We talked about this a bit in the most recent episode of Science… sort of.
Henry Fricke, a geochemist at Colorado College in Colorado Springs, and his colleagues now seem to have hard evidence that sauropod dinosaurs moved hundreds of kilometres every year. They publish their findings today in Nature1.
“In a theoretical sense, it’s not hugely surprising. They are huge — they would probably have eaten themselves out of house and home if they stayed in one place,” says Fricke. “Now we have evidence that demonstrates that, and a method to move forward and study other dinosaurs.”
The evidence collected by Fricke and his colleagues takes the form of fossil enamel chipped from 32 teeth that belonged to sauropods of the genus Camarasaurus. The teeth, which date from the late Jurassic period (160 million to 145 million years ago), were collected in the Morrison basin in Wyoming and Utah.
The researchers measured the ratios of two isotopes, oxygen-16 and oxygen-18, in this enamel, then compared them with the ratios in the sedimentary rocks found in the area. In vertebrates, the oxygen ratio relates to the ratio in the water they were drinking when their teeth were growing; sedimentary rocks record local ratios.
Thus, if the oxygen ratios in a tooth do not match those in the rocks near where the tooth was found, the animal must have been somewhere else when growing that tooth.
That is exactly what the team found. Some teeth matched the basin, but others had a much lower proportion of 18O, indicating that their former owners had probably spent time at higher elevations. Levels of 18O are low over high ground because the heavy isotope is rained out of clouds first as they rise and cool. The Morrison basinCamarasaurus must have migrated at least 300 kilometres between the basin and highlands to the west, says Fricke.