Zombie dragon turtle
I checked the errata and realized why it appears so messed up: its not a "zombie" dragon turtle, it's a "zombie dragon" dragon turtle. Zombie Dragons appear in Draconomicon. Among other things, they use the base HD of the creature, and get many of the creature's base abilities, including a weakened breath weapon, if the original dragon had it, movement modes like flight, immunities, etc. It also explains the apparent error in OOTS: Paladin Blues of Xykon animating a ancient silver dragon: using the zombie dragon template it is possible.
Now it would require the DM to houserule that all attempts to animate dragons produce Draconomicon zombie dragons, if the HD is below double character level. Draconomicon zombies are a bit better than normal ones, so this would be a boost t animate dead, so might not be suitable for some campaigns.