Animals can think IMO, but obviously do it non-linguistically, so it's very hard for us to imagine what processes they use. I had a dog that went blind and he had to learn all sorts of things to get around. He knew exactly how many steps there were in my house, for example, but how he counted them was a mystery to me.
Japan, where I'm living now, is inundated with unbelievably clever crows. How on earth did they work this one out:
Books, Naturally - National Zoo| FONZFor instance, crows of many species learn to drop nuts and other hard food items like clams from just the right height over just the right hard substrate to break them open. But carrion crows living near a driving school in Japan learned to use cars to do the work for them. These crows wait for traffic to stop at an intersection, fly down and place the nuts in front of the tires of the stopped vehicles, then retrieve the nutmeats from the nuts cracked open when the cars ran over them. Over the last 20 years, this behavior gradually spread beyond the immediate vicinity of the school—and people have begun to help the crows by deliberately running over the nuts on the road!
Not only other animals, but humans too. The skills of a baby before it obtains linguistic communication are well documented, including those skills communication is best used for - getting what we want and social interaction.
As for whether thought exists independently from language, it depends what 'thought' is to you. I'm currently using my fingers to type - what I'm typing is governed by language, however, how I type it isn't governed by language at all. I can do many things which require no linguistic ability whatsoever, but you could say they require thought.
Even with more higher functioning thought, a distinction has to be made about what is language and what is a concept. Concepts aren't language. For example, the concept of object permanence - that an object out of sight still exists. This develops in babies before they have any linguistic abilities.
This has been a very interesting thread -- for which language has probably proved inadequate.
I asked someone who taught linguistics in one of the best universities in the U.S about this question before, and she had agreed on what Linguist said. She didn't agree that language and tought occured simultaneously; however, we see both Vigotsky and Whorf critisizing Piage's idea in this case. Yes, there is still a controversy.