Evolution and Systematics

Functional Adaptations

Functional adaptation

Concertina movement navigates tunnels: snakes
 

Some snakes move by passing one or two curves down their bodies (concertina movement) using scales to apply pressure points.

   
  "Snakes can also engage in what's called 'concertina' movement, in which one or two curves pass down the length of an otherwise straight animal. This works well for an animal confined within a channel just a bit larger than itself (such as a rodent's burrow). At least one snake, Bitis caudalis, the South African desert viper, can jump, getting entirely airborne and moving a distance almost equal to its length (Gans 1974)." (Vogel 2003:489)

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  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 1935
Specimens with Sequences: 1830
Specimens with Barcodes: 1446
Species: 477
Species With Barcodes: 415
Public Records: 844
Public Species: 251
Public BINs: 241
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Barcode data

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Wikipedia

Colubridae

The Colubridae (from Latin coluber, snake) are a family of snakes. With 304 genera and 1,938 species,[citation needed] Colubridae is the largest snake family, and includes about two-thirds of all current snake species. The earliest species of the family date back to the Oligocene epoch. Colubrid species are found on every continent except Antarctica.[1]

Description[edit]

While most colubrids are nonvenomous (or have venom that is not known to be harmful to humans) and are mostly harmless, a few groups, such as genus Boiga, can produce medically significant bites, while the boomslang, the twig snakes and the Asian genus Rhabdophis have caused human fatalities.[1][2]

Some of the colubrids are described as opisthoglyphous, meaning they have elongated, grooved teeth located in the back of the upper jaw. The opisthoglyphous dentition appears at least twice in the history of snakes.[2] These are unlike those of vipers and elapids, which are located in the front.[1][2]

Classification[edit]

The Colubridae are not a natural group, as many are more closely related to other groups, such as elapids, than to each other.[3] This family has classically been a garbage bin taxon for snakes that do not fit elsewhere.[4] It is hoped that ongoing research will sort out the relations within this group.

Subfamily Boodontinae (sometimes moved to family Lamprophiidae as subfamily Lamprophiinae)

Subfamily Calamariinae

Subfamily Colubrinae - nearly 100 genera

Subfamily Dipsadinae

Subfamily Homalopsinae - about 10 genera

Subfamily Natricinae - about 30 genera

Subfamily Pareatinae - three genera

Subfamily Psammophiinae

Subfamily Pseudoxenodontinae

Subfamily Pseudoxyrhophiinae - about 20 genera

Subfamily Xenodermatinae

Subfamily Xenodontinae - some 55-60 genera

incertae sedis

References[edit]

  1. ^ a b c Bauer, Aaron M. (1998). Cogger, H.G. & Zweifel, R.G., ed. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 188–195. ISBN 0-12-178560-2. 
  2. ^ a b c Bruna Azara, C. 1995. Animales venenosos. Vertebrados terrestres venenosos peligrosos para el ser humano en España. Bol. SEA, 11: 32-40
  3. ^ Lawson, R; Slowinski, J.B.; Crother, B.I.; Burbrink, F.T. (2005). "Phylogeny of the Colubroidea (Serpentes): New evidence from mitochondrial and nuclear genes". Molecular Phylogenetics and Evolution 37: 581–601. doi:10.1016/j.ympev.2005.07.016. PMID 16172004. 
  4. ^ Fry, B.G.; Vidal, N.; van der Weerd, L.; Kochva, E.; Renjifo, C. (2009). "Evolution and diversification of the Toxicofera reptile venom system". Journal of Proteomics 72: 127–136. doi:10.1016/j.jprot.2009.01.009. 
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Hognose

The hognose snake is a type of colubrid snake characterized by an upturned snout. They are notorious for playing dead when threatened. The hognose snakes consist of three distantly related genera that are artificially grouped together by the "hognose" common name: Heterodon which are predominantly found in United States and northern Mexico, Leioheterodon the Madagascar hognose snakes, and Lystrophis the South American or tri-colored hognose snakes.

Species[edit]

Genus Heterodon:

Western Hognose Snake, Heterodon nasicus

Genus Leioheterodon:

Genus Lystrophis:

Description[edit]

Hognose snakes' most distinguishing characteristic is their upturned snout, which aids in digging in sandy soils by using a sweeping, side to side motion. They also like to burrow in masses of humus.

Hognose snakes are extremely variable in color and pattern, which warns potential predators that they are venomous. H. nasicus and H. kennerlyi tend to be sandy colored with black and white markings, while H. platirhinos varies from reds, greens, oranges, browns, to melanistic (i.e. black) depending on locality. They are sometimes blotched and sometimes solid-colored. L. geayi is a brown or tan colored snake with dark speckling on it. L. madagascariensis is typically green and yellow with a black checkerboard pattern along its back. L. modestus is normally a gold-brown color. The species in the genus Lystrophis are referred to as tri-color hognose snakes and sometimes as false coral snakes because they display alternating bands of red, white, and black.

