The Mysterians, 1957
Sirius as a dog also looked pretty wolf-ish, made sense to distinguish them visually for when they fight... Also, with regards to special effects, it's easier to make a convincing monster that looks unrecognizable in the real world than to make a convincing computer-animated form that is easily recognizable to us in real life. like you don't look at the movie werewolf and go "That looks nothing like the real thing!" ... Also that creature design is unforgettable in my opinion! what a movie...