The short-beaked echidna (Tachyglossus aculeatus), also known as the common echidna, or short-nosed echidna, is one of four living species of echidna, and the only member of the genus Tachyglossus, from Ancient Greek (), meaning "fast", and (), meaning "tongue". It is covered in fur and spines and has a distinctive snout and a specialised tongue, which it uses to catch its insect prey at a great speed. Like the other extant monotremes, the short-beaked echidna lays eggs; the monotremes are the only living group of mammals to do so.
The short-beaked echidna has extremely strong front limbs and claws, which allow it to burrow quickly with great power. As it needs to be able to survive underground, it has a significant tolerance to high levels of carbon dioxide and low levels of oxygen. It has no weapons or fighting ability but deters predators by curling into a ball and protecting itself with its spines. It cannot sweat or deal well with heat, so it tends to avoid daytime activity in hot weather. It can swim if needed. The snout has mechanoreceptors and electroreceptors that help the echidna to detect its surroundings.
During the Australian winter, it goes into deep torpor and hibernation, reducing its metabolism to save energy. As the temperature increases, it emerges to mate. Female echidnas lay one egg a year and the mating period is the only time the otherwise solitary animals meet one another; the male has no further contact with the female or his offspring after mating. A newborn echidna is the size of a grape but grows rapidly on its mother's milk, which is very rich in nutrients. By seven weeks baby echidnas grow too large and spiky to stay in the pouch and are expelled into the mother's burrow. At around six months they leave and have no more contact with their mothers.
The species is found throughout Australia, where it is the most widespread native mammal, and in coastal and highland regions of eastern New Guinea, where it is known as the in the Daribi and Chimbu languages.Flannery, T. 1990. Mammals of New Guinea Robert Brown & Associates It is not threatened with extinction, but human activities, such as hunting, habitat destruction, and the introduction of foreign predatory species and parasites, have reduced its abundance in Australia.
Taxonomy and naming The short-beaked echidna was first described by George Shaw in 1792. He named the species Myrmecophaga aculeata, thinking that it might be related to the giant anteater. Since Shaw first described the species, its name has undergone four revisions: from M. aculeata to Ornithorhynchus hystrix, Echidna hystrix, Echidna aculeata and finally, Tachyglossus aculeatus.Iredale, T. and Troughton, E. 1934. A checklist of mammals recorded from Australia. Memoirs of the Australian Museum 6: i–xii, 1–122 The name Tachyglossus comes from Ancient Greek (), meaning "fast", and (), meaning "tongue", and aculeatus means 'spiny' or 'equipped with spines' in Latin.Augee, Gooden and Musser, p. 5.
The short-beaked echidna is the only member of its genus, sharing the family Tachyglossidae with the extant species of the genus Zaglossus that occur in New Guinea.Augee, Gooden and Musser, pp. 5–9. Zaglossus species, which include the western long-beaked, Sir David's long-beaked and eastern long-beaked echidnas, are all significantly larger than T. aculeatus, and their diets consist mostly of worms and grubs rather than ants and termites.Augee, Gooden and Musser, pp. 7–10. Species of the Tachyglossidae are egg-laying mammals; together with the related family Ornithorhynchidae, they are the only extant monotremes in the world.Augee, Gooden and Musser, p. 10.
The five subspecies of the short-beaked echidna are each found in different geographical locations. The subspecies also differ from one another in their hairiness, spine length and width, and the size of the grooming claws on their hind feet.Augee, Gooden and Musser, pp. 6–7. T. a. acanthion is found in the arid parts of Australia, including the Northern Territory. T. a. aculeatus is found in Queensland, New South Wales, South Australia and Victoria. T. a. lawesii is found in coastal regions and the highlands of New Guinea, and possibly in the rainforests of Northeast Queensland.Griffiths, M.E. 1978. The Biology of Monotremes. Academic Press : New York pages 64–65 T. a. multiaculeatus is found on Kangaroo Island. T. a. setosus is found on Tasmania and some islands in the Bass Strait. Subspecies of the short-beaked echidna lack genetic support, but continue to be used to describe the high morphological diversity within the species. Some authors have suggested that western and central Australian T. a. acanthion differ from those found along the east coast, and that the name T. a. ineptus should be used for the western/central animals. Dietary habits differ between subspecies - T. a. acanthion and T. a. aculeatus, which inhabit arid habitats, predominantly consume ants and termites, whereas T. a. aculeatus and T. a. setosus, from wetter climates, predominantly consume ants and scarab larvae.
The earliest fossils of the short-beaked echidna date back around 15 million years ago to the Miocene epoch, and the oldest specimens were found in caves in South Australia, often with fossils of the long-beaked echidna from the same period. The ancient short-beaked echidnas are considered to be identical to their contemporary descendants except the ancestors are around 10% smaller.Augee, Gooden and Musser, p. 16. This "post-Pleistocene dwarfing" affects many Australian mammals. Part of the last radiation of monotreme mammals, echidnas are believed to have evolutionally diverged from the platypus around 66 million years ago, between the Cretaceous and Tertiary periods. However, the echidna's pre-Pleistocene heritage has not been traced yet, and the lack of teeth on the fossils found thus far have made it impossible to use dental evidence.Augee, Gooden and Musser, pp. 16–17.
