http://books.google.ca/books?id=TzrNgAsJY1MC&lpg=PP1&...
While the use of zero in India may have been influenced by earlier cultures (e.g. Babylon), it's pretty unlikely there was any direct contact that could have spread the use of zero to mesoamerica. Thus, positional number systems with a zero place-holder have been invented independenly at least twice in human history!