THE bulky bodies of large dinosaurs may have allowed them to maintain a high
and stable body temperature without using metabolic energy to keep warm as birds
and mammals must. So say Australian zoologists who have observed the same effect
in crocodiles, the largest reptiles living today.
Gordon Grigg and his colleagues at the University of Queensland in Brisbane
monitored the body temperatures of 11 saltwater crocodiles in northern
Queensland by feeding them chicken carcasses with temperature-sensitive radio
transmitters sewn inside. The largest croc, which weighed more than a tonne, had
an average body temperature 3.7 掳C warmer in summer and 1.9 掳C warmer in
winter than the smallest animals, which weighed less than 50 kilograms. And the
body temperatures of big animals kept within a 2 掳C daily range, compared
with a range of more than 10 掳C for smaller ones.
The researchers also developed equations for heat transfer between a
crocodile and its environment that predicted body temperatures for reptiles of
different body masses. Using these equations, they calculated that a 10-tonne
animal鈥攔oughly 1.5 times as large as Tyrannosaurus rex
鈥攚ould have a body temperature of 36 掳C in summer and 31 掳C in
winter, with a daily temperature fluctuation of less than 0.1 掳C in a
climate like that of northern Queensland today (Journal of Experimental
Biology, vol 202, p 77).
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Because bigger animals tend to be warmer, large dinosaurs living in warm
climates probably faced serious problems of overheating. 鈥淎s you get large, it鈥檚
crucial that you are able to get into the water or the shade,鈥� says Grigg. But
that cost is offset by a big benefit, says James Farlow, a palaeontologist at
Indiana-Purdue University at Fort Wayne鈥攁 large, warm dinosaur would have
the speed and endurance usually associated with birds and mammals.