Plain-Language Summary:
In order to understand how large meat-eating dinosaurs lived, it is important to know how high was their metabolism or more simply, just how warm- or cold-blooded they were. Metabolism plays an important role in determining how much these dinosaurs needed to eat, how fast they grew, how actively they needed to search for food, how much territory they could cover in search of food, and finally, what reproductive strategies they used. Oxygen isotopes (oxygen atoms of two different masses, 18 and 16) may be extracted from their fossilized bones. The variation in the ratio of these two masses of oxygen from bone samples correlate to the temperature range at which these bones were grown while the dinosaurs lived. Very low ranges of body temperatures of land vertebrates that experience seasonal temperature changes generally correlate to higher metabolic rates. Results from Giganotosaurus and Tyrannosaurus (two of the largest meat-eating dinosaurs in Earth history) indicate that they both maintained constant body temperatures like most modern warm-blooded animals. However, they likely did so with metabolisms lower than modern mammals and birds and higher than modern lizards and crocodiles.
Reese E. Barrick and William J. Showers, Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695-8208