Lab 5: Lepidosauria pt 2: Serpentes & Ophidia
Within Eureptilia, two major lineages of extant reptiles exist: Archosauromorpha and Lepidosauromorpha, which includes Spenodota (Tuatara), Sauria (Lizards) and Serpentes (Snakes). Serpentes are highly derived, legless lizards with great diversity (~3400 spp). They have an interesting skeletal anatomy because they lack a pectoral girdle and fore limbs, and have only a rudimentary pelvic girdle, which are visible externally in some species (Pythonidae) in the form of cloacal spurs. Additionally, serpentes can have between 120-240 vertebrae, and each vertebrae in the neck and trunk have a pair of ribs to help with flexibility.
The skull of serpents is a modified diapsid skull with an extreme reduction in the number of bones. It is highly kinetic, having a condition called streptostyly, whereby the quadrate bone rotates to allow the mouth to be opened larger (Fig.1). This condition and the general tooth and cranial anatomy allows the jaws to act as a ratchet to aid in swallowing food. Look at the video below of a black mamba in South Africa eating a mouse and ratcheting it into its mouth. Additionally, there are no arches of bone that connect the dermal plates and the mandibular symphysis is not fused. Snakes typically have teeth on the maxillary and palatal series. Refer to Fig 2. for a labeled skull of a snake.
|Fig 2. Skull of Serpentes labeled|
Serpentes move via lateral undulation and can be terrestrial, fossorial, aquatic, or marine. They lack a tympanum and Eustachian tube and have a transparent scale called a spectacle that covers the eye. They capture and consume prey using just their mouth and body by constricting, swallowing whole, or injecting venoms. The teeth of serpentes are recurved, to force prey one direction, and can be categorized based on their anatomy as aglyphous, opisthoglyphous, proteroglyphous, or solenoglyphous.
Aglyphous teeth are the plesiomorphic condition and are the typical, conical, recurved teeth without grooves, found in all species of snakes. On Fig 5., the blue circle shows aglyphous teeth.
|Fig 3. Cranial anatomy with aglyphous teeth|
Opisthoglyphous, or rear-fanged teeth, are slightly recurved or straight and found as a pair or more of larger teeth at the back of the maxilla (Fig 4.). These typically have grooves to facilitate venom delivery. This dentition type is found in members of Colubridae.
|Fig 4. Cranial anatomy with opisthoglyphous teeth|
|Fig 5. Cranial anatomy with opisthoglyphous teeth (red) and aglyphous teeth (blue)|
Proterglyphous, or front-fanged teeth, are straight or slightly curved fangs attached to a reduced maxilla that is stationary. Therefore, these fangs tend to be static and immovable (Fig 6.). These fangs are hollow in the center and have a groove at the top to inject venom into prey. This dentition type is found in members of Elapidae
|Fig 6. Cranial anatomy with proteroglyphous teeth|
Solenogylphous teeth are completely hollow and positioned on a highly movable maxilla, which allows these fangs to be retracted and protracted. This allows for a deep injection of venom into prey. These teeth are only found in members of Viperidae.
|Fig 7. Cranial anatomy with solenoglyphous teeth|
Phylogeny and Diversity
Snakes can be divided into two major groups: Scolecophidia, the worm snakes which have reduced bones, akinetic skulls, are fossorial, and eat invertebrates and their larvae, and Alethinophidia, the true snakes. The families this lab focuses on are: Pythonidae, Boidae, Colubridae, Elapidae, and Viperidae. There has been a recent controversy and revision to the family Colubridae, which used to include three subfamilies Natricinae, Dipsadinae, and Colubrinae. However, these subfamilies have been elevated to families, so now there are 3 new families: Natricidae, Dipsadidae, and Colubridae. Below are the important families, their distribution, and common characteristics.
Family: Typhlopidae (Cosmopolitan Blind Snake)
10 genera; 252 species
Distribution: Cosmopolitan in tropical areas
Characteristics: Within the clade Scolecophidia, these snakes are primarily fossorial and prey on termites, termite larvae, eggs and soft-bodied arthropods.
Family: Leptotyphlopidae (Slender Blind Snakes; Thread Snakes)
2 subfamilies with 4 and 8 genera, respectively
Distribution: Tropics and subtropics of Africa; temperate zone in the American west to southern Utah; southwest Asia
Characteristics: Leptotyphlopidae make up the thinnest-bodied members of the Scolecophidians. They are fossorial and live in habitats from semi-desert to tropical. Their prey primarily consists of termites and the snakes exhibit a mechanism to allow them to inhabit the termite nests without detection and attack.
