I didn't notice at first, but the stage 4 boss is an R-Type style battle cruiser. And the boss right after looks like their version of "Gomander & Outslay" or whatever they're called.
In the level after that one, there's a dragon with a dobkeratops tail, who is suddenly metallic after being defeated in the previous game...
Maybe this is old news because these are pretty old games.
Irem and Konami had some similar themes with these games, like the bio-mechanical enemies. Some of it is also hardware limitations. At the time, it was standard practice to use many round sprites to make a tail or snake, so you see lots of similar designs across different games. Ridley from Super Metroid used the multi-sprite tail as well.