http://www.angelfire.com/or2/marvel/images/longshot.jpg
and his bones weigh less because they r hollow just ta let ya know
As I recall, an issue of X-Force depicted Hank McCoy, the Beast, announcing that Shatterstar and Longshot share identical DNA. However, Shatterstar is said to be from 100 years later than Longshot in the Mojoverse timeline, and one has to wonder how two people with supposedly identical DNA, or even just quite similar DNA like that of a father and son, could have such major genetic differences as a different number of fingers.
So I'd say Hank goofed there, or maybe it was a plotline that they changed, like the infamous Third Summers Brother plot. Either way it's a moot point.