Bernard Heuvelmans mentions in his Checklist of Supposedly Unknown Animals (Cryptids) from CRYPTOZOOLOGY makes note of amphibious dinosaurian beasts reported in Colombia, Ecuador, Peru, Brazil and Bolivia, but specifically not of the Sauropod type. Part of the reason why is that they are connected to these reports of large three-toed tracks, much like the ones ascribed to the "Congo Dragons" in Africa. For this reason Heuvelmans supposes the living dinosaurs of South America must be ornithopods, more like the Iguanodon. Indeed, Karl Shuker speaks of one of the "Iguanodon" reports from Colombia, presumably identified as such on the basis of the tracks. This can be said to be independant confirmation of Heuvelmans..
What is far more likely is the possibility that Fawcett (and the others) saw the tracks of a supposedly-extinct giant Ice-Age Mammal, the Toxodon, which happened to have three hoofed toes (as does a tapir or a rhino) Life reconstruction of a Toxodon and a depiction of its skeleton. Note the three-toed feet Representation of the South American Water Bull from an early map. The Water-Bull (Toro-agua) is a legendary creature, which just might be intended to depict a surviving Toxodon. Below is a fossilized track of a Toxodon as excavated in South America: it was labelled by the news services as the track of a "Toro" (Bull) despite the fact that it obviously shows three toes on it. Below are some artistic depictions of creatures, which are pointed to by some cryptozoologists in support of the idea that Toxodons persisted into historical times and were known to the civilized peoples that lived in the Andes. The line drawing is mine comparing two different depictions called Alpacas in an illustration in the Hamlyn book South American Indian Mythology; it would seem to me that the larger animal has a pronouncedly heavier build, smaller ears and what could be an enormous open mouth. The Pottery vessel is also from Andean Peru and is from a Creationist site where the animal is identified as a Toxodon. The two depictions are in general agreement. Other depictions of Toxodons are cited especially in the region of Tiahuanoco (Tiwanaku)