Diversity of Snakes

Distribution

3400 species worldwide

160 in NA

23 in MD

Found everywhere except polar regions

Squammate Phylogeny

Snakes are nested

Serpentines and Amphisbenia are monophyletic

Serpentes sister to Anguimorpha/ Iguania clade not polytomy

Fossils

Snakes with legs

oldest is 167 myo

Najash: basal snake, 2 legs

Tetrapods 140 mya used legs to hold onto prey

Diversification

‘Ophidia’ = typical snakes

Serpentes synapomorphies

fossorial origin

>26 presacral vertebrae (usually 120-145)

skull

• reduction in many bones

• absence of both temporal arches

quadrate articuates with supratemporal bone

braincase completely encloses brain

pro-kinetic joint between nares

inc kinesis in jaw

other traits

caudal autonomy absent

forelimbs and pectoral girdle absent

hindlimbs and pelvic girdle reduced or absent

left aortic arch higher (rev in most tetrapods)

left lung reduced, right elongated

foretounge retracts

modified pleurodont

paired clocal scent glands

serpentes synapomorphies

transparent spectacle over eyes

ciliary body of eye lacks muscles

• focuses by moving lense towards/ away from retina

• other vertebrates flex

visual cells of retina lack oil droplets

eye modifications suggest reduced eyes in past

• basal groups fossorial

phylogeny of snakes

ancestral: Scolecophidia

derived: alethinophidia

4 fang types

aglypha: fangless (most snakes)

opisthoglypha: rear fangs

proteroglypha: front groove

solenoglypha: deep grooved

boidae

western and south america

all viviparous

constrictors

• wrap around, stop blood flow

similar to pythons

6 infrared pits

• 3 on each side

• used over heat

viperidae

venomous

• modified digestive enzymes

solenoglyphous fangs fold in mouth

triangular heads

single set of IR oral pits

croatilines with rattles

viperidae delmarva

eastern cotton mouth ‘Agkistrodon contortrix’

• dark pyramid shapes (saddles)

timber rattle snake ‘Croatalus horridus’

Colubridae

common, diverse

1755 sp, monophyletic clades/ subgroups

• colubrinae

• natricinae

• dipsadinae

many constrictors

• gained and lost

• some snail specialists

some opisthoglyphous

colubridae: colubrinae

682 species

generalist or specialist

mostly oviparous

colubrinae delmarva

rough green snake ‘Opheodrys aestivus’

eastern king snake ‘Lampropeltis getula’

corn snake ‘Pantherophis guttatus’

milk snake ‘Lampropeltis triangulum’

scarlet snake ‘Cemophora coccinea’

Eastern rat snake‘Pantherophis alleghaniensis’

eastern black racer ‘Coluber constrictor’

Colubridae: Natricinae

211 sp

Delmarva

• Garter snake‘Thamnophis sirtalis’

• Eastern ribbon snake ‘T. sauritus’

• Queen snake ‘Regina septemvittata’

• Plain-bellied water snake ‘Nerodia erythrogaster’

• DeKays brown snake ‘Storeria dekayi’

• Smooth earth snake ‘Virginia valeriae’

Colubridae: Dipsadinae

733 sp

New world

• Red-bellied snake ‘Storeria occipitomaculata’

• Worm snake ‘Carphopis amoenus’

• Eastern hognose snake ‘Heterodon platirhinos’

• Ring-necked snake ‘Diadophis punctatus’