Nope. c: All are common, and the stuff thats 'Uncommon', really isn't, it just isn't seen as often.
Ex; Out of ten Timber Dwarf Dragons, one will be a gnome that are common. Five will be common (Not including Gnome). Three will be 'uncommon' (With the ram horns, for example.) One will be the 'average rare' (Long horns, ect.) The very rare appear from once in every twenty, to sometimes once in every forty.
c:
% wise,
20% Gnomes
50% Common
20% 'Uncommon'
7% 'Average Rare'
3% Very Rare, Super Rare.