Marsupial mole
Encyclopedia
Marsupial moles is a family of marsupials of the order Notoryctemorphia, consisting of only two extant species:
The two species of marsupial moles are rare and poorly understood burrowing mammal
s of the desert
s of Western Australia
.
Marsupial moles spend most of their time underground
, coming to the surface only occasionally, probably mostly after rain
s. They are blind
, their eyes having become reduced to vestigial lenses under the skin, and they have no external ears, just a pair of tiny holes hidden under thick hair. They do not dig permanent burrow
s, filling the tunnel in behind them as they move.
has evolved to face backwards so that it does not fill with sand, and contains just two teats, so that the animal cannot bear more than two young at a time.
The limbs are very short, with reduced digits. The forefeet have two large, flat claws on the third and fourth digits, which are used to excavate soil in front of the animal. The hindfeet are flattened, and bear three small claws; these feet are used to push soil behind the animal as it digs. In a feature unique to this animal, the neck vertebrae are fused to give the head greater rigidity during digging.
Marsupial moles provide a remarkable example of convergent evolution
, with moles
generally, and with the golden mole
s of Africa
in particular. Although only related to other moles in that they are all mammals, the external similarity is an extraordinary reflection of the similar evolutionary paths they have followed.
They are insectivorous
, feeding primarily on beetle
larva and cossid
caterpillars. Their teeth have a somewhat simplified structure, but their dental formula is similar to that of other marsupials:
ia was hotly debated, some workers regarding it as an offshoot of the Diprotodontia
(the order to which most living marsupials belong), others noting similarities to a variety of other creatures, and making suggestions that, in hindsight, appear bizarre. A 1989 review of the early literature, slightly paraphrased, states:
The mystery was not helped by the complete silence of the fossil
record. On the basis that marsupial moles have some characteristics in common with almost all other marsupials, they were eventually classified as an entirely separate order
: the Notoryctemorphia. Molecular level analysis in the early 1980s showed that the marsupial moles are not closely related to any of the living marsupials, and that they appear to have followed a separate line of development for a very long time, at least 50 million years. However some morphological evidence suggests that they may be related to bandicoot
s.
In 1985, the vast newly discovered limestone fossil deposits at Riversleigh
in northern Queensland
yielded a major surprise: a fossil between 15 and 20 million years old named Yalkaparidon coheni with molars like a marsupial mole, diprotodont-like incisors, and a skull base similar to that of the bandicoots. These features were by no means identical to the living species but clearly related, and possibly even of a direct ancestor. In itself, the discovery of a Miocene
marsupial mole presented no great mysteries. Just like the modern forms, it had many of the features that are assumed to be adaptations for a life burrowing in desert sands, in particular the powerful, spadelike forelimbs. The Riversleigh fossil deposits, however, are from an environment that was not remotely desert-like: in the Miocene, the Riversleigh area was a tropical rainforest
.
One suggestion advanced was that the Miocene marsupial mole used its limbs for swimming rather than burrowing, but the mainstream view is that it probably specialised in burrowing through a thick layer of moss, roots, and fallen leaf litter on the rainforest floor, and thus, when the continent began its long, slow desertification, the marsupial moles were already equipped with the basic tools that they now use to burrow in the sand dunes of the Western Australia
n desert.
(Notoryctes typhlops) or itjaritjari as known by the Pitjantjatjara and Yankunytjatjara people in Central Australia, and the Northern Marsupial Mole
(Notoryctes caurinus), so similar to one another that they cannot be reliably told apart in the field.
The marsupial mole, once classified as a monotreme, is now known to be a marsupial. Its ancestry goes back 50 million years or more, and its precise classification is still a matter for argument.
- Notoryctes typhlops (Southern Marsupial Mole)
- Notoryctes caurinus (Northern Marsupial Mole)
The two species of marsupial moles are rare and poorly understood burrowing mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s of the desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
.
Marsupial moles spend most of their time underground
Fossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...
, coming to the surface only occasionally, probably mostly after rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
s. They are blind
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
, their eyes having become reduced to vestigial lenses under the skin, and they have no external ears, just a pair of tiny holes hidden under thick hair. They do not dig permanent burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
s, filling the tunnel in behind them as they move.
Characteristics
The head is cone-shaped, with a leathery shield over the muzzle, the body tubular, the tail a short, bald stub. They are between 12 and 16 cm long, weigh 40 to 60 grams, and are uniformly covered in fairly short, very fine pale cream to white hair with an iridescent golden sheen. Their pouchPouch (marsupial)
The pouch is a distinguishing feature of female marsupials ; the name marsupial is derived from the Latin marsupium, meaning "pouch". Marsupials give birth to a live but relatively undeveloped fetus called a joey. When the joey is born it crawls from inside the mother to the pouch...
has evolved to face backwards so that it does not fill with sand, and contains just two teats, so that the animal cannot bear more than two young at a time.
The limbs are very short, with reduced digits. The forefeet have two large, flat claws on the third and fourth digits, which are used to excavate soil in front of the animal. The hindfeet are flattened, and bear three small claws; these feet are used to push soil behind the animal as it digs. In a feature unique to this animal, the neck vertebrae are fused to give the head greater rigidity during digging.
