Eocene fossils provide a glimpse of the future (cont.)

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Though this qualitative method supplied general climate and plant distribution patterns, CLAMP (Climate-leaf analysis multivariate program) provides us with a quantitative approach that can be correlated to specific temperature and precipitation ranges. Developed by UCB alumnus Jack Wolfe (University of Arizona), CLAMP uses data obtained by giving a numbered score to shape characters of leaves (e.g., base and apex shape, margin features: smooth vs. toothed, etc.) in modern plant assemblages. By scoring leaves in a fossil assemblage for the same characters, the fossil assemblage can be matched by the CLAMP computer program to the most similar modern assemblage. This provides specific climatic parameters such as mean annual temperature (MAT) and mean annual range of temperature (MART) to the fossil assemblage. Most importantly the modern analyses show that the size and shape of woody plant leaves are climate dependent. Thus, similar climate conditions produce similar leaf size and shape regardless of the taxonomic relationships of the plants. An advantage of CLAMP is that it gives actual climatic values allowing for a better understanding of the magnitude of a warming or cooling event.

The vertebrates illustrate the impact
While plants give us the story of changes in past terrestrial climates, we can turn to the vertebrate record to see how global warming affected the animal communities. One of the most dramatic effects of Eocene warming on vertebrates was a change in species range distribution due to migration.

  Fossil turtle carapace
The fossil carapace of the aquatic turtle Echmatemys, one of the first Asian immigrants into North America and one of the most common turtles in the Eocene. (photo by Pat Holroyd)

Particular cold-intolerant species quickly spread into regions of higher latitude as climates warmed and temperatures increased. Regional warming in the Arctic opened up important migration corridors across the Bering Land Bridge, allowing a massive influx of Asian lineages into North America. UCMP's collections hold one of the best known records of these immigrants, documenting the first appearance of horses and

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