Shrew opossum

Shrew opossums Fossil range: Late Oligocene–Recent PreЄ Є O S D C P T J K Pg N
Caenolestidae
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Infraclass: Marsupialia Superorder: Ameridelphia Order: Paucituberculata Ameghino, 1889 Family: Caenolestidae Trouessart, 1898
Genus
Caenolestinae Caenolestes Lestoros Rhyncholestes Pseudhalmarhiphus (†) Stilotherium (†) Pichipilinae (†) Phonocdromus (†) Pichipilus (†) Pliolestes (†)

Paucituberculata is an order of New World marsupials, whose extant members comprise a single family, Caenolestinae, and are known as shrew opossums, rat opossums, or caenolestids. The living shrew opossums, which are grouped into three genera of seven known species (as of 2014), are characterized by small size, shrew-like appearance; short robust limbs with five digits and the two outside digits longer than the middle three; a distinctive flap of skin on the upper lip; long tails; diprotodont dentition; upper canines that are large stabbing teeth; lower middle incisors that are large and with a forward slope; and the lack of a pouch in the females. They share the unusual characteristic of paired sperm with members of Didelphimorphia (opossums). Caenolestids are found in western South America.

Shrew opossums play a role in food chains as opportunistic feeders, consuming invertebrates, such as beetles, crickets, earthworms, centipedes, grasshoppers, spiders, and so forth, as well as plant material and fungi, while being consumed by a variety of predators.

Overview and description

Paucituberculata (shrew opossums) is one of three orders of New World marsupials, the others being [[Microbiotheria[[ (colocolos) and Didelphimorphia (opossums). Unlike placental mammals (Placentalia), almost all members of Marsupialia lack the placenta that connects the mother with the developing fetus in the womb. Some marsupials have a rudimentary placenta that functions for only a short time, such as the bandicoot. Marsupials also differ from placental mammals in their reproductive traits. The female has two vaginas (the tubular tract leading from the uterus to the exterior of the body). Both of the vaginas open externally through one orifice, but lead to different compartments within the uterus. Males usually have a two-pronged penis, which corresponds to the females' two vaginas.

Marsupial females typically have an external pouch in which the immature young are raised after birth until early infancy. The newborn typically crawl to this pouch after birth, and attach themselves to milk-secreting teats (nipples), and are nursed until they can survive outside the pouch. However, females of the Paucituberculata order lack a pouch.

Marsupials are native to Australia, New Guinea, Tasmania, and the Americas. Ameridelphia is a taxonomic grouping (traditionally a superorder) that includes all marsupials living in the Americas except for the Monito del Monte (Dromiciops), the only extant member of the Microbiotheria order. Australidelphia' is a taxonomic grouping (superorder) that contains roughly three-quarters of all marsupials, including all those native to Australasia and a single species from South America, Monito del Monte. The most basal of all marsupial orders is believed to be the two South American groups Didelphimorphia and Paucituberculata, with the former probably branching first. This indicates that Australidelphia arose in South America along with the other major divisions of extant marsupials, and likely reached Australia via Antarctica in a single dispersal event after Microbiotheria split off. As recently as 20 million years ago, at least seven genera of the Paucituberculata order were in South America. Today, just three genera remain.

Extant shrew opossums are about the size of a small rat, with short robust limbs, with each limb having five digits and outer two digits longer than the middle three digits; the feet are not syndactylous. They have an elongated face with a pointed snout, small eyes, and a slender, long, hairy, rat-like tail, which is not prehensile but is used for balance and support while climbing. Their femurs are slender relative to the very heavy humeri. They have a distinctive flap of skin on the upper lip; this lip flap may help prevent debris from being ingested or interfering with their whiskers.Caenolestes condoresnis has an average weight of 48 grams (1.69 ounces) and length of 260 mm including the tail, while Lestoros inca ranges from 20 to 39 grams in weight and 155 to 195 in length, including the tail (Siciliano Martina 2013a, 2013b, 2013c, 2013d, 2014; ADW 2001).

The dentition of shrews is unique among marsupials. the lower jaw exhibits a large incisor in the middle that is large and with a forward slope and is surrounded by six or seven small, simple incisors, canines, and premolars, all of which are separated by a space. The upper jaw has large and stabbing canines. the first three molars on the upper jaw have a hypocone. The total number of incisors are reduced. The dental formula for genus Caenolestes is I 4/3, C 1/1, P 3/3, M 4/4, 46 teeth total, while for shrew opossums in general it is 4/3-4, 1/1, 3/3, 4/4, 46 or 48 teeth in total (Siciliano Martina 2013a, 2013b, 2013c, 2013d, 2014; ADW 2001).

Caenolestids have peculiarly paired sperm, a trait that they share with members of Didelphimorphia (opossums) (Siciliano Martina 2013d; ADW 2001). It is a characteristics that adds to the evidence for uniting Paucituberculata and Didelphimorphia in the Cohort Ameridelphia (Siciliano Martina 2013d; ADW 2001). No Australian marsupial shows this trait of paired sperm (Siciliano Martina 2013d; ADW 2001). Members of Didelphimorphia, however, have a prehensile tail (a characteristic also not found in any Australian marsupials, nor in Paucituberculata).

