Looking for rock art depicting Homo erectus or similar archaic hominids, I found an interesting anthropomorphic drawing done by some Alakaluf natives which may depict a mylodon.
Mylodons in Patagonia
I have already posted on the Mylodon Cave where in the 1890s some apparently fresh remains of mylodon fur and dung were found. This led scientists to believe that the animal which should have become extinct at the end of the last Ice Age, was still alive somewhere out there in the Patagonian wilderness. It was only much later that the bones were dated and their old age proven (they dated to the Ice Age megafaunal extinction period).
However, at Madre de Dios Island, in the South Pacific Ocean, some ancient rock art, drawn by the Alakaluf canoe people, a strange figure was discovered: 
At first I thought it represented a person (actually the article describes it as "an anthropomorphic figure", but it has a third "leg" right between its other two legs; which may either represent a well endowed male or, more likely, a tail (furthermore, the tail is longer than the two legs).
I am quite certain of this because most other drawings of naked men represent them with "normal" sized penis, as can be seen in the composite below which has several human figures (men) drawn at different locations in Patagonia:
The Alakaluf rock art on the other hand is not human-like, actually the opposite: it has an "animal appearance", long and slender, long tailed, long dangling arms. It even looks hairy due to the dashed or dotted technique used in the drawing.
Anyway, I thought that it would be interesting since the Alakaluf natives lived in this region moving along the Patagonian fjords and sounds in their canoes. They could have easily come across an extant Mylodon in relatively recent times (the rock art is not yet dated) and drawn it.
 Ultima Patagonia 2006 Rapport scientifique Expedition franco-chilienne et internationale a Madre de Dios (Magallanes, Chili). Expédition nationale 2006
de la Féderation Française de Speleologie. Association Centre Terre - www.centre-terre.fr. pp. 89+. Image is Fig. 20.
Mairie Richard, Bernard Tourte, Stephane Jaillet, Joel Despain, Benjamin Lans, Franck Brehier, Luc-Henri Fage, Laurent Morel, et al., (2009). Geomorphic and archaeological feautes of coastal caves in Madre de Dios Archipielago (Patagonia, Chile)Proceedings of 15th International Congress of Speleology, Kerrville, Texas, USA, 19-26 july 2009. Symposium on Karst Islands.
 P. Bosch-Gimpera (1964). El Arte Rupestre de America. Anales de Antropología. Vol 1, No 1. pp. 30+. Fig. 9.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia2011 International Year of Forests Copyright 2009-2011 by Austin Whittall ©