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Elephant shrew

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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 (family Soricidae) 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.[4] In 1997, the biologist Jonathan Kingdon proposed that they instead be called "sengis" (singular sengi),[5] a term derived from the Bantu languages of Africa, and in 1998, they were classified into the new clade Afrotheria.[6]

Elephant shrew[3]
Temporal range: 48–0 Ma[1][2]
Black and rufous elephant shrew, Rhynchocyon petersi, Philadelphia Zoo
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Superorder: Afrotheria
Grandorder: Afroinsectiphilia
Mirorder: Afroinsectivora
Order: Macroscelidea
Butler, 1956
Family: Macroscelididae
Bonaparte, 1838
Type genus
Macroscelides
A. Smith, 1829
Genera

Elephantulus
Galegeeska
Macroscelides
Petrodromus
Petrosaltator
Rhynchocyon

Range map of elephant shrew by genus
R. petersi skeleton, Museum of Osteology
Eastern rock elephant shrew, Elephantulus myurus, South Africa
Bushveld elephant shrew, E. intufi, Namibia

They are widely distributed across the southern part of Africa, and although common nowhere, can be found in almost any type of habitat, from the Namib Desert to boulder-strewn outcrops in South Africa to thick forest. One species, the North African elephant shrew, remains in the semi-arid, mountainous country in the far northwest of Africa. The Somali elephant shrew went unobserved from 1968 to 2020 but was rediscovered by a group of scientists in Djibouti.[7]

Description

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Skeleton of North African elephant shrew.

Elephant shrews are small, quadrupedal, insectivorous mammals. They have scaly tails, long snouts, and bear a superficial resemblance to shrews or rodents. They have long legs relative to their size, which are used to move from one place to another like rabbits. Elephant shrews use their flexible proboscises to search for food, with the length of the snout varying between species.

They are one of the fastest small mammals, having been recorded to reach speeds of 28.8 kilometres per hour (17.9 mph).[8] They vary in size from about 10 to 30 centimetres (3.9 to 11.8 in), from 50 to 500 grams (1.8 to 17.6 oz).[citation needed] One species of giant sengi, the grey-faced sengi, weighs about 700 g. Compared to other mammalian insectivores, sengis have relatively large brains.[9] Their lifespans are about two and a half to four years in the wild.[10][page needed] They have large canine teeth, and also high-crowned cheek teeth similar to those of ungulates.[11] Their dental formula is 1-3.1.4.23.1.4.2-3G[citation needed]

Behavior and ecology

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Although mostly diurnal[12] and very active, they are difficult to trap and very seldom seen; elephant shrews are wary, well camouflaged, and adept at dashing away from threats. Several species make a series of cleared pathways through the undergrowth and spend their day patrolling them for insect life. If the animal is disturbed, the pathway provides an obstacle-free escape route.

Elephant shrews are solitary animals, despite many species living in monogamous pairs. They share and defend their home territory, which is marked using their scent glands.[11] Scent markings are also used for mate attraction.[13]

Short-eared elephant shrews inhabit the dry steppes and stone deserts of southwestern Africa. They can even be found in the Namib Desert, one of the driest regions of the earth. Females drive away other females, while males try to ward off other males. Although they live in pairs, the partners do not care much for each other and their sole purpose of even associating with the opposite sex is for reproduction. Social behaviors are not very common and they even have separate nests. The one or two young are well developed at birth; they are able to run within a few hours.[14]

Female elephant shrews undergo a menstrual cycle similar to that of human females, making it one of the few nonprimate mammals to do so.[15] Elephant shrews were used in the 1940s to study the human menstruation cycle.[16] The elephant shrew mating period lasts for several days. After mating, the pair will return to their solitary habits. After a gestation period varying from 45 to 60 days, the female will bear litters of one to three young several times a year. The young are born relatively well developed, but remain in the nest for several days before venturing outside.[11]

After five days, the young's milk diet is supplemented with mashed insects, which are collected and transported in the cheek pouches of the female. The young then slowly start to explore their environment and hunt for insects. After about 15 days, the young will begin the migratory phase of their lives, which lessens their dependency on their mother. The young will then establish their own home ranges (about 1 km2 (0.39 sq mi)) and will become sexually active within 41–46 days.[17][18]

The thermal characteristics of elephant shrews with similar body size, habitat and distribution are very close in most of the classifications. They can maintain homeothermy in different ambient temperatures where most of the species regulate their body temperature at 35 °C and neither become hyperthermic but they balance the heat offload by increasing the EWL (evaporative water loss).[19]

