Being a huge dinosaur seems to him to be a pretty secure trade, until a rather large comet raps Earth up the side of the face, and there's a phase change. You see, they're sort of unpredictable. When a phase change occurs, all bets are off. In fact no one knows what the bet's about anymore. All reference terms become obsolete.
Nothing is as it was.
If the Big Bang idea of creation has any merit, that's pretty dramatic, even as phase changes go. On a personal phase change level, death sort of gets your attention. A total loss of memory has its challenges. And so on. The possibilities regarding their timing or nature are infinite.