Suspect terranes in western North America contain Permian and Triassic genera that were endemic to the Tethyan region. Trend-surface analysis of modern biogeographic data constitutes a new approach to understanding the origin of these exotic faunas. We use the generic diversity of living reef corals together with paleomagnetic results from Quaternary lavas to calculate the present locations of Easter Island, Hawaii, and Tahiti. The results demonstrate that the eastward decline in coral diversity may be used as a measure of longitude. Similar data from the fossil record should constrain paleogeographic reconstructions of the Pacific region.