What's the best dinosaur to use as a fictional bookmaker mascot?

How to use this answer

This is a reasoned general answer rather than a confirmed bookmaker ruling or a claim about an event that has actually occurred. Exact cases need the facts supplied by the organiser or operator.

Novelty and prop markets depend on their written definitions. Find the precise wording, qualifying period and published result source; an ordinary sporting rule does not always decide how a novelty bet settles.