ABSTRACT: Eating well in the Tertiary: Insect herbivory in the Florissant Fossil Beds, Colorado

Smith, Dena M.
University of Arizona, Tucson.

Geological Society of America Annual Meeting, Toronto, Canada.

Have insect feeding strategies and plant defensive strategies undergone dramatic change over time? I compared the insect-mediated damage on fossilized leaves from Florissant, Colorado with that from Costa Rican lowland rainforests. The 34.5 Ma Florissant Fossil Beds had a predominantly warm-temperate flora, but also contained some sub-tropical species. The Costa Rican floras consist of sub-trapical and tropical species.

Four hundred fossil leaf specimens were examined for the presence or absence of insect damage. The type and number of functional feeding groups evident from the damaged leaves was recorded. these data were compared to modern herbivory levels in Costa Rica and the literature on other Recnt tropical and temperate floras.

The Florissant flora had much lower levels of herbivore damage (32%) than that afound in Recent Costa Rican forests (87%). No single leaf in the Florissant assemblage had more than two types of herbivore damage and the majority (29%) only had one type of attacker. While the majority of leaves in the Costa Rican samples where only attacked by one or two insects groups, leaves damaged by 3-5 herbivores accounted for 12% of the sample.

The diversity and abundance of functional feeding groups in the fossil and Recent samples were not significantly different. However, leaf miners are absent in the Florissant assemblage, while in Costa Rica they account for 2% of all damage on leaves and records of leaf-mining damage on particular tropical and temperate taxa are at much higher levels, ranging from 18-80% of leaves with mining damage.

The differences in these assemblages are not likely to be due to taphonomic bias because leaf mining is much less destructive than other feeding types. This is because only the inner leaf tissue is being removed at the site of the mine. It is possible that differences in climate or spicies composition may explain the differences between the fossil and Recent floras. However, these differences could also represent ecological changes through time.

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