Right, I’ve been looking for a while through almost everything and I can not find a way for the character to spawn in riding a creature. Is it in fact possible and where can I find how to do this? Knowing my luck I’ve probably missed it every time I’ve had a look!
This would need to be done via blueprinting
Check out this stickied thread for info on blueprinting as you will need it for this project 
I believe it would require calling the player riding state on spawn, in addition to casting it to the dino’s riding state after that. I’m not entirely sure though, and just theorizing about how it would be done