I don't think so, because if he went back to the dinosaurs, he'd be -20 billion yrs. old, or something.

AO: You can go back in time, but only to times later than the moment of the construction of the time machine. So if we construct it now, in 2100 they will be able to visit us now, or later, but not earlier.

"If the laws of nature allow the construction of a time machine, maybe it could have occurred naturally a billion years ago. Then people would be able to visit the dinosaurs."