5.3 Pterosaurs

  1. Scientists have long been fascinated with the evolution of pterosaurs—warm blooded, flying reptiles that flourished during the Jurassic and Cretaceous periods, the time of the dinosaurs. Pterosaurs were the first animal after insects to develop powered flight. This ability was enabled by the pterosaur’s hollow bone structure, a structure more similar to modern birds than to ancient dinosaurs. Because of their ability to fly, pterosaurs were able to expand their range and fill many ecological niches1, eventually evolving into dozens of different species that ranged in size from a small bird to a small airplane. However, hollow bones decay more easily than solid bones, making complete pterosaur fossils hard to find. Known fossils are difficult to categorize into evolutionary families. How did the pterosaur evolve over time into the many different species that roamed the Earth? Hidden from scientists’ view were the linking fossils that would indicate how closely related many of the different species were.

    Fossil discoveries allowed scientists to theorize that pterosaurs first split into two subgroups: short-tailed and long-tailed. Short-tailed pterosaurs are categorized into four distinct but evolutionarily related families. Theories about which species of pterosaur belonged in which family have changed over time as new evidence emerges. One of the four families, Gallodactylidae, was created specifically because the swan-beaked pterosaur was thought to be distinct from the members of the other three families. Gallodactylidae are characterized by having fewer than 50 teeth, all of which are present only in the tip of the jaw. As new fossils were found, it was determined that swan-beaked pterosaurs were, in fact, more similar to species from other families than was originally thought. As a result, the family Gallodactylidae was largely disregarded.

    An exciting discovery in China soon reversed that trend. In 2012, a sword-headed pterosaur was discovered that also had teeth only in the front tip of the jaw. Swan-beaked and sword-headed pterosaurs were thought, for this reason, to be similar enough that they likely both directly evolved from a single common ancestor. The new discovery reenergized the belief that Gallodactylidae was its own unique family. Scientists quickly flocked back to the practice of classifying the swan-beaked pterosaur in the family Gallodactylidae, this time along with the sword-headed pterosaur. Like many pterosaur fossils, the 2012 sword-headed pterosaur fossil was incomplete; only the skull and lower jaw were recovered. By categorizing the sword-headed pterosaur as a close relative of the swan-beaked pterosaur, scientists vastly expanded the geographical range of this family. No specimen of Gallodactylidae had ever been discovered in China before this point. Researchers also concluded that the family was far more varied than was originally thought.

    However, a major discovery in 2016 again forced scientists to reevaluate their classification of pterosaurs. Another specimen of the sword-headed pterosaur was discovered, but this time it was nearly complete. The entire skull was present, along with the jawbone and much of the postcranial skeleton2. The fossil was almost perfect, missing only one of the rear legs and two vertebrae3. Analysis of this new fossil had some surprising results. The sword-headed pterosaur was actually different from the swan-beaked pterosaur in important ways. In fact, researchers determined that the sword-headed pterosaur was far more similar to species located in other families than to the swan-beaked pterosaur, with which it had been previously paired.

    Again, the families were reorganized. The sword-headed pterosaur was placed in an entirely different family called Ctenochasmatoidea. This family has been well-studied and is already known to have members in China. While a tentative organization of pterosaurs has helped to clarify which species evolved from a common ancestor and which are less closely related, it is apparent that the classification is far from final. Additional discoveries are likely to further alter scientists’ perspectives on this reptile.

    niches1: positions or functions of an organism in a community of plants and animals
    postcranial skeleton2: all or part of the bones behind the skull
    vertebrae3: bones found in the spine

  2. Now answer the questions.

  3. P1 Paragraph 1
    S1 Scientists have long been fascinated with the evolution of pterosaurs—warm blooded, flying reptiles that flourished during the Jurassic and Cretaceous periods, the time of the dinosaurs.
    2 Pterosaurs were the first animal after insects to develop powered flight.
    3 This ability was enabled by the pterosaur’s hollow bone structure, a structure more similar to modern birds than to ancient dinosaurs.
    4 Because of their ability to fly, pterosaurs were able to expand their range and fill many ecological niches, eventually evolving into dozens of different species that ranged in size from a small bird to a small airplane.
    5 However, hollow bones decay more easily than solid bones, making complete pterosaur fossils hard to find.
    6 Known fossils are difficult to categorize into evolutionary families.
    7 How did the pterosaur evolve over time into the many different species that roamed the Earth?
    8 Hidden from scientists’ view were the linking fossils that would indicate how closely related many of the different species were.

