If you consider that the tail is part of the vertebrae, then I guess it can be argued that several animals use their vertebrae as a weapon or for a form of self protection.
Mammals that use their vertebrae for protection
The best examples of creatures that use their vertebrae for defense or protection are monitor lizards and komodo dragons.
For example, here's a Youtube clip of a komodo dragon tail whipping an unsuspecting girl:
Obviously, they are both REPTILES and actually very few mammals use their spines to protect themselves, as a mammals spine is usually fairly sensitive.
However, I have found one example of a mammal using its vertebra to protect itself:
Meet the Potto
These guys have a weird little trick they use to defend themselves:
They have spines on their vertebrae, which stick out from their furry neck and shoulders. These spines are so sharp they can be even used as a weapon: essentially allowing the potto to "neck-butt" enemies.
More often though, they use them as a shield, and may also make it trickier for predators to land the "killer bite" which is usually aimed at the neck or head area.