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The fossil remains of the first flying vertebrates, the [#permalink]
31 Dec 2004, 15:16
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
(5) 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 ques-
tions scientists have puzzled over.
Perhaps the least controversial assertion about the
(10) 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 winglike membrane.
(15) 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
(20) 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
(25) their overall structure and proportions. This is not sur-
prising because the design of any flying vertebrate is
subject to aerodynamic constraints. Both the pterosaurs
and the birds have hollow bones, a feature that repre-
sents a savings in weight. In the birds, however, these
(30) bones are reinforced more massively by internal struts.
Although scales typically cover reptiles, the
pterosaurs probably had hairy coats. T.H. Huxley rea-
soned that flying vertebrates must have been warm-
blooded because flying implies a high rate of
(35) metabolism, which in turn implies a high internal tem-
perature. 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
(40) relatively thick hairlike fossil material was the first clear
evidence that his reasoning was correct.
Efforts to explain how the pterosaurs became air-
borne have led to suggestions that they launched them-
selves by jumping from cliffs, by dropping from trees.
(45) 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 rese-
mbled a bat's and could serve as hooks by which the
animal could hang in preparation for flight. The second
(50) 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
(55) control their flight once airborne.
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
3. According to the passage, the skeleton of a
pterosaur can be distinguished from that of a bird by
(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
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
(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
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
(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
(E) They lived primarily in a forestlike 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
(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
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