Class Reptilia

1. Distinguishing features that set the reptiles apart from the amphibians
1. Fully terrestrial
1. Dry, skin with scales; glandless skin that resists desiccation
2. Lay eggs on dry land; no need to return to water for reproduction due to shelled, amniotic egg - complex membrane system of:
1. amnion - encloses the developing embryo
2. yolk sac - contains the embryo's food and energy reserves in the form of lipids
3. allantois - serves as a surface for gas exchange through the shell and encloses a chamber which sequesters nitrogenous wastes produced by the embryo during development
3. Exclusively internal fertilization
2. No larval stages
3. No metamorphosis
2. Introductory Classification, Taxonomical, and Ecological Aspects
1. Classified into four taxonomic groups
1. lizards and snakes of the order Squamata
2. crocodiles and alligators of the order Crocodilia
3. turtles of the order Testudines
4. tuatara of the order Rhynchocephalia
2. Numbers, habitats, and distribution
1. 7000 species total, world wide
2. 300 sp. in the U.S.
3. Occupy both aquatic and terrestrial habitats
4. tuatara of order Sphenodonta (Rhynchocephalia) - only two spp. Sphenodon spp.; found in New Zealand
3. General Reptilian Characteristics
1. Possess both endo- and exoskeletons
1. endoskeleton - bony
2. exoskeleton - composed of horny, epidermal scales and sometimes bony dermal plates (turtles); very few to, usually, no glands in integument
2. Paired limbs except for snakes and some spp. of lizards; tetrapodal in most cases
3. Bony endoskeleton with well-developed rib cage and sternum forming a protective thoracic section
4. Respiration by lungs; no gills; cloaca used for respiration in some spp.; respiration through the skin during embryo development
5. Heart usually 3-chambered; 4-chambered in crocodiles
6. Ectothermic heterotherms
7. Paired metanephric kidneys; uric acid is the main nitrogenous waste
8. Very well-developed nervous system, especially within the cranium and with regard to optic nerves and sense organs; very well-developed visual sensory system
9. Separate sexes; internal fertilization
10. Shelled eggs (see also earlier)
1. shell of inorganic calcareous material or organic, proteinateous, protective leathery material
2. extra-embryonic membranes
1. amnion - inner part of a double membrane that surrounds the embryo; located directly outside of the embryo
2. chorion - outer membrane which is part of the double membrane; located just out side of the amnion
3. yolk sac
4. allantois
4. Details of Reptilian Classification
1. Order Testudines - turtles
1. General characteristics
1. exoskeleton of bony, dermal plates
1. carapace - dorsal plates
2. plastron - ventral plates
2. jaws without teeth
3. vertebra and ribs are fused to the shell
2. Representative sp. - Chelydra serpentina, snapping turtle
2. Order Squamata - snakes and lizards
1. General characteristics
1. skin of horny, epidermal scales composed of keratin - structural protein
2. skin is shed during molting and new scales are produced
3. jaws with teeth; sometimes in the form of fangs for injection of venom in some spp.
2. Suborder Sauria - lizards; tetrapodal spp.; paired respiratory and urinogenital organs
3. Suborder Serpentes - snakes; limb-less spp.; paired respiratory and urinogenital organs
4. Suborder Amphisbaenia - worm lizards; limbless except for one sp. with short front legs; only one lung
3. Order Crocodilia - crocodiles and alligators
1. 4-chambered heart
2. crocodiles have relatively long, slender snouts
3. alligators have shorter broader snouts
4. Order Sphenodonta (Rhynchocephalia) - Sphenodon punctatus, tuatara
5. Specific Reptilian Characteristics
1. Skin (integument)
1. exoskeleton of scales composed of the protein keratin; differ from fish scales in that fish scales are composed of bony material
2. epidermis of thin layer of cells below scales
3. dermis of thick layer of cells below epidermis; contain chromatophores
2. powerful jaws for carnivorous feeding; therefore, they take in mostly protein and excrete nitrogenous waste in the form of uric acid to conserve water
3. all reptiles possess copulatory organs which allow for exclusively internal fertilization
4. very efficient double circulatory system of either a 3- or 4-chambered heart; high blood pressure
5. very efficient lungs in all spp.
6. paired well-developed metanephric kidneys for efficient removal of uric acid from blood
7. very well-developed limbs in most spp.
8. very well-developed nervous and sensory systems, especially in snakes
6. Specific Reptilian Representatives and Additional Details
1. turtles of the order Testudines - distinguishing feature - shell of dorsal carapace and ventral plastron
2. snakes and lizards of order Squamata
1. suborder Sauria - limbed lizards; include:
1. geckos - small, agile, mostly nocturnal spp. with adhesive toe pads which allow them to walk upside-down and on vertical surfaces
2. iguanas - brightly colored lizards with ornamental structures such as crests, frills, and throat fans around head and neck
3. skinks - small snake-like; slender bodies with very small limbs
4. chameleons - catch prey with very long, sticky tongue that reaches lengths greater than that of their own entire body; change color to match environment.
