Causinae

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Causinae
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Viperidae
Subfamily: Causinae
Cope, 1860
Genus: Causus
Wagler, 1830
Synonyms
  • Causinae - Cope, 1860[1]

  • Causus - Wagler, 1830
  • Distichurus - Hallowell, 1842
  • Heterophis - Peters, 1862
  • Dinodipsas - Peters, 1882[1]

Common names: night adders.[2][3]  
 
The Causinae are a monotypic subfamily of venomous vipers found only in subsaharan Africa.[1] It was created for the genus Causus; a group considered to be among the most primitive members of the family Viperidae based on head scalation, oviparity, venom apparatus and the fact that they have round pupils.[2][3] Six species are currently recognized.[4]


Description

These snakes are fairly stout, never growing to more than 1 m in length.[3]

As opposed to most vipers where the head is distinct from the neck and covered with small scales, in Causus the head is only slightly distinct from the neck and covered with 9 large symmetrical head shields. Also, the eyes have pupils that are round instead of elliptical like other vipers. The rostral scale is broad, sometimes pointed or upturned. The nostril is located between 2 nasals and an internasal. The frontal and supraocular scales are long. A loreal scale is present, separating the nasal and preoculars. The suboculars are separated from the supralabials. The mandible has splenial and angular elements.[2]

The fangs are different too. Unlike other vipers there is no hinge action where the prefrontal bone engages the frontal. However, since the maxillary bones rotate almost as far, the fangs can still be erected. The fangs themselves are relatively short. A fine line, or suture, is also present along the length of the fang, representing the vestigial edge where the groove lips meet (from incomplete fang canal closure).[2]

The body is cylindrical or slightly depressed and moderately slender. The dorsal scales are smooth or weakly keeled with apical pits. The ventral scales are rounded and the anal plate single. The tail is short and the subcaudals can be either single or paired.[2]

Among the viperids, another unique characteristic of this genus is that several species have venom glands that are not confined the temporal area as with most vipers, but are exceptionally long and extend well down the neck.[3] These venom glands, located on either side of the spine, may be up to 10 cm in length, with long ducts connecting them to the fangs.[5]

There are also other internal differences that set the Causinae apart: they have unusually long kidneys, a well-developed tracheal lung with two tracheal arteries, and the liver overlaps the tip of the heart.[2]

Geographic range

Found only in Subsaharan Africa.[1]

Behavior

Despite their common name, this genus is active during the day as well as at night. When disturbed, they will engage in a ferocious hissing and puffing threat display. It may lift the first part of its body off the ground in a coil and make a powerful swiping strike -- juveniles have even been known to come off the ground! Others specimens may raise the first part of their body off the ground, flattening the neck and moving forward, tongue extended, like a small cobra.[3] The rather frantic strikes are often combined with attempts to quickly glide away.[6]

Feeding

Feed almost exclusively on toads and frogs.[3] There are reports of gluttony: when prey is abundant, they may eat until they are literally unable to swallow any more food.[6]

Reproduction

All Causus species lay eggs (oviparious), which among vipers is considered to be a more primitive trait, though not unique.[2] The average clutch consists of some two dozen eggs that require an incubation period of about 4 months. Hatchlings are 10-12.5 cm in length.[6]

Captivity

Best kept in dry and well-ventilated cages that include places to hide, fresh water and a basking spot slightly warmer than the rest of the cage (26 to 27 °C). They will accept pre-killed mice as food, but as they are voracious feeders, care must be taken to prevent obesity by overfeeding.[6]

Venom

In spite of their enormously developed venom glands, night adders don't always use them to subdue their prey. The venom would act fast enough, but often they simply seize and swallow their prey instead.[5]

Causus venom is weak and tends only to dribble from the fangs, so that relatively little is ever injected. Envenomation normally causes only local pain and swelling.[2] Antivenin treatment should not be necessary. Nevertheless, South African polyvalent serum is known to be effective against the venom of at least two species.[7]

No recent deaths have been reported due to this species. Earlier reports of fatalities were based on anecdotal evidence; it is likely the species involved were not properly identified or that the cases were grossly mismanaged.[7]

Species

Species[4] Authority[4] Common name Geographic range
C. bilineatus Boulenger, 1905 Two-striped night adder Angola, Zambia, Southern DR Congo.
C. defilippii (Jan, 1863) Snouted night adder South-East Africa
C. lichtensteinii (Jan, 1859) Lichtenstein's night adder Equatorial Africa, Zambia, Cameroon to Ivory Coast
C. maculatus (Hallowell, 1842) West African night adder Most of Sub-Saharan Africa north of the equator
C. resimus (Peters, 1862) Green night adder Most of equatorial Africa
C. rhombeatusT (Lichtenstein, 1823) Common night adder Sub-Saharan Africa

T) Type species.

Taxonomy

Some herpetologists argue that the phylogenetic position of Causus has not been sufficiently resolved and regard it as a genus of the subfamily Viperinae instead. There has been a long-standing tendency to assume that the night adder group is either basal to all other viperines, or even to all viperids. In the latter case, it would deserve a separate subfamily. However, there have also been some studies that suggest that, despite its very different appearance, Causus may even be rooted within the Viperinae, in which case it should not be in a separate subfamily. More evidence will be needed before this dispute is finally put to rest.

See also

Cited references

  1. 1.0 1.1 1.2 1.3 McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Mallow D, Ludwig D, Nilson G. 2003. True Vipers: Natural History and Toxinology of Old World Vipers. Krieger Publishing Company, Malabar, Florida. 359 pp. ISBN 0-89464-877-2.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Spawls S, Branch B. 1995. The Dangerous Snakes of Africa. Ralph Curtis Books. Dubai: Oriental Press. 192 pp. ISBN 0-88359-029-8.
  4. 4.0 4.1 4.2 Causus (TSN 634411) at Integrated Taxonomic Information System. Accessed 18 March 2007.
  5. 5.0 5.1 Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. ISBN 0-448-11856-4.
  6. 6.0 6.1 6.2 6.3 Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN 0-8069-6460-X.
  7. 7.0 7.1 Spawls S, Howell K, Drewes R, Ashe J. 2004. A Field Guide To The Reptiles Of East Africa. A & C Black Publishers Ltd., London. 543 pp. ISBN 0-7136-6817-2.