PLoS ONE 4, e7783 (2009)

Two methods for estimating animal metabolic rates have been applied to extinct dinosaurs to show which of the bipedal species may have been warm- or cold-blooded. Herman Pontzer of Washington University in St Louis, Missouri, and his colleagues tested the models on 14 species, from small bird-like creatures to the large tyrannosaurus. The models, which predict metabolic rates on the basis of anatomy and the energetic cost of walking or running, suggest that the five largest species — each weighing more than 20 kilograms — had a higher metabolic output and were thus warm-blooded. Only the smallest species tested, a 0.25-kilogram Archaeopteryx, was deemed to be cold-blooded.