Book 32, Question 43
Why are reptiles called cold-blooded if their blood isn’t always cold?
“Cold-blooded” is an old way to say that a reptile’s body temperature depends on the world around it.
A lizard sitting in the sun can have blood that is warm, even warmer than yours. Scientists prefer the word ectotherm, which means “heat from outside.” Birds and mammals are endotherms, making heat inside. Both ways work well for staying alive.