Reptilian Groups Chapter 26. I. Diversity First truly terrestrial vertebrates 7000 species; 300 in U.S. Age of Reptiles lasted over 165 my, including.
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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
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)
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
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
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
(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
(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
(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
(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
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