A while ago I mentioned that there might be unrecognized survivors of South America’s local placental lineages (Meridiungulata and Xenarthra). Unrecognized because very divergent, like golden moles, which are Afrotheria. Shoot, maybe even metatherians or some relative of necrolestes.
But where to look? Tepuis might be good candidates. They’re remnants of a sandstone plateau that once covered the area between the north border of the Amazon basin and the Orinoco. These mesas are isolated from the surrounding forest and have lots of endemic flora and fauna. Some have almost constant cloud cover and have hardly been explored.