| Shrew opossums Temporal range: Priabonian-Recent
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| Caenolestes sangay | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Infraclass: | Marsupialia |
| Order: | Paucituberculata |
| Family: | Caenolestidae Trouessart, 1898 |
| Type genus | |
| Caenolestes Thomas, 1895
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| Genera | |
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| Synonyms | |
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The family Caenolestidae contains the seven surviving species of shrew opossum: small, shrew-like marsupials that are confined to the Andes mountains of South America.[1] The order is thought to have diverged from the ancestral marsupial line very early. They were once included in the superorder but it is now known that Ameridelphia is paraphyletic, having given rise to Australidelphia, and thus could be considered an evolutionary grade.[2] Genetic studies indicate that they are the second most basal order of marsupials, after the didelphimorphs.[2] As recently as 20 million years ago, at least seven genera were in South America. Today, just three genera remain. They live in inaccessible forest and grassland regions of the High Andes.
Shrews 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. Traditionally, it was thought that shrew opossums lost ground to these and other placental invaders that fill the same ecological niches. Evidence suggests, however, that both groups not only overlap, but do not seem to be in direct competition, and the marsupials' larger size seems to imply that they prey on shrews and rodents.[3] Several opossums, such as Monodelphis, also occupy small insectivore niches.
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 burrows and on surface runways. Like several other marsupials, they do not have a pouch, and it appears that females do not carry the young constantly, possibly leaving them in the burrow.[4]
Largely because of their rugged, inaccessible habitat, they are very poorly known and have traditionally been considered rare. Several ecological factors, including density of forest, contribute to the part of the forests the shrew opossums occupy. Recent studies suggest they may be more common than had been thought. Their karyotype has also been described through contemporary research in order to better understand this organism.[5]
- ^ Gardner, A.L. (2005). "Family Caenolestidae". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 19–20. ISBN 978-0-8018-8221-0. OCLC 62265494.
- ^ a b Nilsson, M. A.; Churakov, G.; Sommer, M.; Van Tran, N.; Zemann, A.; Brosius, J.; Schmitz, J. (2010-07-27). "Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions". PLOS Biology. 8 (7): e1000436. doi:10.1371/journal.pbio.1000436. PMC 2910653. PMID 20668664.
- ^ Luis, A. V.; Patterson, B. D. (1996-02-16). "A New Species of Northern Shrew-Opossum (Paucituberculata: Caenolestidae) from the Cordillera Del Condor, Ecuador". Journal of Mammalogy. 77 (1): 41–53. doi:10.2307/1382707. JSTOR 1382707.
- ^ Patterson (2008), page 126
- ^ Kelt, Douglas A.; Martínez, David R. (1989). "Notes on Distribution and Ecology of Two Marsupials Endemic to the Valdivian Forests of Southern South America". Journal of Mammalogy. 70 (1): 220–224. doi:10.2307/1381695. JSTOR 1381695.