The biological order Paucituberculata contains the five surviving species of shrew opossum: small, shrew-like marsupials which are confined to the Andes mountains of South America. It is thought that the order diverged from the ancestral marsupial line very early. As recently as 20 million years ago, there were at least 7 genera in South America. Today, just 3 remain.
Shrew oppossums are largely carnivorous. Although typically small—about the size of a small rat at 9 to 14cm long—they are active hunters of insects, earthworms, small vertebrates and insects. They have small eyes and poor sight, and hunt in the early evening and at night, using their hearing and long, sensitive whiskers to locate prey.
Largely because of their rugged, inacessable habitat, they are very poorly known and have traditionally been considered rare. Recent studies suggest that they may be more common than had been thought.