Agkistrodon bilineatus
Mexican Mokassinotter ( Agkistrodon b. Bilineatus )
The Mexican Mokassinotter ( Agkistrodon bilineatus ) is a snake species of the subfamily of pit vipers. Sometimes it is also called Mexican copperhead. It comes with three subspecies found in coastal areas from northern Mexico to Costa Rica. The species inhabits there, especially tropical deciduous and dry forests. It feeds on a wide range of small vertebrates.
The Mexican Mokassinotter is feared in many parts of its range because of their easy excitability, their aggressiveness and their toxicity and has at least according to older reports caused a number of deaths. It is now, however, due to the progressive destruction of their habitat for the most endangered species of snakes of America.
- 9.1 Notes and references
- 9.2 Literature
Description
The Mexican Mokassinotter is a medium to large, powerful snake with a relatively long tail. The total length is in adult animals usually over 80 cm, the previously known maximum length is 138 cm. On the tail accounts for males on average, depending on the population 19-23 % of the total length, in females 16-22 %.
Squamation
The type shows how all the species usually 9 large symmetrical shields on top of the head. However, the parietals are often particular to the tail end (posterior) fragmented into several smaller scales, in some individuals also Frontale is fragmented or the Praefrontalia are separated by an elongated middle scale. The number of supralabials is 7 to 9, the number of 8 to 13 Infralabialia
The dorsal scales are in the middle of the body in 21-25, arranged in the center in 23 longitudinal rows. The number of ventral scales ( Ventralschilde ) varies in males 127-142, females 128-144, the number of Subcaudalia 55-71 in males and 46-67 in females.
Coloring
The basic color of the top is individual-, to origin and age-dependent very variable dark gray to almost black, dark gray-brown, dark yellow, reddish or reddish brown. On this base color are located on the top 10-19, depending on the population, on average, 12-15 brown to blackish transverse bands, which are irregularly bounded by diagonal, white, cream or yellow spot rows. The transverse bands are usually lighter than the base color, but with age, the same colors more and more. In general, large individuals are darker than smaller animals. The belly is gray, gray-brown or reddish brown and irregularly mottled light.
Very striking the head is drawn. The sides of the head show in almost all populations of two parallel, wide, bright ( most yellow ) strip. The upper side of the head strip extending from the front tip of the rostral canthus along the back over the edges of the Internasalia which Präfrontalia and then Supraocularia. From the upper Postocularia on the second horizontal row of the temporal Then he bends downwards and often combines with the rear end of the lower side of the head strip. The upper side of the head missing strips only in adult animals from southern Honduras, Nicaragua and Costa Rica. The lower side of the head strip is much wider than the top and starts at the rostral or the Praenasalia and then runs the supralabials back to the corner of the mouth. Thereafter, the lower side of strip bends downwards and runs further to the rear. In contrast to the very similar Agkistrodon taylori this lower side stripes in the Mexican Mokassinotter down is dark confined front of the jaw edge in the front, so not covered as in A. taylori the entire lower outer edge of the supralabials. One or both head strip may be interrupted on the back of the head. Rostral and Mental show a broad, vertical, bright stripes.
The lower half of the iris is orange, russet or brown, the top half is much paler. The tongue is orange, red, or orange - pink with yellow tips.
In young animals the distal half of the tail is light yellow or light yellow-green.
Distribution and habitat
The area of the type comprised of mainly coastal areas in Central America. On the Pacific coast the spread from southern Sonora in northern Mexico extends south to Costa Rica. The distribution area in the Atlantic Ocean near is much smaller and limited to the Yucatan Peninsula and the north of Belize. Most proofs are from altitudes below 600 m, a maximum of the kind in western Mexico was found in 1500 m height.
The descriptions of the habitat requirements of the Mexican Mokassinotter were partly contradictory; the species was described by some authors as inhabiting soil, other than semi -aquatic. Mostly inhabited the kind seasonal dry forests, so tropical dry forests, thorn bush forests and savannas. However, the species is quite adaptable, some populations inhabit permanently wet coastal marshes or the environment of ponds, others come in areas off with a pronounced and prolonged dry season, where to stay, the animals during the rainy season in temporary ponds and flooded areas. Finally, the species was also observed on rocky slopes that stay all year without water.
System
Today, three subspecies are recognized. The distribution areas of the subspecies are directly adjacent; in the edge regions, there is in each case a mixing zone.
