The southern marsupial mole (Notoryctes typhlops), also known as the itjaritjari () or itjari-itjari, is a mole-like marsupial found in the western central deserts of 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. It also lacks complete eyes as it has little need for them. It feeds on earthworms and larvae.
History of discovery
Although the southern marsupial mole was probably known by Aboriginal Australians for thousands of years, the first specimen examined by the scientific community was collected in 1888. Stockman W. Coulthard made the discovery on Idracowra Pastoral Lease in the Northern Territory by following some unusual prints that lead him to the animal lying under a tussock. Not knowing what to do with the strange creature, he wrapped it in a kerosene soaked rag, placed it in a revolver cartridge box and forwarded it to E. C. Stirling, the Director of the South Australian Museum. Due to the poor transportation conditions of the time, the specimen reached its destination in a badly decomposed state. Hence, Stirling was unable to find any evidence of the pouch or epipubic bones and decided the creature was not a marsupial.
Nineteenth century scientists believed that marsupials and eutherians had evolved from the same primitive ancestor and were looking for a living specimen that would serve as the missing link. Because the marsupial mole closely resembled the golden moles of Africa, some scientists concluded that the two were related and that they had found the proof. This, however, is not the case, as became obvious by examining better-preserved specimens that had a marsupial pouch. The striking similarities of the two species are, in fact, the result of convergent evolution.
Taxonomy and phylogeny
Although the family Notoryctidae is poorly represented in the fossil record there is evidence of at least one distinct genus Yalkaparidon, in the early Miocene sediments in the Riversleigh deposit in northern Australia.
Due to their highly specialized morphology and the fact that notoryctids share many common characteristics with other marsupials, there has been much debate surrounding their phylogeny. However, recent molecular studies indicate that notoryctids are not closely related to any of the other marsupial families and should be placed in an order of their own, Notoryctemorphia.
Furthermore, molecular data suggests that Notoryctemorphia separated from other marsupials around 64 million years ago. Although at this time South America, Antarctica and Australia were still joined the order evolved in Australia for at least 40-50 million years. The Riversleigh fossil material suggests that Notoryctes was already well adapted for burrowing and probably lived in the rainforest that covered much of Australia at that time. The increase in aridity at the end of Tertiary was likely one of the key contributing factors to the development of the current highly specialized form of marsupial mole. The marsupial mole had been burrowing long before the Australian deserts came into being.
Morphology
The southern marsupial mole is small in size, with a head and body length varying from 121 to 159 mm, a tail length of 21–26 mm and a weight of 40-70 g. The body is covered with short, dense, silky fur with a pale cream to white color often tinted by the iron oxides from the soil which gives it a reddish chestnut brown tint. It has a light brownish pink nose and mouth and no vibrissae.
The cone shaped head merges directly with the body, and there is no obvious neck region. The limbs are short and powerful, and digits III and IV of the manus have large spade-like claws. The dentition varies with individuals and, because the molars have a root of only one third of the length, it has been assumed that moles cannot deal with hard food substances. The dorsal surface of the rostrum and the back of the tail have no fur and the skin is heavily keratinized. There is no external evidence of the eyes, and the optic nerve is absent. It does, however, have a pigment layer where the eyes should be, probably a vestige of the retina. Both lachrymal glands and Jacobson's organ are well developed, and it has been suggested that the former plays a role in lubricating the nasal passages and Jacobson's organ.