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Echidna

For other uses, see Echidna (disambiguation).

Echidnas /ɨˈkɪdnə/, sometimes known as spiny anteaters,[1] belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. The four extant species, together with the platypus, are the only surviving members of that order and are the only extant mammals that lay eggs.[2] Their diet consists of ants and termites, but they are not closely related to the true anteaters of the Americas. They live in Australia and New Guinea.

Echidnas evidently evolved between 20 and 50 million years ago, descending from a platypus-like monotreme.[3] This ancestor was aquatic, but echidnas are adapted to life on land.[3]

The echidnas are named after the "Mother of monsters" in Greek mythology, despite not resembling the mythological creature.

Description[edit]

A short-beaked echidna building a defensive burrow in French Island National Park (43 seconds)
Spines and fur of an echidna
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.

Echidnas are small, solitary mammals[4] covered with coarse hair and spines. Superficially, they resemble the anteaters of South America and other spiny mammals such as hedgehogs and porcupines. They are usually black or brown in colour. There have been several reports of 'albino' echidnas, their eyes pink and their spines white.[4] They have elongated and slender snouts that function as both mouth and nose. Like the platypus, they are equipped with electrosensors, but while the platypus has 40,000 electroreceptors on its bill, the long-billed echidna has only 2,000, and the short-billed echidna, which lives in a drier environment, has no more than 400 located at the tip of its snout.[5] They have very short, strong limbs with large claws, and are powerful diggers. Echidnas have tiny mouths and toothless jaws. The echidna feeds by tearing open soft logs, anthills and the like, and using its long, sticky tongue, which protrudes from its snout, to collect prey. The short-beaked echidna's diet consists largely of ants and termites, while the Zaglossus species typically eats worms and insect larvae.[6] They have no teeth, and break down their food by grinding it between the bottoms of their mouths and their tongues.[7] The echidnas' ears are slits on the sides of their heads that are usually unseen due to the fact that they are blanketed by their spines. The external ear is called the "pinna", which is created by a large cartilaginous funnel, deep in the muscle.[4]

Echidnas do not enjoy extreme temperatures, and use caves and rock crevasses to hide from harsh weather conditions. Echidnas can be found in forests, woodlands, snuggled under vegetation, roots or piles of debris. They sometimes hide in other animal burrows, such as rabbits and wombats. Echidnas have large territories causing their areas to overlap.[7] In addition, echidnas are decent swimmers. When swimming, echidnas expose their snout and some of their spines. They are known to journey their way to water in order to groom and bathe themselves.[8]

Long-beaked echidnas have sharp, tiny spines on their tongues that help capture their prey.[6] The echidnas feces are 7 centimeters long and are cylindrical in shape; they are usually broken and unrounded.[7] When eating they consume large amounts of dirt and ant hill material, which makes up majority of their feces.[8]

Echidnas and the platypus are the only egg-laying mammals, known as monotremes. The female lays a single soft-shelled, leathery egg 22 days after mating, and deposits it directly into her pouch. Hatching takes place after 10 days; the young echidna then sucks milk from the pores of the two milk patches (monotremes have no nipples) and remains in the pouch for 45 to 55 days,[9] 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.

The neocortex makes up half of the echidna's brain,[10] compared to 80% of a human brain.[11][12] 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.[13] Contrary to previous research, the echidna does enter REM sleep, but only when the ambient temperature is around 25 °C (77 °F). At temperatures of 15 °C (59 °F) and 28 °C (~82 °F), REM sleep is suppressed.[14] The average lifespan of an echidna in the wild is estimated around 16 years. When fully grown a female can weigh up to 4.5 kilograms and a male can weigh up to 6 kilograms.[7] You can determine the echidnas' sex by their size; males are 25% larger than females. As well, the reproductive organs differ even though both sexes have a single opening they use to urinate, release their faeces and use to mate.[4]

Male echidnas have non-venomous spurs on the hind feet.[15]

Reproduction[edit]

Male echidnas have a four-headed penis. 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 has sex, it alternates heads in sets of two.[16] When not in use, the penis is retracted inside a preputial sac in the cloaca. The male echidna's penis is 7 centimeters long when erect, and its shaft is covered with penile spines.[17]

It is a challenge to study the echidna in their natural habitat and they show no interest in mating while in captivity. Therefore, no one has 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 has only resulted in the penis swelling.[16]

Breeding season begins in late June and extends through September. Males will form lines up to ten individuals long, the youngest echidna trailing last, that follow the female and attempt to mate. During a mating season an echidna may switch between lines. This is known as the "train" system.[7] Two weeks after mating, a single fertilized egg, weighing 380 milligrams and being about 1.4 centimeters long, is implanted in a rear-facing pouch that has developed on the female, where it is held for ten days before hatching. The young echidna, called a puggle, is then held in the pouch for two to three months before being expelled.[8] Puggles will stay within their mother's den for up to a year before leaving.[7]

Threats[edit]

