Tenrecidaetenrecs
Members of this remarkable family do not have a wide geographic distribution. They are most numerous and diverse on the island of Madagascar, but a few species are also found in western central Africa. Tenrecs have radiated such that they include species that resemble, both morphologically and ecologically, widely diverse mammals including hedgehogs, shrews, opossums, mice and even otters; and members of the family occupy a diverse collection of habitats, including aquatic, arboreal, terrestrial and fossorial. Currently, we recognize 10 genera of extant tenrecids and 24 species. These are divided into three subfamilies, the Tenrecinae and Oryzoryctinae (both confined to Madagascar) and the Potamogalinae (west-central Africa).
Tenrecs lack jugals, and their zygomatic arches are incomplete. Their tympanic bones are annular, and the squamosal contributes to the roof of the tympanic cavity. The dental formula of tenrecs varies consirably among species, reflecting the diversity of the group: 2-3/2-3, 1/1, 2-3/2-3, 2-4/2-3 = 32-40. The upper molars are zalambdodont, except in the African otter shrews (Potamogalinae), in which they are dilambdodont. The urogenital and anal apertures are included in a cloaca, and the eyes are small. Many tenrecs do not maintain a constant body temperature, but rather let their bodies cool down while they are at rest. At least one species hibernates. Curiously, male tenrecids lack a scrotum and the testes remain within the body cavity.
Members of the large subfamily Tenrecinae are relatively large (up to the size of a cat) and highly variable in body form. All have spines, which are barbed and detachable in some forms and controlled by a well-developed muscle called the panniculus carnosus. Tenrecines are mostly nocturnal and mostly omnivorous. One genus, Hemicentetes, uses its quills to produce sounds that are important in commnication. The Oryzoryctinae are small. Like the Tenrecinae, this subfamily is contains a number of genera and species. They lack spines. Most are shrew-like or mole-like, but one species, in the genus Limnogale, is aquatic. Some are highly fossorial. The Potamogalinae is made up of three species, all aquatic forms called otter-shrews. Potamogale is large, around 600 mm in length and 1 kg in weight, and much modified for aquatic life. Potamogalines probably represent an early branch of the family.
The fossil record of tenrecids is relatively poor. The oldest known fossils are from the Miocene in East Africa and the Pleistocene in Madagascar, but the group is certainly considerably older. Recent molecular evidence (Murphy et al. 2001) suggests that they should be removed from the Insectivora and placed within a group of African mammals, the Afrotheria, which includes aardvarks, elephants, hyraxes, sea cows, elephant shrews, and golden moles as well as tenrecs.
References and literature cited:
Macdonald, D., ed. 1984. The Encyclopedia of Mammals. New York, Facts On File Publications.
Murphy, W.J., E. Eisirik, S.J. O'Brian, O. Madsen, M. Scally, C.J. Douady, E. Teeling, O.A. Ryder, M.J. Stanhope, W.W. de Jong, and M.S. Springer. 2001. Resolution of the early placental mammal radiation using Bayesian phylogenetics. Science 294238-2351.
Nowak, R.M., and J.L. Paradiso. 1983. Walker's Mammals of the World, 4th ed., Vol. I. Baltimore, Johns Hopkins University Press.
Vaughan, T.A. 1972. Mammalogy. Philadelphia, W.B. Saunders Co.
Yates, T. L. 1984. Insectivores, elephant shrews, tree shrews, and dermopterans. Pp. 117-144 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.
Contributors
Deborah Ciszek (author), University of Michigan-Ann Arbor, Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.
Glossary
- bilateral symmetry
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having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- chemical
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uses smells or other chemicals to communicate
- endothermic
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animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- motile
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having the capacity to move from one place to another.
- sexual
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reproduction that includes combining the genetic contribution of two individuals, a male and a female
- tactile
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uses touch to communicate