Echidnas (), sometimes known as spiny anteaters, monotremes (egg-laying mammals) belonging to the family Tachyglossidae , living in Australia and New Guinea. The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the only surviving members of the order Monotremata. as the animal was perceived to have qualities of both mammals and reptiles. An alternative explanation is a confusion with .
A synonym for the echidna, in a mid-19th century British Encyclopaedia, is, “hedgehog of the Colonists at Sidney [sic]”.
Physical characteristics
Echidnas are medium-sized, solitary mammals covered with coarse hair and spines. This is similar to the platypus, which has 40,000 electroreceptors on its bill, but the long-beaked echidna has only 2,000, while the short-beaked echidna, which lives in a drier environment, has no more than 400 at the tip of its snout.
The first European drawing of an echidna was made in Adventure Bay, Tasmania by 's third lieutenant George Tobin during William Bligh's second breadfruit voyage.
Diet
The short-beaked echidna's diet consists mostly of ants and termites, while the Zaglossus (long-beaked) species typically eat worms and insect larvae. Echidnas' faeces are long and are cylindrical in shape; they are usually broken and unrounded, and composed largely of dirt and ant-hill material.
Due to their low metabolism and accompanying stress resistance, echidnas are long-lived for their size; the longest recorded lifespan for a captive echidna is 50 years, with anecdotal accounts of wild individuals reaching 45 years. Contrary to previous research, the echidna does enter REM sleep, but only in a comfortable temperature around 25 °C (77 °F). At lower or higher temperatures of 15 °C (59 °F) and 28 °C (82 °F), REM sleep is suppressed. and is about long. While hatching, the baby echidna opens the leather shell with a reptile-like egg tooth. Hatching takes place after 10 days of gestation; the young echidna, called a puggle, born larval and fetus-like, then sucks milk from the pores of the two milk patches (monotremes have no teats) and remains in the pouch for 45 to 55 days, During mating, the heads on one side "shut down" and do not grow in size; the other two are used to release semen into the female's two-branched reproductive tract. Each time it copulates, it uses the pair of heads opposite those it used the previous time. These may be used to induce ovulation in the female.
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It is a challenge to study the echidna in its natural habitat, and they show no interest in mating while in captivity. Prior to 2007, no one had ever seen an echidna ejaculate. There have been previous attempts, trying to force the echidna to ejaculate through the use of electrically stimulated ejaculation in order to obtain semen samples but this has only resulted in the penis swelling.
Evolution
thumb|Short-beaked echidna skeleton
The divergence between oviparous (egg-laying) and viviparous (offspring develop internally) mammals is believed to date to the Triassic period. Most findings from genetics studies (especially of nuclear genes) are in agreement with the palaeontological dating, but some other evidence, like mitochondrial DNA, give slightly different dates.
Molecular clock data suggest echidnas split from platypuses between 19 and 48 million years ago, so that platypus-like fossils dating back to over 112.5 million years ago represent basal forms, rather than close relatives of the modern platypus.
Taxonomy
Echidnas are a small clade with two extant genera and four species.
- Eastern long-beaked echidna (Z. bartoni), of which four distinct subspecies have been identified.
Tachyglossus
thumb|In Australia, the short-beaked echidna may be found in many environments, including urban parkland, such as the shores of [[Lake Burley Griffin in Canberra, as depicted here.]]
The short-beaked echidna (Tachyglossus aculeatus) is found in southern, southeast and northeast New Guinea, and also occurs in almost all Australian environments, from the snow-clad Australian Alps to the deep deserts of the Outback, essentially anywhere ants and termites are available. It is smaller than the Zaglossus species, and it has longer hair.
thumb|A [[short-beaked echidna curled into a ball; a foot is visible on the right.]]
Despite the similar dietary habits and methods of consumption to those of an anteater, there is no evidence supporting the idea that echidna-like monotremes have been myrmecophagous (ant or termite-eating) since the Cretaceous. The fossil evidence of invertebrate-feeding bandicoots and rat-kangaroos, from around the time of the platypus–echidna divergence and pre-dating Tachyglossus, show evidence that echidnas expanded into new ecospace despite competition from marsupials.
Additionally, extinct echidnas continue to be described by taxonomists;
Megalibgwilia
The genus Megalibgwilia is known only from fossils:
- M. hacketti (previously classified in the genus Zaglossus) from Pleistocene of Western Australia.
As food
The Kunwinjku people of Western Arnhem Land (Australia) call the echidna ngarrbek, and regard it as a prized food and "good medicine". The echidna is hunted at night, gutted, and filled with hot stones and mandak (Persoonia falcata) leaves. According to Larrakia elders Una Thompson and Stephanie Thompson Nganjmirra, once captured, an echidna is carried attached to the wrist like a thick bangle.
In popular culture
- The echidna appears on the reverse of the Australian five-cent coin.
- An echidna named Millie was one of the three official mascots for the 2000 Summer Olympics in Sydney.
- The Sonic the Hedgehog franchise features a range of anthropomorphic animals, one of the most prominent being Knuckles the Echidna.
See also
- List of mammal genera
- List of recently extinct mammals
- List of prehistoric mammals
Notes
References
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