Could be something like Kamen Rider Slash (any better ideas?)

Each of his mode changes (like arms or wheels) are different dinos, and maybe each of his different season upgrades are the names of the ancient time periods? Like his first form is "Triassic" second "Jurassic" third "Cretaceous" and final form "Mesozoic."

The kaijin can be a play on fossils and have a very skeletal aesthetic, maybe?

What would the collectible be? The driver?

http://static.tvtropes.org/pmwiki/pu..._king_2190.jpg

*yawns

There's your new rider.

Themes themes huh...
So far the ones I've used and are planning to use in my fanworks are:

Videogames (Virtune)
Art (Shade)
Weather ( Stratos)
Opera
Lovecraft
Aliens
Ancient Artifacts / Archeology
Monster Summoning (ala persona)
Gambling (slot machines/cards/etc)

Somewhere in the future I know toei will use at least one of these

All this talk about trains, bikes, and automobiles... you people are so boring, confined to your pathetic dry, solid ground.

We need a Jet Rider. And/or a maritime rider.

what about a rocket....wait they already did that :)
As for maritime rider .... we still have Aqua

He's still 37 years in the future, he doesn't count.

While Drive is all about cars and motorcycles.

How about for the next themes...
1) Jets & birds + bats
2) Pirates + Aquatic Mammals + Fishes

What about disks? Can those work?

How about gods?
Kamen Rider Izanagi, KR Quetzacoatl, and KR Anubis~

But we already have an Odin.