2. suborder Serpentes - snakes
1. entirely limb-less; lack both pectoral and pelvic girdles
2. the pelvic girdle does persist in pythons and boas
3. numerous vertebrae, rigid ribs, and strong vertebral column allow quick, efficient lateral movement through undulations of the body wall muscles.
4. the skull is highly specialized and allows for a special feeding apparatus that enables them to consume prey much larger than their own diameter
1. the 2 halves of the jaw are joined only by muscles and skin, allowing them to be dislocated so that large prey can be swallowed
2. also, many of the skull bones are loosely held together so that the entire skull can flex asymmetrically to enhance the swallowing process
3. to allow the snake to keep breathing during swallowing, the tracheal opeing is pushed forward between the 2 jaw halves into an area where air can enter
5. chemical sensation in snakes by:
1. Jacobson's organs - pair of pit-like structures in the roof of the mouth; lined with olfactory epithelia that are highly folded to provide increased surface area for efficient detection of volatile chemicals
2. the forked tongue picks up chemical from the air and conveys them to the mouth where the tips are inserted into the Jacobson's organs
3. sensory information is then transmitted to the brain where the chemical scents are identified.
6. locomotion by:
1. lateral undulation - S-shaped movement by exerting force against surface irregularities such as rocks, plants, and other features of the terrain
2. concertina movement - enables some snakes to move through a narrow passage, such as when climbing trees by moving with in and using irregular channels in the bark
3. retilinear movement - in a straight line, such as when stalking prey; use ventral scales in an alternating pattern of movement, contraction, fixation, and streching to achieve movement
4. sidewinding - used by desert vipers to move across loose sandy surfaces with minimal surface contact
7. heat sensitivity and detection in certain spp.:
1. Classification and taxonomy of heat sensitive spp. of snakes:
• Family Viperidae - have tubular fangs at the front of the mouth
• Subfamily Crotalinae - pit vipers - posses heat-sensitive pits on their heads between the nostrils and eyes:
• all of the familiar N.A. poisonous snakes are pit vipers
• include spp. of rattlesnakes, the water moccasin, and the copperhead
• the nerves in the pits respond to radiant energy in the long-wave infrared region of the spectrum (5000 - 15,000 nm)
• they are especially sensitive to the heat of warm-bodied birds and mammals
• may be able to detect temperature changes of only 0.003 degree C
8. use of venom in certain spp.:
1. Classification and taxonomy of venomous snakes (four families):
• Family Viperidae - (see also above under heat detection) - all vipers have a pair of hollow fangs for injectionof venom into prey
• Subfamily Crotalinae - pit vipers - (see above) - 12 out of 8000 bites from pit vipers reported yearly in the U.S. result in death
• Family Elapidae - cobras, mambas, and coral snakes; have short permanently erect fangs as opposed to the flexible fangs of vipers; venom must be injected by chewing
• Family Hydophiidae - includes the highly poisonous sea snakes
• Family Coubridae - large family of mostly the familiar, non-venomous snakes, but does include two poisonous snake spp. which have fangs at the back of the mounth - use their venom, usually, to traquilize prey that has been caught by constriction
9. types of snake venom
• Neurotoxic - acts on nervous system; primarily on optic and phrenic (diaphram) nerves, therefore causing blindness and respiratory paralysis respectively.
• Hemolytic - breaks down blood cells, vessels, and causes bleeding into internal body cavities.
3. reproduction in snakes
1. Most snakes are oviparous - lay shelled, fertilized eggs from which the young hatches
2. some spp. are ovoviviparous - eggs hatch inside of mother
3. A few spp. are viviparous - embryo develops in a placenta- like structrue inside of mother's uterus
3. Suborder Amphisbaenia - wormlizards; the reptilian version of caecilians
1. limbless, burrowers which are neither worms nor true lizards
2. Amphisbaenia - amphi - "double" "walding on both sides or both ends"
3. can move both forward and backward with equal efficiency
4. look like earthworms (segmented-looking body (p. 530, fig. 25-20)
5. lay hard-shelled eggs and are fully terrestrial
7. Order Crocodilia - crocs and gators
8. Order Sphenodonta (Rynchocephalia) - tuatara (Sphenodon punctatus) of New Zealand
1. simplest of all reptiles
2. possesses a parietal or pineal median eye which is coverd with scales and is visually, non-functional; it is speculated that it functions as a light sensor to influence the amount of time they send basking.
3. the parietal eye has a retina and lens; is located on the top of the head; is not one of the other two distinct, lateral eyes which are functional