Fine, but we’re also discussing animals with the capacity to become sentient, which in this discussion seems to be assimilated to the ability to make and use tools, master fire, etc. That imposes stricter limits than simply the possibility of animal life.
We’ve also got to distinguish between intelligent creatures and creatures that are likely to build spaceships. It’s pretty easy to imagine an Earth species of elephant or dolphin or octopus that has intelligence comparable to a human, but would such a species be likely to smelt metal, live in cities, build electical generators, fly airplanes and rockets, and travel to the Moon?
And of course, an intelligent dolphin or elephant or octopus or dinosaur is very unlikely to think much like a human. Human ideas about mating, child-raising, kinship, sociality and such aren’t going to make sense to a species of intelligent octopi that lay thousands of eggs and die soon after the eggs are hatched. And while there are several species of animals on Earth that have rudimentary tool use, there’s never been another species of tool users like humans. Tool use seems to my intuition to be even more unlikely an adaptation than language and extreme sociality.
I think this is not so much because of any scientific principles as it is production costs. If you want a man to play an alien, you get one that’s man-sized. One-inch tall men are hard to find in Hollywood, and they’re probably not union. Cartoons, books, and clever films often have races of unusual size. From Tolkien to Carrol, from The Twilight Zone to The Simpsons, the concept has been explored.