Look! There's a slippery "wireless mouse" in the desert

Today's species is very suitable for playing memes. But I don't want to play it, because the most suitable meme for it is Shukaku of the Sand, and I hate Gaara the most in Naruto.

In fact, there is no need for a meme. The appearance of the desert golden mole can capture the hearts of many people. From above, its round body with no visible limbs, rolling on the sand like a drop of mercury. It is extremely cute.

Swimming in the sand

There are 21 species of golden moles, all living in sub-Saharan Africa. People once thought they were relatives of moles, but molecular studies have shown that they belong to the order Afrotheria and are related to elephants and manatees.

The Grant's golden mole (Eremitalpa granti) is the only species of the genus Eremitalpa and the smallest of the family Eremitalpa (up to 35 grams). There are two subspecies of the golden mole, E. granti granti, which lives in Little Namqualand and the Southwestern Cape Province of South Africa, and E. granti namibensis, which lives in the Namibian Desert. E. granti granti sometimes burrows in the soil like a mole, while E. granti namibensis lives in the most bizarre medium of all burrowing mammals: it swims in the sand.

The plump Cape golden mole (Chrysochloris asiatica), by Cornelis van Noorde | Wikimedia Commons

The desert golden mole moves in the desert surface, using its powerful forelimbs to scoop sand, and occasionally lifting its head and shoulders to support the sand piled above. Unlike animals that dig holes in the soil, the desert golden mole does not dig tunnels, nor does it have permanent nests. It digs forward relentlessly, and the tunnel collapses behind it. This mode of movement is called sand swimming. Animals that are good at digging are very strong. JA Bateman observed a golden mole (the specific species is unknown, but it was not a desert golden mole) in the laboratory. He once used a 9-kilogram weight to press on the cage, but it was pushed by this little guy.

Traces of golden mole excavation | Planet Earth: Deserts

The entire body of the desert golden mole is highly adapted to underground life. Its hair has a flat cross-section, and its scales are small and smooth, overlapping densely, making the body surface smoother, reducing the wear and tear of the hair, as well as the resistance of traveling through the sand. This has an unexpected result. When light passes through the scales, thin film interference occurs, making the hair of the desert golden mole appear iridescent.

Figure a, Cape golden mole; Figure b, iridescent hair; Figure c, non-iridescent hair | Holly K Snyder et al. / Biology Letters (2012)

There is a hard and thick skin in front of the nose of the desert golden mole, which protects the nostrils and also serves as a "drill" to push away the sand. There are blocking structures in the nostrils and the ear holes are covered by hair, all to prevent sand from entering. The forelimbs lack the fifth finger, and the first, second and third fingers are particularly thick and have huge claws. The skull of the golden mole is conical, which is different from the flat skull of the mole.

The combined effects of the oxygen-deficient underground environment, the energy consumption of digging, and the lack of food resources have shaped the desert golden mole into an energy-saving mode by natural selection. Its metabolic rate is 22% of the expected metabolic rate for a body of the same size, and its food intake is also small relative to its body size. As a result, the desert golden mole has a poor ability to regulate its body temperature, which varies with the temperature of the surrounding sand, ranging from 19°C to 38°C. The surface temperature of the Namibian Desert can reach 50°C under the sun, but as long as you drill 10 cm, the temperature of the sand will drop significantly, so the desert golden mole hides under the sand during the day to avoid death from heat stroke.

Strange hearing aid

The desert golden mole forages at night, and its main food is a termite with the scientific name Psammotermes allocerus. It also eats other insects and lizards. The Namibian Desert is one of the most biologically scarce environments. There are some grassy hills scattered in the endless sea of ​​sand, where termites gather. The journey to find food is long, and (as you have seen) the desert golden mole is blind. The eyes of the desert golden mole are extremely small, covered with skin, and the optic nerve has degenerated. And according to the observations of the experimenters, it is not sensitive to sounds transmitted in the air. The blind and "deaf" desert golden mole relies on a special sound.

There are three small bones in the ears of mammals, the malleus, saddle bone and stapes, which are used to conduct the sound received by the eardrum. Generally speaking, the small bones are the smallest of all bones, but the malleus of the desert golden mole is very large, weighing up to 60 mg (the human malleus is only 28 mg).

Human auditory ossicles | Anatomist90 / Wikimedia Commons

The malleus of different species of golden moles. The second one from the right is the desert golden mole. The first and largest one is the giant forest golden mole (Chrysospalax villosus). Some golden moles have an enlarged malleus and some do not. The relationship between them is not yet fully understood. | Robert J. Asher et al. / MC Evolutionary Biology (2010)

Mammals mainly perceive sounds propagated in the air, but sound waves propagated in solids will reach the ossicles through the skull, which is called inertial bone conduction. When conducting sound, the ossicles form a rotating lever structure. Generally speaking, the center of gravity of the malleus of an animal will not deviate too much from the axis around which the lever rotates, otherwise a lot of unnecessary noise will be heard due to inertial bone conduction. However, the center of gravity of the super malleus of the desert golden mole is far away from the axis of rotation, so it deliberately increases inertial bone conduction. In addition, the huge malleus has a large inertia and can remain still when conducting vibrations.

When foraging, desert golden moles occasionally bury their heads in the sand, using their skulls to pick up low-frequency vibrations in the sand and transmit them to their auditory bones. Perhaps because of the wind, the sounds made by the hills and the sand have different amplitudes and frequencies, acting as a beacon of sound, guiding the most bizarre and adorable burrowing animals to visit.