There is not a patron saint for everything.
However, you can often stretch the patronage of a saint to include similar categories.
E.g., there is no patron saint of pigeons. However, St. Denis is the patron saint of doves.
There is not now, nor is there ever likely to be, a patron saint of dinosaurs. However, St Francis of Assisi, patron saint of animals, would be a good choice. If the dinosaur is purple and named Barney, then St Antony the Abbot, patron saint of domestic animals, might be more appropriate.