Is the Australian mole (Notoryctes) a supermole?

Also please see https://www.youtube.com/watch?v=tyWF1G8_ExQ&t=7s

The marsupial mole (Notoryctes, https://en.wikipedia.org/wiki/Marsupial_mole and https://www.abc.net.au/news/2023-06-17/elusive-marsupial-mole-spotted-uluru-swims-in-sand/102482890 and https://books.google.com.au/books?hl=en&lr=&id=5IqhZoTEF10C&oi=fnd&pg=PA464&dq=Marsupial+mole&ots=KQKu9dlYtl&sig=6N4ZqycOmL5In2yGuKzJVJ7tIF8&redir_esc=y#v=onepage&q=Marsupial%20mole&f=false) superficially resembles placental moles, despite being unrelated to them.

This is one of the most striking examples known of evolutionary convergence (https://en.wikipedia.org/wiki/Convergent_evolution).

However, the marsupial mole does not merely combine the presence of a pouch with the disappearance of eyes and ears.

As research gradually uncovers the details about the only Australian mole, what is emerging is that this is more than a lookalike.

The marsupial mole may indeed be the quintessential mole. It not only matches, but possibly surpasses, the adaptive extremes shown by subterranean mammals on other continents.

The marsupial mole has a large, bare pad on the head (https://www.bbc.com/news/world-australia-68720246). This has not been studied, but appears to be a blunt instrument of subterranean locomotion.

Unlike other moles, the marsupial mole has fused vertebrae in the neck, which presumably allows great pressure to be placed on the head as a ramrod.

Typical moles (Talpidae, https://en.wikipedia.org/wiki/Talpidae) lack a burrowing organ on the head, instead having pointed muzzles as soft as those of shrews.

Golden moles (Chrysochloridae, https://en.wikipedia.org/wiki/Golden_mole), the moles of Africa, have a tough nose used as a wedge (https://afrotheria.net/golden-moles/photos.php). However, the bare pad is far too small to extend to the forehead.

If typical moles and golden moles are not as extremely adapted to butting through the earth as is the marsupial mole, this may be because they repeatedly commute along tunnels once they have constructed them.

The marsupial mole appears to have no open tunnels, instead forcing its way afresh through every centimetre of earth in the course of its locomotion (https://www.publish.csiro.au/am/AM13015).

In this sense, the marsupial mole may be the ultimate subterranean mammal.

A failure to construct tunnels explains why, unlike other moles, the marsupial mole does not make molehills.

The Namib golden mole (Eremitalpa, https://en.wikipedia.org/wiki/Grant%27s_golden_mole) also lacks molehills. However, it differs from the marsupial mole by depending partly on swimming through the relatively loose sand at the surface of dunes. They maintain their body temperatures, remain active and warm even under the snows of winter, and reproduce relatively rapidly.

The forefoot of the marsupial mole is extreme, since the claws form a vertical spade (https://www.abc.net.au/news/2024-04-07/-northern-marsupial-mole-kakarratul-sighted-/103662744).

Typical moles have different forefeet, essentially broad paws projecting sideways as if from the neck (https://www.sci.news/biology/european-moles-sand-08805.html and https://www.parchilazio.it/cammino_naturale_dei_parchi-schede-7288-animalisulcammino_la_talpa_europea and https://nature.guide/card.aspx?lang=en&id=579), and used for raking relatively crumbly soil sideways.

Whereas the claws of typical moles move beside the body, those of the marsupial mole cleave the sand downwards, in front of the body.

Golden moles have pick-like claws on digits number 2 and 3 of the forefoot, held horizontal instead of vertical.

The marsupial mole has similar claws in digits 2 and 3. However, it has an additional, particularly large claw on digit 4, which forms the main blade of the articulated spade.

Typical moles lack external ears, but retain internal ear bones capable of hearing low-pitched vibrations underground.

The marsupial mole is unique among moles, because its entire ear is degenerate. The extremely small size of its internal ear bones suggest that the marsupial mole is nearly deaf as well as blind (https://www.mdpi.com/2073-4425/14/11/2018 and https://www.pnas.org/doi/abs/10.1073/pnas.94.25.13754).

This contrasts with the golden moles, in some of which the size of the ear bones exceeds that of surface-dwelling mammals, proportional to body size.

The tail of the marsupial mole is odd, inviting further study. Its appearance suggests that the tail may be used as a prop, allowing extra pressure to be placed on the head and claws. If so, the use of the tail in digging is unprecedented among subterranean mammals. No-one has yet a found a way to observe the marsupial mole in action underground.

