Golden mole

Golden moles are small insectivorous burrowing mammals endemic to Southern Africa. They comprise the family Chrysochloridae and as such they are taxonomically distinct from the true moles, family Talpidae, and other mole-like families, all of which, to various degrees, they resemble as a result of evolutionary convergence.

Golden moles[1]
Temporal range: Lutetian–Recent[2]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Afrosoricida
Suborder: Chrysochloridea
Broom, 1915
Family: Chrysochloridae
Gray, 1825
Genera
Chrysochloris asiatica Cape golden mole adult, showing the digging claw, absence of external eye and a hint of the iridescence of the fur. The rhinarium is not obvious in this photograph.

Characteristics and affinities

Like most burrowing mammals with similar habits, the Chrysochloridae have short legs with powerful digging claws, very dense fur that repels dirt and moisture, and toughened skin, particularly on the head. Their eyes are non-functional and covered with furred skin. The external ears are just tiny openings. In particular, golden moles bear a remarkable resemblance to the marsupial moles of Australia, family Notoryctidae, which they resemble so suggestively that at one time, the marsupial/placental divide not withstanding, some argued that they were related. Considerations that influenced the debate might have included the view that the Chrysochloridae are very primitive placentals and the fact that they have many mole-like specializations similar to specializations in marsupial moles. The rhinarium is a greatly enlarged, dry leathery pad that protects their nostrils while the animal digs. In this respect too, they resemble the marsupial moles. Some authors claim their primary sense is of touch, and they are particularly sensitive to vibrations which may indicate approaching danger.[3] Note below however, the observations on the malleus in the middle ear.

The species range in size from about 8 to about 20 cm. They have muscular shoulders and the forelimbs are radically adapted for digging; all the toes on the forefeet have been reduced, except for a large, pick-like third claw on the third toe. The fifth digit is absent and the first and fourth digits are vestigial. The adaptations of the hind feet are less dramatic, they retain all five toes and are webbed as an adaptation to efficient backward shovelling of soil loosened by the front claws.

At one time the Chrysochloridae were regarded as primitive. Supporting arguments included: that they were thought to have originated in Gondwana, that they had a low resting metabolic rate, and they could switch off thermoregulation when inactive. Like the tenrecs, they possess a cloaca, and males lack a scrotum. However, such points are no longer regarded as strongly suggestive of golden moles as undeveloped "reptilian mammals"; some are seen rather as adaptations to regional climatic conditions. Going into a torpor when resting or during cold weather enables them to conserve energy and reduce urgent requirements for food. Similarly, they have developed particularly efficient kidneys and most species do not need to drink water at all; in fact they tend to drown easily if they fall into water.

Habits and ecology

Most species of Chrysochloridae live almost exclusively underground in their respectively preferred environments, beneath either grassveld, forest, swamps, deserts, or mountainous terrain. However, Chrysospalax species tend to forage above ground in leaf litter in forests or in meadows. Eremitalpa species such as Grant's golden mole live in the sandy Namib desert, where they cannot form tunnels because the sand collapses. Instead during the day, when they must seek shelter, they "swim" through the loose sand, using their broad claws to paddle, and dive down some 50 cm to where it is bearably cool. There they enter a state of torpor, thus conserving energy.[4] At night they emerge to forage on the surface rather than wasting energy shifting sand. Their main prey are termites that live under isolated grass clumps, and they might travel for 6 kilometres a night in search of food. They seek promising clumps by listening for wind-rustled grass-root stresses and termites' head-banging alarm signals, neither of which can be heard easily above ground, so they stop periodically and dip their heads under the sand to listen.[4]

Most other species construct both foraging superficial burrows and deeper permanent burrows for residence. Residential burrows are relatively complex in form, and may penetrate as far as a metre below ground and include deep chambers for use as bolt-holes, and other chambers as latrines. They push excavated soil up to the surface as mole-hills, or compact it into the tunnel walls. They feed on small insects and earthworms or small vertebrates such as lizards or burrowing snakes. They depend on their sense of hearing to locate much of their prey, and the cochleas of a number of golden mole species have been found to be long and highly coiled, which may indicate a greater ecological dependence on low frequency auditory cues than we see in Talpid moles.[5]

Some species also have hypertrophied middle ear ossicles, in particular the malleus, which apparently is adapted towards the detection of seismic vibrations.[6][7] In this respect there is some apparent convergent evolution to burrowing reptiles in the family Amphisbaenidae.

Reproduction

Females give birth to one to three hairless young in a grass-lined nest within the burrow system. Breeding occurs throughout the year. The adults are solitary, and their burrowing territory may be aggressively defended from intruders, especially where resources are relatively scarce.[3]

Status

Of the 21 species of golden mole, no fewer than 11 are threatened with extinction. The primary causes are sand mining, poor agricultural practices, increasing urbanisation, and predation by domestic cats and dogs.

Classification

The taxonomy of the Chrysochloridae is undergoing a review in the light of new genetic information. They have traditionally been listed with the shrews, hedgehogs and a grab-bag of small, difficult-to-place creatures as part of the order Insectivora. Some authorities retain this classification, at least for the time being. Others group the golden moles with the tenrecs in a new order, which is sometimes known as Tenrecomorpha, while others call it Afrosoricida and reserve Tenrecomorpha for the family Tenrecidae.

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References
  1. Bronner, G.N.; Jenkins, P.D. (2005). "Order Afrosoricida". 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. 77–81. ISBN 978-0-8018-8221-0. OCLC 62265494.
  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. Kuyper, Margaret (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 764–765. ISBN 978-0-87196-871-5.
  4. Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press
  5. Crumpton, Nick; Kardjilov, Nikolay; Asher, Robert J. (2015-08-01). "Convergence vs. Specialization in the ear region of moles (mammalia)". Journal of Morphology. 276 (8): 900–914. doi:10.1002/jmor.20391. ISSN 1097-4687. PMID 25858660.
  6. Mason, Matthew J. (2003-08-01). "Morphology of the middle ear of golden moles (Chrysochloridae)". Journal of Zoology. 260 (4): 391–403. doi:10.1017/S095283690300387X. ISSN 1469-7998.
  7. Mason, Matthew J.; Narins, Peter M. (2001-01-01). "Seismic Signal Use by Fossorial Mammals". American Zoologist. 41 (5): 1171–1184. CiteSeerX 10.1.1.547.3698. doi:10.1093/icb/41.5.1171. JSTOR 3884562.
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