We’re not 100% sure on this. It was thought for a long time that as dinosaurs were reptiles, they must have been cold blooded. However, some recent studies suggest that they were maybe warm blooded: http://www.natureworldnews.com/articles/3029/20130718/dinosaurs-warm-blooded-study.htm. The argument is that if they were cold blooded they would not have been able to generate enough muscle power to chase their prey.
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