I would look into the model class, particularly the Ender Dragon model class, to see how the wings are animated.
If you want a good place to start, looking at the chest model class can help. It shows the barebone basics of how a multi-boned/part mob works, with each 'box' having a different rotation around whatever axis, allowing you to rotate it somewhat like this:
public ModelRenderer segment;
public ModelSnake() {
this.segment.addBox(0.0F, -5.0F, -14.0F, 14, 5, 14, 0.0F);
this.segment.rotationPointX = 1.0F;
this.segment.rotationPointY = 7.0F;
this.segment.rotationPointZ = 15.0F;
}
public void renderAll() {
this.segment.render(0.0625F);
}