The fossil remains
of the first flying vertebrates, the pterosaurs, have intrigued paleontologists
for more than two centuries. How such large creatures, which weighed in some
cases as much as a piloted hang-glider and had wingspans from 8 to 12
meters, solved the problems of powered flight, and exactly what these creatures
were—reptiles or birds—are among the questions scientists have puzzled over.
Perhaps the least
controversial assertion about the pterosaurs is that they were reptiles. Their
skulls, pelvises, and hind feet are reptilian. The anatomy of their wings suggests
that they did not evolve into the class of birds. In pterosaurs a greatly
elongated fourth finger of each forelimb supported a wing-like membrane. The
other fingers were short and reptilian, with sharp claws. In birds the second
finger is the principal strut of the wing, which consists primarily of
feathers. If the pterosaurs walked on all fours, the three short fingers may
have been employed for grasping. When a pterosaur walked or remained
stationary, the fourth finger, and with it the wing, could only turn upward in
an extended inverted V-shape along each side of the animal’s body.
The pterosaurs
resembled both birds and bats in their overall structure and proportions. This
is not surprising because the design of any flying vertebrate is subject to aerodynamic
constraints. Both the pterosaurs and the birds have hollow bones, a feature
that represents a savings in weight. In the birds, however, these bones are
reinforced more massively by internal struts.
Although scales
typically cover reptiles, the pterosaurs probably had hairy coats. T. H. Huxley
reasoned that flying vertebrates must have been warm-blooded because flying
implies a high rate of metabolism, which in turn implies a high internal
temperature. Huxley speculated that a coat of hair would insulate against loss
of body heat and might streamline the body to reduce drag in flight. The recent
discovery of a pterosaur specimen covered in long, dense, and relatively thick
hairlike fossil material was the first clear evidence that his reasoning was
correct.
Efforts to explain
how the pterosaurs became airborne have led to suggestions that they launched
themselves by jumping from cliffs, by dropping from trees, or even by rising
into light winds from the crests of waves. Each hypothesis has its difficulties.
The first wrongly assumes that the pterosaurs’ hind feet resembled a bat’s and
could serve as hooks by which the animal could hang in preparation for flight.
The second hypothesis seems unlikely because large pterosaurs could not have
landed in trees without damaging their wings. The third calls for high waves to
channel updrafts. The wind that made such waves however, might have been too
strong for the pterosaurs to control their flight once airborne.
Questions:
1. It
can be inferred from the passage that scientists now generally agree that the
(A) enormous
wingspan of the pterosaurs enabled them to fly great distances
(B) structure
of the skeleton of the pterosaurs suggests a close evolutionary relationship to
bats
(C) fossil
remains of the pterosaurs reveal how they solved the problem of powered flight
(D) pterosaurs
were reptiles
(E) pterosaurs
walked on all fours
2. The
author views the idea that the pterosaurs became airborne by rising into light
winds created by waves as
(A)
revolutionary
(B) unlikely
(C)
unassailable
(D) probable
(E) outdated
3. According
to the passage, the skeleton of a pterosaur can be distinguished from that of a
bird by the
(A) size of its
wingspan
(B) presence of
hollow spaces in its bones
(C) anatomic
origin of its wing strut
(D) presence of
hooklike projections on its hind feet
(E) location of
the shoulder joint joining the wing to its body
4. The
ideas attributed to T. H. Huxley in the passage suggest that he would most
likely agree with which of the following statements?
(A) An animal’s
brain size has little bearing on its ability to master complex behaviors.
(B) An animal’s
appearance is often influenced by environmental requirements and physical
capabilities.
(C) Animals
within a given family group are unlikely to change their appearance
dramatically over a period of time.
(D) The origin
of flight in vertebrates was an accidental development rather than the outcome
of specialization or adaptation.
(E) The
pterosaurs should be classified as birds, not reptiles.
5. It
can be inferred from the passage that which of the following is characteristic
of the pterosaurs?
(A) They were
unable to fold their wings when not in use.
(B) They hung
upside down from branches as bats do before flight.
(C) They flew
in order to capture prey.
(D) They were
an early stage in the evolution of the birds.
(E) They lived
primarily in a forest-like habitat.
6. Which
of the following best describes the organization of the last paragraph of the
passage?
(A) New
evidence is introduced to support a traditional point of view.
(B) Three
explanations for a phenomenon are presented, and each is disputed by means of
specific information.
(C) Three
hypotheses are outlined, and evidence supporting each is given.
(D) Recent
discoveries are described, and their implications for future study are
projected.
(E) A summary
of the material in the preceding paragraphs is presented, and conclusions are
drawn.
7. It
can be inferred from the passage that some scientists believe that pterosaurs
(A) lived near
large bodies of water
(B) had sharp
teeth for tearing food
(C) were
attacked and eaten by larger reptiles
(D) had longer
tails than many birds
(E) consumed
twice their weight daily to maintain their body temperature
Answers:
1.
D
|
2.
B
|
3.
C
|
4.
B
|
5.
A
|
6.
B
|
7.
A
|
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