Argentine Armadillo Abattoir Question

AVI found a report about what looks like 19,000BC butchery in far South America. Why, he asks, did such early humans not do in the megafauna, as later ones seem to have done (though there are claims for climate change and meteors, and possibly all-of-the-above)?

I've seen a few artists' reconstructions showing fur-clad proto-Indians doing in mammoths. The weapons are generally spears, and spear points show up in mammoth bones. I don't recall seeing any images that included another tool, developed about 21,000BC (perhaps not in time for the earliest waves into the Americas): dogs.

I'd think it would be much safer and more effective to go after a mega-critter with a spear after it has been nicely tired out by your own private wolf-pack, or while it is confused which foe to face first.

I wonder how you'd estimate the effectiveness of hunting a lone mammoth (not going to have much success attacking a herd) with and without dogs to chivvy it. Without practicing various tactics on elephants, of course.

UPDATE: Found a picture.