Leioheterodon are the largest of the hognose snakes, capable of reaching lengths of 1.8 m. H. platirhynos gets slightly larger than other species of the genus, reaching lengths of 80 cm, where other species in the genus as well as Lystrophis species usually average around 65 cm at adult size.

Hognose snakes (Heterodon) are rear-fanged. The fangs have been referred to as just "enlarged teeth", but they are genuine fangs that are used for prey restraint. Despite the common belief, there is no evidence to support the fangs being used for "toad popping". Under this belief, the toads inflate their lungs to make swallowing difficult, but the fangs would penetrate the lungs and deflate them. However, whole toads with intact lungs are commonly regurgitated by recently captured hognoses.

The colouration of this essentially spotted snake is extremely variable, with colour phases ranging from yellow and brown to black and grey. The most reliable field work is the turned-up, hog-like snout, which is used for digging out the toads that are its primary food.

Behavior[edit]

Juvenile hognose playing dead

When threatened, hognose snakes will flatten their necks and raise their heads off the ground, like a cobra, and hiss. They may sometimes feign strikes, though they will almost never bite unless one were to smell like their prey. This behavior has earned them several nicknames, such as "puff adder", "blowing adder", "flathead", "spreadhead", "spreading adder" or "hissing adder". Note, though, the nickname "puff adder" is only a nickname, and is not scientifically correct. There is a highly venomous viper from Africa called the puff adder, Bitis arietans.

If this threat display does not work to deter a would-be predator, hognose snakes will often roll onto their back and play dead, going so far as to emit a foul musk and fecal matter from their cloaca and let their tongue hang out of their mouth, sometimes accompanied by small droplets of blood. If they are rolled upright while in this state, they will often roll back as if insisting they really are dead. It has been observed that the snake, while appearing to be dead, will still watch the threat that caused the death pose. The snake will 'resurrect' sooner if the threat is looking away from it than if the threat is looking at the snake.[1] Hognose snakes are not easily angered however and one would have to be deliberately irking them to provoke a reaction. They are rather timid snakes and will often hide from predators by burrowing down into leaves, sand etc.

Giant Malagasy Hognose Snake, Leioheterodon madagascariensis

Diet[edit]

Heterodon are diurnal active foragers that typically consume their prey live without any constriction or body pinning, primarily relying on only their jaws as a weapon.

For most hog nose snakes the bulk of their diet is made up by rodents, and lizards. H. platirhinos is an exception, and specializes in feeding on toads although other food items such as eggs, insects and mice can make up as much as 50% of their diet.

In captivity[edit]

Hognose snakes are frequently found in herpetoculture. H. nasicus are often considered to be the easiest to care for, and captive bred stock is easily found. H. platirhinos is also commonly found, but their dietary requirements can be a challenge for some keepers, and there is anecdotal evidence to suggest that feeding them a diet of exclusively rodents contributes to liver problems and a shortened life span.[2] Leioheterodon species are imported regularly from Madagascar, and are not often bred in captivity and get much larger, so can pose a set of different challenges for care. Lystrophis species are fairly new to the commercial reptile trade, and are now commonly bred in captivity, but can be some of the more expensive hognose snakes available.

Toxicity[edit]

There has been some debate over whether hognoses are venomous. Their saliva is toxic to small prey such as frogs and toads, and thus meets the definition of venom. However, it is not likely to cause serious injury to humans, particularly as hognoses are rear-fanged[3] and do not bite in defense (i.e., the only way to get bitten by a hognose snake is to smell like their prey). In rare cases, humans may experience local swelling and blistering as a result of a bite.

Popular culture[edit]

"Half a mile down to Morgan Creek, leaning heavy on the end of the week.
Hercules and a hognosed snake, down on Copperline, we were down on Copperline."[4]

References[edit]

  1. ^ Burghardt, G.M.; Greene, H.W. (1988). "Predator simulation and duration of death feigning in neonate hognose snakes". Animal Behaviour 36 (November–December): 842–44. doi:10.1016/S0003-3472(88)80127-1. 
  2. ^ Hognose.com: Eastern Hognose Species Description
  3. ^ Hognose Snake Care Sheet
  4. ^ "Carolina on my mind: The James Taylor story," exhibit at the Chapel Hill Museum, Chapel Hill, North Carolina. Information retrieved 2007-12-24.
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