The short-beaked echidna was commonly called the spiny anteater in older books, though this term has fallen out of fashion since the echidna is only very distantly related to the true anteaters. It has a variety of names in the indigenous languages of the regions where it is found. The Noongar people from southwestern Western Australia call it the . In Central Australia southwest of Alice Springs, the Pitjantjatjara term is or , from the word for spike of porcupine grass (Triodia irritans). The word can also mean 'slowpoke'. In the Wiradjuri language of Central NSW, it is called .
In the central Cape York Peninsula, it is called in Pakanh, where is a qualifier meaning 'meat' or 'animal', in Uw Oykangand and in Uw Olkola, where is a qualifier meaning 'meat' or 'animal'. In the highland regions of southwestern New Guinea, it is known as the in the Daribi and Chimbu languages. The short-beaked echidna is called in the Motu language of Papua New Guinea.Ross, Malcolm; Pawley, Andrew; Osmond, Meredith (eds). The lexicon of Proto Oceanic: The culture and environment of ancestral Oceanic society . Volume 4: Animals . 2011. Pacific Linguistics 621.
Description
Short-beaked echidnas are typically in length, with of snout, and weigh between .Egerton, p. 38. However, the Tasmanian subspecies, T. a. setosus, is smaller than its Australian mainland counterparts.Augee, Gooden and Musser, p. 6. Because the neck is not externally visible, the head and body appear to merge. The earholes are on either side of the head, with no external pinnae. The eyes are small, about in diameter and at the base of the wedge-shaped snout.Augee, Gooden and Musser, p. 55. The nostrils and the mouth are at the distal end of the snout;Augee, Gooden and Musser, p. 2. the mouth cannot open wider than . The body of the short-beaked echidna is, with the exception of the underside, face and legs, covered with cream-coloured spines. The spines, which may be up to long, are modified hairs, mostly made of keratin.Augee, Gooden and Musser, p. 35. Insulation is provided by fur between the spines, which ranges in colour from honey to a dark reddish-brown and even black; the underside and short tail are also covered in fur.
The echidna's fur may be infested with the flea, Bradiopsylla echidnae, which is about long.
The limbs of the short-beaked echidna are adapted for rapid digging; they are short and have strong claws. Their strong and stout limbs allow it to tear apart large logs and move paving stones, and one has been recorded moving a stone; a scientist also reported that a captive echidna moved a refrigerator around the room in his home.Augee, Gooden and Musser, p. 100. The power of the limbs is based on strong musculature, particularly around the shoulder and torso areas.Augee, Gooden and Musser, pp. 100–101. The mechanical advantage of its arm is greater than that of humans, as its biceps connects the shoulder to the forearm at a point further down than for humans,Augee, Gooden and Musser, pp. 101–102. and the chunky humerus allows more muscle to form.Augee, Gooden and Musser, p. 102.
The claws on the hind feet are elongated and curved backward to enable cleaning and grooming between the spines. Like the platypus, the echidna has a low body temperature—between —but, unlike the platypus, which shows no evidence of torpor or hibernation, the body temperature of the echidna may fall as low as . The echidna does not pant or sweatAugee, Gooden and Musser, pp. 90–91. and normally seeks shelter in hot conditions.Augee, Gooden and Musser, p. 91. Despite their inability to sweat, echidnas still lose water as they exhale. The snout is believed to be crucial in restricting this loss to sustainable levels, through a bony labyrinth that has a refrigerator effect and helps to condense water vapour in the breath.Augee, Gooden and Musser, pp. 114–115. The echidna does not have highly concentrated urine, and around half of the estimated daily water loss of occurs in this manner, while most of the rest is through the skin and respiratory system. Most of this is replenished by its substantial eating of termites—one laboratory study reported ingestion of around a day, most of which was water.Augee, Gooden and Musser, pp. 115. This can be supplemented by drinking water, if available, or licking morning dew from flora.Augee, Gooden and Musser, p. 116.
In the Australian autumn and winter, the echidna enters periods of torpor or deep hibernation. Because of its low body temperature, it becomes sluggish in very hot and very cold weather.
Like all monotremes, it has one orifice,Augee, Gooden and Musser, p. 3. the cloaca, for the passage of faeces, urine and reproductive products. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip,Augee, Gooden and Musser, p. 79. which is nearly a quarter of his body length when erect. The gestating female develops a pouch on her underside, where she raises her young.Augee, Gooden and Musser, p. 4.
The musculature of the short-beaked echidna has a number of unusual aspects. The panniculus carnosus, an enormous muscle just beneath the skin, covers the entire body.Griffiths M, Walton DW (Editor), Richardson BJ (Editor), Fauna of Australia Volume 1B, AGPS Canberra, 1989. By contraction of various parts of the panniculus carnosus, the short-beaked echidna can change shape, the most characteristic shape change being achieved by rolling itself into a ball when threatened, so protecting its belly and presenting a defensive array of sharp spines. It has one of the shortest spinal cords of any mammal, extending only as far as the thorax. Whereas the human spinal cord ends at the first or second lumbar vertebra, for the echidna it occurs at the seventh thoracic vertebra. The shorter spinal cord is thought to allow flexibility to enable wrapping into a ball.Augee, Gooden and Musser, p. 53.