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Echidna

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Echidnas
Temporal range:Miocene–Holocene
Short-beaked echidna
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Monotremata
Superfamily: Ornithorhynchoidea
Family: Tachyglossidae
Gill,1872
Type genus
Tachyglossus
Illiger,1811
Species

GenusTachyglossus
T. aculeatus
GenusZaglossus
Z. attenboroughi
Z. bruijnii
Z. bartoni
Genus †Megalibgwilia
†M. owenii
†M. robusta
Genus †Murrayglossus
†M. hacketti

Echidna range
Short-beaked echidna
Western long-beaked echidna
Eastern long-beaked echidna
Sir David's long-beaked echidna

Echidnas(/ɪˈkɪdnəz/), sometimes known asspiny anteaters,[1]are quill-covered[2]monotremes(egg-layingmammals) belonging to thefamilyTachyglossidae/tækiˈɡlɒsɪdiː/,living inAustraliaandNew Guinea.The fourextantspecies of echidnas and theplatypusare the only living mammals that lay eggs and the only surviving members of theorderMonotremata.[3]The diet of some species consists of ants and termites, but they are not closely related to the Americantrue anteatersor tohedgehogs.Their young are calledpuggles.

Echidnas evolved between 20 and 50 million years ago, descending from aplatypus-like monotreme.[4]This ancestor was aquatic, but echidnas adapted to life on land.[4]

Etymology

Echidnas are possibly named afterEchidna,a creature fromGreek mythologywho was half-woman, half-snake, as the animal was perceived to have qualities of both mammals and reptiles.[citation needed] An alternative explanation is a confusion with Ancient Greek:ἐχῖνος,romanized:ekhînos,lit. 'hedgehog, sea urchin'.[5]

Physical characteristics

Echidnas are medium-sized, solitary mammals covered with coarse hair andspines.[6]The spines are modified hairs and are made ofkeratin,the same fibrous protein that makes up fur, claws, nails, and horn sheaths in animals.[2]

Spinesof the echidna

Superficially, they resemble the anteaters of South America and other spiny mammals such ashedgehogsandporcupines.They are usually black or brown in coloration. There have been several reports ofalbinoechidnas with pink eyes and white spines.[6]They have elongated and slender snouts that function as both mouth and nose, and which haveelectrosensorsto find earthworms, termites, ants, and other burrowing prey.[7]This is similar to theplatypus,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.[8]

Echidnas have short, strong limbs with large claws, and are powerful diggers. Their hind claws are elongated and curved backwards to aid in digging. Echidnas have tiny mouths and toothless jaws, and feed by tearing open soft logs,anthillsand the like, and licking off prey with their long, sticky tongues. The ears are slits on the sides of their heads under the spines. Theexternal earis created by a large cartilaginous funnel, deep in the muscle.[6]At 33 °C (91.4 °F), echidnas also possess the second-lowest active body temperature of all mammals, behind the platypus.

Despite their appearance, echidnas are capable swimmers, as they evolved fromplatypus-like ancestors.When swimming, they expose their snout and some of their spines, and are known to journey to water to bathe.[9]

The first European drawing of an echidna was made inAdventure Bay, TasmaniabyHMSProvidence's third lieutenantGeorge TobinduringWilliam Bligh's second breadfruit voyage.[10]

Diet

Theshort-beaked echidna's diet consists mostly of ants and termites, while theZaglossus(long-beaked) species typically eat worms and insect larvae.[11]The tongues oflong-beaked echidnashave sharp, tiny spines that help them capture their prey.[11]They have no teeth, so they break down their food by grinding it between the bottoms of their mouths and their tongues.[12]Echidnas'faecesare 7 cm (3 in) long and are cylindrical in shape; they are usually broken and unrounded, and composed largely of dirt and ant-hill material.[12]

Like all mammals, echidnas feed their young on milk, which contains various factors to sustain their growth and development.[13][14]

Habitat

Echidnas do not tolerate extreme temperatures; they shelter from harsh weather in caves and rock crevices. Echidnas are found in forests and woodlands, hiding under vegetation, roots or piles of debris. They sometimes use the burrows (both abandoned and in use) of animals such as rabbits andwombats.Individual echidnas have large, mutually overlapping territories.[12]

Anatomy

Echidnas and platypuses are the only egg-laying mammals, themonotremes. The average lifespan of an echidna in the wild is estimated at 14–16 years. Fully grown females can weigh about 4.5 kilograms (9.9 lb), the males 33% larger, at about 6 kilograms (13 lb).[12]Though the internal reproductive organs differ, both sexes possess an identical single cloaca opening for urination, defecation, and mating.[6]

Male echidnas have non-venomousspurson the hind feet, similar to the venomous male platypus.[15]

Due to their lowmetabolismand 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.[16]

The echidna's brain is halfneocortex,[17]compared to 80% of a human brain.[18][19]Contrary to previous research, the echidna does enterREMsleep, 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.[20]

Reproduction

The female lays a single soft-shelled, leathery egg 22 days after mating, and deposits it directly into her pouch. An egg weighs 1.5 to 2 grams (0.05 to 0.07 oz)[21]and is about 1.4 centimetres (0.55 in) long. Whilehatching,the baby echidna opens the leather shell with a reptile-likeegg tooth.[22]Hatching takes place after 10 days ofgestation;the young echidna, called a puggle,[23][24]born larval and fetus-like, then sucksmilkfrom theporesof the twomilk patches(monotremes have nonipples) and remains in the pouch for 45 to 55 days,[25]at which time it starts to develop spines. The mother digs a nursery burrow and deposits the young, returning every five days to suckle it until it is weaned at seven months. Puggles will stay within their mother's den for up to a year before leaving.[12]

