http://www.galeon.com/norteargentino/leyendas.htm

A short summary:
Ucumar is a “bear-man” that lives in the wilderness and mountain ranges in the frontier with Bolivia…
The legend says, “that the mother of Ucumar is a young huntress that was lost in the jungle and
was captured by a bear. They gave birth to the whole Ucumar race”.
Description:
It has a big belly, long, black hair, the hair covers a semi-human face, legs are similar to a bear, but the big toe is wide open. Some people says it has the feet backwards, which disorients the people who follows its tracks. Tracks are common near water sources.
Small eyes, it posseses an extraordinary strenght and if the wind is favorable, it is possible to hear its strong howling. People is afraid of Ucumar, because it kindnaps humans of the opposite sex, and procreates with them.
Kidnapped people tells always a similar story: they lived in a cave, but Ucumar covers the entrance of the cave with a big stone. When the hybrids of Ucumar and the humans grow up, they inherit the great strenght of the beast and are able to remove the stone, thus liberating the kidnapped people, who is able to return to their villages. Ucumar is generous with the captured people, it takes care of them, it feeds them with honey and fruits”.

[Backward feet and kidnapping are also said about central american Sisimite. The big stone stories and the people returning to their villages appear also in some native american bigfoot stories. The indians also call Ucumar to the andean bear, and this remind me of some european folk tales, where the bear man is also the wild man in some cases]

Is it possibly that the Ucumar Zupai is a ground sloth that adopts a bipedal plantigrade stance? That would explain the large feet, the claws, and possibly the teeth as well. After all, we don’t really know what the relationship between a surviving ground sloth and fossil ground sloths would be. And I’m not sure you could safely assume that a ground sloth would be as slow-moving as its arboreal cousins.

Also, a ground sloth would be more “bear-like” than a bipedal ape.

Ucumar Zupai = Bear Devil (or more likely, Devil Bear). See comment here.

Unless you disagree that ukumari/ucumari/ucumar are the same word in Quechua. In which case, you know more Quechua than I do, which is not unlikely.