I'm taking a class in college about Dinosaurs and fossils and it's pretty amusing. Very first thing our teacher said was that most of what we know about dinosaurs is wrong and the only true dinosaurs existed late Triassic to Jurassic Periods. All Dinosaurs are land based reptiles, and Marine Reptiles and Flying Reptiles like Pterosaurs aren't dinosaurs.
Starting to get more interested in the class as we move forward. Also according to this, we only have 4 Dinosaur based Fossil Pokemon, the fossils from Gen 4 and from Gen 6.
The entire line's Japanese names iirc are phrases. Like Bulbasaur's name is "Isn't this strange?" and Venusaur's is Strange Flower. Ivysaur's is "it seems strange" or "strange grass". All three are speculated to be based off some Cambrian Mammal like reptile called Dicynodonts or Kannemeyeria (which is a large species of Dicynodont). I think fans are still speculating the origin of these three.
So it could go either way with how ambiguous Bulbasaur's line is. I'll at least file in favor for reptile since they don't look like frogs to me. Can't see a repeat of all one type of species happening again though unless they do all mammal since majority of the remaining 6 choices are mammal with only 1 reptile left.
So far based on each of the fundamental designs of the starters, each fire starter has some representation in the Chinese Zodiac.
Charmander = Dragon
Cyndaquil = Mouse
Torchic = Rooster
Chimchar = Monkey
Tepig = Boar
Fennikin = Dog
Leaving Horse, Ox, Ram, Rabbit, Snake, and Tiger left. Both Ram and Rabbit seem to be favorites for this generation based of speculation and fanart.