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.

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

"All members of genus Caenolestes are found within the northern Andes Mountains."

Gray-bellied shrew opossums (Caenolestes caniventer) Siciliano Martina 2013a.

Andean shrew opossums or Andean caenolestid (Caenolestes condorensis) . Siciliano Martina 2013b.

Blackish shrew opossums (Caenolestes convelatus) are found within two ranges, western Columbia as well as north central Ecuador. Siciliano Martina, L. 2013c.

Silky shrew opossums (Caenolestes fuliginosus) Siciliano Martina, L. 2014.

The 4 known species of northern shrew-opossums, Caenolestes (Paucituberculata: Caenolestidae), are restricted to the northern Andes of South America. Five specimens of a new species of Caenolestes were collected in Sangay National Park on the eastern slopes of the Andes in Ecuador. Review of museum specimens revealed 6 additional specimens of this species, here named Caenolestes sangay. All specimens were collected in cloud forest habitats from 2,050 to 3,500 m above sea level along a recently constructed highway.

Incan shrew opossums (Lestoros inca) Siciliano Martina, L. 2013d.

Chilean shrew opossums (Rhyncholestes raphanurus) Moore, A. 2013.

References

ISBN links support NWE through referral fees

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

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

A new species of shrew-opossum (Paucituberculata: Caenolestidae) with a phylogeny of extant caenolestids Reed Ojala-Barbour *, C. Miguel Pinto , Jorge Brito M. , Luis Albuja V. , Thomas E. Lee, Jr. , and Bruce D. Patterson

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