World's smallest fossil monkey found in Amazon jungle. Some 18 million years ago, a tiny monkey weighing little more than a baseball lived in the Amazon rainforest, the smallest fossil monkey known worldwide. The finding is based on a single tooth, twice the size of a pinhead, which scientists recently uncovered in a river bank in southeastern Peru. The specimen helps bridge a 15-million-year gap in the fossil record for New World monkeys. Source 8e.