Running Dog Appears to Morph Into Human in Creepy Video

There's a mystery brewing down in Mexico, where surveillance footage appears to show a dog running down the street and morphing into a human!!!

Ya gotta see the video ... there's a creature running past someone's house -- an audible bark makes this seem like a dog -- and then as the critter gets a little farther down the road, the figure shapeshifts into a person.

This thing starts out low to the ground as it runs by the house, and then rises up into an upright position.

Whatever this is, it looks like it goes from being down on all fours to standing tall on two legs in the blink of an eye.

The video was shot on September 27 at 1:42 AM and it's left folks baffled ... with all kinds of theories as to what this may show.

Maybe it's a Chupacabra ... but check out the clip, and decide for yourself.