Technically, we already are hovering around that territory with the flightless birds, crocs and company but I think it’d be awesome if we had giant insects/arachnids and all other manner of creatures. Mammals, crustaceans, etc. There’s so much potential.
I imagine the game will EVENTUALLY add some but hope it isn’t strictly to the exclusion of other classes of species. I feel it would be more well-received if it was a case of gradual expansion into different species as opposed to “this update we added bugs! this update we added deep water dwellers!” and so on.