Many of the fossil Pokemon aren't based off of Dinosaurs, but more off of sea life. Both Kabutops, Omastar, and they're whole lines are water type. Kabtops resembles eurypterids, prehistoric arthropods which hunted in seas and rivers. Kabuto is based off of horseshoe crabs and Trilobites. Both Omastar and Omanite are based off of a type of ammonite, which are extinct marine animals. Cradily and Lileep are based off of sea lilies. Armaldo is based off of Anomalocaris, which lived in the water. Anorith is also based off of a Anomalocaris, but also appears to be based on a Trilobite, which both lived in the water. Aerodactyl is based off a pterosaurs, and Rampardos and Bastiodon are definitely not water type or anything related to water, but we should definitely look to water as one of the probable fossils in 5th generation. Personally, I want a fossil tree (Something like Sudowoodo and Abomasnow mixed) and a fossil Kronosaurus. Although the Idea of an electric fossil sounds cool, some millions of years ago, the animals probably didn't have electricity. (I can see flaws with this argument, though)
(All the facts on what Pokemon are based off of came from Bulbapedia)