When I was a kid, my favorite dinosaur was the brontosaurus. I used to daydream about riding on the head of one of these giants, floating slowly through the treetops as my friend chomped down bale after bale of leaves.
The other day there was something about dinosaurs on the radio, and I realized that I hadn't heard or read mention of the brontosaurus in years.
Well, it turns out that there never was such a thing. The guy, Othniel C. Marsh, who discovered the Apatosaurus, thought he found a similar species that was much larger, and named it brontosaurus ("Thunder Lizard," which would also be a good name for a metal band). The bigger creature turned out, though, to be just a full-grown Apatosaurus; the first one he found was a juvenile.
So now you know.