Why dinosaur here? I mean the sentence suggests that dinosaur here is someone undesirable or expendable, but is there any quality about dinosaur that made people adopt its name for such meanings?So, why the different treatment of Stronach's defection versus O'Brien's? Because in the overwhelming view of the Liberal punditocracy, Stronach holds the "correct" view in favour of same-sex marriage, while O'Brien, who is opposed, can be dismissed as a "dinosaur" whose loss to the Grits is no big deal.
Thank you very much!
Dinosaurs are extinct. A metaphorical dinosaur is a person who has outlived the popularity/acceptance/importance of his views/opinions.