Serpentes

I. Synapomorphies

II. Movement

III. Skull morphology

IV. Sensory adaptation - finding prey

V. Killing Prey

VI. Mimicry

VII. Snake Families

I. Serpentes – synapomorphies

• Limbless (or nearly so) – pectoral girdle & forelimbs totally absent

• Highly kinetic skull that enables them to swallow prey that are much larger than themselves

• Numerous vertebrae are

• No eyelids/no external ears –• Long slender curved pleurodont teeth, some with

specialized adaptations

Snakes have numerous vertebrae, each w/a pair of ribs in the neck and trunk that create

II. MovementA. Rectilinear motion = individual

movement of ventral scutesB. Lateral undulation =

C. Concertina motion = accordion style

D. Sidewinding = body thrown in air in sideways arcs

Fig. 4-28

III. Skull morphology

A. Modified for feeding– the skull is highly specialized and allows for a

special feeding apparatus that enables them to consume prey much larger than their own diameter

– the 2 halves of the jaw are joined only by muscles and skin,

– also, many of the skull bones are loosely held together so that the entire skull can flex asymmetrically to enhance the swallowing process

B. Fang/tooth morphology

Teeth: located in two rows along the top and bottom jaw

3 types of teeth:

IV. Sensory adaptation – finding prey A. Vision:

B. Infrared receptors

C. Jacobson's organs - pair of pit-like structures in the roof of the mouth; lined with olfactory epithelia that are highly folded to provide increased surface area for efficient detection of volatile chemicals

Single Pair of "Dual" chambers

Higher Sensitivity dual chamber pit improves sensitivity

Directional Information target is straight ahead when temperatures are same in both pits

Depth Perception anterior angle of pits provides "binocular" overlap snake can judge distance to prey

V. Killing PreyA. Constriction –strikes prey, loop of body thrown

on and around prey, additional coils of body encircle the prey

B. Biting –

C. Venom –

Snake Venom ~20 different types of toxic enzymes

1) Myotoxic –

2) Neurotoxic -

3) Hemolytic -

A muscular contraction pushes venom from the bottom of the cobra's fangs, while air expelled from the cobra's lung blows or sprays the venom at its intended victim.

Snake fangs:

1) Rear-fanged snakes

2) Hollow-fanged snakes

3) Hinge-fanged snakes

Inland taipan Oxyuranus microlepidotus

VI. Reproduction

Courtship can be quite lengthy Females lay down a pheromonetrail…

Or males can give off pheromones…

“breeding ball”

VII. Batesian Mimicry in snakes:

Dispholidus Thrasops

ModelMimic

LampropeltisMicrurus

ModelMimic

Review of snake adaptations that make them amazing predators

Elongated body coupled with numerous vertebrae allows for advanced movement

Kinetic skull modified for feedingTeeth and fangs for prey capture and

venom deliveryVenom for digestion and immobilizationJacobson’s organ Pit organs

Anomalepididae – Early Blindsnakes-Rhamphotyphops, parthenogenic

TyphlopidaeWidely distributed.Similar to the related families Anomalepidae and Leptotypholidae, the typhlopids are small snakes (usually <30 cm) with blunt heads and short, blunt tails. Due to their burrowing life style their eyes are vestigial.-lay eggs which may be retained in several species until the embryos are well developed.

Leptotyphlopidae – Threadsnakes or wormsnakes

Dinner for this threadsnake is an ant pupa often found under rocks or inside rotting logs.

Leptotyphlopidae comprises about 90 species in two genera (Leptotyphlops and Rhinoleptis). -tropical distribution, and are found in tropical North and South America, Africa, and the Middle East and northwest India. They live in a variety of habitats, from rainforests to semideserts, and from termite burrows to trees tops.

Uropeltidae – Shield-tail Snakes -presence of a large keratinous shield at the tip of their tail Southern India and Sri Lanka -Viviparous

Cylindrophiidae (some consider these members of Uropeltidae)-Asian pipesnakes are shiny, stout, blunt-headed and short-tailed burrowers. They have black-and-white checkered bellies-Cylindrophis uses a head-mimicry display w/ the tail for defense mechanism

Aniliidae – False coralsnake

Anilius scytale

Brightly banded in red and black (but without yellow bands), hence often called "false coral snake" (but it is not venomous). Fossorial, found in tropical rainforests of the Amazon BasinVestigial hind limbs and a pelvic girdle are present as well. Vestigial eyes lie beneath a large head shield.

Boidae – BoasRelatively large, stout snakes Most occur in the Neotropics although some species occur on Madagascar and in the southwest Pacific.Viviparous-vestigial hind limbs, “cloacal spurs”

Pythonidae – Pythonstropical and subtropical – Africa, India, Australia - constricting snakes. These snakes lay leathery eggs. The female incubates the eggs and keeps them warm by constriction of her muscles, which generates heat. Most species are nocturnal with heat sensitive pits in their mouths.

Acrochordidae – File snakesAdapted to aquatic lifestyle - Occur in both fresh & salt waterDistributed in the Indo-Australian region Fish eatersOvoviviparous & viviparous

Viperidae – Vipers & Pitvipers (Crotalines)

Crotalus

Typically have broad, triangular heads. Most are also heavy-bodied with relatively short, stender tails. Their long fangs permit deep penetration and envenomation of prey. The hinged-fang mechanism allows their storage against the roof of the mouth when not in use. Widely distributed (except Australia)Pit-organs of the crotalines lie on each side of the head between the nostril and eye and contain infrared receptors

This structure is made of loosely attached horny segments. A new segment is added each time the snake sheds. When vibrated, the rattle makes a buzzing sound characteristic of a disturbed rattlesnake.

Fangs are permanently erect on the anterior ends of largely immovable maxillae and fit into grooved slots in the buccal floor when the mouth is closed. Found worldwide in tropical and subtropical regions except for Europe. Most oviporous, some ovoviviporous

Elapidae – Cobras, seasnakes, mambas, death adders

Death adder

Black mamba

Colubridae – diverse (1,800 sp.)Mostly Non-venomous (to humans), rear-fanged

Boomslang – Venomous Colubrid