Reptilian GroupsChapter 26

I. Diversity

First truly terrestrial vertebrates7000 species; 300 in U.S.Age of Reptiles lasted over 165 my, including

dinosaursMass extinction at end of Mesozoic; modern

lineages are survivors Lizards and snakes underwent further

radiation into diverse and abundant groups

Carboniferous Forest

II. Origin & Adaptive Radiation Arose from amphibian-

like tetrapods, the anthracosaurs, during Carboniferous

3 lineages: Anapsids—turtles Diapsids—

ichthyosaurs, lizards, snakes, crocodilians, tuatara, plesiosaurs; this lineage also gave rise to birds

Synapsids—mammal-like reptiles (all extinct)

Tetrapod Skulls

III. Characteristics A. Skin

Tough, dry, scaly which protects and prevents dessication

Epidermis shed periodically in lizards and snakes; formed of scales made of keratin

Turtles add new layers under old, forming platelike scutes

Crocodiles and many lizards also have bony plates called osteoderms beneath scales

Thicker dermis has chromatophores that provide color

B. Shelled Egg Main factor in reptiles success Shell permits eggs to be laid

on land; porous, parchment-like or leathery

Extraembryonic membranes from previous aquatic stages maintained; protective membranes support development

Allantois is respiratory surface and chamber for storing waste

Chorion allows oxygen and carbon dioxide to pass easily

Young hatch as lung-breathing mini adults

C. Reptilian Jaws

Jaw muscles become larger to allow for mechanics of chewing

D. Internal Fertilization

Required because sperm must reach egg before it is enclosed

Males have copulatory organ; testes produce sperm

Female has oviducts and paired ovaries; oviducts secrete albumin and shells for eggs

E. Circulatory System Changes

Right and left atria completely partitionedRight atrium receives deoxygenated blood

from body; left oxygenated blood from lungsVentricle incompletely separated but only a

little mixture of the blood occurs In crocodilians, ventricles are completely

separatedBlood pressure is also higher than

amphibians

F. Lungs

Better developed Pull air in by enlarging

thoracic cavity: Snakes and lizards

move rib cageTurtles and

crocodilians move internal organs to create negative pressure

G. Water Conservation

Metanephric kidney which concentrates solutes and excretes wastes as uric acid; uric acid has low solubility and precipitates readily requiring less water for elimination

Salt glands nears eyes or nose secrete excess salts

H. Support of Limbs for Locomotion

Better body support (except limbless reptiles)Walk with legs splayed outwards and body

close to groundMost dinosaurs and some modern lizards

have more efficient method with legs directed beneath body

I. Nervous System

More complexBrain small but cerebrum a little larger; in

crocodilians a true cerebral cortex permitting more complex behaviors

Sense organs well developed except hearing Jacobson’s organ is highly developed in

lizards and snakes to detect odors carried to senses by tongue

IV. Reptilian OrdersA. Anapsida; Order Testudines

1. General CharacteristicsAppeared in Triassic, 200 myaShells have dorsal carapace and ventral

plastron; outer horny layer and inner layer of bone

Limbs and limb girdles far from ribsNo teeth; use horny plates to rip food

2. Respiration

Can’t expand chest because of rigid shellMovement of abdominal and pectoral

muscles associated with limbs create space for air to move in or compress viscera to push air out

Movement of limbs helps ventilate lungsSome aquatic turtles gain enough oxygen by

pumping water in and out of mouth cavity

3. Reproduction

OviparousEggs buried in ground in nest; no care of

young In crocodiles, some turtle families, and some

lizards, nest temperature determines sex of offspring; low temperatures are males and higher temperatures are females

4. Types

Giant turtlesMarine turtles may reach 2 m long and 725 kg in

weight; Galapagos tortoises reach several hundred kilograms

Low metabolic activity allows lifespan of 150 yrs Box turtle

Hinged plastron allows it pull in all parts and close up completely

Snapping turtlesReduced shell prevents full withdrawl of bodyStrong jaws used defensively and for huntingEat fish, frogs, waterfowl

B. Diapsida; Order Squamata

Most recent and diverse, making up 95% of living reptiles

Lizards appeared in Permian but did not radiate until Cretaceous

Snakes appeared in late CretaceousAmphisbaenas appeared in early Cenozoic

a. General Characteristics

Lost dermal bone by temporal opening allowing for a kinetic skull, one that has movable joints

