As far as I can tell, there's only one mutant of each species. Although are we 100% sure that all of these are the mutated variants? The Rex, Ceratosaurus, and Ankylosaurus for sure are; but when compared to, say, the mutant Ankylosaurus, the "mutant" Stegosaurus, Trike, and Parasaurolophus seem rather tame as far as exaggerated body parts go, they just seem to be a different color. Are we certain that those aren't just a different color and not mutated? This is all just speculation from watching tons of gameplay videos and livestreams, mind you, as I can't actually play the game yet.
And I believe if you see the dinosaur in the binocs and the species doesn't show up, it is mutated. The game manual says that DinoHunt Inc. officially denies having any mutated dinosaurs on the island, so it makes sense that they won't show up on their equipment if you find one.
"No, sir. I'll take my Tyrannosaurus without feathers, thank you."