The Perro Cimarrón is Uruguay's national dog-breed with a history stretching back to the colonization of the country. It is a decendant of the dogs brought over to the continent by the Spanish & Portuguese explorers. The dogs of the explorers was of mixed parentage, mostly working Molossers and hunting dogs. These dogs were left in Uruguay, and a huge population of wild dogs was formed. Uruguay had such problems with wild dogs that every citizen was obligated to hunt and kill the wild dogs.
Some farmers did catch dogs instead of killing them, and they soon realized the dogs usefullness as watchdogs and at farmwork, especially working on the cattle. From these dogs the modern Cimarrón developed, probably with some infusion of additional Molosser blood later.

Perro Pampa, the wild dog of Uruguay in the old days.

This breed is still almost unknown outside of Uruguay, but the Uruguayan Kennel Club are working to get the breed known and finally international recognized by the FCI, but this will still take many years to accomplish.
There have been a few exports from Uruguay, and some specimens now lives in Europe. There sure will be more exports in the years to come, when rare breed entusiasts discover the Cimarrón Uruguayo.