Six-legged camel

In an alternate timeline which the Earth was devastated by a nuclear war started by the experiments of Theodore Cassells, the camels, alongside some humans which derived on the mutes, evolved on a six-legged species. these were mounted by the Mutes. A single Mute rider chased the Third Doctor when arrived to the alternate Earth, but was knocked by a metal piece threw by Brod. The camel remained with its unconscious rider.

The camels presumably were erased of the timeline when the History was restored.(A Stitch in Time (comic story))