Friday, March 23, 2012

Lab #6 Serpentes and Ophidia: Alex Valigosky and Jeff Walker

Serpentes and Ophidia

Serpentes, or the snakes, are Lepidosaurs, and more precisely Squamates.  This puts them in the clade that contains all of the lizards; snakes are highly-derived lizards.  A major united characteristic of snakes is the evolutionary loss of legs, though, as we have pointed out in the previous blog about lizards, leglessness has evolved multiple times and Serpentes are not the only legless lizards.  Artifacts of legs and pelvic girdles can be spotted in basal snakes, such as members of Boidae, as small projections called spurs near the cloaca that aid the snakes in mating.

The tree of life - Serpentes
The tree above details the hypothesized evolutionary relationships of various clades of Serpentes.  The most basal members are those of the Scolecophidia (worm snakes, blind snakes, and file snakes); these are mostly tiny fossorial snakes that live under ground or in the substrate.  The Alethinophida are the "real snakes".  This clade includes the Henophida (old snakes) and Caenophida (new snakes).  It is within the Henophida that we find such families as the Pythonidae and the Boidae and within the Caenophidia that we find families such as the Colubridae, the Viperidae, and the Elapidae. While there may be as few as 16 families, most of which are certianly monophyletic, depending upon the possible elevation of various subfamilies to family status, there may very well be many more.  

Lily - Ball Python - Python regius
Pythonidae, the pythons, is a clade of 8 genera and some 37 species, found throughout sub-saharan Africa and through south and south east Asia and Australia.  These large constrictors can live in various habitats and are all oviperous (clutch increases proportional with body size). Pythons have the incredible adaptation of cranial infrared receptors located in interlabial pits, which allow them to see heat (these evolved independently of the infrared receptors of Viperidae, below).    

Boidae, the Boas (2 subfamilies with 11 genera, and over 60 species), can be found in western North America to southern sub-tropical South America, the West Indies, central Africa to south Asia, Madagascar, and in the South-west Pacific Island.  These are also small to large constrictors; they also have cranial infrared receptors located in interlabial pits and cloacal spurs.

Colubridae is an extensive and diverse, but certainly monophyletic group of snakes.  Seven sub-families are recognized, including: Colubrinae, Natricinae and Dipsadinae. This is a highly specious group with a world-wide distribution.

The Colubrinae is a grab-bag of misfit colubrids.  8 genera can be found in Ohio: Opheodrys vernalis (smooth green snake), Opheodrys aestivus (rough green snake), Coluber constrictor foxii (blue racer, above center), Coluber constrictor constrictor (northern black racer), Pantherophis obsoletus obsoletus (black rat snake), Pantherophis vulpina (fox snake, above upper-right), Lampropeltis triangulum triangulum (eastern milk snake, above left), and Lampropeltis getula nigra (black kingsnake; Lampropeltis getula californiae, california kingsnake pictured above lower-right, *not an Ohio species, but closely related)

The Natricinae mainly prey upon fish and amphibia (1 species known to eat crayfish, the queensnake). They are generally freshwater snakes and semi-aquatic or fully aquatic, and found throughout North America to northern Central America, Africa and Eurasia.  American species are exclusively viviparous, whereas old-world taxa tend to be oviperous.  There are some 13 species found in Ohio: 5 species of Thamnophis (garter snakes, above top-left (2 snakes), bottom-left, and ribbon snakes), 3 species Nerodia (water snakes, above top-center, bottom-center), 3 species of Storeria (Brown and redbelly snakes), Regina septemvittata (queen snake, above bottom-right and top-right), and Virginia valeriae valeriae (eastern smooth earth snake). 

 The Dipsadinae [Also known as the Xenodontinae] can be found throughout the new world.  These are diurnal hunters (with long muscular bodies and slender heads) or nocturnal hunters/searchers (with slender bodies and blunt, over-sized heads).  Clutch size is highly variable (directly associated with body size).  Four species can be found in Ohio: Diadophis punctatus edwardsi (northern ringneck snake), Heterodon platyrhinos (eastern hognose snake, above left and bottom-right), Carphophis amoenus amoenus (eastern worm snake, above center and upper-right), and Carphophis amoenus helenae (midwest worm snake).

Viperidae, the vipers, includes 3 subfamilies: Azemiopionae, Crotalinae, and Viperinae, with a total of 40 genera.  Vipers have a world-wide distribution with the exception of Papuaustrailia and the oceanic islands. These are highly venomous snakes with highly derived fang-apparati (solenogyphous fangs, the maxilla is highly kinetic).  Many vipers have cranial infrared receptors in loreal pits or beneath scale surface (as opposed to the  interlabial pits of old-snakes) and many of the more-derived species also have rattles.  There are 3 Ohio species (pictures to be added soon - camera malfunction): Agkistrodon contortrix mokasan (northern copperhead: mokasan),  Sistrurus catenatus catenatus (eastern massassauga), and Crotalus horridus (timber rattlesnake).  The massassauga rattlesnake is wet/prairie specialist, while timber rattlesnake is hardwood-forest specialist; copperheads lack rattles.

Elapidae (pictures to be added soon - camera malfunction) - (southern North America to southern South America, Africa, southern Asia to southeastern Australia, and the tropical Indian and Pacific oceans) some of the most highly venomous snakes and includes many marine taxa.  There are two sub-families: Elapinae includes the cobras, mombas, crates, and the Hydrophiinae, which includes the sea snakes (recognizable by their reduced ventral scales and laterally flattened caudal regions; adaptations obtained in the move from land to back to water).  Elapinaes are primarily terrestrial, some are arboreal and fossorial.

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