A study suggests that dinosaurs were not cold-blooded or warm-blooded, but something in between. via nature:
The work stakes out a rare middle ground in the long-running debate over whether dinosaurs were ‘cold-blooded’ ectotherms, which use the environment to adjust their internal temperature, or ‘warm-blooded’ endotherms, which regulate their body temperature from within. “There’s a third way,” says John Grady, a biologist at the University of New Mexico in Albuquerque.
Today, that middle ground is occupied by animals including tuna, lamnid sharks and leatherback turtles. Studying how those creatures control their body heat might help to reveal how dinosaurs did it millions of years ago, Grady says. Mesotherms burn energy from within to regulate their body heat, but not to a constant temperature as a mammal or bird would do. Tuna, for instance, stay up to 20 °C warmer than the surrounding water, except when they dive deep into colder waters, when their metabolic rate can also plunge.
To work out where in the metabolic spectrum dinosaurs lay, Grady and his colleagues compiled a database of growth rates in 381 animal species, including 21 dinosaurs. The analysis, published today in Science1, took data from earlier studies that estimated growth rates in a number of ways. For dinosaurs, that included techniques such as counting the number of growth rings in fossilized bone, to estimate an individual’s age, and measuring the length of its bones, to estimate total mass. The animals ranged from slow-growing crocodiles to fast-growing horses.
The team then compared how fast each animal grows with how much energy it burns and found that mammals, which grew ten times faster than reptiles, also had metabolic rates that were ten times faster. The researchers used that information to infer the metabolic rates of dinosaurs.
Dinosaurs ended up mid-way along the scale, in a state that Grady’s team dubbed mesothermy.
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