Lecture 13 - Reptilia

Lecture 13 - Reptilia

1. Class Reptilia

   • Approx. 6,000 spp. in the 4 major groups
     • on all land masses except polar regions
     • Advantages Over Amphibians
       • 1. Amniotic eggs will calcareous or leathery shell that prevents desiccation while also used as a respiratory surface
         • (amniotic fluid and allantois)
         • 2. Scaly, water-tight skin preventing desiccation
           • 3. Rotation of limbs to ventral side of body
             • 4. Increased jaw mechanism to handle larger/harder insect prey

2. Order: Testudines (turtles)

   • Approx. 240 spp.
     • General Characteristics:
       • A. Oviparous, laying eggs on land
         • B. 2 parts of bony shell, to which vertebrae are fused
           • Carapace & Plastron
           • Morphology reflects ecology
           • C. Teeth absent, replaced by keratinized beak
   • Two Groups:
     • Pleurodires - side-necked turtles
       • Cryptodires - "hidden"-necked turtles
   • How System Work
     • Respiration
       • Lungs attached to top, sides of carapace
         • Muscles force viscera (organs) upwards against lungs to compress; expand visceral cavity to decompress
           • Exhale
             • transverse abdominous; posterior limiting membrane
             • pectoralis; shoulder girdle
           • Inhale
             • abdominal oblique
             • serratus
     • Behavior
       • Social Dominance
         • a. ritualized head movements
           • b. biting and ramming
       • Reproduction
         • Courtship displays
           • claw vibrating
         • Nesting
           • a. all species bury eggs
             • b. typically 40-60 days to hatch
               • c. some lay in fall; eggs exhibit diapause
     • Development of Young
       • Temperature-dependent gender determination
         • - common among turtles
           • - higher temperatures produce larger gender; female turtles
             • - Ca. 3 - 4* C separates males, females
               • Narrow temperature window, environmental variability ensure production of males, females
                 • Ex: sunny vs. shaded nest sites
                   • Others?
                     • ground temperature
                       • rainy or humid
                         • global warming

3. Order: Crocodylia

   • Approx. 22 spp. primarily tropical
     • General Characteristics:
       • A. Oviparous, constructing terrestrial nests for eggs
         • B. Thecodont teeth, well-developed palate
           • C. Laterally-compressed tail
             • D. 4-chambered heart
               • E. 1st evidence of neocortex tissue in brain
                 • leads to complex behavior
   • 3 Families
     • Alligatoridae
       • - broad snouts
         • - only upper teeth show when jaw closed
           • - carnivorous.. but fruits/veggies too
     • Crocodylia
       • - narrow snouts
         • - 4th lower incisor protrudes when jaws closed
           • - Largely piscivorous
     • Gavialidae
       • - long narrow snouts
         • - 4th lower incisor protrudes when jaws closed
           • - carnivorous.. but fruits/veggies too
   • Unique Adaptations, Behaviors
     • Dorsal eyes, nostrils
       • remain hidden while being able to see, breathe
     • Secondary palate
       • separates nasal passage from mouth
     • Pressure receptors
       • bulges on upper, lower jaws
       • similar function to neuromast cells
     • Four-chambered heart
       • right, left ventricle, atrium
       • variable blood flow when active, at rest, under water
       • when sunning, can "heat rapidly" by increasing flow to limbs
     • Gastroliths
       • actively swallowed stones; "stomach stones"
       • Function(s):
         • - help control buoyancy
           • - digestion
     • Nictitaing membrane
       • second eyelid; closes front to back
       • facilitates underwater vision; improved eye protection
     • Reproduction
       • complex courtship behaviors; posturing, head-slapping, bellowing
       • females bury eggs in mound nests; defend eggs, young
       • temperature-dependent gender determination
         • greater than or equal to 34*C = males
         • less than or equal to 30*C = females
       • hatchlings call to parents before emerged from egg
       • stimulates male and/or female to excavate nest
       • adults of some species break open to assist hatchlings
     • Ecosystem Engineers
       • "Alligator holes"
         • disturb, clear muck, wetland vegetation with snout, limbs
         • create depression with body, tail
         • remains wet during drier seasons

