Dinosaurs ‘neither warm nor cold blooded’

Dinosaurs fit in an intermediate class between warm and cold blooded animals, a study in the journal Science claims. Scientists compared the growth rates of hundreds of living and extinct species, using growth rings and bone size to calculate the rates for dinosaurs. They linked growth rate to metabolic rate, the measure of energy use that divides warm and cold blooded animals. The study suggests that the dinosaurs fall into a middle category, in a fresh contribution to an enduring debate.

Warm blooded animals, like mammals and birds, need a lot of fuel and use that energy to their advantage, including faster movement and boosted brain power. In burning all that food they also maintain a high, stable body temperature. Cold blooded animals are more economical, but lack those advantages.

“If I were eating sandwiches all day… I might have to eat five,” explained John Grady, the study’s first author and a PhD student at the University of New Mexico. “But a reptile [my size] can eat maybe a couple of sandwiches in a whole week.”

Scientists define these different strategies as “endothermy” (endo for inside; therm for heat) and “ectothermy”. The question of which biological system underpinned the lumbering success of the dinosaurs is arguably “the last big one”, Mr Grady told the BBC – following other big debates over their extinction and their relationship to birds. Edited from Dinosaurs ‘neither warm nor cold blooded’.

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One Response to Dinosaurs ‘neither warm nor cold blooded’

  1. alfy says:

    Given that the “cold-blooded” state must have been the original condition for vertebrates, it is not surprising that there must have been some intermediate state before a constant body temperature was achieved. This research gives us some clues as to that intermediate state. Bear in mind the dinosaurs flourished in the Mesozoic era when temperatures on earth were relatively high. It would have been much easier to maintain a warm internal body temperature than in later times.

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