Acanthophis

Acanthophis
Acanthophis laevis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Genus: Acanthophis
Species

See taxonomy

Acanthophis is a genus of elapid snakes. Commonly called death adders, they are native to Australia, New Guinea and nearby islands, and are among the most venomous snakes in the world. The name of the genus derives from the Ancient Greek acanthos/ἄκανθος "spine" and ophis/ὄφις "snake", referring to the spine on the death adder's tail.

Seven species are listed by ITIS,[1] though it remains unclear how many species this genus includes, with figures ranging from 4 to 15 species being quoted (see Taxonomy).

Contents

Description

Death adders are very viper-like in appearance, having a short, robust body, triangular shaped heads and small subocular scales. They also have vertical pupils and many small scales on the top of the head. Their fangs are also longer and more mobile than for most other elapids, although still far from the size seen in some of the true vipers. Despite their name and appearance, they are not vipers at all. This is a case of convergent evolution.

They normally take 2–3 years to reach adult size. Females are generally slightly larger than the males. They can also be easily distinguished from other Australian snakes because of a small, worm like lure on the end of their tail, which is used to attract prey. Most have large bands around their bodies, though the color itself is variable, depending on their locality. Colors are usually black, grey or red and yellow, but also include brown and greenish-grey.

Hunting

Unlike most snakes, death adders do not actively hunt, but rather lie in ambush and draw their prey to them. When hungry, death adders bury themselves amongst the substrate. This may be leaf litter, soil or sand, depending on their environment. The only part of themselves they expose are their head and their tail, both generally very well camouflaged. The end of the tail is used for caudal luring and when wiggled is easily mistaken for a grub or worm. An unsuspecting bird or mammal will eventually notice the 'easy lunch' and attempt to seize it. Only then will the death adder move, lashing out with the quickest strike of any snake in the world.[2] A death adder can go from a strike position, to strike and envenoming their prey, and back to strike position again, in less than 0.15 of a second.[2]

Venom

Death adders can inject on average 40–100 mg of highly toxic venom with a bite. The LD50 of the venom was reported as 0.4–0.5 mg/kg subcutaneous and it is completely neurotoxic, containing neither haemotoxins nor myotoxins, unlike most venomous snakes.

A bite from a death adder can cause paralysis which seems minor at first but can cause death from a complete respiratory shutdown in six hours. Symptoms of envenomation can be reversed through the use of death adder antivenom, or using anticholinesterases, which break the synaptic blockade by making acetylcholine more available to the parasympathetic nervous system, thus mitigating the effects of the venom.

Before antivenom was introduced, it is reported that about 50% of death adder bites were fatal. Deaths are much rarer nowadays as the anti-venom is widely available and the progression of envenomation symptoms is slow.

Taxonomy

Although the death adders resemble vipers of the Viperidae family, they are really members of the Elapidae family, being more closely related to cobras, mambas, and coral snakes.

It remains unclear how many species this genus includes. Traditionally, only A. antarcticus, A. praelongus and A. pyrrhus have been recognized. In 1998 five new species were described (A. barnetti, A. crotalusei, A. cummingi, A. wellsei and A. woolfi)[3] and in 2002 an additional three were described (A. groenveldi, A. macgregori and A. yuwoni).[4] These were received with scepticism,[5][6][7] and only A. wellsi, where an extended description has been published,[5] has been widely recognized.[1][8] Further confusion exists over the death adders from Papua New Guinea and Indonesia. They have variously been placed in A. antarcticus or A. praelongus. In 2005 it was shown that neither is appropriate, and the New Guinea death adders fall into two main clades:[9] The rather smooth-scaled A. laevis complex (including death adders from Seram), and the rough-scaled A. rugosus complex. The latter can be divided into two sub-clades; one, A. rugosus sensu stricto, from southern New Guinea, and a second, A. hawkei, from northern Queensland and the Northern Territory in Australia. It is likely some of these include more than one species, as populations included in e.g. A. laevis show extensive variation in both pattern and scalation.[9]

Species

Species[1][8] Authority[8] Subspecies* Common name Geographic range
A. antarcticusT (Shaw, 1794) 2[10] Common death adder Australia[9]
A. hawkei Wells & Wellington, 1985 1 Barkly Tableland death adder Australia[11]
A. laevis Macleay, 1878 None[12] Smooth-scaled death adder Indonesia, Papua New Guinea[12]
A. praelongus Ramsay, 1877 None[13] Northern death adder Australia[9]
A. pyrrhus Boulenger, 1898 None[14] Desert death adder Australia[14]
A. rugosus Loveridge, 1948 None[15] Rough-scaled death adder Australia, Indonesia[15]
A. wellsi Hoser, 1998 1[16] Pilbara death adder Australia[16]

*) Not including the nominate subspecies.
T) Type species.

References

  1. ^ a b c "Acanthophis". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=700200. Retrieved 10 March 2011. 
  2. ^ a b Fastest striking snake
  3. ^ Hoser, R. (1998): Death adders (genus Acanthophis): an overview, including descriptions of five new species and one subspecies. Monitor 9(2): 20-30, 33-41. available online
  4. ^ Hoser, R. (2002): Death Adders (Genus Acanthophis): An Updated overview, including descriptions of 3 New Island species and 2 New Australian subspecies. Crocodilian - Journal of the Victorian Association of Amateur Herpetologists, September 2002: 5-11, 16-22, 24-30, front and back covers. available online
  5. ^ a b Aplin, K.P. & S.C. Donnellan (1999): An extended description of the Pilbara Death Adder, Acanthophis wellsi Hoser (Serpentes: Elapidae), with notes on the Desert Death Adder, A. pyrrhus Boulenger, and identification of a possible hybrid zone. Records of the Western Australian Museum 19: 277-298.
  6. ^ Wüster, W., B. Bush, J.S. Keogh, M. O'Shea & R. Shine (2001): Taxonomic contributions in the "amateur" literature: comments on recent descriptions of new genera and species by Raymond Hoser. Litteratura Serpentium 21: 67-79, 86-91. available online (PDF)
  7. ^ Williams, D., W. Wüster & B. Fry (2006): The good, the bad and the ugly: Australian snake taxonomists and a history of the taxonomy of Australia's venomous snakes. Toxicon 48: 919-930. available online (PDF)
  8. ^ a b c Reptile Database (version 10 March 2011). Acanthophis.
  9. ^ a b c d Wüster, W., A.J. Dumbrell, C. Hay, C.E. Pook, D.J. Williams & B.G. Fry (2005): Snakes across the Strait: Trans-Torresian phylogeographic relationships in three genera of Australasian snakes (Serpentes: Elapidae: Acanthophis, Oxyuranus and Pseudechis). Molecular Phylogenetics and Evolution 34(1): 1-14. available online (PDF)
  10. ^ Reptile Database (version 10 March 2011). Acanthophis antarcticus.
  11. ^ Reptile Database (version 10 March 2011). Acanthophis hawkei.
  12. ^ a b Reptile Database (version 10 March 2011). Acanthophis laevis.
  13. ^ Reptile Database (version 10 March 2011). Acanthophis praelongus.
  14. ^ a b Reptile Database (version 10 March 2011). Acanthophis pyrrhus.
  15. ^ a b Reptile Database (version 10 March 2011). Acanthophis rugosus.
  16. ^ a b Reptile Database (version 10 March 2011). Acanthophis wellsi.

External links

Media related to [//commons.wikimedia.org/wiki/Category:Acanthophis Acanthophis] at Wikimedia Commons