Big Dinosaurs had hot blood

New Scientist:

The debate over whether dinosaurs were cold-blooded like modern reptiles, or warm-blooded like us, may finally have been settled. According to some elegant biophysics, they were both – depending on how big they were.

The speed at which certain crucial biochemical reactions common to all life take place depends on temperature. Gillooly’s team found that this relationship means that a few constant values, arranged in a simple equation, can describe the relationship between temperature, metabolic or growth rate, and body mass. And the equation works across a very wide range of creatures – from plankton to blue whales.

And it turns out that the bigger the dinosaur, the hotter it was. The smaller species were indeed like modern reptiles, with body temperatures around 25°C – the ambient environmental temperature for their era.

But as dinosaurs got bigger, and the ratio of their surface area to their volume fell, they became less efficient at dissipating metabolic heat – especially as they surpassed 600 kg. The 13-tonne Apatosaurus (formerly Brontosaurus) reached 41°C. This is pretty hot compared to humans, at a mere 37°C.

Neat.

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