Cerastes (genus)

Cerastes
Desert horned viper, C. cerastes
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Reptilia Order: Squamata Suborder: Serpentes Family: Viperidae Subfamily: Viperinae Genus: Cerastes Laurenti, 1768
Synonyms
Cerastes - Laurenti, 1768 Aspis - Laurenti, 1768 Cerastes - Wagler, 1830 Gonyechis - Fitzinger, 1843

Common names: horned vipers, North African desert vipers.

Cerastes is a genus of small, venomous vipers found in the deserts and semi-deserts of northern North Africa eastward through Arabia and Iran. Three species are currently recognized.

Description

C. cerastes, horned individual.

Cerastes are small snakes, averaging less than 50 cm in length, but are relatively stout in appearance. The head is broad, flat and distinct from the neck. The head is covered with tubercularly keeled scales, which usually number 15 or more across, and a supraorbital horn may be present over each eye in some species. The snout is short and wide and the eyes, which are set well forward, are small to moderate in size. The body is short, stout and cylindrically depressed. The tail is short and tapers abruptly behind the vent. The dorsal scales are small, with serrated keels, in 23-35 rows at midbody.

Although Cerastes are often referred to as horned vipers, only the two larger species, C. cerastes and C. gasperettii, are known to have horns, and even these do not always have them. Individuals with and without horns occur within the same populations and even within the same litters.

When present, each horn consists of a single long, spinelike scale that can be folded back into an indentation in the postocular scale. They fold back in response to direct stimulation, thus streamlining the head and easing passage through burrows. Horns occur more often in individuals from sandy deserts as opposed to stony deserts. Specimens without horns have a prominent brow ridge instead.

The purpose of the horns is the subject of much speculation. One theory is that they to allow a buildup of sand above the eyes while keeping it out of the eyes themselves. Another, more recent theory is simply that the horns serve to break up the outline of the head, making them harder for prey animals to spot.

Geographic range

North Africa eastward through Arabia and Iran. Mallow et al. (2003) describe the genus as being restricted to the deserts of North Africa and southwestern Asia, with the Negev desert acting as a filter zone between the three species mentioned in the table below.

Habitat

Desert and semi-desert.

Behavior

This genus is nocturnal and terrestrial (not known to climb into bushes), often hiding by burying themselves in the sand. Although often described as slow moving, these snakes are also capable of sidewinding. When doing so, that can move quickly across the sand.

Cerastes species are not known to be particularly ill-tempered ("fairly placid"), but when threatened they will often stand their ground and form C-shaped coils that are rubbed together to produce a rasping or crackling sound, similar to Echis. With enough provocation, they will strike from this position.

These snakes are capable of "sinking" quickly down into loose sand, using their keeled, angled and serrated lateral scales in a rocking motion. This process begins at the tail and moves forward until the entire head is buried and only the eyes and nostrils are exposed. They can bury themselves this way whether in an outstretched or a coiled position. See video.

Feeding

These are ambush predators that lie buried in the sand, waiting for prey to happen by. Their diet consists mainly of rodents, birds and lizards.

Reproduction

All three species lay eggs. However, those of C. vipera hatch within hours of deposition as opposed to many weeks -- something not previously observed in other African snakes, most of which lay eggs that hatch weeks later or give birth to live young.

Venom

Unlike Echis, to which they bear a passing resemblance, Cerastes species are not known to be ill-tempered and their venom, which is a cytotoxin, is not particularly potent. Bites can be painful and should always be taken seriously, but little venom is injected and few fatalities are known. Bites do occur, especially in the Suez Canal region, but no statistical data in available.

Species

Species	Authority	Common name	Geographic range
C. cerastesT	(Linnaeus, 1758)	Saharan horned viper	Arid north Africa (Morocco, Western Sahara, Mauritania and Mali, eastward through Algeria, Tunisia, Niger, Libya and Chad to Egypt, Sudan, Ethiopia and Somalia) through Sinai to the northern Negev of Israel. In the Arabian Peninsula, it occurs in Yemen and extreme southwestern Saudi Arabia.
C. gasperettii	Leviton & Anderson, 1967	Arabian horned viper	Found in the Arava valley, located on the border between southern Israel and Jordan, eastwards through Jordan and Iraq to Khuzistan Provence in southwestern Iran. In the Arabian Peninsula it has been found in Kuwait, Saudi Arabia, Oman, Quatar, United Arab Emirates and Yemen.
C. vipera	(Linnaeus, 1758)	Sahara sand viper	Arid North Africa: Mauritania, Western Sahara, Morocco, Algeria, Mali, Tunisia, Libya, Niger, Chad and Egypt. Sinai Peninsula: Egypt and Israel.

^T) Type species.

Taxonomy

Although it would seem that Laurenti changed his mind in 1768 and decided to name this genus Aspis, instead of Cerastes as he did earlier, this was eventually rejected. The ICZN later placed the name Cerastes on the Official List of Generic Names in Zoology (name no. 1539), while the name Aspis was placed on the Official Index of Invalid Generic Names in Zoology (name no. 1630).

See also

• Viperinae.
• List of viperine species and subspecies.
• True vipers - Common names.
• Snakebite.

Other references

• Cohen AC, Meyers BC. 1970. A function of the horn in the sidewinder rattlesnake Crotalus cerastes, with comments on other horned snakes. Copeia, American Society of Ichthyologists and Herpetologists, 3:574-5.
• Green HW. 1988. Antipredator mechanisms in reptiles. In: Gans C, editor. The Biology of the Reptilia. Vol. 16. New York: Academic Press. pp 212-317.
• Kramer E, Schnurrenberger H. 1958. Zur Schlangenfauna von Libyen. Die Aquarien- und Terrarien-Zeitschrift XI.2., 1.2.:57-9.
• Mohamed AH, Khaled LZ. 1966. Effect of venom of Cerastes cerastes on nerve tissue and skeletal muscle. Toxicon, Great Britain, 3:233-4.
• Mohamed AH, Abdel-Baset A, Hassan A. 1980. Immunological studies om monovalent and bivalent Cerastes antivenin. Toxicon, Great Britain, 18:384-7.
• Schnurrenberger H. 1959. Observations on behavior in two Libyan species of viperine snake. Herpetologica, Herpetologist's League, 15:70-2.
• Sterer Y. 1992. A mixed litter of horned and hornless Cerastes cerastes. Israel Journal of Zoology, 37:247-9.
• Werner YL, Verdier A, Rosenman D, Sivan N. 1991. Systematics and zoogeography of Cerastes (Ophidia: Viperidae) in the Levant: 1, Distinguishing Arabian from African "Cerastes cerastes." The Snake, The Japan Snake Institute, Yabuzuka Honmachi, Nittagun, Gunma Prefecture, Japan, 23:90-100.
• U.S. Navy. 1991. Poisonous Snakes of the World. New York: Dover Books. (Reprint of US Govt. Printing Office, Washington D.C.) 133 pp. ISBN 0-486-26629-X.

External links

• Template:EMBL genus