Inland taipan

Among the Aboriginal people from the area now known as Goyder Lagoon in north‑eastern South Australia, the inland taipan was traditionally known as dandarabilla.^[8][9]

The inland taipan was first described scientifically in 1879, when two specimens were collected at the junction of the Murray and Darling Rivers in north‑western Victoria. Frederick McCoy described these as Diemenia microlepidota, the "small‑scaled brown snake".^[8][10] In 1882 a third specimen was collected near Bourke, New South Wales, and William John Macleay described it as Diemenia ferox, believing it to be a different species.^[21][5][7] No further material was collected until the 1970s.

In 1896, George Albert Boulenger transferred both taxa to the genus Pseudechis (black snakes), treating them as Pseudechis microlepidotus and P. ferox.^[5] In 1956, working solely from the published descriptions and notes, James Roy Kinghorn regarded ferox as a synonym of microlepidotus and proposed the new genus Parademansia for the species.^[21]

In 1963, Eric Worrell considered Parademansia microlepidotus conspecific with Oxyuranus scutellatus (then commonly known simply as the "taipan").^[5] However, in September 1972 an unclassified snake head collected by a grazier on a Channel Country station west of Windorah in south‑western Queensland was sent to the Queensland Museum. Herpetologists Jeanette Covacevich and Charles Tanner travelled to the site, located 13 live specimens, and thereby rediscovered the long‑lost "western taipan" Parademansia microlepidotus.^[10]

In 1976, Covacevich and Wombey argued that Parademansia microlepidotus was sufficiently distinct to warrant generic recognition, a view shared by Harold Cogger.^[5] Subsequently, Covacevich, McDowell, Tanner and Mengden (1981) compared anatomical characters, chromosomes, and behaviour of the two then‑recognised species Oxyuranus scutellatus and Parademansia microlepidota and concluded that both belonged in a single genus. The older name Oxyuranus (erected in 1923), therefore, had priority and was adopted for the combined genus.^[22][23]

The current binomial name of the inland taipan has therefore been Oxyuranus microlepidotus since the early 1980s.^[22][23] The generic name Oxyuranus derives from the Greek oxys ("sharp" or "needle‑like") and ouranos ("arch", specifically the arch of the palate), referring to the needle‑like anterior process on the palatal arch.^[24] The specific epithet microlepidotus is from Latin and means "small‑scaled", referring to the small body scales, and is the origin of the common name "small‑scaled snake".^[25]

Once Covacevich et al. (1981) had shown that the fierce snake (formerly Parademansia microlepidota) belonged to the genus Oxyuranus, the name "taipan" (derived from the Aboriginal term dhayban) was retained for O. scutellatus, which became known as the coastal taipan (or "eastern taipan"), while O. microlepidotus came to be widely referred to as the "inland (or western) taipan").^[10]

The inland taipan occurs on cracking‑clay plains in semiarid regions near the border of Queensland and South Australia.^[7][26]

In Queensland, the species has been recorded from the Channel Country bioregion,^[27] including Diamantina National Park, Durrie Station, Morney Plains Station^[28] and Astrebla Downs National Park.^[29] In South Australia it has been observed in the Marree–Innamincka NRM district,^[30][31] including Goyder Lagoon,^[32] the Tirari Desert, Sturt Stony Desert, Coongie Lakes, Innamincka Regional Reserve and near Oodnadatta.^[33] An isolated population is also known from near Coober Pedy, South Australia.^[2][3][34]

Two historical records exist from further south‑east, at the junction of the Murray and Darling Rivers in north‑western Victoria (1879) and near Bourke, New South Wales (1882), but the species has not been recorded from either state since the late 19th century.^[2][7]

The inland taipan is typically dark tan in overall colour, varying from a rich, dark brown to a brownish light green depending on season. The back, flanks, and tail may show various shades of brown and grey. Many dorsal scales have broad blackish margins, which because the scales are arranged in diagonal rows, align to form broken chevron‑like markings that slope backwards and downwards. The lowermost lateral scales frequently have a yellowish anterior edge. The dorsal scales are smooth and lack keels.

