This story about monkey communication is worth a pointer:
Having spent months recording the monkeys calls in response to both natural and artificial stimuli, a group led by Klaus Zuberbhler of the University of St. Andrews in Scotland argues that the Campbells monkeys have a primitive form of syntax. This is likely to be a controversial claim because despite extensive efforts to teach chimpanzees language, the subjects showed little or no ability to combine the sounds they learned into a sentence with a larger meaning. Syntax, basic to the structure of language, seemed be a uniquely human faculty.
I can’t tell from the linked story how strong the evidence is, although there are interesting illustrations.