Lizards & Snakes & Tuatara Part II

VERTEBRATE ZOOLOGY (VZ Lecture18 – Spring 2012 Althoff - reference PJH Chapters 13 &

14)

copperhead

• Squamata (order) lineage ________ (suborder)

• Long-standing hypothesis: that snakes evolved from a subterranean lineage of lizards with greatly reduced eyes

followed by more recent extant species of surface-dwelling snakes where eyes “redeveloped” after nearly disappearing in earlier forms

• With recent fossil discoveries, there is still much uncertainty regarding the evolutionary history of snakes

Snakes

• 3 infraorders: ScoleocophidiaAlethinophidiaColubroidea

• Out of ~2,900 species of snakes, most (~2,350) from the infraorder Colubroidea….

1,800+ in the family ______________ alone --sp. found on all continents

--many have venom to kill prey but lack specialized hollow teeth for injecting venom

Extant Snakes

eastern milk snake

• Some species have remnants of pelvic girdle, others no trace of pelvic girdle

• General body form types: (A) slow-moving constrictors (B) longer-faster: visually-oriented snakes (C) arboreal—longer yet (D) small, rounded head with little distinctionbetween head and tail, reduced eyesize (E) large head and stout body—to accommodate large prey (F) flattened tail (side-to-side) & valves that close the nostrils…for diving

Extant Snakes

Fig. 13-4, p338 PJH

A

B

Fig. 13-4, p338 PJH

C

EF

• ____________________ important in most snakes: forked tongue, with widely separated tips than can move independently

a) “collect” molecules from air or ground b) transfer those molecules from tongue, when retracted, to the vomeronasal organs

• _________________________: typical of nonconstrictors that can move quickly, frequently raising the head to look around. Many arboreal species have enlarged eyes…and overall longer body length enables them to go to tips of branches to pursue prey

Detection of Prey

parrot snake - Costa Rica

worm snake - Tennessee

BURROWING

ARBOREAL

grass snake

Forked tongue

tongue

vomero-nasal organ

nerve brain

A

B

A

B

_________________

_________________

• Foraging behaviors very diverse among squamates (i.e., snakes and lizards)….

• Most feeding specializations are related to changes in the structure of the skull and jaws.

• Most of these specializations associated with a) loss of _____________________ b) loss of _________________ bone that

formed that lower temporal bar

Foraging & Feeding

Fig. 13-6, p343 PJH

Lowertemporalfenestra

qj

sq

j“early” form (Permian Petrolacosaurus)

qj

sq

j “modern” Tuatara

qj

sq

j

“modern” collared lizardjqj

sq

qjj

“modern” snake = loss of upper temporal arch,not one but two places

po

q

sq

• They not only had a a) loss of lower temporal barb) loss of quadratojugal bone that formed

that lower temporal bar

they also had the loss of a second temporal bar which was formed by a connection

________ the postorbital and squamosal bone

• Result even more flexibility of the skull

• Additional increase in flexibility achieved by flexibility of the joints between other bones in the palate and the roof of the skull

For snakes…

• Among advanced snakes, their skulls are considerably more flexible than those of lizards

• Sometimes commonly referred to as “unhinging” of the jaw, snakes do not “unhinge” their jaws. They simply have a design that allows extreme movement of the jaws.

• Their skulls have ___ links, with joints between them that permit rotation of the jaw. The “links” are paired (each side of head) and they can function independent of the opposite side “paired” link. Coupled with the pterygoquadrate ligament and the quadrato-supratemporal tie, they can have considerable sideward movement and rotation.,

For snakes…

Fig. 13-7, p344 PJH

LA

TE

RA

L V

IEW

VE

NT

RA

L V

IEW

1

23

4

5

6

1

7

7

8

8 “________” of flexibility

• Mandibles, at the front end, are joined _____ by muscles and skin…not rigid bone like for lizards. Allows extreme spread sideways and forward and backwards independently.

also for snakes…

• A—without fangs (ex. African python)

• B & C—OPISTHOGLYPHOUS—fangs in the rear of the maxilla (ex.false viper) (“behind” and “knife”)

• D—SOLENOGLYPHOUS—fangs on a rotating maxilla (ex. African puff adder) (“pipe”)

• E—PROTEROGLYPHOUS—permanently erect fangs at the front of the maxilla (“first”)

3 lineages of “venom” snakes---same function, different designanother example of __________ ___________

Dentition of snakes

Fig. 13-9, p346 PJH

AB

C

D E

OPISTHOGLYPHOUS

SOLENOGLYPHOUS PROTEROGLYPHOUS

• OPISTHOGLYPHOUS—fangs in the rear of the maxilla, _____________________________ that may conduct saliva to wound

• SOLENOGLYPHOUS—fangs on a rotating maxilla, __________. Longer fangs allows deeper penetration. Venom kills & aids digestion. Prey often allowed to ‘escape’ and tracked down when dead.

• PROTEROGLYPHOUS—permanently erect fangs at the front of the maxilla, _________________

Dentition of snakes