Lack of direct evidence, such as well-preserved organs, makes it a difficult question to answer. Fricke, now at Colorado College, performed the work while at the Carnegie Institute of Washington. He and co-author Raymond Rogers of Macalester College present their results in this month's issue of the journal Geology . Analyzing oxygen chemistry is a popular method for evaluating ancient climates and fossils, but Fricke is the first to try the method on dinosaur teeth.
Oxygen atoms can have three different masses, known as isotopes.
Scientists know that rainwater at higher latitudes contains more lighter oxygen isotopes than rainwater at lower latitudes. Previous studies have shown that rainwater's isotope ratio affects the ratio recorded in tooth enamel, since animals drink rainwater. But a cooler body temperature skewers the ratio. Fricke found that overall, the teeth of all the species studied reflected the rainwater ratio of the latitude. But he was surprised to find the crocodile teeth had slightly lower levels of lighter isotopes than the dinosaurs.