Shrew opossums 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.

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. Shrew opossums have lost ground to these and other placental invaders that fill the same ecological niches. Nevertheless, the ranges of shrew opossums and shrews overlap broadly.

Classification

Within the family of the Caenolestidae, seven species are known, as of 2014, with the most recent species, Caenolestes caenolestid identified in 2013 by Ojala-Barbour et al.:

• Genus Caenolestes
  • Gray-bellied caenolestid, Caenolestes caniventer
  • Andean caenolestid, Caenolestes condorensis
  • Northern caenolestid, Caenolestes convelatus
  • Dusky caenolestid, Caenolestes fuliginosus
  • Eastern caenolestid, Caenolestes sangay
• Genus Lestoros
  • Peruvian or Incan caenolestid, Lestoros inca
• Genus Rhyncholestes
  • Long-nosed caenolestid, Rhyncholestes raphanurus

Overview of species

All members of genus Caenolestes, the northern shrew opossums, are found in the northern Andes of South America. They are solitary and primarily active at night and in the early evening. They are adept climbers, but terrestrial and reside in tunnels during the day (Siciliano Martina 2013b).

Caenolestes caniventer. Gray-bellied shrew opossums are found mainly on the Pacific slopes of the Andes in central Ecuador and northwestern Peru, typically at elevations above 1500 meters. The coarse thickness of their brownish-black fur offers a distinction from their close relative, C. fuliginosus the silky shrew opossum (Siciliano Martina 2013a).

Caenolestes condorensis. The Andean shrew opossums or Andean caenolestid have only been noted in the eastern slopes of the Andes in Ecuador, but may well exist in the same environment in Peru. The area they are found is unique in that it has almost constant precipitation between rain and cloud condensation, drought is almost never experienced, and the area may only experience a couple of hours of sunlight in a day. They have coarse fur like the gray-bellied shrew opossums but can be distinguished by the upper canines (Siciliano Martina 2013b).

Caenolestes convelatus. Blackish shrew opossums have been found in two ranges, one in western Columbia and the other in north central Ecuador. They have been foud from 1,100 meters in elevation to 4,100 meters (Siciliano Martina 2013c).

Caenolestes fuliginosus. Silky shrew opossums have been found in Columbia, northwestern Venezuela, and central Ecuador, between 1,400 and 4,300 meters. They are more delicate in build than other members of Caenolestes and tend to be smaller. They have semi-prehensile tails that help in climbing (Siciliano Martina 2014).

Caenolestes sangay. This species was reported in 2013 by Ojala-Barbou et al. The specimens were found in Sangay National Park in Ecuador, on the eastern slopes of the Andes, with additional specimens found in a review of holdings in museums.

Lestoros inca. The Incan shrew opossums have been found in the norther Andes of Bolivia and Peru, at elevations from 1800 to 3600 meters. There are suggestions that they may prefer environments that are less wet than other members of this order, although they also have been found in wet mossy areas. They are similar in appearance to members of the Caenolestes genus but have smaller upper canines (Siciliano Martina 2013d).

Rhyncholestes raphanurus. The Chilean shrew opossums have only been reported in a small geographic range in southern Chile, Chiloe Island, and a small area of southern Argentina, residing at elevations from sea level to 1135 meters, and most commonly caught at below 600 meters. They live in temperate forest habitats. Males have single rooted, conical upper canines and females have double-rooted canines. They are quite small in size, ranging from 10 to 13 centimeters (Moore 2013).

References

ISBN links support NWE through referral fees

• Animal Diversity Web (ADW). 2001. Paucituberculata. Animal Diversity Web. Retrieved May 22, 2014.

• Moore, A. 2013. Rhyncholestes raphanurus, Chilean shrew opossums. Animal Diversity Web. Retrieved May 22, 2014.

• Ojala-Barbour, R., C. M. Pinto, J. Brito M., L. Albuja V., T. E. Lee, and B. D. Patterson. 2013. et al. A new species of shrew-opossum (Paucituberculata: Caenolestide) with a phylogeny of extant caenolestids. Journal of Mammalogy 94(5): 967-982. Retrieved May 28, 2014.

• Siciliano Martina, L. 2013a. Caenolestes caniventer, gray-bellied shrew opossums. Animal Diversity Web. Retrieved May 22, 2014.

• Siciliano Martina, L. 2013b. Caenolestes condorensis, Andean caenolestid. Animal Diversity Web. Retrieved May 22, 2014.

• Siciliano Martina, L. 2013c. Caenolestes convelatus, blackish shrew opossums. Animal Diversity Web. Retrieved May 22, 2014.

• Siciliano Martina, L. 2013d. Lestoros inca, Incan shrew opossums. Animal Diversity Web. Retrieved May 22, 2014.

• Siciliano Martina, L. 2014. Caenolestes_fuliginosus, Silky shrew opossums. Animal Diversity Web. Retrieved May 22, 2014.

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