Sauropods, the long-necked, long-tailed and four-footed dinosaurs that weighed as much as 80 tons, pose a scientific riddle. How did these massive beasts, the largest critters to ever walk on land, keep from overheating?
They did so quite nicely, suggests a chemical analysis of their teeth. The study released Thursday by the journal Science, reports that sauropod dinosaur body temperatures fell within the range of modern-day birds and mammals, 96 to 101 degrees.
They must have kept cool somehow. The study authors, led by Caltech’s Robert Eagle, note a long-running debate among paleontologists over whether dinosaurs were cold-blooded or warm-blooded, which their results inform, but fail to settle:
For the majority of the time since dinosaurs were first named in 1842 it was assumed that their metabolism was similar to ectothermic “cold-blooded” reptiles that derive the heat they need to function from the environment, rather than endothermic “warm-blooded” mammals and birds, that have higher and more stable body temperatures regulated by internal metabolic heat production. However, in the 1960’s and 1970’s evidence began emerging that endothermy could be more consistent with observations on the behavior, paleogeographic distribution (e.g., polar dinosaurs), and anatomy of non-avian dinosaurs.
In the study, the researchers analyzed fossil teeth from three dinosaur species, Giraffatitan, a Diplodocid and Camararsaurus, which date to the late Jurassic, more than 144 million years ago. Because carbon and oxygen atoms combine in different amounts in teeth at different body temperatures, the ratio of the two atoms in the fossils served as a thermometer for the long dead dinosaurs. Past analysis by some researchers had suggested the beasts should have had body temperatures as high as 104.
So what did the tooth study find? The Giraffatitan teeth pointed to a body temperature of 100.8 Fahrenheit; the Diplodocid came in at 92.5; and the Camararsaurus measured 96.3. Since the Diplodocid teeth measurements looked a little shaky, the team concludes they can safely peg the temperature range of the sauropods at roughly 96 to 101.
Asked whether the tooth technique seemed like a good way to get at dinosaur body temperatures, paleontologist Martin Sander of Germany’s University of Bonn said, “The answer is yes because the technique is very simple in that it needs no extra information, unlike previous methods where you needed to know the composition of the water that the dinosaur drank.”
But paleontologist Kevin Padian of the University of California, Berkeley, was more cautious, saying, “The technique used in this paper needs more ground-truthing, but it seems promising. The problem is that we don’t have an independent test of how far off the results could be,” by email.
“In general, body temperatures of vertebrates reflect the combined influences of metabolism, size, environmental temperature and, in some cases, specialized physiological strategies for heat regulation,” the study authors note. “Therefore our data, taken in isolation, are not unambiguous indicators of endothermy (warm-bloodedness) vs. ectothermy (cold-bloodedness). However, they do place quantitative constraints on sauropod physiology, limiting the range of possible thermoregulatory (body temperature) strategies.”
Like previous studies, Sander says, “this one is not able to prove that dinosaurs were warm-blooded. This is because the dinosaurs measured by the authors were all large, like most dinosaurs, and thus had a high body temperature anyway.”
“This is because even a cold-blooded animal generates heat in its muscles while moving which then accumulates in a large body that has a small surface area relative to its size. It thus is generally agreed that large dinosaurs must have had a high body temperature, and that their main problem was how to avoid overheating, not how to avoid cooling down. So to find out whether dinosaurs were warmblooded, you would have to apply the new method to dinosaurs smaller than about 100 pounds. If you still would see high temperatures, that would be a pretty good indicator of warm-bloodedness,” Sander says, by email.