A short-beaked echidna building a defensive burrow inFrench Island National Park(43 seconds)

Male echidnas have a four-headed penis.[26]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 itcopulates,it alternates heads in sets of two.[27][28]When not in use, the penis is retracted inside apreputialsac in the cloaca. The male echidna's penis is 7 centimetres (2.8 in) long when erect, and its shaft is covered withpenile spines.[29]These may be used toinduce ovulationin the female.[30]

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 ofelectrically stimulated ejaculationin order toobtain semen samplesbut this has only resulted in the penis swelling.[28]

Breeding seasonbegins in late June and extends through September. During mating season, a female may be followed by a line or "train" of up to 10 males, the youngest trailing last, and some males switching between lines.[12]

Threats

Echidnas are very timid. When frightened, they attempt to partially bury themselves and curl into a ball similar to ahedgehog.Strong front arms allow echidnas to dig in and hold fast against a predator pulling them from the hole.

Their many predators includeferal cats,foxes,domestic dogs,andgoannas.Snakes pose a large threat when they slither into echidna burrows and prey on the spineless young puggles.

They are easily stressed and injured by handling. Some ways to help echidnas include picking up litter, causing less pollution, planting vegetation for shelter, supervising pets, reporting hurt echidnas, and leaving them undisturbed.[12]

Evolution

Short-beaked echidna skeleton

The divergence between oviparous (egg-laying) and viviparous (offspring develop internally) mammals is believed to date to theTriassicperiod.[31]Most findings from genetics studies (especially of nuclear genes) are in agreement with the paleontological dating, but some other evidence, like mitochondrial DNA, give slightly different dates.[32]

Molecular clockdata suggest echidnas split from platypuses between 19 and 48 million years ago, so thatplatypus-like fossilsdating back to over 112.5 million years ago representbasalforms, rather than close relatives of the modern platypus.[4]This would imply that echidnas evolved fromwater-foraging ancestors that returned to land living,which put them in competition with marsupials.[further explanation needed]Although extant monotremes lack adult teeth (platypuses have teeth only as juveniles), many extinct monotreme species have been identified based on the morphology of their teeth.[7]Of the eight genes involved in tooth development, four have been lost in both platypus and echidna, indicating that the loss of teeth occurred before the echidna-platypus split.[22]

Further evidence ofwater-foraging ancestorscan be found in some of the echidna's anatomy, includinghydrodynamicstreamlining, dorsally projecting hind limbs acting as rudders, and locomotion founded on hypertrophied humeral long-axis rotation, which provides an efficient swimming stroke.[4]

Oviparousreproduction in monotremes may give them an advantage overmarsupialsin some environments.[4]Their observed adaptive radiation contradicts the assumption that monotremes are frozen in morphological andmolecular evolution.

It has been suggested that echidnas originally evolved inNew Guineawhen it was isolated from Australia and from marsupials. This would explain their rarity in the fossil record, their abundance in present times in New Guinea, and their original adaptation to terrestrial niches, presumably without competition from marsupials.[33]

Taxonomy

Cladogram of Tachyglossidae by Upham et al. 2019[34][35]
Tachyglossidae

Echidnas are a smallcladewith two extantgeneraand fourspecies.[36]The genusZaglossusincludes three extant and two fossil species, with only one extant species from the genusTachyglossus.

Zaglossus

TheWestern long-beaked echidna,which is endemic toNew Guinea

The three livingZaglossusspecies areendemictoNew Guinea.[36]They are rare and are hunted for food. They forage inleaf litteron theforest floor,eatingearthwormsandinsects.The species are

The one fossil species is:

Tachyglossus

In Australia, the short-beaked echidna may be found in many environments, including urban parkland, such as the shores ofLake Burley GriffininCanberra,as depicted here.

Theshort-beaked echidna(Tachyglossus aculeatus) is found in southern, southeast and northeastNew Guinea,and also occurs in almost all Australian environments, from the snow-cladAustralian Alpsto the deep deserts of theOutback,essentially anywhere ants and termites are available. It is smaller than theZaglossusspecies, and it has longer hair.

Ashort-beaked echidnacurled into a ball; the snout 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 myrmecophagic (ant or termite-eating) since theCretaceous.The fossil evidence of invertebrate-feedingbandicootsand rat-kangaroos, from around the time of the platypus–echidnadivergenceand pre-datingTachyglossus,show evidence that echidnas expanded into new ecospace despite competition from marsupials.[38]

Additionally, extinct echidnas continue to bedescribedbytaxonomists;

Megalibgwilia

The genusMegalibgwiliais known only from fossils:

Murrayglossus

The genusMurrayglossusis known only from fossils:[39]

  • M. hacketti(previously classified in the genusZaglossus) from Pleistocene ofWestern Australia.

As food

TheKunwinjkupeople ofWestern Arnhem Land(Australia) call the echidnangarrbek,[40]and regard it as a prized food and "good medicine".[note 1][41]The echidna is hunted at night, gutted, and filled with hot stones and mandak (Persoonia falcata) leaves.[42]According toLarrakiaelders Una Thompson and Stephanie Thompson Nganjmirra, once captured, an echidna is carried attached to the wrist like a thick bangle.[citation needed]

See also

Notes

  1. ^Reverend Peterson Nganjmirra, personal comment.

References

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Bibliography

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