[quote=Windstormugly]
I'll just have to add to this I feel.Size and mass changing morphing are well within the science of most sci-fi stories. And to be a shape-shifter means being able to take a wide variety of forms, whereas this would be a single shape-change, logically a compaction of the bones and tissue. Which is not that special I might add.
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If you compact the tissue than the dragons would be very stiff unless they hardly had tissue to begin with if they are going to be tightened that greatly or there would hardly be much of a change. What I was suggesting is basically the same thing but with the latter where there isn't too much of a dramatic change. I'm not saying size and mass changing aren't within sci-fi's forte but I am saying that a dragon [b]completely[/b] changing naturally would be unlikely. 

Also no, to be a shape sifter all they need is the simple ability to change from one shape to another naturally, though then there is the problem of if they were capable from changing from one shape to another than they are also capable in changing into other shapes as well and would more likely be doing such on a cellular level. 

What's being done here is that the dragon is still a dragon but is also capable in taking a more bipedal stance added with the more feral one too. Both of which is basically what spike was talking about and while main muscles would probable compact like you said their main body structure wouldn't take too much of a dramatic change. If their legs are hind, even when bipedal their legs would still hold a similar shape overall. But a dragon shifting it's body from the classical feral Dragon (more likely what spike is wanting) to a more human shape (which would take too dramatic of changes to efficiently happen, especially in the feet and legs area.)

Also, you must be who jest has been talking about, if I'm correct. A pleasure to meet you.