Elephant shrew

Elephant shrews[1] Fossil range: Early Oligocene–Recent PreЄ Є O S D C P T J K Pg N [2]
Short-eared Elephant Shrew (Macroscelides proboscideus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Eutheria
Superorder:	Afrotheria
Order:	Macroscelidea Butler, 1956
Family:	Macroscelididae Bonaparte, 1838
Genera
Rhynchocyon Petrodromus Macroscelides Elephantulus

Elephant shrews or jumping shrews are small insectivorous mammals native to Africa, belonging to the Macroscelididae family, in the order Macroscelidea. Their traditional common English name comes from a fancied resemblance between their long noses and the trunk of an elephant, and an assumed relationship with the true shrews (family Soricidae) in the order Insectivora because of their superficial similarities. As it has become plain that the elephant shrews are unrelated to the shrews, the biologist Jonathan Kingdon has proposed that they instead be called sengis^[3], a term derived from the Bantu languages of Africa.

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 north-west of the continent.

Characteristics

Elephant shrews are small animals with brownish gray coats. Elephant shrews vary in size from about 10 to almost 30 centimeters, from just under 50 g to over 500 g. The Short-eared Elephant Shrew has an average size of 150 millimetres (5.9 in). All are quadrupedal with mouse-like tails, and rather long legs for their size which are used to move in a hopping fashion like rabbits. Although the size of the trunk varies from one species to another, all are able to twist it about in search of food. Their life span is about two and a half to four years in the wild.^[4] They have large canine teeth, and also high-crowned cheek teeth like those of ungulates^[5]. Their dental formula is:

Although mostly diurnal 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 disturbed, the pathway provides an obstacle-free escape route.

Elephant shrews are not highly social animals, but many live in monogamous pairs, which share and defend a home territory, which they mark using scent glands^[5]. The Rhynchocyon species also dig small conical holes in the soil, bandicoot style, but others may use natural crevices, or make leaf nests.

Short-eared elephant-shrews inhabit dry steppes and stone deserts of Southwestern Africa. They even can be found in the Namib-desert, one of the driest regions of the earth. Elephant-shrews live in pairs and defend territories. 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 around just a few hours after birth.^[6]

Females give birth to litters of one or three young several times a year, after a gestation period varying from 45 to 60 days. The young are born relatively well developed, but remain in the nest for several days before venturing outside^[5].

The mating period lasts for several days and is followed by six weeks of gestation. After mating, the pair will return to their solitary habits. The female then will give birth to 1-2 young in one of her leaf nests. Only for nursing purposes are the young visited by the mother. After 5 days the young are fed mashed insects with the milk, which are collected and transported in the cheek pouches of the female. The young then slowly start to explore their environment and start to hunt for insects. After about 15 days, the young will begin the migratory phase of their life which lessens the dependency of the young on their mother. The young will then establish their own home ranges (about 1 km²) and will become sexually active within 41-46 days.^[7][8]

Feeding habits

All elephant-shrews eat mainly invertebrates, such as insects, spiders, centipedes, millipedes, and earthworms. 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 somewhat of a challenge for the elephant shrew. For example, a giant 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 when available, especially new leaves, seeds, and small fruits. ^[9]

Evolution

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The topic of elephant shrew evolution, especially how it relates to mammalian evolution, is a highly debated subject. Elephant-shrews have been grouped with rats, aardvarks, shrews, and even elephants. ^[10] Based on appearances alone, one can conclude this animal is related to elephants because of the trunk, but the tail looks like a rat tail. So where does the elephant-shrew fit in evolution? In order to figure out how the elephant-shrews evolved, a group used a computerized cladistics program to examine the nucleotide or amino acid sequences of six different genes or proteins taken from 12 species, each representing a different order of placental mammals: human, horse, bovine, dog, pangolin, elephant, hyrax, aardvark, elephant shrew, rabbit, rat, and armadillo. From their results, they concluded the elephant shrew, the elephant, and the aardvark were all closely related members of the paenungulate clade.

