In this lab we continued looking at members of Squamata, the clade that includes lizards and snakes, focusing specifically on snakes (Serpentes/Ophidia) this time. Squamates are members of Lepidosauria, which also includes Sphenodontida, and the general characteristics of these clades are described in our “Lepidosauria part I” blog. As was also discussed in the earlier blog, snakes are highly derived lizards, such that the clade Sauria, which traditionally included only lizards, should be expanded to include snakes and lizards to make it monophyletic. Snakes are limbless (although some retain rudiments of the hind limb and pelvic girdle), lack external ear openings, and lack eyelids. The elongation of snakes is primarily achieved by elongation of the trunk and increases in the number of presacral vertebtrae.
Due to their lack of limbs, most snakes must consume their prey whole (those that don’t dismember their prey with their coils and then swallow the pieces whole), and derived snakes have highly specialized and kinetic skulls that allow them to swallow prey that may be much larger than a snake’s own head. Snake exhibit extreme streptostyly, meaning that the quadrate articulates loosely with the supratemporal at its dorsal end and the lower jaw and its ventral end, which makes the lower jaw highly mobile. Snakes also have kinetic articulations between the supratemporal and parietal, dentary and compound bone of the lower jaw, prefrontal and maxilla, and frontal and maxilla. Snakes also have a ligamentous mandibular symphysis between their dentaries, which allows the right and left sides of the jaws to stretch apart, further facilitating the swallowing of large prey. Points of articulation are circled in the figure below.
Most snake teeth are recurved, conical, or laterally compressed, and are solid and lack grooves. These teeth are referred to as aglyphous and are the only type of teeth present in Clades such as Boidae and Pythonidae. Many snakes possess specialized enlarged teeth that aid in venom delivery (fangs) in addition to the relatively unspecialized aglyphous teeth. Fangs fall into three categories: 1) opisthoglyphous fangs are found in members of Colubridae, and are enlarged teeth at the posterior end of the maxilla which may or may not be grooved to aid in venom delivery; 2) proteroglyphous fangs are found in members of Elapidae, and are enlarged, hollow teeth used for venom delivery and positioned on reduced, immobile or relatively immobile maxillae at the front of the mouth; and 3) solenoglyphous fangs are found in members of Viperidae, and are enlarged, hollow teeth used for venom delivery that are positioned at the front of the mouth on reduced, highly mobile maxillae, which allow the fangs to swing outwards during a strike.
Family Pythonidae (8 genera, 37 species): Pythons are found in Sub-Saharan Africa and South and Aoutheast Asia to Australia. They occur in a variety of habitat, from rain forests to deserts to semiaquatic environments. Cranial infrared receptors in interlabial pits are found in many species of pythons. All members of Pythonidae have aglyphous teeth, with no specialized fangs. All pythons are oviparous and some species possess remnants of limb or girdle elements.
Family Boidae (2 subfamilies): Boas are found in Western North America to southern South America, West Indies, central Africa to South Asia, Madagascar, and Southwest Pacific Islands. Cranial infrared receptors in interlabial pits are found in many species of boas. All members of Boidae have aglyphous teeth, with no specialized fangs. Hindlimb vestiges are present as cloacal spurs and pelvic remnants remain in some species of Boidae.
Subfamily Boinae (7 genera, 47 species): Members of Boinae are characterized by having labial sensory pits and caudal vertebrae that have simple neural arches. All members are also viviparous. Many members are arboreal, although the species Eunectes is aquatic.
Subfamily Erycinae (4 genera, 17 species): Members of Erycinae are characterized by lacking labial sensory pits and caudal vertebrae that have forked neural arches. Some members of this subfamily are semifossorial, and occur in arid to moist habbits. All members are also viviparous.
Family Colubridae (7 subfamilies): Colubridae is the most speciose family of snakes, and taxonomy within this clade is still being resolved. Colubrids possess either opisthoglyphous or completely aglyphous dentition, lack infrared receptors, and possess no remnants of limb or girdle elements. They are found worldwide, except for on Antarctica and oceanic islands, and inhabit a wide range of habitats.
Subfamily Colubrinae (100+ genera, ± 650 species): Colubrinae is a highly diverse subfamily with a worldwide distribution and few defining characteristics. Colubrines exhibit a wide range of body forms, and range from aquatic to desert inhabitants to inhabitants of montane forests. They range from fossorial to arboreal, and may be dietary specialists or generalists. Colubrines are primarily oviparous, though some taxa are viviparous. Colubrinae contains several Ohio species: 1) Opheodrys veralis (smooth green snake), 2) O. aestivus (rough green snake; observed in lab), 3) Coluber constrictor foxii (blue racer; observed in lab) and C. c. constrictor (northern black racer), 4) Pantherophis obsoletus obsoletus (black rat snake; observed in lab), 5) P. vulpinus (fox snake; observed in lab), 6) Lampropeltis triangulum triangulum (eastern milk snake; observed in lab), and 7) L. getula nigra (black kingsnake; observed in lab). Colubrinae also includes the indigo snake, Drymarchon corais, which is the largest North American snake.