Feeding habits

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Elephant shrews mainly eat insects, spiders, centipedes, millipedes, and earthworms. While awake, as much as 80% of their time may be spent foraging.[20] An elephant shrew uses its nose to find prey and uses its tongue to flick small food into its mouth, much like an anteater. Eating large prey can pose a challenge; an elephant shrew struggling with an earthworm must first pin its prey to the ground with a forefoot. Then, turning its head to one side, it chews pieces off with its cheek teeth, much like a dog chewing a bone. This is a sloppy process, and many small pieces of worm drop to the ground; these are simply flicked up with the tongue. Some elephant shrews also feed on small amounts of plant matter, especially new leaves, seeds, and small fruits.[17]

Evolution

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A number of fossil species are known, all from Africa. They were separate from the similar-appearing order Leptictida. A considerable diversification of macroscelids occurred in the Paleogene period. Some, such as Myohyrax, were so similar to hyraxes that they were initially included with that group, while others, such as Mylomygale, were relatively rodent-like. These unusual forms all died out by the Pleistocene.[21] Although macroscelids were classified in the past with many groups, often on the basis of superficial characteristics, considerable morphological and molecular evidence places them within Afrotheria, at the base of Afroinsectivora.[22]

In terms of timing, the divergence between macroscelids and afrosoricidans is thought to have occurred roughly 57.5 million years (Ma) ago, in the late Paleocene, while the diversification of extant macroscelids apparently began when the Rhynchocyon lineage split off about 33 Ma ago, in the early Oligocene.[23] Elephantulus is considered to have separated from Macroscelidini later in the Oligocene, about 28.5 Ma ago.[23]

Phylogeny

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Afrotheria
A cladogram of Afrotheria based on molecular evidence[22]
Cladogram of living elephant shrews[24][23]
 Macroscelididae 

Classification

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Main article: List of macroscelids
 
Round-eared elephant shrew, Macroscelides proboscideus, Basel Zoo
 
Four-toed sengi, Petrodromus tetradactylus, Mozambique
 
North African elephant shrew, Petrosaltator rozeti, Morocco

The 20 species of elephant shrew are placed in six genera, three of which are monotypic:

