On Earth in the distant past, Ian Chesterton found an animal skull with no horns or antlers, suggesting that it came from a horse (TV: An Unearthly Child) or deer. (PROSE: Doctor Who and an Unearthly Child)
The Judoon had horns. Removing the horn of a Judoon captain was considered a dishonour and therefore the worst of insults. (TV: Fugitive of the Judoon)