrates evolved into land vertebrates has been difficult for evolutionary biologists to study, in part because the shift from water to land appears to have occurred rapidly and has yielded a scarce fossil record. Prior to the advent of DNA sequencing, the primary guideposts in tracing the emergence of tetrapods have been morphological considerations, which have highlighted the coelacanth and the lungfish as species of interest.

Coelacanths and lungfish are distinct from other fish in that they are lobe-finned species. Lobe-finned species, like ray-finned fishes such as tuna and trout, possess not cartilage but a bony skeleton, a key prerequisite for survival on land. Lobe-finned fish species are distinguished from ray-finned species by fins that are joined to a single bone and which thus have the potential to evolve into limbs. Coelacanths and lungfish are two of the only lobe-finned species that are not extinct, and since they have evolved minimally since the time of the appearance of tetrapods, they are sometimes referred to as "living fossils." In fact, the first live coelacanth was discovered more than 100 years after the species had been discovered in fossilized form.

Whether the coelacanth in particular is rightly called a living fossil and whether it is the closest living relative of the original tetrapods are two questions that have been illuminated more recently by genetic analysis. The coelacanth's genome has recently been sequenced, and this analysis has led to the conclusion that the lungfish is the closer relative of tetrapods. Moreover, the coelacanth DNA has shown evolution over time--although at a rate much slower than that of most animals. Possibly, the fish's morphology and its environment deep in the Indian Ocean have created favorable conditions allowing a more slowly evolving species to have survived for the last 400 million years.

1. The passage provides information in support of which of the following assertions?

A. Although a set of possible evolutionary paths leading to a specific result can be identified, no one of them can be conclusively identified as correct.
B. Physical similarities between species give some justification to believe those species may have an evolutionary link.
C. Studies of living fossils enable conclusions about evolutionary history that could not be drawn based on other types of evidence.
D. Species with close physical similarities may nevertheless have widely different evolutionary histories.
E. How quickly an organism's DNA changes over time indicates the role that organism has played in the evolution of related species.


2. According to the passage, coelacanths and lungfish were initially of interest in the study of the evolution of land vertebrates because

A. they both had evolved minimally since the time of the appearance of tetrapods
B. they both had fins joined to a single bone and which thus had the potential to evolve into limbs
C. they both have generous fossil records and can be studied also in living form
D. the coelacanth's genome has been sequenced
E. they both are distinct from other fish and also are found in deep ocean environments


3. The author discusses the evolution of coelacanth DNA in the highlighted text primarily in order to

A. clarify that coelacanths are not accurately referred to as living fossils
B. distinguish the evolutionary role of the coelacanth from that of the lungfish
C. illustrate a unique characteristic of lobe-finned fish species
D. support a claim that that coelacanths are better adapted to survive than are most species of fish
E. illustrate how differences in a species' DNA over time can establish whether that species is likely to have played a particular role in evolution


4. It can be inferred from the passage that which of the following is a true statement about the evolution of a species?

A. If a species evolves more slowly than competing species, it will have to seek out a new environment in which to live in order to survive.
B. The longer a species survives without going extinct, the more likely it is to maintain identical or nearly identical DNA over time.
C. A species' rate of evolution can be inferred from the degree of change over time of its morphology.
D. A species' rate of evolution is driven partly by the degree of harshness of the conditions in which it lives.
E. If true living fossils exist, they are not lobe-finned fish.


5. The author suggests that which of the following is an evolutionary disadvantage of the prominence of cartilage in fish?

A. A lessened ability to compete with coelacanths and lungfish
B. The absence of a fossil record
C. An increase in the rate of the change of a species' DNA over time
D. A decrease in the ability to survive deep in the Indian Ocean
E. An inability to survive on land


6. The primary purpose of the third paragraph is to

A. draw a conclusion based on information presented in the previous paragraph
B. introduce a topic that is not discussed earlier in the passage
C. introduce evidence that contradicts a view presented earlier in the passage
D. answer questions raised in the previous two paragraphs
E. describe a different method of arriving at a conclusion reached in the previous paragraph


7. In the passage, the author is primarily concerned with doing which of the following?

A. Explaining characteristics of lobe-finned fish that establish their role in the evolution of tetrapods
B. Comparing the evolutionary history of the coelacanth with that lungfish
C. Refuting the validity of terming the lobe-finned fish in question "living fossils"
D. Pointing out features of the coelacanth and lungfish that make them superior to ray-finned species
E. Explaining how the lungfish possesses the necessary characteristics to survive on land