References

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  1. ^ Martin Pickford; Brigitte Senut; Helke Mocke; Cécile Mourer-Chauviré; Jean-Claude Rage; Pierre Mein (2014). "Eocene aridity in southwestern Africa: timing of onset and biological consequences". Transactions of the Royal Society of South Africa. 69 (3): 139–144. doi:10.1080/0035919X.2014.933452. S2CID 128423895.
  2. ^ Martin Pickford (2015). "Chrysochloridae (Mammalia) from the Lutetian (Middle Eocene) of Black Crow, Namibia" (PDF). Communications of the Geological Survey of Namibia. 16: 105–113.
  3. ^ a b Schlitter, D.A. (2005). "Order Macroscelidea". 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. 82–85. ISBN 978-0-8018-8221-0. OCLC 62265494.
  4. ^ Nishihara, Hidenori; Satta, Yoko; Nikaido, Masato; Thewissen, J. G. M.; Stanhope, Michael J.; Okada, Norihiro (2005). "A Retroposon Analysis of Afrotherian Phylogeny". Molecular Biology and Evolution. 22 (9): 1823–1833. doi:10.1093/molbev/msi179. PMID 15930154.
  5. ^ Kingdon, J. (1997). The Kingdon Field Guide to African Mammals. London: Academic Press. ISBN 978-0-691-11692-1.
  6. ^ 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.
  7. ^ Briggs, Helen (18 August 2020). "Elephant shrew rediscovered in Africa after 50 years". BBC News. Retrieved 19 August 2020.
  8. ^ Davies, Ella (16 January 2014). "Secrets of the sengi: the world's fastest small mammal". BBC Nature. Archived from the original on 2014-01-16.
  9. ^ Iwaniuk, A.; Kaufman, J.A.; Turner, G.H.; Holroyd, P.A.; Rovero, F.; Grossman, A. (2013). "Brain Volume of the Newly-Discovered Species Rhynchocyon udzungwensis (Mammalia: Afrotheria: Macroscelidea): Implications for Encephalization in Sengis". PLOS ONE. 8 (3): e58667. Bibcode:2013PLoSO...858667K. doi:10.1371/journal.pone.0058667. PMC 3596274. PMID 23516530.
  10. ^ Encyclopedia of Animals. Online database: EBSCO Publishing.
  11. ^ a b c Rathbun, Galen B. (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 730–733. ISBN 978-0-87196-871-5.
  12. ^ Conniff, Richard. Shrewd Configuration, Smithsonian, June 2005. pp. 26-28.
  13. ^ Rathbun, Galen B.; Woodall, Peter F. (March 2002). "A bibliography of elephant‐shrews or sengis (Macroscelidea)". Mammal Review. 32 (1): 66–70. doi:10.1046/j.1365-2907.2002.00092.x. ISSN 0305-1838.
  14. ^ "Short-eared elephant-shrew (Macroscelides proboscideus) - A "living fossil" from the Namib-desert". Natur Spot. Archived from the original on 19 July 2011. Retrieved 1 February 2010.
  15. ^ van der Horst, Cornelius; Gillman, Joseph (1941). "The menstrual cycle in Elephantulus". The South African Journal of Medical Sciences. 6: 27–47.
  16. ^ Carter, A.M. (2018). "Classics revisited: C. J. Van der Horst on pregnancy and menstruation in elephant shrews". Placenta. 67: 24–30. doi:10.1016/j.placenta.2018.05.010. PMID 29941170. S2CID 49414099.
  17. ^ a b Rathbun, Galen B. (September 1992). "The Fairly True Elephant-Shrew". Natural History. 101. New York.
  18. ^ Unger, Regina. "Short-eared Elephant-Shrews". Retrieved 1 February 2010.
  19. ^ Downs, Colleen T.; Perrin, M.R. (1995). "The thermal biology of three southern African elephant-shrews". Journal of Thermal Biology. 20 (6): 445–450. doi:10.1016/0306-4565(95)00003-F.
  20. ^ Cooke, F.; Bruce, J. (2004). The Encyclopedia of Animals: A Complete Visual Guide. University of California Press. p. 243. ISBN 978-0-520-24406-1. Retrieved 2 August 2024.
  21. ^ Savage, RJG & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. p. 54. ISBN 978-0-8160-1194-0.
  22. ^ a b Tabuce, R.; Asher, R. J.; Lehmann, T. (2008). "Afrotherian mammals: a review of current data" (PDF). Mammalia. 72: 2–14. doi:10.1515/MAMM.2008.004. S2CID 46133294. Archived from the original (PDF) on 2021-02-24. Retrieved 2020-08-15.
  23. ^ a b c d Heritage, S.; Rayaleh, H.; Awaleh, D.G.; Rathbun, G.B. (2020). "New records of a lost species and a geographic range expansion for sengis in the Horn of Africa". PeerJ. 8: e9652. doi:10.7717/peerj.9652. PMC 7441985. PMID 32879790.
  24. ^ Upham, Nathan S.; Esselstyn, Jacob A.; Jetz, Walter (2019). "Inferring the mammal tree: Species-level sets of phylogenies for questions in ecology, evolution and conservation". PLOS Biol. 17 (12): e3000494. doi:10.1371/journal.pbio.3000494. PMC 6892540. PMID 31800571.
  25. ^ Smit, H.A.; Robinson, T.J.; Watson, J.; Jansen Van Vuuren, B. (October 2008). "A new species of elephant-shrew (Afrotheria:Macroselidea: Elephantulus) from South Africa". Journal of Mammalogy. 89 (5): 1257–1269. doi:10.1644/07-MAMM-A-254.1.
  26. ^ Krásová, Jarmila; Mikula, Ondřej; Šumbera, Radim; Horáková, Sylvie; Robovský, Jan; Kostin, Danila S.; Martynov, Aleksey A.; Lavrenchenko, Leonid A.; Bryja, Josef (2021). "The Rufous Sengi is not Elephantulus—Multilocus reconstruction of evolutionary history of sengis from the subfamily Macroscelidinae". Journal of Zoological Systematics and Evolutionary Research. 59 (4): 918–932. doi:10.1111/jzs.12460. ISSN 1439-0469. S2CID 233667864.
  27. ^ Agwanda B. R., Rovero F., Lawson L. P., Vernesi C., & Amin R. (2021), "A new subspecies of giant sengi (Macroscelidea: Rhynchocyon) from coastal Kenya", Zootaxa, 4948 (2): zootaxa.4948.2.5, doi:10.11646/zootaxa.4948.2.5, PMID 33757027{{citation}}: CS1 maint: multiple names: authors list (link)
  28. ^ Carlen, E.J.; Rathbun, G.B.; Olson, L.E.; Sabuni, C.A.; Stanley, W.T.; Dumbacher, J.P. (2017). "Reconstructing the molecular phylogeny of giant sengis (Macroscelidea; Macroscelididae; Rhynchocyon)". Molecular Phylogenetics and Evolution. 113: 150–160. doi:10.1016/j.ympev.2017.05.012. PMID 28552433.
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