The hero shrew (''Scutisorex somereni''), also known as the armored shrew,
is a large
shrew
Shrews (family Soricidae) 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 fa ...
native to the
Congo Basin
The Congo Basin (french: Bassin du Congo) is the sedimentary basin of the Congo River. The Congo Basin is located in Central Africa, in a region known as west equatorial Africa. The Congo Basin region is sometimes known simply as the Congo. It con ...
of Africa. Its features are typical of a
white-toothed shrew
The white-toothed shrews or Crocidurinae are one of three subfamilies of the shrew family Soricidae.
The outer layer of these shrews' teeth is white, unlike that of the red-toothed shrews. These species are typically found in Africa and souther ...
− short legs, slender snout, dense fur − except for a highly unusual
spinal column
The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
. It has corrugated interlocking
vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
that are unique among
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s except for its
sister species,
Thor's hero shrew
Thor's hero shrew (''Scutisorex thori'') is an extant species of shrew native to the Democratic Republic of the Congo. It and its sister species, the hero shrew (''Scutisorex somereni''), are the only mammal species known to have interlocking ver ...
. This unique adaptation allows the animal to bear a huge amount of weight on its back − according to an expedition team.
The hero shrew lives in both lowland and mountain forests. They live in the undergrowth, feeding primarily on invertebrates. The evolutionary benefit of its unusual spine is not known; it is hypothesized that it allows the animal to push itself under logs and between palm leaves and the tree's trunk to find food. Local tribes of people believe the hero shrew holds magical powers. It is classified as
Least Concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
by
IUCN
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
.
Description
Externally, the hero shrew resembles a typical large shrew. It has short legs, a slender snout, and small eyes. It has dense, coarse fur that is gray in color. It has two types of fur; some hair strands provide sensory functions while other produce scent. The hero shrew aggressively marks its territory, contorting its body to mark objects with its scent. It is thought that the odor repels other members of its species. The chemical it emits can discolor its fur yellow.
The hero shrew lives in the forest undergrowth in sparsely populated areas, which leads to it rarely being seen by humans. It is primarily an
insectivore
A robber fly eating a hoverfly
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
The first vertebrate insectivores wer ...
, but will eat small amphibians and lizards in the wild, and bird and mammal meat in captivity. A fully grown hero shrew's body is in length with a tail of .
It weighs .
It does not exhibit
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
. The breeding habits of the hero shrew have not been observed.
Adaptations
The vertebrae of the hero shrew are thick, corrugated cylinders.
The vertebrae interlock on their sides and lower surfaces. The animal's spine has bony projections that mesh to form a very strong, yet flexible backbone.
The differences are especially pronounced in the lower back between the rib cage and hips.
The hero shrew has 11
lumbar vertebrae, in contrast to a typical mammal which has 5 such vertebrae. The spine of the hero shrew accounts for 4% of its body weight, in contrast to 0.5–1.6% for a typical small mammal.
The ribs of the shrew are thicker than those of similarly sized mammals and the spinal muscles are significantly different. Its abdominal muscles are reduced, while its spinal muscles are enlarged. As a result, the hero shrew has a peculiar gait with its spine flexing in a snake-like manner.
During an expedition to the Congo region in the 1910s, the natives demonstrated the remarkable strength of the hero shrew to naturalists Herbert Lang and James Chapin. After some mystical preparation, an adult male estimated to weigh stepped on a shrew and balanced himself on one foot. After several minutes, the man stepped off and the shrew left unharmed.
The combination of animal's vertebral strength and its convex curvature behind the shoulder kept its vital organs from being crushed in the demonstration.
The feat represented a weight of roughly 1000 times the animal's body weight, the equivalent of a human holding 10 elephants.
[ Relative to body size, the hero shrew's spine is roughly four times more robust than any other vertebrate (excluding its sister species).]
Despite its great strength, the hero shrew's spine is easily flexed sagittally (the muscles for doing this are well developed).[ As a result, the animal can turn 180° within a burrow only slightly wider than the shrew.] However, the animal has very little ability to extend its spine or bend it laterally.[ Its intervertebral joints are five times more resistant to twisting along the axis than a common rat, adjusted for size.]
