Thursday, February 27, 2014

Laboratory #5:
Lepidosauria: Serpentes & Ophidia
 
By: Meghan Kelley and Katie Sagarin


 
INTRODUCTION:

Squamata is composed of lizards, within Sauria, and snakes, within Serpentes, which together make up about 8000 different species that have been classified and are found on every continent, except Antarctica.  While lizards and snakes may appear different, snakes are actually a group of highly derived lizards, including specialized physical morphology and physiological functions, such as advanced chemosensory perception and envenomation of prey. Serpentes is further divided into two infra-orders: Scolecophidia and Alethinophidia. Scolecophidia are a smaller, more basal group whose members are fossorial and have akinetic skulls. Alethinophidia contains all the more well-known “typical” snakes, such as Pythonidae, Boidae, Colubridae, Elapidae, and Viperidae, which are represented in the photos above in order from left to right, respectively.
 
GENERAL MORPHOLOGY:
The closest relative to snakes are the varanid lizards, which have elongate necks, forked tongues, and streptostyly, a type of jaw articulation that allows the mouth to be opened wide.
 
 

 
Figure 1: The top picture is a varanid lizard skull, which has a reduced number of bones and fusion of many skull regions, similar to a snake's skull, shown in the bottom two images.  An additional similarity between the varanids and snakes articulation is that the quadrate (circled in red) drops down and re-positions more vertically, in order the fully open the mouth via streptostyly.  The bottom right picture shows the vertical position of the quadrate bone.
 In comparison to varanids, snakes have lost their limbs and modified their skulls even more extremely. The rami of the jaw do not fuse, allowing the jaw to be expanded laterally. Many snakes also use ratchet feeding, moving one side of their skull at a time to pull their prey into their throat. Because snakes tend to eat prey larger than their heads, many have a protrusible trachea which allows them to breathe while their mouths are full, as seen in Figure 2.


Figure 2: In the top diagram, the venom gland and duct (red), the protrusible trachea, and the chemo-sensing forked tongue, that brings in scent to the Jacobson's organ, are labeled. On the lower jaw of the snake skull in the lower picture, it is clear that the rami, or two mandibular regions, are not fused.

VENOM DELIVERY & DENTITION:
Snakes can have some combination of four tooth conditions. The most basic is aglyphous teeth, which point straight down in the mouth and are generally conical or laterally compressed. Opisthoglyphous teeth point posteriorly and are generally positioned at the back of the maxilla to keep prey in the mouth. Proteroglyphous teeth are the most anterior on the maxilla and are hollow for venom delivery, and are only found within the family Elapidae. Lastly, solenoglyphous teeth are hollow, retractable teeth on a kinetic maxilla, perfect for venom injection. They are only found within the family Viperidae. All four teeth types are pictorially represented in Figure 3, and the potential evolution of these derived teeth is shown in Figure 4.
 
 



Figure 3: These are the four types of teeth that developed in different snake groups, shown with their groove or channel of venom delivery, indicating that proteroglyphous and solenoglyphous are the more efficient venom delivery systems.
Figure 4: The four teeth conditions in snakes phylogenetically developed at different rates with the deriving of modified salivary glands that became venom glands. "Glyphous" refers to the channels or grooves in some teeth types that function as a delivery system for venom. a) This is a color-coded phylogenetic tree of approximate development of differing teeth types. Front-fanged in this figure refers to the relative position of either proteroglyphous (Elapidae) or solenoglyphous (Viperidae) fang types.  Aglyphous, or non-grooved teeth, are considered the basal condition of teeth in snakes and are found to some extent in all snakes.  b) These are lateral views of the four teeth conditions; white circles represent the fangs that are present. c) This is a palatal view, in which the red region is the maxilla region, and the fangs are circled in black. This image is taken from Vonk et al., 2008.
FAMILY CHARACTERISTICS:

-Pythonidae: Contains 9 genera, distributed throughout sub-Saharan Africa, and south and southeast Asia to Australia, spanning deserts and forests alike. They are large to giant snakes with teeth on their premaxilla (except in Aspidites). Many have infrared receptors in labial pits which allow them to perceive body heat signatures. All species of Pythonidae are oviparous, and most coil around their eggs to incubate them. Some species have reportedly been known to eat tigers.

Ohio species: NONE

-Boidae: Contains 12 genera, distributed throughout western North Africa to South America and the Caribbean, up the west coast of North America, and southwestern Asia/the Middle East. Boas are small to large, but contain the largest species of snake, Eunectes murinus, the anaconda. Most have infrared receptors in inter-labial pits (Figure 5), and cloacal spurs, which are vestiges of  hind limbs.
 
 
Figure 5: Notice the conspicuous inter-labial pits laterally positioned from the nostrils, under the eyes.
 
Ohio species: NONE

-Elapidae: Contains 62 genera, distributed mainly in the southern hemisphere or near the equator. Elapids are proteroglyphous, and do not have infrared receptors. Elapids cover a wide range of lifestyles, from arboreal to fossorial to aquatic. This family includes coral snakes, sea snakes, cobras, and death adders.

