New data about blood flow rates in the bones of various animals suggests that they were. Roger Seymour of the University of Adelaide and his colleagues compared the size of nutrient foramens in living and extinct creatures to come to their conclusion.
Nutrient foramens are the tiny holes in bones that allow blood to enter and nourish the cells inside the bone. More active animals require a greater nutrient supply to their bone cells, and thus have larger nutrient foramens. In general, mammals have foramens that are ten times larger than those of comparably sized reptiles. This increase in size correlates well with maximum metabolic rates.
Next, the researchers determined the sizes of the nutrient foramens in fossilized dinosaur bones. They surveyed ten species, which included quadrupeds and bipeds, carnivores and herbivores. Surprisingly, the nutrient foramens in all ten species were larger than those of mammals!
There is mounting evidence that dinosaurs were not cold-blooded, but could control their internal temperatures. This new data suggests that, far from being sluggish lumberers, they may have led extremely active lives.