Chapter 7 - Ectothermic?

On the other side of the train stretched a dry, rocky plain that looked like a prehistoric desert. As they slowed down, a lizard, about ten feet long, slithered out from behind some big rocks. He had a tall sail, like a big fin, running all along his back.

"What kind of dinosaur is that?"

"A dimetrodon. Technically, because he has a different kind of bone structure, he's not really a dinosaur at all—just a big lizard."

"Is his sail only for decoration?"


"No. Dimetrodons are ectothermic — that means cold-blooded. They need heat from the sun to live, but too much sun makes them overheat, so scientists think reptiles like the dimetrodon used their sails to help regulate body temperature."

"Aren't dinosaurs ecto...ecto... What was that?"


"Thanks. Aren't they all cold-blooded, too?"

"Scientists used to think so. But after a lot of studying, they now think dinosaurs were warm-blooded, or endothermic."

"Gee. Just like people," Tim said.

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