Squamata, which is composed of Sauria and Serpentes contains over 8,000 species. Sauria makes up most of this group; however, it is essential to recognize that snakes are very derived lizards. Currently, there are at least 16 families of snakes, but there may be as many as 23. As with other reptile groups, there is a family/sub-family debate: confusion lies over whether scientists should elevate sub-families to family level or leave them where they are.
An important distinction between snakes and lizards is cranial kinesis. Snakes are streptostylic, while lizards are not. This trait allows snakes to widely open their lower jaw.
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| Streptostyly and cranial kinesis in action. |
In a snake, teeth lie on the dentary, maxilla, palatine, and lateral areas of the pterygoid. Most of these teeth are re-curved to more efficiently keep prey inside the mouth. Fangs are specialized teeth which only some snakes possess. These fangs can simply be grooved, or they can be specialized venom-delivery apparatuses.
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| Aglyphous teeth. |
Four major categories of teeth and fangs exist:
1. Aglyphous snakes possess no fangs. They have typical, conical or laterally compressed, re-curved teeth. These fangless teeth are found in every type of snake.
2. Opisthoglyphous refers to the condition of having rear fangs. This dentition is found in colubrid snakes.
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| Solenoglyphous fangs and aglyphous teeth. |
3. Proteroglyphous snakes display a front-fanged condition. These fangs are completely folded and are hollow in the center. This type of fang dentition is found in the family Elapidae.
4. The most derived type of snake fang is the solenoglyphous fang. These fangs are completely hollow. Snakes with this type of fang are able to retract (swing) their fangs down, allowing them to inject their prey with venom. This derived dentition is only found in the family Viperidae.
This lab was centered on 5 families of snakes: Pythonidae, Boidae, Colubridae, Elapidae, and Viperidae.
(* Indicates Ohio species in JCU collection)
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| A member of Pythonidae |
Pythonidae:
Distribution: Sub-Saharan Africa, South and Southeast Asia to Australia.
Number of genera: 8
Characteristics and biology: Large to giant snakes; aglyphous; terrestrial and arboreal; some are semi-aquatic; all are oviparous.
Boidae:
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| Erycinae: Charina (rubber boa) |
Distribution: Western North America to southern sub-tropical South America, West Indies, central Africa to South Asia, Madagascar, and Southwest Pacific islands.
Characteristics and biology: Small to large snakes; most have cranial infrared receptors in interlabial pits.
Subfamily: “Boinae”
Number of genera: 7
Characteristics and biology: Mostly arboreal; largest-bodied clade; all viviparous.
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| Erycine: Eryx (sand boa aka Celo) |
Subfamily: Erycinae
Number of genera: 4
Characteristics and biology: Usually in semiarid to arid habitats; robust, cylindrical bodies, short tails, blunt heads, small eyes; predominately nocturnal; all are viviparous.
Colubridae:
Distribution: Worldwide, except Antarctica and oceanic islands
Characteristics and biology: Inclue aglyphous, opisthoglyphous and proteroglyphous taxa; paraphyletic.
Subfamily: Natricinae
Number of genera: 38
Characteristics and biology: Many are aquatic.
Ohio species:
*Nerodia sipedon sipedon (Northern Water Snake)
N. s. pleuralis (Midland Water Snake)
N. erythrogaster neglecta (Copperbelly Water Snake)
*Regina septemvittata (Queen Snake)
Thamnophis butleri (Butler’s Garder Snake)
*Thamnophis sirtalis sirtalis (Eastern Garder Snake)
T. radix radix (Eastern Plains Garder Snake)
T. sauritus sauritus (Eastern Ribbon Snake)
T. sauritus septentrionalis (Northern Ribbon Snake)
*Storeria dekayi wrightorum (Midland Brown Snake)
*S. dekayi dekayi (Northern Brown Snake)
*S. occipitomaculata occipitomaculata (Northern Redbelly Snake)
Virginia valeriae valeriae (Eastern Smooth Earth Snake)
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| Representatives of Natricinae (clockwise from left): Regina septumvitatta, Storeria dekayi, Nerodia sipedon sipedon, Storeria occipitomaculata, Thamnophis sirtalis sirtalis |
Subfamily: Dipsadinae
Number of genera: Over 90
Characteristics and biology: Occur in all habitats.
Ohio species:
*Diadophis punctatus edwardsi (Northern Ringneck Snake)
*Heterodon platyrhinos (Eastern Hognose Snake)
*Carphophis amoenus amoenus (Eastern Worm Snake)
C. a. helenae (Midwest Worm Snake)
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| Representatives of Dipsadinae (L to R): Diadophis punctatus edwardsi, Heterodon platyrhinos, Carphophis amoenus |
Subfamily: Colubrinae
Number of genera: More than 100
Characteristics and biology: Very diverse in body form; predominately oviparous.
Ohio species:
Opheodrys vernalis (Smooth Green Snake)
*O. aestivus (Rough Green Snake)
*Coluber constrictor foxii (Blue Racer)
C. c. constrictor (Northern Black Racer)
*Pantherophis obsoletus obsoletus (Black Rat Snake)
*P. vulpinus (Fox Snake)
*Lampropeltis triangulum triangulum (Eastern Milk Snake)
*Lampropeltis getula nigra (Black Kingsnake)
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| Representatives of Colubrinae (clockwise from top left): Pantherophis obseletus obseletus, Lampropeltis triangulum triangulum, Lampropeltus getula nigra, Opheodrys aestivus, Coluber constrictor foxii |
Elapidae:
Distribution: Southern North America to southern South America, Africa, southern Asia to southern Australia, and the tropical Indian and Pacific Oceans.
Characteristics and biology: Venomous snakes; proteroglyphous.
Subfamily: Elapinae
Number of genera: 17
Characteristics and biology: Predominately terrestrial; Mostly oviparous.
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| Hydrophiinae. Note the paddle-like tail on the left. |
Subfamily: Hydrophiinae
Number of genera: 43
Characteristics and biology: Terrestrial and aquatic; sea snakes have paddle-like tail; all sea snakes are viviparous, birth occurs in water; sea kraits are oviparous.
Viperidae:
Distribution: Wordwide, except Papuaustralia and oceanic islands
Characteristics and biology: Venomous; Solenoglyphous; Most have robust bodies and triangular heads.
Subfamily: Viperinae
Number of genera: 13
Characteristics and biology: Lack loreal pits; most are terrestrial.
Subfamily: Crotalinae
Number of genera: 26
Characteristics and biology: Well developed loreal pit for infrared receptors; Most are viviparous.
Ohio species:
*Agkistrodon contortrix mokasan (Northern Copperhead: Mokasan)
*Sistrurus catenatus catenatus (Eastern Massassauga)
*Crotalus horridus (Timber Rattlesnake)
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| Representatives of Crotalinae (L to R): Sistrurus catenatus catenatus, Agkistrodon contortrix contortrix, Crotalis horridus |
Until next time...at the zoo!
MH & KG
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