Echidnas are very timid animals. When they feel endangered they curl into a ball allowing their spines to shield them. Although they have a way to protect themselves, the echidnas still face many dangers. Some predators include wild cats, foxes, domestic dogs and goannas. Snakes pose as a large threat to the echidna species because they slither into their burrows and prey on the young spineless puggles. Some precautions that can be taken include keeping the environment clean by picking up litter and causing less pollution, planting vegetation for echidnas to use as shelter, supervising pets, reporting hurt echidnas or just leaving them undisturbed. Grabbing them may cause stress or not picking them up correctly may result in injury.[7]

Evolution[edit]

Short-beaked echidna skeleton

Molecular clock data suggest echidnas split from platypuses between 19 and 48 million years ago, and that platypus-like fossils dating back to over 112.5 million years ago therefore represent basal forms, rather than close relatives of the modern platypus.[3] This would imply that echidnas evolved from water-foraging ancestors that returned to living completely on the land, even though this put them in competition with marsupials. Consequently, oviparous reproduction in monotremes may have given them an advantage over marsupials, a view consistent with present ecological partitioning between the two groups.[3]

Taxonomy[edit]

Echidnas are classified into three genera.[18] The genus Zaglossus includes three extant species and two species known only from fossils, while only one extant species from the genus Tachyglossus is known. The third genus, Megalibgwilia, is known only from fossils.

Zaglossus[edit]

The three living Zaglossus species are endemic to New Guinea.[18] They are rare and are hunted for food. They forage in leaf litter on the forest floor, eating earthworms and insects. The species are:

The two fossil species are:

Tachyglossus[edit]

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.

A short-beaked echidna curled into a ball, the snout is visible on the right

Megalibgwilia[edit]

The genus Megalibgwilia is known only from fossils:

Echidnas in popular culture[edit]

References[edit]

  1. ^ "Short-Beaked Echidna, Tachyglossus aculeatus". Park & Wildlife Service Tasmania. Retrieved October 2012. 
  2. ^ Stewart, Doug (April–May 2003). "The Enigma of the Echidna". National Wildlife. 
  3. ^ a b c d Phillips, MJ; Bennett, TH; Lee, MS (October 2009). "Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas". Proc. Natl. Acad. Sci. U.S.A. 106 (40): 17089–94. doi:10.1073/pnas.0904649106. PMC 2761324. PMID 19805098. 
  4. ^ a b c d Augee, Michael; Gooden, Brett; Musser, Anne (2006). Echidna : extraordinary egg-laying mammal ([Second ed.] ed.). Collingwood: CSIRO. p. 3. ISBN 978-0-643-09204-4. 
  5. ^ "Electroreception in fish, amphibians and monotremes". Map of Life. 7 July 2010. 
  6. ^ a b "Zaglossus bruijni". AnimalInfo.org. 
  7. ^ a b c d e f g Carritt, Rachel. "Echidnas: Helping them in the wild". NSW National Parks and Wildlife Service. Retrieved 13 April 2013. 
  8. ^ a b c "Short-beaked Echidna". Department of Primary Industries, Parks, Water, and Environment. Retrieved 13 April 2013. 
  9. ^ "Short-beaked echidna (Tachyglossus aculeatus)". Arkive.org. 
  10. ^ Gill, Victoria (19 November 2012). "Are these animals too 'ugly' to be saved?". BBC News. 
  11. ^ Dunbar, R.I.M. (1993). "Coevolution of neocortical size, group size and language in humans". Behavioural and Brain Sciences 16 (4): 681–735. doi:10.1017/S0140525X00032325. 
  12. ^ Dunbar, R.I.M. "The Social Brain Hypothesis". University of Colorado at Boulder, Department of Psychology and Neuroscience. Retrieved 4 January 2014. 
  13. ^ Cason, M. (2009). "Tachyglossus aculeatus". Animal Diversity. Retrieved October 2012. 
  14. ^ Nicol, SC; Andersen, NA; Phillips, NH; Berger, BJ (March 2000). "The echidna manifests typical characteristics of rapid eye movement sleep". Neurosci. Lett. 283 (1): 49–52. doi:10.1016/S0304-3940(00)00922-8. PMID 10729631. 
  15. ^ Griffiths, Mervyn (1978). The biology of the monotremes. New York: Academic Press. ISBN 0123038502. 
  16. ^ a b Shultz, N. (26 October 2007). "Exhibitionist spiny anteater reveals bizarre penis". New Scientist. Retrieved 27 October 2006. 
  17. ^ Larry Vogelnest; Rupert Woods (18 August 2008). Medicine of Australian Mammals. Csiro Publishing. ISBN 978-0-643-09928-9. Retrieved 15 March 2013. 
  18. ^ a b Flannery, T.F.; Groves, C.P. (1998). "A revision of the genus Zaglossus (Monotremata, Tachyglossidae), with description of new species and subspecies". Mammalia 62 (3): 367–396. doi:10.1515/mamm.1998.62.3.367. 

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