The marsupial mole differs in habitat from other moles. It is widespread in, and apparently restricted to, hummock grassland (https://www.anbg.gov.au/photo/vegetation/hummock-grasslands.html and https://www.publish.csiro.au/am/AM00115).

This is a peculiar type of 'desert' restricted to Australia, sandy and dry but vegetated (https://www.inaturalist.org/posts/58175-the-australian-empty-quarter-epitome-of-a-nutrient-desert#).

Failure of Europeans and domestic animals to exploit hummock grassland owes more to this land's extreme nutrient-poverty than its aridity (https://www.inaturalist.org/posts/58175-the-australian-empty-quarter-epitome-of-a-nutrient-desert).

This semi-desert is even less fertile than the Sahara, so that 20% of Australia remains deserted to this day, despite the availability of groundwater in boreholes.

The main cover consists of grasses (Triodia, https://en.wikipedia.org/wiki/Triodia_scariosa) more spiny, unpalatable, and flammable than any common grass on other continents.

Although sand is extensive on the other southern continents, no mole lives in vegetated sand under dry conditions far inland.

Typical moles are widespread in the Northern Hemisphere (https://people.wku.edu/charles.smith/faunmaps/Talpidae.htm). However, they depend on the organic, loamy soils of deciduous woodlands.

Golden moles in Africa extend to sandy substrates in coastal areas. However, they are absent from the only habitats comparable to that of the marsupial mole: the Kalahari in southern Africa (https://en.wikipedia.org/wiki/Kalahari_Desert), and sandy parts of the Sahel at the edge if the Sahara (https://en.wikipedia.org/wiki/Sahel).

There are no moles today in central and South America, although fossil moles related to armadillos have been excavated. The most mole-like species alive now is the lesser fairy armadillo (Chlamyphorus truncatus, https://www.inaturalist.org/taxa/47097-Chlamyphorus-truncatus), restricted to a small area of sandy soil in semi-arid Argentina (https://upload.wikimedia.org/wikipedia/commons/2/29/Lesser_Fairy_Armadillo_area.png).

What little is known of the diet of the marsupial mole suggests an unusual reliance on insect larvae (https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.2011.00889.x). I suspect that the tropical species of marsupial mole (Notoryctes caurinus) may depend partly on the brood (eggs, larvae, pupae) of ants, which it raids by burrowing from one subterranean ant nest to another.

By comparison:

• The lesser fairy armadillo also eats ants, at least in the form of workers and soldiers (https://animalia.bio/pink-fairy-armadillo?endemic=21#:~:text=Ants%20and%20larvae%20are%20their,option%20for%20their%20underground%20lifestyle.).
• Typical moles, and most species of golden moles, eat mainly earthworms (https://www.inaturalist.org/observations?place_id=6986&taxon_id=333586&view=species), shunning ants.
• The Namib golden mole instead eats mainly termites (Psammotermes, https://www.inaturalist.org/observations?place_id=any&taxon_id=643360&view=species), which differ from Australian termites in being at home on loose sand dunes.

Subterranean mammals have to devote most of their food energy to the strenuous work of burrowing. However, they save energy when resting, because the underground environment has a comfortable temperature and a poor supply of oxygen.

In addition, protection from predators means that subterranean mammals do not need to devote much energy to reproduction.

The resting metabolism of golden moles and armadillos is even slower than that of most marsupials. However, further research may show that the reproduction of the marsupial mole is particularly slow.

If so, it is possible that the marsupial mole devotes less of its energy to offspring, and more of its energy to locomotion, than any other subterranean mammal. Typical moles are different, because they have a rich supply of earthworms in ventilated tunnels.

The marsupial mole stretches our concept of the genetic plasticity of marsupials. It may also be a 'supermole' in stretching adaptive limits beyond those of placental moles. The broad hard organs of its head and forefeet, and to a lesser degree hindfeet and tail, equip it to burrow afresh to each meal, despite the poor food to be found in a habitat lacking both nutrients and water.

Genetic constraints and geographical isolation therefore fail to explain the absence of other body forms (equivalent to bears, pigs, primates, otters, cats, and ruminants) in the indigenous fauna of Australia.

In particular, the lack of mole-rats in Australasia is unlikely to be an accident of history. All other continents (including central and South America) have rodents resembling gophers, derived from a total of eight families which have independently undergone reduction of eyes, ears, tails, and resting metabolic rates (https://www.jstor.org/stable/2096793).

However, the supply of edible tubers appears to be smaller in hummock grassland than in the Kalahari. Possibly, mole-rats failed to evolve in Australia because of a lack of suitable tubers as food.

Publicado el julio 9, 2024 08:36 MAÑANA por milewski