Reptilian Groups

Chapter 26

I. Diversity

     First truly terrestrial vertebrates 7000 species; 300 in U.S.

Age of Reptiles lasted over 165 my, including dinosaurs Mass 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

     T ough, 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 partitioned Right atrium receives deoxygenated blood from body; left oxygenated blood from lungs Ventricle incompletely separated but only a little mixture of the blood occurs In crocodilians, ventricles are completely separated Blood pressure is also higher than amphibians

F. Lungs

  Better developed Pull air in by enlarging thoracic cavity:  Snakes and lizards move rib cage  Turtles 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 ground Most dinosaurs and some modern lizards have more efficient method with legs directed beneath body

I. Nervous System

    More complex Brain 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 Orders A. Anapsida; Order Testudines

     1. General Characteristics Appeared in Triassic, 200 mya Shells have dorsal carapace and ventral plastron; outer horny layer and inner layer of bone Limbs and limb girdles far from ribs No teeth; use horny plates to rip food

2. Respiration

    Can’t expand chest because of rigid shell Movement 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 lungs Some aquatic turtles gain enough oxygen by pumping water in and out of mouth cavity

3. Reproduction

   Oviparous Eggs 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 turtles  Marine 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 turtles  Reduced shell prevents full withdrawl of body  Strong jaws used defensively and for hunting  Eat 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 Cretaceous Amphisbaenas 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 snakes Family 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