Because dinosaurs went extinct 65 million years ago.
He finishes her drink EDIT: Apparently this is Conan's joke, so all credit goes to him. I just heard it from a friend of mine and I had no idea.
Or, Laurie Hefner or Grant - Horton Hears a Hugh
Because pterodactyls are extinct.
She goes to the bathroom.
Down in the mouth!
Ereptile dysfunction
Their P is silent.
Because the 'p' is silent.