The rounded snout, head and neck are usually noticeably darker than the body – glossy black in winter and dark brown in summer. This darker pigmentation is thought to assist thermoregulation by allowing the snake to absorb heat while exposing only a small portion of the body at the entrance of a burrow. The eyes are of moderate size with dark brown to blackish irises and without a distinct pale ring around the pupil.

The species has 23 rows of dorsal scales at midbody, 55–70 divided subcaudal scales, and a single anal scale. The average total length is about 1.8 m (5.9 ft), although larger individuals can attain 2.5 m (8.2 ft).^[59] The fangs measure about 3.5–6.2 mm, somewhat shorter than those of the coastal taipan.^[35]

Inland taipans are oviparous, typically producing clutches of 10–24 eggs. Eggs are usually laid in abandoned mammal burrows, deep rock crevices, or similar sheltered sites. Incubation lasts about two months, though the duration is influenced by temperature and humidity. Reproductive output appears to depend in part on food availability; in years when prey is scarce, females may not breed or may lay smaller clutches.^[7]

In captivity, inland taipans generally live for around 10–15 years, although longer lifespans have been recorded. An individual at Australia Zoo reportedly lived for more than 20 years.^[35]

In the wild, the inland taipan is a dietary specialist that feeds almost exclusively on small to medium‑sized mammals,^[60][61] particularly rodents such as the long-haired rat (Rattus villosissimus), plains rat (Pseudomys australis), introduced house mouse (Mus musculus), and various dasyurid marsupials. In captivity, the species also takes day‑old chicks.^[7]

Unlike many other highly venomous snakes, which often strike once and then retreat while the prey succumbs, the inland taipan typically employs a rapid, close‑quarters attack. It may deliver up to eight envenoming bites in a single attack,^[7][20] frequently snapping its jaws several times to inflict multiple puncture wounds.^[62][7] During this attack, the snake commonly maintains physical contact with the prey, using its body to restrain the animal while repeatedly biting. This strategy injects large quantities of extremely toxic venom deeply into the tissues, causing almost immediate incapacitation and leaving the prey little opportunity to struggle or inflict injury on the snake.^[63]

The inland taipan has few natural predators as an adult, but juveniles are vulnerable. The mulga snake (Pseudechis australis) is resistant to the venom of many Australian snakes and has been documented preying on young inland taipans.^[64] The large monitor lizard perentie (Varanus giganteus) shares much of the inland taipan's habitat, and once large enough, readily preys on venomous snakes, including taipans.^[65]

Many experienced reptile keepers consider the inland taipan to be comparatively placid to handle, at least in controlled conditions,^[7] although its potential to inflict a rapidly fatal bite means that extreme caution is always required.

In the wild, inland taipans are seldom encountered by the general public because of their remote distribution and their tendency to remain underground for much of the day. If a person approaches quietly without causing strong vibrations or noise, the snake may not perceive them as a threat and may remain motionless or attempt to retreat.^[66][67][68] Nevertheless, a safe distance must always be maintained because any bite is a medical emergency.

When threatened, the inland taipan usually attempts escape, but if it is cornered, provoked,^[69] mishandled^[70] or prevented from fleeing,^[71] it adopts a characteristic threat posture in which the anterior body is raised in a tight, low, S‑shaped curve with the head oriented towards the source of danger. If the warning is ignored, it may strike with great speed and precision, and it envenomates in the vast majority of bites.^{[7][71][72][73]}

Clinical toxicologist, venom researcher, and herpetologist Scott A. Weinstein and colleagues have noted that only a small number of inland taipan bites have been documented in the medical literature. In an analysis published in Toxicon, they reported 11 well‑documented cases of envenoming, only two of which were inflicted by wild snakes. They emphasised that, when indicated, early administration of adequate antivenom, combined with rapid pressure‑immobilisation first aid and efficient retrieval of victims from remote locations (preferably by well‑equipped aircraft), is central to achieving favourable outcomes.^[74]

