Yeah this is exactly wha tthe fossil pokemon need to be! Classic dinosaurs are the best
Like although Kabutops line and Omastar line are pretty neat, they were based on a trilobite and an ammonyte respectively. Armaldo and Cradily lines are ok but again are based on early cambrian era life forms which lived way before dinosaurs. For me, the only 'classic' fossil pokemon are Aerodactyl, Rampardos line and Bastiodon line as they are reminiscent of actual dinosaurs/reptiles of the jurassic and cretaceous era (in aerodactyls case anyway).
Anyway the stegosaurus seems like a great idea
rock electric is an interesting mix and one not yet seen in pokemon.
New idea anyway: I think there should be a fossil pokemon of an ankylosaurus or Euoplocephalous which would pretty much have to be a rock/steel typing as its basically a walking tank. It should have high attack, defence and HP but low speed, and special attack with alright special defence.
Next idea is to make a Baryonyx pokemon. Eventually it could evolve into a Spinosaurus as they are very similar to each other. Baryonyx fed supposedly on fish for its main diet so water typing maybe? And instead of the traditional rock typing associated with fossils make it a dark type as it looks pretty evil. Or perhaps make it dark/fighting - perfect tyranitar counter and in JP 3 the spinosaurus and Tyrannosaurus fought with the spino winning, so hey why not? The possibilities for it are endless
I apologise if these animals have already been mentioned!