The webmasters don’t need to create a separate XML Sitemap file for AMP-pages. John Mueller, Google search rep comments this in response to a question from one of the Twitter specialists.
According to Mueller, the links with the rel = amphtml attribute is enough for Google to index the AMP-version.
It should be mentioned that Google started displaying AMP-pages on the mobile devices in September. Before this page format could be only available in «Top Stories» news block.
Google has added a new tool called "Check AMP page" to Search Console last week. It will help you to find out if there are any errors in the pages of this format and what steps should be taken in each separate case.