Ohio species: NONE

-Colubridoidea: Contains more than 100 genera, distributed globally. Colubridae contains the most species of any family of snakes. Some colubrids have opisthoglyphous dentition, and have a variety of body forms, with almost no distinct physiology tying them together as a group.

Ohio species:
Opheodrys vernalis (Smooth Green Snake)

Opheodrys aestivus (Rough Green Snake)
 
Figure 6: Opheodrys aestivus, the rough green snake, is different from the smooth green snake because of its conspicuously keeled scales that give it a rough texture.
Coluber constrictor (Blue Racer)

Pantherophis vulpina (Fox Snake)
 
Pantherophis obsoletus (Black Rat Snake)
Figure 7: Top row from left to right includes a juvenile and an adult blue racer, while the bottom left is a fox snake and the bottom right is a black rat snake.  Some of the most important ways of telling confusing snake species apart is by including the type of habitat that they are found in; for example, black rat snakes and fox snakes are usually found in dryer forested habitats, sometimes arboreal, and blue racers are found in wet, possibly marshy terrestrial habitats.
Lampropeltis getula (Black Kingsnake)

Lampropeltis triangulum (Eastern Milk Snake)

Figure 8: On the left, the black kingsnake is represented, and the Eastern milk snake is shown on the right.
-Natricidae: Contains 38 genera distributed from North to Central America, Africa, and Eurasia through the East Indies. Many members of Natricidae are aquatic, both fresh- and salt-water. The New World species are all viviparous, while the Old World species are mainly oviparous.

Ohio species:

Nerodia sipedon pleuralis (Midland Water Snake)
Nerodia erythrogaster (Copperbelly Water Snake)
Nerodia sipedon sipedon (Northern Water Snake)
Regina septemvittata (Queen Snake)

Figure 9: Left is the Northern Water Snake, and right is the Queen Snake, both of which are very common, especially in the Midwest.
Thamnophis butleri (Butler's Garter Snake)
Thamnophis radix (Eastern Plains Garter Snake)
Thamnophis sauritus (Ribbon Snake)
Thamnophis sirtalis (Eastern Garter Snake)

Figure 10: This is the common Eastern Garter Snake; however, there is much variation in color and striping within this species and within the genus Thamnophis.
 
Storeria occipitomaculata (Red-belly Snake)
Storeria dekayi (Northern Brown Snake)
 

Figure 11: Red-belly snake is on the right, and the Northern Brown Snake is on the left. Both are photos taken in the field in the eastern U.S.

 
Virginia valeriae (Smooth Earth Snake)
 
-Dipsadidae: Contains 97 genera, distributed throughout the New World. Again, this is a highly diverse group that occurs in all habitats, except marine.

Ohio species:
Diadophis punctatus edwardsi (Northern Ringneck Snake):
 
Heterodon platyrhinos (Eastern Hognose Snake):
 
Carphophis amoenus (Worm Snake):



-Viperidae: Contains 37 genera, distributed globally except for Oceania, Madagascar, and the Arctic. Vipers have tubular, solenoglyphous teeth (perfect for venom injection), and triangular heads. Members of the subfamily Crotalinae have an infrared-sensing pits between their eyes and nostrils, allowing them to “see” heat signals stereoscopically. Other Viperidae taxa simply have infrared receptors beneath scale surfaces.

Ohio species:

Agkistrodon contortrix mokasan (Northern Copperhead: Moccasin)
Crotalus horridus (Timber Rattlesnake)
Sisturus catenatus catenatus (Eastern Massassauga):
 
PICTURES CITED:
Photos under title:
 
 
 
 
 
General Morphology:
 
 
 Venom Delivery and Dentition:
 
Vonk, F. J., J. F. Admiraal, K. Jackson, R. Reshef, M. A. G. Bakker, K. Vanderschoot, I. van den Berge, M. van Atten, E. Burgerhout, A. Beck, P. J. Mirtschin, E. Kochva, F. Witte, B. G. Fry, A. E. Woods, and M. K. Richardson. 2008. Evolutionary origin and development of snake fangs. Nature: 630-633.
 
Family Characteristics:
 
 
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Sunday, February 23, 2014

Lab 5: Serpentes & Ophidia- Kim & Meaghan



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.

videoThe 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. 
Fig1. Streptostyly
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.


Family: Dipsadidae
                  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.


Family: Natricidae
                  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.

Ohio Species: 
Viperidae

   

Agkistrodon contortrix mokasan (Northern Copperhead)
   

Sistrurus catenatus catenatus (Eastern Massassauga)
   
Crotalus horridus (Timber rattlesnake)



Colubridae
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)

Dipsadidae
Diadophis punctatus edwardsi (Northern ring-neck snake)

Heterodon platyrhinos (Eastern hognose)

Carphophis amoenus amoenus (Eastern worm snake)

Carphophis amoenus helenae (Midwest worm snake)


Natricidae
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)


      Thamnophis sauritus sauritus (Eastern ribbon snake)

Thamnophis sauritus septentrionalis (Northern ribbon 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.