First off, dinosaurs aren’t reptiles per say, and a good bit of evidence points to them not being cold blooded often. It’s not always a binary option either, a mesotherm is between warm and cold blooded, and if I recall correctly, a good number of dinosaurs were thought to be this.
And, this not being a binary option, you can better imagine this being a stepwise adaptative process according to your environment. There’s pros and cons to each, with warm blooded often allowing you to be much more active (and survive colder climates), but much less energy efficient (and thus requiring more intake).
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