The order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Paucituberculata (icon) contains the six surviving species of shrew opossum: small, shrew

Shrew

A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...

-like marsupial

Marsupial

Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...

s which are confined to the Andes

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

 mountains of South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

. 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. Insectivore

Insectivora

The order Insectivora is a now-abandoned biological grouping within the class of mammals...

s were entirely absent from South America until the Great American Interchange

Great American Interchange

The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...

 three million years ago, and are currently present only in the northwestern part of the continent. Shrew opossums have lost ground to the these and other placental

Eutheria

Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...

 invaders that fill the same ecological niche

Ecological niche

In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...

s. 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 insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, earthworm

Earthworm

Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...

s 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 whisker

Whisker

Whisker may refer to:* an element of box plots* cat's whisker diode, a thin wire used as a contact on a crystal radio receiver* facial hair, hair on the face of a human* vibrissa, a hair on the face of a mammal, used for sensing the surroundings...

s 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
  Caenolestes
  The common shrew opossums , are members of the Caenolestidae family....
  
  
  • Gray-bellied Caenolestid, Caenolestes caniventer
  • Andean Caenolestid
    Andean caenolestid
    The Andean caenolestid , or Andean shrew opossum, is a species of shrew opossum in the family Caenolestidae. It is known from one location at an altitude of 2000 m in the Cordillera del Cóndor in Ecuador....
    
    , 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.