where his civilizations, including our own

Anyway, I think your theory is good except for the connection between metabolism and teeth. Birds have a very high metabolism and they don't have teeth at all. You could say that 'well, birds fly', but it seems increasingly likely that they inherited the metabolism from dinosaurs, who had teeth that shed. (And of course, we would also be ignoring all the birds who went back to ground and kept their metabolism without their teeth.)