Range and status
The hero shrew is found in tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equatori ...
in the Congo Basin
The Congo Basin (french: Bassin du Congo) is the sedimentary basin of the Congo River. The Congo Basin is located in Central Africa, in a region known as west equatorial Africa. The Congo Basin region is sometimes known simply as the Congo. It con ...
and nearby mountains, over an altitudinal range of 700 to 2230 m. It appears to be dependent on forest habitat. In the mountains it is often present near streams. Its range includes Burundi
Burundi (, ), officially the Republic of Burundi ( rn, Repuburika y’Uburundi ; Swahili language, Swahili: ''Jamuhuri ya Burundi''; French language, French: ''République du Burundi'' ), is a landlocked country in the Great Rift Valley at the ...
, the Democratic Republic of the Congo
The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...
, Rwanda
Rwanda (; rw, u Rwanda ), officially the Republic of Rwanda, is a landlocked country in the Great Rift Valley of Central Africa, where the African Great Lakes region and Southeast Africa converge. Located a few degrees south of the Equator ...
, and Uganda
}), is a landlocked country in East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territor ...
, but apparently does not extend west of the Oubangi River
The Ubangi River (), also spelled Oubangui, is the largest right-bank tributary of the Congo River in the region of Central Africa. It begins at the confluence of the Mbomou (mean annual discharge 1,350 m3/s) and Uele Rivers (mean annual discharge ...
.
The hero shrew is listed as a Least Concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
species by the International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
(IUCN). It is thought to have a large population and relatively wide distribution. Its distribution overlaps multiple protected areas and thus the hero shrew is unlikely to experience significant population decline in the near future.
Adaptive significance
Typically, the backbone is thought to be one of the most conserved parts of the skeleton. Why the hero shrew did not follow this pattern has presented a significant puzzle. Prior to 2013, there was no satisfactory explanation for adaptive advantage of the strong spine. In 1974, Jonathan Kingdon
Jonathan Kingdon (born 1935 in Tanzania) is a zoologist, science author, and artist; a research associate at the University of Oxford.
He focuses on taxonomic illustration and evolution of the mammals of Africa. He is a contributor to The Oxford B ...
suggested that the robust spine and associated posture keeps the animal's body clear of wet ground in swampy habitats. An alternate idea was that the intricate spine somehow evolved as the consequence of some unrelated adaptive factor, as in the spandrels of St. Marco hypothesis. Neither idea had strong scientific support.[ In 1998, ]Dennis Cullinane
Dennis or Denis is a first or last name from the Greco-Roman name Dionysius, via one of the Christian saints named Dionysius.
The name came from Dionysus, the Greek god of ecstatic states, particularly those produced by wine, which is someti ...
and his colleagues undertook an extensive survey of hero shrew's anatomy and concluded there was no obvious functional significance for the adaptation.
In 2013, a team headed by William T. Stanley of the Field Museum
The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...
proposed that ''Scutisorex'' may use their exceptional spines to lever logs or dead palm leaves, enabling access to invertebrate prey such as earthworms
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...
(Oligochaeta) (An interview with William Stanley: ). Although this behavior has not been directly observed, when local people are collecting beetle larvae in a similar fashion, they often encounter the shrews. Scientist Kristofer Helgen called the new theory "the first compelling explanation for the adaptive significance of the unusual spine."
Initial scientific description
The hero shrew was first described in 1910 by Oldfield Thomas
Michael Rogers Oldfield Thomas (21 February 1858 – 16 June 1929) was a British zoologist.
Career
Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and subspecies for the first time. He was appoin ...
from a single specimen found in Uganda. But its unique spinal structure was not discovered until 1917, when J. A. Allen examined a preserved specimen from the American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
. The name "hero shrew" stems from the local Mangbetu name for the animal.
Cultural significance
The hero shrew is revered in its homeland. Its extraordinary strength has led to the shrew being used as a talisman by the local Mangbetu people.[ Tradition holds that any part of the shrew, even its ashes, will provide ]