Shrew opossum

The order Paucituberculata contains the six 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 seven genera in South America. Today, just three genera remain. They live in inaccessible forest and grassland regions of the High Andes. Insectivores were entirely absent from South America until the Great American Interchange three million years ago, and are currently present only in the northwestern part of the continent. Shrew opossums have lost ground to these and other placental invaders that fill the same ecological niches. Nevertheless, the ranges of shrew opossums and insectivores overlap broadly.

Shrew opossums (also known as rat opossums or caenolestids) are about the size of a small rat (9–14 cm long), with thin limbs, a long, pointed snout and a slender, hairy tail. They are largely carnivorous, being active hunters of insects, earthworms and small vertebrates. 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. They seem to spend much of their lives in underground burrows and on surface runways.

Largely because of their rugged, inaccessible 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.

Classification
Within the family of the Caenolestidae, six species are known:


 * Genus Caenolestes
 * Gray-bellied Caenolestid, Caenolestes caniventer
 * Andean Caenolestid, Caenolestes condorensis
 * Northern Caenolestid, Caenolestes convelatus
 * Dusky Caenolestid, Caenolestes fuliginosus
 * Genus Lestoros
 * Peruvian or Incan Caenolestid, Lestoros inca
 * Genus Rhyncholestes
 * Long-nosed Caenolestid, Rhyncholestes raphanurus

However, Bublitz suggested in 1987 that there were actually two Lestoros and Rhyncholestes species (those listed here plus L. gracilis and R. continentalis). This is, however, not accepted by most scientists.