Fish and Game officials said that the male mountain lion that injured the dog near Preston, Idaho, was killed last week near the Utah border.
What the hunter discovered after examining the corpse can only be described as bizarre, even monstrous, CNN reported.
A photo released by Idaho Fish and Game shows the big cat had another set of fully-formed teeth and whiskers growing out of the top of its head.
They say it's possible the teeth could be the remnants of a conjoined twin that died in the womb and was absorbed into the other fetus. They then grew on their own.
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Another explanation is a so-called 'teratoma' tumour. This type of abnormality, whose Greek name translates to 'monster tumour,' can grow teeth and hair. In humans, it can grow fingers and toes.
Mountain lions are common, though rarely seen, in Idaho and can be legally hunted. They usually prey on deer, elk, moose and other wild animals but sometimes attack domesticated pets and livestock.
The owner of the dog, badly injured by the mountain lion said his pet was recovering. The dog suffered puncture wounds to its body, the report said.