Researchers collected over 3,500 fossils from from 25 quarries in Patagonia. Each fossil was examined for four types of insect damage:
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.
Below is an example.
Insect Damage
They were then compared to approximately 2700 fossils from three sites in North America. The results:
The researchers found that the number of damage types at each of the four major Patagonian quarries significantly exceeds each of the three North American samples. The number of functional feeding groups is also greater than all North American samples for three of the four major quarries. The diversity of damage types and feeding groups at the Patagonian sites for individual plant species hosts is also highest.
"Insect damage on leaves, the remains of insect meals, is uniquely valuable data," says Wilf. "While actual insect fossils can give us taxonomic information, leaf damage provides unique ecological data about which and how many kinds of insects were eating and interacting with ancient plant species in the deep past. Also, insect damage on fossil plants, which can be very abundant, can give us a great deal of information about insects at times and places with very few insect fossils."
The research design was extremely rigorous. The North American fossils were collected by the same team and members of that team helped collect the Patagonian fossils (to insure identicle collection methods). Two of the researchers scored all the insect damage (to insure consistancy in the scoring). Samples were then adjusted for size. All in all an impressive piece of research. Incidentally, if a creationist ever tells you we can't learn about the past because humans wern't around to witness it you can point them to this post - which shows, in a very convincing fashion, that we can.
Also, the same team published an earlier study which gives a few more details. You can find a summary of that earlier work here.
Here is a few paragraphs to tide you over till you get there:
Many Eocene fossil sites in North America have been collected 100 years or more. Laguna del Hunco, though known for 80 years, is now the first of this age from South America to be heavily and quantitatively sampled. Quantitative sampling, where every specimen is tallied and identified, allows sample size to be taken into account when comparing recovered diversity. The age of the deposit was also not well constrained.
The researchers collected more than 1,500 fossils and identified more than 100 different fossil leaf species including dicots, monocots, conifers, ginkgophytes, cycads and ferns. They also identified a variety of seeds, fruit and flowers. In total, they more than tripled the known diversity of the site in two weeks. Using paleomagnetic dating, which uses the Earth's magnetic pole reversals, and argon argon dating, which compares the amounts of two isotopes of argon one of which is produced by the natural radioactive decay of potassium, the researchers dated the fossils to a half million year interval between 52 and 53 million years ago. These are the first high-precision ages for the deposit, which now can be correlated anywhere in the world.
I will be republishing this, in a slighttly different form, over at Transitions this evening.
