origin - Does Kanima's mythology match any historical stories/works or is it only written for Teen Wolf?

According to this interview with Teen Wolf creator Jeff Davis, the Kanima is, at least loosely, based on South American mythology. He says the original Kanima was a "were-jaguar" (that is, half-man, half-jaguar; named in analogy with "werewolf"). The Wikipedia article on the were-jaguar suggests that it may have been inspired by a venomous toad thought to resemble a jaguar. However, the Teen Wolf version is more like a reptile. Davis says

I ... saw CONAN THE BARBARIAN. And one indelible image that was left in my mind was the scene where James Earl Jones starts to transform into a gigantic snake. That look stuck with me and that’s what we went for

So the name may come from South American mythology, but the appearance has a more modern origin.