Marsupial moles provide a remarkable example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
, with moles
Mole (animal)
Moles are small cylindrical mammals adapted to a subterranean lifestyle. They have velvety fur; tiny or invisible ears and eyes; and short, powerful limbs with large paws oriented for digging. The term is especially and most properly used for the true moles, those of the Talpidae family in the...
generally, and with the golden mole
Golden mole
Golden moles are small, insectivorous burrowing mammals native to southern Africa. They form the family Chrysochloridae, and are taxonomically distinct from the true moles which they resemble due to convergence...
s of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
in particular. Although only related to other moles in that they are all mammals, the external similarity is an extraordinary reflection of the similar evolutionary paths they have followed.
They are insectivorous
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
, feeding primarily on beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
larva and cossid
Cossidae
Cossidae, the cossid millers or carpenter millers, make up a family of mostly large miller moths. Ths family contains over 110 genera with almost 700 known species, and many more species await description...
caterpillars. Their teeth have a somewhat simplified structure, but their dental formula is similar to that of other marsupials:
Evolution
For many years their place within the MarsupialMarsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
ia was hotly debated, some workers regarding it as an offshoot of the Diprotodontia
Diprotodontia
Diprotodontia is a large order of about 120 marsupial mammals including the kangaroos, wallabies, possums, koala, wombats, and many others. Extinct diprotodonts include the rhinoceros-sized Diprotodon, and Thylacoleo, the so-called "marsupial lion"....
(the order to which most living marsupials belong), others noting similarities to a variety of other creatures, and making suggestions that, in hindsight, appear bizarre. A 1989 review of the early literature, slightly paraphrased, states:
- When Stirling (1888) initially was unable to find the epipubic bones in Marsupial Moles, speculation was rife: the Marsupial Mole was a monotremeMonotremeMonotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
, it was the link between monotremes and marsupials, it had it closest affinities with the (placental) golden moleGolden moleGolden moles are small, insectivorous burrowing mammals native to southern Africa. They form the family Chrysochloridae, and are taxonomically distinct from the true moles which they resemble due to convergence...
s, it was convergent with edentatesXenarthraThe superorder Xenarthra is a group of placental mammals , existent today only in the Americas and represented by anteaters, tree sloths, and armadillos. The origins of the order can be traced back as far as the Paleogene in South America...
, it was a polyprotodont diprotodont, and so on.
The mystery was not helped by the complete silence of the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record. On the basis that marsupial moles have some characteristics in common with almost all other marsupials, they were eventually classified as an entirely separate order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
: the Notoryctemorphia. Molecular level analysis in the early 1980s showed that the marsupial moles are not closely related to any of the living marsupials, and that they appear to have followed a separate line of development for a very long time, at least 50 million years. However some morphological evidence suggests that they may be related to bandicoot
Bandicoot
Bandicoots are a group of about 20 species of small to medium-sized, terrestrial marsupial omnivores in the order Peramelemorphia.- Etymology :...
s.
In 1985, the vast newly discovered limestone fossil deposits at Riversleigh
Riversleigh
Riversleigh, in North West Queensland, is Australia's most famous fossil site. The 100 km² area has fossil remains of ancient mammals, birds and reptiles of Oligocene and Miocene age...
in northern Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
yielded a major surprise: a fossil between 15 and 20 million years old named Yalkaparidon coheni with molars like a marsupial mole, diprotodont-like incisors, and a skull base similar to that of the bandicoots. These features were by no means identical to the living species but clearly related, and possibly even of a direct ancestor. In itself, the discovery of a Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
marsupial mole presented no great mysteries. Just like the modern forms, it had many of the features that are assumed to be adaptations for a life burrowing in desert sands, in particular the powerful, spadelike forelimbs. The Riversleigh fossil deposits, however, are from an environment that was not remotely desert-like: in the Miocene, the Riversleigh area was a tropical rainforest
Rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
.
One suggestion advanced was that the Miocene marsupial mole used its limbs for swimming rather than burrowing, but the mainstream view is that it probably specialised in burrowing through a thick layer of moss, roots, and fallen leaf litter on the rainforest floor, and thus, when the continent began its long, slow desertification, the marsupial moles were already equipped with the basic tools that they now use to burrow in the sand dunes of the Western Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n desert.
Classification
There are thought to be two species: the Southern Marsupial MoleSouthern Marsupial Mole
The Southern Marsupial Mole is a mole-like marsupial found in the desert of southwest Australia. It is extremely adapted to a burrowing way of life. It has large, shovel-like forepaws and silky fur, which helps it move easily. The Southern Marsupial Mole also lacks complete eyes as it has little...
(Notoryctes typhlops) or itjaritjari as known by the Pitjantjatjara and Yankunytjatjara people in Central Australia, and the Northern Marsupial Mole
Northern Marsupial Mole
The Northern Marsupial Mole or Northwestern Marsupial Mole is a species of marsupial in the Notoryctidae family. It is endemic to Australia. Its natural habitat is hot deserts. The Northern Marsupial Mole is yellow in color. Its diet consists of insect pupae and larvae. It lacks eyes and barely...
(Notoryctes caurinus), so similar to one another that they cannot be reliably told apart in the field.
The marsupial mole, once classified as a monotreme, is now known to be a marsupial. Its ancestry goes back 50 million years or more, and its precise classification is still a matter for argument.