  4. According to paragraph 1, all of the following are true statements about pterosaurs EXCEPT:

    1. Pterosaurs were able to spread further because of their flight.
    2. The bones of pterosaurs were hollow.
    3. Pterosaurs varied in size notably.
    4. Pterosaurs were the first animal to develop powered flight.
    1. P2 Paragraph 2
      S1 Fossil discoveries allowed scientists to theorize that pterosaurs first split into two subgroups: short-tailed and long-tailed.
      2 Short-tailed pterosaurs are categorized into four distinct but evolutionarily related families.
      3 Theories about which species of pterosaur belonged in which family have changed over time as new evidence emerges.
      4 One of the four families, Gallodactylidae, was created specifically because the swan-beaked pterosaur was thought to be distinct from the members of the other three families.
      5 Gallodactylidae are characterized by having fewer than 50 teeth, all of which are present only in the tip of the jaw.
      6 As new fossils were found, it was determined that swan-beaked pterosaurs were, in fact, more similar to species from other families than was originally thought.
      7 As a result, the family Gallodactylidae was largely disregarded. 

    2. By stating that the swan-beaked pterosaur was “distinct” from the members of the other three families, the author means that

      1. it was different from previously discovered pterosaurs
      2. it fell into expected patterns for pterosaur fossils
      3. the three families represented a comprehensive categorization of pterosaurs
      4. it could have been categorized into any of the three families

    3. The word “disregarded” in the passage is closest in meaning to

      1. ignored
      2. celebrated
      3. known
      4. hoped for
    1. P3 Paragraph 3
      S1 An exciting discovery in China soon reversed that trend.
      2 In 2012, a sword-headed pterosaur was discovered that also had teeth only in the front tip of the jaw.
      3 Swan-beaked and sword-headed pterosaurs were thought, for this reason, to be similar enough that they likely both directly evolved from a single common ancestor.
      4 The new discovery reenergized the belief that Gallodactylidae was its own unique family.
      5 Scientists quickly flocked back to the practice of classifying the swan-beaked pterosaur in the family Gallodactylidae, this time along with the sword-headed pterosaur.
      6 Like many pterosaur fossils, the 2012 sword-headed pterosaur fossil was incomplete; only the skull and lower jaw were recovered.
      7 By categorizing the sword-headed pterosaur as a close relative of the swan-beaked pterosaur, scientists vastly expanded the geographical range of this family.
      8 No specimen of Gallodactylidae had ever been discovered in China before this point.
      9 Researchers also concluded that the family was far more varied than was originally thought.

    2. According to paragraph 3, which of the following led scientists to reclassify the swan-beaked pterosaur as a member of the family Gallodactylidae?

      1. The organizational structure of subgroups and families
      2. The discovery of a new and seemingly similar fossil
      3. The fact that sword-headed and swan-beaked pterosaurs evolved from different ancestors
      4. The overwhelming scientific evidence that many pterosaurs belonged in a new family

    3. Which of the following can be inferred from paragraph 3 about the theory that swan-beaked and sword-headed pterosaurs had the same ancestor?

      1. It was based on comparison of completed fossils.
      2. It tried to account for the pterosaur’s ability to fly.
      3. Researchers assumed that a partial fossil provided enough data for meaningful conclusions.
      4. It challenged the 2012 discovery of a sword-headed pterosaur.

    4. The word “ancestor” in the passage is closest in meaning to

      1. location
      2. predecessor
      3. food source
      4. time period
    1. P4 Paragraph 4
      S1 However, a major discovery in 2016 again forced scientists to reevaluate their classification of pterosaurs.
      2 Another specimen of the sword-headed pterosaur was discovered, but this time it was nearly complete.
      3 The entire skull was present, along with the jawbone and much of the postcranial skeleton.
      4 The fossil was almost perfect, missing only one of the rear legs and two vertebrae.
      5 Analysis of this new fossil had some surprising results.
      6 The sword-headed pterosaur was actually different from the swan-beaked pterosaur in important ways.
      7 In fact, researchers determined that the sword-headed pterosaur was far more similar to species located in other families than to the swan-beaked pterosaur, with which it had been previously paired.

