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.
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 |
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)
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.
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