From the original Monster Manual…
W is for Wyvern
The original art for this is for sale here.
You can follow the other “W” entries as people post them to Twitter this morning by following the #AlphaBeasts hashtag. View all previous AlphaBeasts entries at the AlphaBeasts Tumblr: http://alphabeasts.tumblr.com/. You can also find some submission guidelines there, as well as links to bestiaries and lists of creatures.