    2. All of the following are mentioned in paragraph 4 as true about the 2016 discovery of a pterosaur fossil EXCEPT:

      1. the fact that scientists focused their research on the skull
      2. the presence of much of the postcranial skeleton
      3. the classification of the fossil as a sword-headed pterosaur
      4. the fact that the fossil was missing vertebrae

    3. In paragraph 4, why does the author provide details about which parts of the fossil were discovered in 2016?

      1. To evaluate the level of research done on sword-headed pterosaurs
      2. To illustrate the effectiveness of new fossil discovery techniques
      3. To demonstrate the difficulty of finding a complete pterosaur fossil
      4. To emphasize that this fossil was more complete than previously discovered fossils

    4. Which of the sentences below best expresses the essential information in the highlighted sentence of paragraph 4? Incorrect choices change the meaning in important ways or leave out essential information.

      1. The swan-beaked pterosaur and the sword-headed pterosaur are considered identical by researchers.                                     
      2. Researchers now pair the swan-beaked pterosaur with the sword-headed pterosaur.
      3. Researchers have located the sword-headed pterosaur in other families.
      4. Researchers now consider the sword-headed pterosaur less like the swan-beaked pterosaur and more like species of other families.
    1. P5 Paragraph 5
      S1 Again, the families were reorganized.
      2 The sword-headed pterosaur was placed in an entirely different family called Ctenochasmatoidea.
      3 This family has been well-studied and is already known to have members in China.
      4 While a tentative organization of pterosaurs has helped to clarify which species evolved from a common ancestor and which are less closely related, it is apparent that the classification is far from final.
      5 Additional discoveries are likely to further alter scientists’ perspectives on this reptile.

    2. The word “tentative” in the passage is closest in meaning to

      1. adaptive
      2. firm
      3. provisional
      4. controversial

    3. According to paragraph 5, which of the following is NOT an accurate conclusion about the pterosaur classification system?

      1. Additional discoveries will probably change what scientists believe about it.
      2. The opinions of researchers will likely remain unchanged over time.
      3. It includes at least one family that has been researched deeply.
      4. It helps make clear the common ancestry of certain species.

    4. Why does the author mention the family “Ctenochasmatoidea”?

      1. To complete the list of pterosaur families
      2. To emphasize the differences among the four pterosaur families
      3. To illustrate a reorganization of the pterosaur classification system
      4. To show that not all pterosaurs had the power of flight
  9. P3 Paragraph 3
    S1–2 An exciting discovery in China soon reversed that trend. In 2012, a sword-headed pterosaur was discovered that also had teeth only in the front tip of the jaw.
    3 A Swan-beaked and sword-headed pterosaurs were thought, for this reason, to be similar enough that they likely both directly evolved from a single common ancestor.
    4–6 B The new discovery reenergized the belief that Gallodactylidae was its own unique family. Scientists quickly flocked back to the practice of classifying the swan-beaked pterosaur in the family Gallodactylidae, this time along with the sword-headed pterosaur. Like many pterosaur fossils, the 2012 sword-headed pterosaur fossil was incomplete; only the skull and lower jaw were recovered.
    7–8 C By categorizing the sword-headed pterosaur as a close relative of the swan-beaked pterosaur, scientists vastly expanded the geographical range of this family. No specimen of Gallodactylidae had ever been discovered in China before this point.
    9 D Researchers also concluded that the family was far more varied than was originally thought.

  10. Look at the part of the passage that is displayed above. The letters [A], [B], [C], and [D] indicate where the following sentence could be added.

  11. Species that have common ancestors are generally categorized within the same evolutionary family.
    Where would the sentence best fit?

    1. Choice A
    2. Choice B
    3. Choice C
    4. Choice D

  12. An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

  13. The classification of pterosaurs is an area of interest to scientists.

    1. As new discoveries are unearthed, scientists continue to change the way they classify the families of short-tailed pterosaurs.
    2. The most well-studied family of pterosaurs is the Gallodactylidae family, which continues to be a source of much debate among scientists.
    3. The 2012 discovery of a sword-headed pterosaur was incomplete, containing only the skull and a portion of the jaw.
    4. The number of teeth that a pterosaur has is critical to its correct classification.
    5. Living in the time of the dinosaurs, pterosaurs were reptiles that had the power of flight, making their fossils particularly difficult to discover.
    6. The discovery of two different fossils of sword-headed pterosaurs has led to recent reorganizations of the families of pterosaurs.