- A. b. bilineatus; the nominate form has the largest area of distribution; it extends to the Pacific Ocean from Mexico to El Salvador. The upper side of the head strip starts at the rostral and runs back over the canthus and the Supraocularia and then diagonally across the second row of the temporal. The lower side of the head light strip starts at or near the internals sale and extends from the front to the back of the nasal supralabials. The basic color of the trunk and transverse bands is approximately equal, the transverse bands do not usually have bright spots in the center. The belly is mottled throughout. Chin and throat are drawn strikingly bright.
- A. b. howardgloydi; the circulation area covers the pacific regions near from Honduras to Costa Rica. The lower side of the head light strip is divided in the front, the two parts meet at an angle at the boundary between the second and third Supralabiale. This lower side of the head strip is also emphasized at the top by a narrow dark line. The lower portions of the Supralabiale are pale and unmarked and have the same color as the Infralabialia and chin and throat. The upper side of the head strip is narrow and often interrupted behind the eye or lack there all. The basic color of the chin and throat is orange or brownish orange and the level of the first to sixth Ventral sharp deducted from the remaining dark Ventralia. The median longitudinal third or quarter of the abdomen is weak or not spotted. Young animals are red or reddish.
- A. b. russeolus; the subspecies inhabited the Yucatan Peninsula and northern Belize. The upper side of the head strip is often narrow and interrupted behind the eye. The lower side of the head strip is wider than the upper and to the rear of the mouth irregular angle; it dissolves there often in single spots or Strichel on. The cross bands of the fuselage is mostly noticeable also in adult animals.
The closest relative of the species is Agkistrodon taylori, this was separated only in 2000 as a separate species from the Mexican Mokassinotter.
Activity and lifestyle
The species is, like all species of the genus mainly at dusk and at night active. The animals, as far as known, only on the ground or in the water.
Nutrition
The food spectrum is very broad as in the other species of the genus and encompasses virtually all small vertebrates of the respective habitat, ie amphibians, reptiles, birds and small mammals, pups use their bright tail end as moving bait and eat probably invertebrates.
In a study in Costa Rica were found as food by young snakes frogs and small lizards, adult animals, however, were eating mammals and the comparatively large black iguanas ( Ctenosaura sp.). Were detected as prey by a representative of mouthed ( Hypopachus variolosus ), a representative of the Leptodactylidae ( Leptodactylus poecilochilus ), which belongs to the skinks Mabuya unimarginata that to the rail lizards belonging Ameiva undulata, the Common Black Iguana ( Ctenosaura similis ), to the sting pocket mice belonging Liomys salvini and a representative of cotton rats ( Sigmodon hispidus ).
Reproduction
Mexican Mokassinottern bring their boys and all the species alive to the world, so are viviparous. The number of young snakes per litter is 3 to 20, usually 5-10; the young animals have a total length of 25 to 32 cm. Four captive born pups weighed 7.7 to 9.3 g in Costa Rica find pairings from December to April instead and the young are born from June to August. Information on the average and maximum age of free- living individuals are unknown, in captivity, a maximum age of at least 24 years demonstrated.
Poison and medical importance
Venoms of pit vipers are by far the most complex natural toxins. They contain a mixture of enzymes, low molecular weight polypeptides, metal ions and other, in their function so far poorly understood components. Just as diverse are the effects of these toxins.
The venom of A. bilineatus is highly protein- degrading and therefore leads to the destruction of tissue. It causes severe pain, redness, swelling and necrosis around the bite site. The poison hemolytic and anticoagulant, so that patients bleed from the bite site. It also contains the enzyme phospholipase A2, which has a toxic effect on the muscle fibers. The tissue damage may be irreversible and associated with a permanent loss of function of the affected limb.
The species is feared in their area of distribution because of their aggressiveness and has a number of deaths caused, in part, within a few hours after the bite. Larger studies on the epidemiology are so far apparently not before, but overall medical significance is compared with occurring in the same habitat types of the American Terciopelos and rattlesnakes appears to be small.
Inventory and risk
There are no reliable data on the size of the total population. The species is, however, completely disappeared in the last 50 years at least in parts of its range in Mexico and Guatemala, or is there at least become very rare. Main risk factors are habitat destruction through the conversion of their habitats into agricultural land and the extreme human persecution. The IUCN therefore classifies the Mexican Mokassinotter as a sort of early warning one ( " near threatened " ), Campbell and Lamar include the nature of the most endangered species of snakes of the Americas.