Family: Pythonidae (Pythons)
9 genera; 36 species
Distribution: Sub-Saharan Africa; South and Southeast Asia to Australia
Characteristics: Pythons are large (often giant) snakes that occur in a wide range of habitats ranging from deserts to rainforests. Pythons have pit organs for infrared detection associated with their upper lip (as well as other locations). Pythons have a non-protrusable tracheal tube, so they must hold their breath while eating. Python also display rudimentary limbs, spurs, located on either side of the cloacal opening.
Family: Boidae (Boas)
3 subfamilies; 12 genera
Distribution: Western North America to southern sub-tropical South America; West Indies; central Africa to South Asia; Madagascar; Southwest Pacific islands
Characteristics: Boas can range between being small to giant snakes (possibly up to 11.5m total length). Boas have cranial infrared receptors. This family also exhibit cloacal spurs.
Family: Viperidae (Vipers and Pit Vipers)
3 subfamilies; 37 genera
Distribution: Worldwide (except Papuaustralia and oceanic islands)
Characteristics: Vipers are venomous snakes with tubular solenoglyphous fangs found on the maxilla. They have infrared receptors located beneath the scale surface. Vipers are identifiable by their characteristic triangularly shaped head.
Family: Elapidae (Cobras; Kraits; Sea Snakes; Death Adders; Allies)
62 genera; 347 species
Distribution: Southern North America to southern South America; Africa; southern Asia to southern Australia; tropical Indian and Pacific Oceans
Characteristics: These venomous snakes have small, proteroglyphous fangs on the maxilla that are visible when the mouth is closed. Elapids have a laterally compressed body ending in a tail so compressed that it appears paddle-like, effective for its aquatic lifestyle. Laying eggs is the only on land activity for many genera in this family. Other genera, such as the mamba, are terrestrial and arboreal while others are fossorial.
Family: Colubridae (Common Snakes)
>100 genera; +/-682 species
Distribution: Nearly worldwide except Antartica, most of the north Artic and oceanic islands
Characteristics:This family is highly diverse in all characteristics including ecology, behavior and body form.
97 genera; 733 species
Distribution: Most of the New World
Characteristics: Highly diverse in body form, ecology and behavior, molecular data provides support to inhabitants of this family.
38 genera; >211 species
Distribution: North America to northern Central America; Africa; Eurasia through the East Indies
Characteristics: This family consists of snakes that range from small to large size and habitats include many freshwater aquatic and some marine environments, terrestrial and fossorial.
Agkistrodon contortrix mokasan (Northern Copperhead)
Sistrurus catenatus catenatus (Eastern Massassauga)
Crotalus horridus (Timber rattlesnake)
Opheodrys vernalis (Smooth green snake)
Opheodrys aestivus (Rough greensnake)
Coluber constrictor foxii (Blue racer)
Coluber constrictor constrictor (Northern Black racer)
Pantherophis obsoletus obsoletus (Black rat snake)
Pantherophis vulpine (Fox snake)
Lampropeltis triangulum triangulum (Eastern milksnake)
Lampropeltis getula nigra (Black kingsnake)
Diadophis punctatus edwardsi (Northern ring-neck snake)
Heterodon platyrhinos (Eastern hognose)
Carphophis amoenus amoenus (Eastern worm snake)
Carphophis amoenus helenae (Midwest worm snake)
Nerodia sipedon sipedon (Northern watersnake)
Nerodia sipedon pleuralis (Midland watersnake)
Nerodia erythrogaster neglecta (Copperbelly watersnake)
Regina septemvittata (Queen snake)
Thamnophis butleri (Butler’s garder snake)
Thamnophis sirtalis sirtalis (Eastern garder snake)
Thamnophis radix radix (Eastern plains garder snake)
Storeria dekayi wrightorum (Midland brownsnake)
Storeria dekayi dekayi (Northern brownsnake)
Storeria occipitomaculata occipitomaculata (Northern redbellied snake)
Virginia valeriae valeriae (Eastern smooth earth snake)
These photos are from The Reptile database. The subspecies with no pictures were grouped together on the site, and therefore had no individual pictures.