Also joining this group was the hyrax, a small, superficially guinea pig-like mammal with molars akin to those of a rhinoceros, but incisors like a rodent's; its classification had long been controversial. ^[11] However, work done by Naylor from Yale University and Brown from the University of Michigan started to investigate the previous work done. Their results showed the work done to group the mentioned members into the paenungulate was completely wrong. Naylor and Brown used similar methods to group known phylogenetic trees to see what the nucleotide sequences they would come up with. The results contradicted the previous work. The molecular tree clustered frogs and chickens in a clade with fish, even though these three species do not derive from a recent common ancestor. To make matters worse, echinoderms (which include the sea urchin and the starfish) branched closer to the vertebrates than did amphioxus, a primitive marine chordate that is well established as one of the closest living invertebrate relatives of the vertebrates. ^[12] Taxonomists are still working to figure out where elephant-shrews fit into mammalian evolution.

Classification

In the past, elephant shrews have been classified with the shrews and hedgehogs as part of the Insectivora; regarded as distant relatives of the ungulates; grouped with the treeshrews; and lumped in with the hares and rabbits in the Lagomorpha. Recent molecular evidence, however, strongly supports a superorder Afrotheria which unites tenrecs, and golden moles with certain ungulates or mammals that were previously presumed to be ungulates, including hyraxes, sirenians, aardvarks and elephants, as well as the elephant shrews.

A number of fossil species are also known, all of them from Africa. Some, such as Myohyrax, were so similar to hyraxes that they were initially misidentified as belonging to that group, while others, such as Mylomygale were relatively rodent-like. These unusual forms all died out by the Pleistocene^[2].

An elephant shrew from Frankfurt Zoo.

A male Black and Rufous Elephant Shrew at the National Zoo.

There are 16 species of elephant shrew in four genera, two of which are monotypic.

• ORDER MACROSCELIDEA^[1]
  • Family Macroscelididae
    • Genus Elephantulus
      • Short-snouted Elephant Shrew, Elephantulus brachyrhynchus
      • Cape Elephant Shrew, Elephantulus edwardii^[13]
      • Dusky-footed Elephant Shrew, Elephantulus fuscipes
      • Dusky Elephant Shrew, Elephantulus fuscus
      • Bushveld Elephant Shrew, Elephantulus intufi
      • Eastern Rock Elephant Shrew, Elephantulus myurus
      • Somali Elephant Shrew, Elephantulus revoili
      • North African Elephant Shrew, Elephantulus rozeti
      • Rufous Elephant Shrew, Elephantulus rufescens
      • Western Rock Elephant Shrew, Elephantulus rupestris
    • Genus Macroscelides
      • Short-eared Elephant Shrew, Macroscelides proboscideus
    • Genus Petrodromus
      • Four-toed Elephant Shrew, Petrodromus tetradactylus
    • Genus Rhynchocyon
      • Golden-rumped Elephant Shrew, Rhynchocyon chrysopygus
      • Checkered Elephant Shrew, Rhynchocyon cirnei
      • Black and Rufous Elephant Shrew, Rhynchocyon petersi
      • Grey-faced Sengi , Rhynchocyon udzungwensis ^[14]

External links

• Elephant Shrew: Wildlife summary from the African Wildlife & Reptiles Foundation
• California Academy of Sciences: Elephant-Shrews
• New Species Of Giant Elephant-shrew Discovered

References

• Murata Y, Nikaido M, Sasaki T, Cao Y, Fukumoto Y, Hasegawa M, Okada N. Afrotherian phylogeny as inferred from complete mitochondrial genomes. Mol Phylogenet Evol. 2003 Aug;28(2):253-60.
• Murphy WJ, Eizirik E, Johnson WE, Zhang YP, Ryder OA, O'Brien SJ. Molecular phylogenetics and the origins of placental mammals. Nature. 2001 Feb 1;409(6820):614-8.
• Tabuce R, Marivaux L, Adaci M, Bensalah M, Hartenberger JL, Mahboubi M, Mebrouk F, Tafforeau P, Jaeger JJ. Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade. Proc Biol Sci. 2007 May 7;274(1614):1159-66.