Subfamily Dipsadinae (90+ genera, 700+ species, synonym: Xenodontinae): Dipsadinae is another highly diverse subfamily of colubrids. Dipsadines are found in the Americas and inhabit all non-marine habitats. They range from terrestrial to arboreal, and most are dietary generalists. Members of Dipsadinae are opisthoglyphous. Dipsadines are primarily oviparous. Dipsadinae includes several Ohio species: 1) Diadophis punctatus edwardsi (northern ringneck snake; observed in lab), 2) Heterodon platyrhinos (eastern hognose snake; observed in lab), and 3) Carpophis amoenus (worm snake; observed in lab).
Subfamily Natricinae (38 genera, 195+ species): Many natricines are semiaquatic to aquatic in freshwater, with others being primarily terrestrial to semifossorial. Aquatic species prey primarily on fish and amphibians, though some are dietary specialists. All New World natricines are viviparous, and Old World natricines are primarily oviparous. Members of Natricinae are opisthoglyphous. Natricinae contains several Ohio species: 1) Nerodia sipedon sipedon (northern water snake; observed in lab), N. s. pleuralis (midland water snake); 2) Nerodia erythrogaster neglecta (copperbelly water snake); 3) Regina septemvittata (queen snake; observed in lab); 4) Thamnophis butleri (Butler’s garter snake); 5) T. sirtalis sirtalis (eastern garter snake; observed in lab); 6) T. radix radix (eastern plains garter snake); 7) T. sauritus sauritus (eastern ribbon snake); 8) T. s. septentrionalis (northern ribbon snake); 9) Storeria dekayi (brown snake; observed in lab); 10) S. occipitomaculata occipitomaculata (northern redbelly snake; observed in lab); and 11) Virginia valeriae valeriae (eastern smooth earth snake).
Family Elapidae (2 subfamilies): Elapids are found from Southern North America to southern South America, Africa, southern Asia to southern Australia, and the tropical Indian and Pacific Oceans. All elapids are venomous and have proteroglyphous fangs. No cranial infrared receptors are present and girdle and limb elements are absent.
Subfamily “Elapinae” (17 genera, 130+ species): This somewhat diverse subfamiliy contains mostly terrestrial snakes, although some arboreal and aquatic species are present. They are mainly predators of vertebrates, and are mostly oviparous, although a few species are viviparous.
Subfamily Hydrophiinae (43 genera, 165+ species): This group of Elapids are characterized by having palatine bones that lack choanal processes. Both terrestrial and aquatic species are found within this subfamily. “True” sea snakes belong to this group, and are characterized by having a laterally compressed body, a paddle like tail, and loss of enlarged ventral scales. All sea snakes are viviparous. Sea kraits have good terrestrial locomotion, and are oviparous.
Family Viperidae (3 subfamilies): Viperidae has a very large distribution, and is considered worldwide except Papuaustralia and oceanic islands. All viperids are venomous and have solenoglyphous fangs. Cranial infrared receptors are present in some species and girdle and limb elements are absent externally and internally.
Subfamily Azemiopinae (monotypice, Azemiops feae): This species is found in southern China, Burma, and Vietnam. They lack labial pits and has a distinct choanal process of the palatine. Azemiopinae are semifossorial and it is unknown if they are oviparious or viviparous.
Subfamily Crotalinae (26 genera, 160+ species): Members of Crotalinae are found in Southwest and southern Asia and the Americas. They have loreal pit infrared receptors and have a small choanal process on the palatine. These snakes are mainly nocturnal, and prey mainly on vertebrates. They are found in a variety of habits, such as deserts, to cool mountain forests, to wet tropical lowlands. They are maninly terrestrial, but some species are semiaquatic and arboreal. Most are viviparous, although a small number of species are oviparous. Crotalinae contains several Ohio species: 1) Agkistrodon contortrix mokasan (northern copperhead, observed in lab); Sistrurus catenatus catenatus (eastern massassauga, observed in lab); and Crotalus horridus (timber rattlesnake, observed in lab).
Subfamily Viperinae (13 genera, 65+ species): Members of Viperinae are found in Africa, Europe, and Asia. They are characterized by lacking loreal pits and a choanal process on the palatine. Most members of this subfamily are terrestrial, and occur in desert to forest habitat. Many species are diurnal, although others are nocturnal hunters. This subfamily includes some species that are viviparous, and some that are oviparous.