Can seize and manipulate prey with jaws and force jaws closed

Skull mobility is major factor in diversity

b. Reproduction

Some viviparous or ovoviviparous;associated with colder climates. Eggs retained longer in oviduct

Oviparous; associated with warmer climates

c. Suborder: Sauria

Terrestrial, burrowing, aquatic, aerial, arboreal Survive well in hot, dry regions External ear; day-active lizards have rods & cones;

nocturnal have only rods Keep body temperature constant by behavioral

regulation Conserve water by producing semisolid urine with

highly crystalline uric acid Some store fat in tails to provide energy and water

during drought Geckos—small, nocturnal, adhesive pads on toes Chameleons—arboreal, color changing, long tongue Iguanids—many New World lizards Gila monster, beaded lizard, and komodo dragon only

ones with venomous bites

Lizards

d. Suborder: Amphisbaenia

Most lack any trace of external limbs; skin in rings; resemble earthworms

Eyes and ears rudimentary and hidden under skin

1 species in Florida but mainly South America and tropical Africa

e. Suborder: Serpentes

(1) Feeding

Can eat prey several times their own diameter

Two halves are loosely joined allowing them to spread apart

Skull bones loosely articulated so mouth can accommodate large prey

To allow breathing during slow process of swallowing, tracheal opening extended

Has extra skin infolded between scales; this unfolds during a big meal

Hunting and Feeding

(2) Senses Eyes have reduced mobility and

permanent corneal membrane for protection

Most have poor vision except arboreal snakes

No external ear and do not respond to sounds

Can feel vibrations, especially low frequencies, and those in ground

Chemical senses primary on used for hunting

Jacobson’s organs are pair of pits in roof of mouth; lined with olfactory receptors and forked tongue picks up particles and conveys them past organ

Pit vipers( rattlesnakes) have pits that detect heat emitted by warm-bodied prey

(3) Movement Limbless and have lost

pectoral and pelvic girdles (except pythons)

Vertebrae shorter and wider to allow undulation

Lateral undulation is S-shaped movement that pushes against rough ground and water

Concertina movement is extension of S-shaped loops to strike or to climb trees

Rectilinear movement is straight using minute lifting of consecutive ribs

Sidewinding is sideways looping by desert vipers that “walks” them across sand

(4) Venom/Venomous Snakes

Vipers have hollow fangs that are hinged and inject venom as snake strikes

Family Viperidae—New World and Old World vipers with and without pits

Family Elapidae—cobras, mambas, coral snakes, and kraits

Family Hydrophiidae—sea snakesFamily Colubridae—most non venomous but

boomslang and African twig snake are

Venomous Snakes

Fangs

(5) Snakebites 8000 snake bites each year in

U.S.; 12 fatal; In India and Burma alone 200,000 bites/year; 25,000 fatalities worldwide

Most venom a combination of types

Neurotoxins act on nervous system causing blindness and stopping respiration

Hemorrhagin type breaks down blood vessels, allowing blood to leak into spaces

Sea snakes and Australian tiger snake have most deadly venom per unit but large venomous snakes deliver more venom, making the king cobra the most dangerous

“Red next to yellow, kill a fellow.”

Snake Bites

(6) Reproduction

Most oviparous, laying eggs under logs, rocks, or in holes

Pit vipers are ovoviviparous

Some are viviparous Sperm may be retained

and several egg clutches can be laid from a single mating

f. Order Sphenodonta Tuatara sole survivor of

group that evolved 200 mya and went extinct 100 mya

3 species live in New Zealand; once widespread but now restricted to small islands

Has a well developed median parietal eye buried beneath the skin; function is unknown

Lives in burrows Slow growing and may live

to 77 years Slowest rates of evolution

among vertebrates

g. Order Crocodilia Sole survivor of archosaurs; group radiated

into dinosaurs and birds Have changed little since evolved in Mesozoic Long, well reinforced skull and jaw muscles for

powerful bite; teeth set in sockets Complete secondary palate; feature only

shared with mammals; 4 chambered heart like birds and mammals

Oviparous, laying eggs in nest of vegetation Alligators and caimans—New World—broad

snout Crocodiles—widely distributed; also saltwater Gavials—India and Burma—very narrow snout

Crocodilians