How many individual dinosaurs were there?

My son Ben and I visited the Minnesota science museum last night. An interactive display featured children's questions, including one I've almost wondered about -- how many individual dinosaurs were there?

The guest paleontologist took a rather wild statistical swag at it. Sad to say, I can't recall whether he said "40 quadrillion" or 40,000 quadrillion. I think it was the former. In any case he was far braver than the Google responses, which decline to answer the far duller question of how many have been identified based on the fossil record. Cowardly wimps.

That's 40 million billion, or roughly the national debt in dollars of the United States in 2000. About 5 million dinosaurs for each human alive today. That's fecundity. It gives one a sense of how successful triceratops must have been, and how many wonders remain forever lost (barring a time machine).

Actually, the question I've wondered is how many individual Homo erectus (erecti?) there were to have generated as many fossils as we find ...

I'm surprised science and history books don't give us more numbers. You get a very different sense of American history when you realize how very few people lived in Boston. Just about everyone in town must have known Ben Franklin ...