Biologists are now working to find out what caused the lion's deformity. (Associated Press photo)
A hunter tracking down a mountain lion that attacked a dog in the US state of Idaho has stumbled upon a rare deformed big cat, triggering an Internet sensation on the biological mystery.
Officials of Fish and Game, the department that manages Idaho's wildlife resources, said that the male mountain lion that injured the dog near Preston 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.
Wildlife officials say they have never seen a deformity like that - but have offered up several theories.
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.
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.
Fox News reported that the deformed mountain lion has become an Internet sensation after a photo featuring its unusual deformity was posted online and shared around the world.
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.