Gigantothermy

Gigantothermy is when really big animals maintain a high body temperature even though they're cold-blooded. Imagine a huge dinosaur, like a brachiosaurus, sitting in the sun all day. When the sun gets hot, it warms up the dinosaur's body because it's so big. Then at night, when the sun goes down and it gets colder, the dinosaur's body stays warm because it's already so big and has stored up heat. Basically, gigantothermy is like having a built-in heating system that helps keep big animals warm.