The average venom yield per bite of an adult inland taipan has been estimated at about 44 mg, with a recorded maximum of 110 mg. For comparison, typical yields for the Indian cobra (Naja naja) are around 169 mg (maximum 610 mg), and for the North American eastern diamondback rattlesnake (Crotalus adamanteus) about 410 mg (maximum 848 mg).^[86]

The median lethal dose (LD₅₀) of inland taipan venom in mice, administered subcutaneously – the route most relevant to typical snake bites – is approximately 0.025 mg/kg,^[6][86] or as low as 0.01 mg/kg when dissolved in bovine serum albumin.^[6][87] This is markedly lower (i.e. more toxic) than values reported for many other dangerously venomous snakes, including the beaked sea snake (Enhydrina schistosa; 0.164 mg/kg), Indian cobra (0.565 mg/kg), and eastern diamondback rattlesnake (11.4 mg/kg).^[86] Although the inland taipan’s total venom yield is smaller than that of the coastal taipan, its venom is almost four times as toxic on a weight‑for‑weight basis.^[88][89] A single bite is estimated to contain enough venom to kill at least 100 adult humans.

Intravenous, intraperitoneal, and intramuscular LD₅₀ values for inland taipan venom have not been systematically determined in the published literature.^[90]

For many years, Belcher's sea snake (Hydrophis belcheri) was popularly but erroneously described as the most venomous snake, largely because toxicity data from different modes of administration were conflated in a widely read book, Snakes in Question: The Smithsonian Answer Book (1996). Venom researcher Bryan Grieg Fry has pointed out that LD₅₀ values can only be meaningfully compared when determined using the same route of administration; otherwise, comparisons are invalid.^[91] Belcher's sea snake venom, tested intramuscularly, has reported LD₅₀ values of 0.24 mg/kg^[92] and 0.155 mg/kg,^[90] less toxic than several other sea snake venoms, including that of the olive sea snake (Aipysurus laevis; 0.09 mg/kg) and especially the black‑banded robust sea snake (Hydrophis melanosoma; 0.082 mg/kg intramuscularly). The latter species has also been tested subcutaneously (0.111 mg/kg), a value comparable to that of the coastal taipan and still less than one-fourth as toxic as inland taipan venom. Based on subcutaneous LD₅₀ values, Dubois' sea snake (Aipysurus duboisii) currently ranks as the most toxic of the sea snakes (0.044 mg/kg), yet its venom remains less than half as lethal as that of the inland taipan.^[90]

Experimental work indicates that the venoms of juvenile and adult inland taipans are similar in composition and toxicity; juvenile venom is not significantly weaker than adult venom.^[64][93]

The venom of the inland taipan contains a complex mixture of toxins, including:^[72]

• Potent neurotoxins:
  • Presynaptic beta‑neurotoxins such as paradoxin (PDX)^[87] (PDX is considered to be among the most potent beta‑neurotoxins yet described; it interferes with the release of the neurotransmitter acetylcholine from nerve endings, leading to neuromuscular blockade.)^[87]
  • Postsynaptic neurotoxins such as oxylepitoxin-1^[94] α-oxytoxin 1, and α-scutoxin 1^[95]
• Hemotoxins with strong procoagulant activity, affecting blood clotting
• Myotoxins that damage muscle tissue
• Possible toxins
  • Nephrotoxins, affecting the kidneys
  • Haemorrhagins, which damage the vascular endothelium^[96]
• The enzyme hyaluronidase, which facilitates rapid spread of venom through tissues^[7]

Ronelle Welton of James Cook University has noted that despite their medical importance, the venoms of Oxyuranus species remain relatively understudied at the molecular level. As of 2005, the amino‑acid sequences of only seven inland taipan venom proteins had been deposited in the SWISS‑PROT database.^[25]