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 e- valve 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 em
A. revolutionary
B. unlikely
C. unassailable
D. probable
Fossils are the remains and traces of ancient plant and animal lives that are more than 10,000 years old. They range in size from microscopic structures to dinosaur skeletons and complete bodies of enormous animals. Skeletons of extinct species of human are also considered fossils.
An environment favorable to the growth and later preservation of organisms is required for the occurrence of fossils. Two conditions are almost always present: The possession of hard parts, either internal or external, such as bones, teeth, scales, shells, and wood; these parts remain after the rest of the organism has decayed. Organisms that lack hard parts, such as worms and jelly fish have left a meager geologic record. Quick burial of the dead organism, so that protection is afforded against weathering, bacterial action, and scavengers.
Nature provides many situations in which the remains of animals and plants are protected against destruction. Of these, marine sediment is by far th
A. a dinosaur.
B. a woolly mammoth.
C. a human ancestor.
D. a worm.
It remains to be seen whether the reserves of raw materials would be sufficient to supply a world economy which would have grown by 500 per cent. South-East Asia alone would have an energy consumption five times greater than that of Western Europe in 1970. Incidentally, if the underdeveloped countries started using up petrol at the same rate as the industrialized areas, then world reserves would already be exhausted by 1985.
All this only goes to show just how important it is to set up a plan to conserve and divide up fairly natural resources on a worldwide scale.
This is a matter of life and death because world population is exploding at an incredible rate. By the middle of the next century population will expand every year by as much as it did in the first 1500 years after Christ. In the southern, poor, parts of the globe, the figures are enough to make your hair stand on end. Even supposing that steps are taken to stabilize world population in the n
A. there will certainly not be enough raw materials for the world economy in the year 2008.
B. world petrol supplies will have been exhausted by 1985
C. we need to use natural resources carefully and divide them up equally
D. to show down the economic growth in developed countries might be a possible solution to the problem
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