4. Order: Rhynchocephalis

   • 2 spp. in New Zealand
     • Oviparous, sexually mature at 20, lives to 50
       • pineal eye (unlensed dorsomedially placed)
         • Acrodont teeth with 4 upper jaw rows, primarily insectivous

5. Order: Squamata; Suborder: Sauria (lizards)

   • Approx. 3,760 spp., global distribution except polar regions
     • Eyelids and external ear present
       • Paired kidneys placed posteriorly
   • Social Behavior
     • dominancy, territoriality, courtship
       • push-ups, gulag (dewlap) fanning, and head bobs
         • very similar regardless of situation; complex, responses matter
           • Aggressive response = male Passive response = female
             • Ex: Green Anoles
               • A. assertion-challenge
               • B. Aggressive posturing; if intruder is male
               • C. Courtship; if intruder is female
   • Other interesting aspects of Lizard Ecology
     • Caudal anatomy
       • - dropping of tail to escape predator - effective, but comes with a price     * loss of communication      * reduced fat storage - come skinks eat autotomized tails
     • Reproduction
       • Oviparity
         • - external development; eggs - ancestral form - low cost; multiple clutches possible
       • Viviparity
         • - internal development; eggs - derived form - high cost; single clutch only
       • Parthenogenesis
         • all female populations
           • typically originate from hybridization between bisexual species
             • EX: Whiptails
               • clone themselves; offspring are the same as her
           • unisexual reproduction, no fertilization

6. Order: Squamate; Suborder: Amphisbaenia

   • Fossorial adaptations include:
     • a. limblessness, but with vestigial girdles
       • b. elongated bony with annuli to facilitate bi-directional movement
         • c. only 1 lung
           • d. external ears absent
             • e. skull entirely compact bones; with flattened snout

7. Order: Squamata; Suborder: Serpentes (snakes)

   • Approx. 2,400 spp.
   • General Characteristics:
     • eyelids, external ears, tympanum, eustacian tubes absent
       • girdles extremely vestigial or absent, sternum absent
         • urinary bladder absent, 1 lung
           • mandibular symphysis absent, skull bones loosely connected
   • Most (67%) extant species belong to Family: Colubridae
     • a. no trace of pelvic girdle
       • b. single carotid artery
         • c. highly kinetic (moveable) skull
           • d. most non-venomous
     • Chemosensation is important
       • a. forked tongue; separated tips move independently
         • b. projected, captures chemical stimuli; retracted, stimuli transferred to vomeronasal organs
   • Types of Movement
     • Lateral Undulation or serpentine locomotion
       • - series of irregular curves, each pressing against object - lateral force canceled by subsequent curve
     • Rectilinear locomotion
       • - rib muscles lift sections of body off ground, stretch forward - primarily heavy-bodied snakes; slow movement, but useful for stalking
     • Concertina locomotion
       • - anchor posteriorly with "loops"; stretch forward; anchor anteriorly; draw rear forward - adapted for use in narrow passages -ex: rodent burrows, pipes in your house 
     • Sidewinding locomotion
       • - raise sections of body in "loops", thrust forward and set on ground - force exerted downward  - primarily used by desert species
   • Feeding Specializations
     • increased flexibility, movement of skull
       • - sides move independently; complex; 3-dimensional
     • constriction and venom
       • - permit taking of larger prey while minimizing risk of injury - shortened vertebrae, truck muscles permit tight lopping by constrictors     - cause of death for prey = suffocation Venom: mixture of enzymes, phosphates and other compounds
     • fangs
       • specialized, enlarged teeth associated with venom glands
       • Dentition/Placement of Fangs
         • Aglyphous
           • no fangs, smaller teeth ex: constrictors
           • Opisthoglyphous
             • fangs on posterior end of maxilla; smaller teeth in front fangs hollow or solid ex: boomslang, false viper
             • Proteroglyphous
               • fangs on front of maxilla; smaller teeth behind fangs hollow; permanently erect ex: Coral snakes
               • Solenoglyphous
                 • fangs only teeth on maxilla fangs hollow; moveable; longer ex: viperids