Using Isotopes to Determine the Constancy of Temperature Throughout the Body of the Dino.

Scientists have determined that the ratio of certain Stable (in other words non-radioactive) Isotopes is controlled by temperature. In Geology and Paleontology the ratio: ¹⁸O/¹⁶O is most commonly used to determine temperature variation (Note that the number indicates the atomic mass – ¹⁸O is oxygen with an atomic mass of 18, while ¹⁶O is oxygen with an atomic mass of 16).

Now, no one claims to be able to tell exactly what the body temperature of a dino was – there are too many variables that can affect these ratios. Instead, scientists are trying to determine if the body temperature of dinos was constant from the tips of their extremities to the center of their body core (chest trunk), a condition called homeothermy. The way you do this is to sample bone from the limbs, tail, and ribs and compare their isotopic ratios. Modern homeothermic animals (like us) exhibit less than a 4^oC variation in temperature between hands/feet and body core (ribs). Heterotherms (generally cold-blooded animals) exhibit greater variation. So while the isotopes cannot tell us the exact body temperature, differences in the isotope ratios can tell us approximate temperature differences between parts of the body. What does the isotope data tell us? Look at the graph below.

Based on these results (using roughly 4^oC as a boundary), most of the dinosaurs studied were homeotherms. The varanid is a Cretaceous relative of the modern Komodo Dragon and definitely cold-blooded (this is our experimental control), and it shows up as a definite heterotherm, just as we would expect. Only the poor nodosaur (a member of the Ankylosauria) shows up as a heterothermic dinosaur.