What an amazing time resolution for 34 million years ago! Could the temperature changes recorded reflect seasonal eel migration, rather than changes in the Gulf of Mexico? Are the results consistent between otoliths found in close association? Does this offer a method of more precise dating similar to the use of tree rings?

Gordon C. Fisher
Ankara, Turkey

Linda C. Ivany of Syracuse (N.Y.) University says her analysis of fossil otoliths differs from the dating of past climate changes or other events through the study of tree ring growth because her analysis looks only at small temperature variations from disconnected periods of time. Ivany says the trends that allowed her and her colleagues to identify the changes in seasonal temperature before the extinction event about 34 million years ago were consistent in samples taken from the same place and those from nearby sediments of similar age. Finally, Ivany notes that the same types of eels that produced the fossil otoliths still live in the tropics today. The modern eels migrate neither geographically nor up and down in the water. Therefore, she’s convinced that the changes recorded in the otoliths reflect actual changes in climate. “We keep our fingers crossed and assume the eels behaved in the past as they do today,” she notes .—S. Perkins