Did Dinosaurs Have Warm or Cold Blood?

It's a question that has been asked for many years with no conclusive answer.  Dinosaurs were reptiles, which have cold blood, but the closest descendents of the dinosaurs today are birds, which are warm blooded.  Scientists now believe they have answered the question, and the answer is...neither.  It was a trick question after all, as it appears dinosaurs were actually something in between warm and cold blooded.  

Cold blooded animals, or ectotherms, depend on their environment to heat up their bodies.  It's the reason you won't find many reptiles in polar climates, they can't get enough energy in the cold to do anything.  Warm blooded animals, or endotherms, control their own temperatures through adjusting their metabolism.  These are what most people know, but there are a couple other means of temperature regulation out there.  There are gigantotherms, animals which maintain body heat through sheer mass.  Crocodiles are an example of this, and since dinosaurs could grow quite large, it would make sense for them to be gigantotherms too.  Right?

Dinosaurs were actually mesotherms, which are animals that generate some body heat, but do not maintain a constant temperature.  Again, mesotherms tend to be big, although not always.  The echidna, which is a small, egg-laying mammal, is a mesotherm, as are great white sharks and tuna.  The advantage for dinosaurs being mesotherms is that it allowed to move, grow, and reproduce faster than normal reptiles could, while their lower metabolism allowed them to get by on less food.  A modern-day mammalian predator could not find enough food to survive if it were the size of a T-rex.  There were a lot of dinosaurs, some may have been ectotherms or endotherms, and the winged dinosaurs present further mysteries, but in general, they were mesotherms.

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