I'm looking for examples of typological traits that are common in languages of the Americas and rare in languages elsewhere. Traits could be at any level of description — phonological, morphosyntactic, semantic, whatever.
Edit To clarify, I don't need to find traits that are common throughout the Americas. It would be enough to say, for instance, "XYZ is quite common in Mesoamerica, and it's rare everywhere else, including the rest of the Americas and all of the Old World."
(I'm looking for examples in support of the idea that it's important to do research on languages of the Americas. I'd like to go beyond the general principle that typological balance is A Good Thing, and be able to pull out a few concrete examples of the form "If we'd never studied languages of the Americas, we wouldn't know about XYZ.")