The researchers were very careful in the field to ensure they achieved an unbiased sample. They also used computerized resampling methods to eliminate any possible bias from unequal sample sizes.
"We used identical collection methods for all the fossil leaf collections," says Wilf. "For example, Kirk Johnson and his crews collected the fossils at both Green River and Republic and he also was on our Patagonia expeditions, so we can easily compare the samples. In collecting, we count every leaf that we find and we collect every identifiable leaf that has insect damage. Conrad Labandeira and I scored all of the thousands of leaves from the four fossil floras for insect damage using the same proceedures." The researchers took the 3599 specimens collected in Patagonia from 25 quarries. The fossils are housed at the MEF in Trelew which Ruben Cuneo directs. These fossil leaves grew during the Eocene global climatic optimum, the warmest time period in the last 70 million years. During this time, there were no polar ice caps and alligators were found above the Arctic circle.
The researchers classified damage by feeding group and damage type. The four feeding groups are those insects that feed on the external leaf, chewing holes, edges and other leaf parts; those insects that mine tissues inside the leaf; those that produce bulbous galls and those that pierce and suck the leaves. Because different insects chew, mine, gall and pierce in different ways, the researchers recognized 52 discrete damage types from the four feeding groups. They applied these categories to both bulk samples from single quarries and to individual leaf species.
The insect damage on the 3599 fossil leaves from Patagonia was compared to the 1019 fossil leaves from Republic, 894 leaves from Green River and 792 leaves from Sourdough.
The Republic site is the most similar to the Laguna del Hunco site in terms of volcanic setting, age, environment and
Contact: A'ndrea Elyse Messer