Ancient Leaves and Insect Extinctions
Read the following abbreviated version of a newspaper article and answer these questions.
a) What was the question being investigated by the scientists?
b) What observations did the scientists make during their investigations?
c) What was the principal conclusion of their research?
When a 6-mile-wide asteroid slammed into Earth 65 million years ago, it wiped out the dinosaurs, about 80% of the world’s plant species, and all animals bigger than a cat. But what happened to the bugs?
It’s been tough for scientists to determine how the insects fared because bugs rarely leave behind fossils. But a Denver paleontologist and his Smithsonian Institution colleagues found a way around the problem: By studying insect damage etched into thousands of fossil leaves, they determined that many plant-eating bugs perished in the big impact.
“These little insects are leaving their calling cards on the fossil leaves, and we have an excellent fossil record of leaves,” said Kirk Johnson, curator of paleontology at the Denver Museum of Nature & Science. “So by looking at the insect damage on the leaves before and after the dinosaur extinctions, we can make a pretty good educated guess of
what happened to the insects.”
Johnson and his collaborators estimate that 55% to 60% of plant-eating insects were exterminated. Over the past 20 years, Johnson has collected 13,441 plant fossils from quarries in southwestern North Dakota. When the asteroid hit Mexico’s Yucatan Peninsula, it threw up clouds of dust that traveled around the globe. Johnson pulled the fossils from rock layers directly above and below those sediments. At the time, southwestern North Dakota was a warm, forested plain with lots of broad-leafed trees.
Some leaves, now stored at the Denver museum and at Yale University, are up to a foot long. Individual leaf veins are visible, as are the diagnostic chomp marks, tunnels, and holes left by prehistoric beetles, grasshoppers, butterflies, caterpillars and moths. Some insects are specialists, relying on a single species of plant for sustenance; others are generalists that feed on several plant types. By analyzing insect-damaged leaves before and after the impact, the researchers determined that the generalists survived, while 70% of the specialists did not.
Source: Jim Erickson, Rocky Mountain News (Denver), February 22, 2002, page 7A.
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