The crayfish thing has too different a face for every evolution. Colosstrich needs to feel more together as a design and there should be hints of where its headed in the second stage, like how the middle stage between the little fire lizard and Charizard was a meaner leaner lizard. The fire dog is alright but there already is an Arkanine and a wolf with a volcano on its back would be a much more fat wolf. On concept alone I like the seafoodmon and firewolf best.
Art wise your art looks a bit flat. Try and think of your drawings as 3d objects and sketch the volumes of those out before you put down the final lines.