herpetology chapter 4 pt 3 (exam 1)

relationship among the major clades

1. scolecophidia
2. alenthinophidia

alenthinophidia

caenophidia

caenophidia

colubroidea

defining features of scolecophidia (6)

blind snakes (scolecophidia)

\

1. typically small
2. short, blunt tail often tipped with a spine and smooth scales
3. blunt head
4. vestigial eyes
5. retain vestiges of pevlic girdle
6. all oviparous

defining features of uropeltidae (2)

shield tailed snakes (alethinophidia)

\

1. head is conical, slender, often narrower than the trunk, has a distinct keel
2. the tail is blunt and in many species capped with a single large scale with a rough surface

defining features of bolyeriidae (2)

split jaw snakes (alethinophidia)

\

1. have maxillary (upper jaw) bones that are divided by a joint into anterior and posterior sections
2. mandibles are jointed and both upper and lower jaws can be bent around prey

defining features of boidae (3)

boas (alethinophidia)

\

1. specialized labial infrared sensitive sensors
2. males of many species retain vestiges of a pelvis and femurs in the form of spur-like structures that grab female during mating
3. viviparity is the ancestral condition

defining features of pythonidae (2)

pythons (alethinophidia)

\

1. infrared sensitive sensors between the labial scales but unlike boids, these sensors have distinct pits
2. males also have pelvic spurs

defining features of acrochordidae (4)

file snakes (caenophidia)

\

1. all aquatic
2. loose baggy skin with small tubercles and triangularily keeled scales (skin feels like sandpaper)
3. water moves rapidly over body surface through interscalar channels (may be adaptation for staying hydrated during rare migration of land)
4. nearly incapable of movement on land

defining features of viperidae (2)

vipers (colubriodea)

\

1. long fangs that fold against roof of mouth when not in use
2. terrestrial, semi-aquatic, arboreal

defining features of colubridae (6)

colubrids (colubriodea)

\

1. largest and most diverse family
2. several dangerously venomous species
3. much of north american snake fauna
4. no marine or burrowing species
5. diverse diets
6. mostly oviparous

defining features of elapidae (4)

cobras, coral snakes, mambas, kraits, sea snakes, and relatives (colubriodea)

\

1. wide range of habitats and diets
2. proteroglyph dentition
3. relatively immobile maxillae may bear solid teeth posterior to the fang
4. all venomous but some are too small to post a threat to humans

defining features of lamprophiidae (3)

house snakes, sand snakes, stiletto snakes, and others (colubriodea)

\

1. extremely elongate, extend behind head into dorsal neck region
2. maxilla is greatly reduced and bears a pair of enormous hollow fangs
3. strikes with lateral and posterior stabbing motions of the head

skull

less bones than the lizard skull

vertebrae

120-500 total vertebrae dependent on length

\
have ribs

tail

tail vertebrae have no ribs or very small ribs

morphology related to habitat (3)

1. arboreal (compressed body, long tail, large eyes, etc)
2. fossorial (small body, small eyes, narrow/pointed snout, etc)
3. aquatic (laterally compressed body, dorsal/terminal displacement of eyes/nostrils)

limb remnants

vestigial pelvic elements

\
external: boidae, pythonidae

\
internal: scolecophidia, aniliidae, loxocemidae, tropidophiidae

skull of snakes (5)

1. loss of both upper and lower temporal bars
2. elongation of quadrate and supratempoeral bones
3. brain encased in frontals and parietals
4. prokinesis
5. streptostyly

prokinesis in snakes

between the frontals and nasal region

streptostyly

detition

all snakes have modified pleurodont tooth implantation

4 different tooth arrangements

1. aglyph
2. opisthoglyph
3. proteroglyph
4. solenoglyph

aglyph dentition

maxillary dentition with little variation in size or shape (homodont dentition)

opisthoglyph dentition

“rear fanged” meaning enlarged, grooved fangs on posterior portion of maxilla

\
characteristic of colubrids and most lamprophiids

proteroglyph dentition

each maxilla bears a single hollow fang on its anterior end (usually additional teeth)

\
fang is not erected by rotation of the maxilla around the prefrontal bone

\
characteristics of elapids and the lamprophiid homoroselaps

solenoglyph dentition

have extremely reduced maxilla with a single large hollow fang

\
the fang is erected by the rotation of the maxilla on the prefrontal bone

\
characteristic of vipers and the lamprophiid atractaspis

venom canal

fangs of vipers, elapids, lamprophiids

\
connected to large venom gland (with associated muscles)

\
more elaborate delivery system

venom groove

fangs of colubrids

\
groove associated with venom producing gland (duvernoy’s gland)

\
no muscles/duct

4 types of venom

1. neurotoxic
2. haemotoxic
3. necrotizing
4. anticoagulant

neurotoxic

attacks nervous system

\
elapids

haemotoxic

blood

\
vipers

necrotozing

breaks down tissues

\
vipers

antocoagulant

causes animal to bleed out and blood can’t clot

\
vipers

unique traits of vipers (5)

1. solenoglyph fangs (hinges)
2. heat sensitive pit on face
3. rattlesnake: warning
4. lack pit organs
5. longest fangs of any snake

unique traits of elapids

1. all venomous but some too small for threat
2. hood displays (make head look larger) for threat
3. squirt venom often into eyes
4. aquatic species have narrow bodies and flat tails

are most snakes oviparous or viviparous

oviparous

viviparous groups (3)

1. majority of viperidae/crotalinae
2. boas (boidae)
3. most sea snakes (elapidae: elapinae, hydrophiinae)

sex determination of snakes

genetic (ZW)