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Placental mammals are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young which are then nurtured for a period inside the mother's pouch.
The order Insectivora is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order Eulipotyphla, within the larger clade Laurasiatheria, which makes up one of the most basic clades of placental mammals.
Shrews are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to different families or orders.
Eulipotyphla is an order of mammals suggested by molecular methods of phylogenetic reconstruction, which includes the laurasiatherian members of the now-invalid polyphyletic order Lipotyphla, but not the afrotherian members.
Elephant shrews, also called jumping shrews or sengis, are small insectivorous mammals native to Africa, belonging to the family Macroscelididae, in the order Macroscelidea. Their traditional common English name "elephant shrew" comes from a perceived resemblance between their long noses and the trunk of an elephant, and their superficial similarity with shrews in the order Eulipotyphla. However, phylogenetic analysis has revealed that elephant shrews are not properly classified with true shrews, but are in fact more closely related to elephants than to shrews. In 1997, the biologist Jonathan Kingdon proposed that they instead be called "sengis", a term derived from the Bantu languages of Africa, and in 1998, they were classified into the new clade Afrotheria.
The order Afrosoricida contains the golden moles of Southern Africa, the otter shrews of equatorial Africa and the tenrecs of Madagascar. These three families of small mammals have traditionally been considered to be a part of the order Insectivora, and were later included in Lipotyphla after Insectivora was abandoned as a wastebasket taxon, before Lipotyphla was also found to be polyphyletic.
Tenrecomorpha is the suborder of otter shrews and tenrecs, a group of afrotherian mammals indigenous to equatorial Africa and Madagascar, respectively. The two families are thought to have split about 47–53 million years ago. Potamogalid otter shrews were formerly considered a subfamily of Tenrecidae. The suborder is also presumed to contain the extinct genus Plesiorycteropus, a group of possibly fossorial insectivores similar to aardvarks, which is known to be more closely related to tenrecs of subfamily Tenrecinae than to golden moles of suborder Chrysochloridea.
A tenrec is any species of mammal within the afrotherian family Tenrecidae endemic to Madagascar. Tenrecs are wildly diverse; as a result of convergent evolution some resemble hedgehogs, shrews, opossums, rats, and mice. They occupy aquatic, arboreal, terrestrial and fossorial environments. Some of these species, including the greater hedgehog tenrec, can be found in the Madagascar dry deciduous forests. However, the speciation rate in this group has been higher in humid forests.
Afrotheria is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.
Wastebasket taxon is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined by either their designated members' often superficial similarity to each other, or their lack of one or more distinct character states or by their not belonging to one or more other taxa. Wastebasket taxa are by definition either paraphyletic or polyphyletic, and are therefore not considered valid taxa under strict cladistic rules of taxonomy. The name of a wastebasket taxon may in some cases be retained as the designation of an evolutionary grade, however.
The web-footed tenrec, Malagasy otter shrew, or aquatic tenrec is the only known semiaquatic tenrec, and is found in eastern Madagascar, especially in and around Ranomafana National Park. It grows to between 25 and 39 cm, and was once thought to be extinct. It feeds on crabs, aquatic insects, and crayfish. The population is considered vulnerable. It was formerly placed in the monotypic genus Limnogale, but has been moved to Microgale based on molecular data showing it to be deeply nested within the latter.
The Afroinsectiphilia is a clade that has been proposed based on the results of recent molecular phylogenetic studies. Many of the taxa within it were once regarded as part of the order Insectivora, but Insectivora is now considered to be polyphyletic and obsolete. This proposed classification is based on molecular studies only, and there is no morphological evidence for it.
Soricomorpha is a formerly used taxon within the class of mammals. In the past it formed a significant group within the former order Insectivora. However, Insectivora was shown to be polyphyletic and various new orders were split off from it, including Afrosoricida, Macroscelidea, and Erinaceomorpha, with the four remaining extant and recent families of Soricomorpha shown here then being treated as a separate order. Insectivora was left empty and disbanded.
The Nimba otter shrew is a dwarf otter shrew and belongs to the mammal family Potamogalidae. Otter shrews are shrew-like afrotherian mammals found in sub-Saharan Africa. They are most closely related to the tenrecs of Madagascar. This species belongs to the genus Micropotamogale, literally meaning "tiny river weasel". It is native to the Mount Nimba area which rests along the border of Liberia, Guinea, and Côte d’Ivoire in West Africa.
Amblysomus is a genus of the golden mole family, Chrysochloridae, comprising five species of the small, insect-eating, burrowing mammals endemic to Southern Africa. All five species can be found in South Africa and some are also found in Eswatini and Lesotho.
The pygmy shrew tenrec is a species of placental mammal in the family Tenrecidae. It is endemic to Madagascar. Its natural habitat is subtropical or tropical moist forests. While it is not endangered, its population is slowly declining as it is threatened by habitat loss. This is of concern, though does not yet merit a higher protection level.
The mole-like rice tenrec, also known as the fossorial tenrec or hova rice tenrec, is a species of mammal in the tenrec family. Like all other tenrecs, it is endemic to Madagascar. Its natural habitats are subtropical or tropical moist forests, swamps, freshwater lakes, and irrigated or seasonally flooded agricultural land.
Potamogalidae is the family of "otter shrews", a group of semiaquatic riverine afrotherian mammals indigenous to sub-Saharan Africa. They are most closely related to the tenrecs of Madagascar, from which they are thought to have split about 47–53 million years ago. They were formerly considered a subfamily of Tenrecidae.
References
- ↑ Stanhope, M.J.; Waddell, V.G.; Madsen, O.; de Jong, W.; Hedges, S.B.; Cleven, G.C.; Kao, D.; Springer, M.S. (1998). "Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals". Proceedings of the National Academy of Sciences. 95 (17): 9967–9972. Bibcode:1998PNAS...95.9967S. doi: 10.1073/pnas.95.17.9967 . PMC 21445 . PMID 9707584.
- ↑ Douady, C.J.; Douzery, E.J.P. (2003). "Molecular estimation of eulipotyphlan divergence times and the evolution of "Insectivora"". Molecular Phylogenetics and Evolution. 28 (2): 285–296. doi:10.1016/S1055-7903(03)00119-2. PMID 12878465.
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