The Hound of Sauron

[Shadow of Udûn]

In the Fellowship of the Ring, after the fellowship abandon Caradhras but before they enter Moria, they are attacked by a band of Wargs. There is a fight, and many are killed. However,

when the full light of the morning came no signs of the wolves were to be found, and they looked in vain for the bodies of the dead

What exactly were these creatures?
They seem intelligent, as Gandalf speaks to one of them, and this combined with their disapearance leads one to believe that they were not ordinary wolves.
Were they ordinary Wargs which were being controlled by Sauron, like the birds who acted as his spies, and who then caused their bodies to disapear?
Or where they another kind of monster?