Causinae

Causinae
Common night adder, C. rhombeatus
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]

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] However, this is contradicted by recent molecular studies.^[4][5] Six species are currently recognized.^[6] They are commonly known as night adders.^[2][3]

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 to 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.^[7]

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

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 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.^[8]

Feeding

The diet consists 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.^[8]

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 4-5 inches (10-12.5 cm) in length.^[8]

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.^[8]

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.^[7]

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.^[9]

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.^[9]

Species

Species[6]	Taxon author[6]	Common name	Geographic range
C. bilineatus	Boulenger, 1905	Two-striped night adder	Africa in Angola, Zambia, and southern DR Congo.
C. defilippii	(Jan, 1863)	Snouted night adder	Southeast Africa.
C. lichtensteinii	(Jan, 1859)	Lichtenstein's night adder	Equatorial Africa from Zambia and 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

There has been a long-standing tendency among herpetologists to make assumptions regarding the phylogenetic position of this group. McDiarmid et al. ^[1] suggested that the consensus among the experts in 1999 was that Causus was basal to all viperids and therefore deserved a separate subfamily. However, two more recent molecular phylogenitic studies^[4][5] have shown that Causus is not only not basal to all viperids, but in fact appears to be nested within the viperines. Consequently, recognition of the subfamily Causinae is inappropriate.

See also

• Causinae by common name
• Causinae by taxonomic synonyms
• Snakebite

References

1. ^ ^{a b c d e} 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. ^ ^{a b c d e f g h} 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. ^ ^{a b c d e f} Spawls S, Branch B. 1995. The Dangerous Snakes of Africa. Ralph Curtis Books. Dubai: Oriental Press. 192 pp. ISBN 0-88359-029-8.
4. ^ ^{a b} Nagy, Z.T., Vidal, N., Vences, M., Branch, W.R., Pauwels, O.S.G., Wink, M., Joger, U., 2005. Molecular systematics of African Colubroidea (Squamata: Serpentes) In: Huber, B.A., Sinclair, B.J., Lampe, K.H. (Eds.), African Biodiversity: Molecules, Organisms, Ecosystsms. Proc. 5th Intern. Symp. Trop. Biol. Museum Koenig, Bonn, pp. 221-228.
5. ^ ^{a b} Wüster, W., Peppin, L., Pook, C.E., Walker, D.E., 2008. A nesting of vipers: phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Molecular Phylogenetics and Evolution, 49, 445-459.
6. ^ ^{a b c} , "Causus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=634411. Retrieved 14 August 2006. 
7. ^ ^{a b} Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. ISBN 0-448-11856-4.
8. ^ ^{a b c d} Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN 0-8069-6460-X.
9. ^ ^{a b} 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.

Further reading

• Cope ED. 1860 (dated 1859). Catalogue of the venomous serpents in the museum of the Academy of Natural Sciences of Philadelphia, with notes on the families, genera and species. Proc. Acad. Nat. Sci. Philadelphia 11: 332-347.
• Hallowell E. 1842. Journal of the Academy of Natural Sciences of Philadelphia. 8:336-338.
• Peters. 1862. Monatsberichte der Preussischen Akademie Wissenschaften zu Berlin. 1862:271-279[276].
• Peters. 1882. Sitzungsberichte der Preussischen Akademie Wissenschaften zu Berlin. 1882: 893-896[893].
• Wagler J. 1830. Natürliches system der amphibien, mit vorangehender classification der Säugthiere und vögel. München, Stuttgart und Tübingen. vi, 354 pp., 9 pls.

External links

• Causus at the Reptarium.cz Reptile Database. Accessed 2 August 2007.