Introduction to Reptiles

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Introduction to Reptiles Powered By Docstoc
					Introduction to Reptiles
        November 26
Eric Clelland (clelland@yorku.ca)
 Divemaster, Assistant Scuba Instructor (87)—logged ~750
  dives in all conditions—peaked my interest in Biology
 BSc Ordinary November 94 from Atkinson College
 BSc Hons November 96—faculty of Science; thesis work:
  Reproduction in pond snail Helisoma duryi
 MSc November 99—Role of V-ATPase in Shell Boring
  organ in frilled whelk, Nucella lamellosa
 PhD October 2007—Role of BMP15 in ovarian follicle
  development in zebrafish, Danio rerio
 Presently working with Dr. Kelly on tight junction
  proteins in Tetraodon—hyromineral balance and
  in zebrafish—TJs in ovarian follicles
                Outline

Taxonomy
Characteristic Features of Reptiles
Characteristics and Natural History of
 Extant Reptilian Orders
Sex Determining Mechanisms
    Genetic
    Temperature dependent
Evolution of Amniotes           Reptiles
                        A paraphyletic group ~8000
                        extant species ~340 in
                        CAN/USA
                        Arose from Labyrinthodont
                        amphibians (Carboniferous)
                        specifically Anthracosaurian
                        lineage around 300-350 MYA
                        Age of Reptiles—Mesozoic-
                        additional species being added
                        all the time from fossil record
                        Ended ~ 65 MYA at end of
                        the cretaceous period—
                        asteroid strike, volcanism?
                        Phylogeny of 16 Orders only
                        4 with extant species; turtles-
                        crocodilians-modern lizards
                        and snakes
Cladogram of Amniota
Based on the # of openings in
          the skull
      Characteristics of Reptiles
 Amniotic Egg                   Efficient 3 or 4 chambered
 Ectothermic—temperature         hearts
  regulated behaviourally        Respiration primarily by
  (basking, denning)              lungs *
 Tough, dry, scaly skin-        Metanephric kidneys
                                  produce uric acid, salt
  epidermal scales                glands (water retention)
 Cranial modifications for      Copulatory organs (penis
  seizing, crushing and           or hemipenes) for internal
  partial or full secondary       fertilization
  palate                         Advanced nervous system
 Modifications of                all 12 cranial nerves
  axiallary skeleton (or loss    Parietal eye is found in
  of limbs) for improved          some lizards such as
  mobility                        Tuataras and Iguanas
      Amniotic Egg                             Amniotic or Cleidoic egg
                                               permitted reptiles, birds and
                                               mammals to colonize land
                                               Encloses aquatic phases of
                                               development in the egg
                                               Specialized extra-
                                               embryonic tissues
                                                      amnion
                                                      allantois
                                                      chorion
                                               Outer protective shell
                                               parchment, leathery or
                                               calcified


Amnion provides aquatic environment for developing embryo, allantois
sequesters nitrogenous wastes and with chorion acts in respiration (gas
exchange), provides physical protection and prevents desication. Reptiles
may be oviparous, ovoviviparous or viviparous.
Reptilian skin is tough, horny (keratinized), abrasion resistant and water
tight. Scales are epidermal - can be used to identify species (see the key above)
 Thick underlying dermis contains melanophores (chromatophores) – also
useful for ID. Few glands are found in reptilian skin- few secretions, no sweat
 Bony dermal plates (osteoderms) may be present (Crocodilians for example)
 Epidermis may be shed in its entirety (snakes and lizards) or replaced only when
worn (Crocs)
Colour and scaling useful for identification
Lungs are used for respiration; cutaneous respiration is lost*. Enlargement of thoracic
cavity by muscular contraction provide mechanisms for inflating and deflating lungs. Partial or
full (Crocs) secondary palate separates air passage from the mouth (NO DIAPHRAGM)
Metanephric kidney, w/o loops of Henle, permits production of nearly insoluble uric acid
waste and prevents excessive water loss in feces. Accessory salt glands near eyes, nose also
excrete nitrogenous waste, but primary function is to remove excess salt
Heart is 3 chambered (4 in Crocs) and efficient. RA receives deOx blood, LA Ox blood.
Heart rhythm prevents excessive mixing of blood in common ventricle. Crocodilians have
bird/mammalian type 4 chambered heart. Branchial arches same as that of Anurans, except in
Sphendonta, which retain the carotid duct.
3 Chambered Reptilian Heart and Branchial Arteries




                                    Turtle, Lizard, Snake            Tuatara
  Turtle, Lizard                       Crocodilians
     Snake
                   Reptiles lose branchial arches 1, 2 and 5; retain 3, 4 and 6.
                   Note: Mammals and Birds lose one aortic arch (M-R; B-L)
             Additional Info
*Pond turtles may obtain up to 30% of their
 oxygen through vascularized tissue located
 in the gular (throat) area or the cloaca.

 *Hydrophiidae (sea snakes) absorb nearly
 all their oxygen through their skin
          Taxonomy of Extant Reptiles
   Phylum Chordata: Subphylum Vertebrata:
                         Class Reptilia
                                    Order Sphenodonta(Tuatara)
 Subclass Anapsida                  retains lower cranial arch
         Order Testudinea-          Superorder Archosauria
   Turtles and Tortoises            Order Crocodilia
 Subclass Diapsida
 Superorder Lepdiosauria
 20 loss of lower cranial arch-
  quadrate moves
 Order Squamata
 Suborder
 Lacertilia (lizards)
  Amphisbaenia (ring lizard)
  Serpentes (snakes)
Turtles, Turtles
I love Turtles
                      Turtles
 ~330 species are living today - Aquatic Turtles
  (eg. Painted turtles, Mud turtles, Snapping turtles,
  Soft shelled) Sea Turtles (eg. Greens, Hawksbills,
  Loggerheads, Leatherbacks) and Land Turtles
  (eg. Galapagos and Desert Tortoises) are found
  distributed world wide, except at the poles
 Herbivorous and Omnivorous species
 GSD and TSD species occur -all oviparous.
 Largest turtles are Leatherback Sea Turtles
  (Dermochelys coriacea) can reach 2m in length
  and mass 700kg
 Turtles can be long lived many are recorded at 150
  years or more—due to low metabolic rate
                          Turtles
   Head without temporal openings (Anapsid)
   S necked (Cryptodires) and Side necked (Pleurodires)
   Essentially unchanged for 200 million years
   Body housed in armour consisting of upper carapace and
    lower plastron, usually comprised of bony scutes
   Colouration, number and location of carapace and plastron
    scutes can be used to ID species
   Teeth absent - Horny keratinized jaws
   Vertebrae are fused to carapace - Muscles pull lung open
    for inhalation, other muscles pull girdle bones (pectoral
    and pelvic) inward to force air out of lungs
   Hearing is poor, but olfaction and vision is keen. Turtles
    generally don’t vocalize
 Shells of a Turtle




                      Hinged
Incomplete
                     Squamata
 Lizards, worm lizards and snakes comprise >95% of living
  reptiles
 Most recent, having begun to diverge in the late Jurassic
 Many species are viviparous—the condition having arisen
  at least 100 separate times, perhaps due to increased egg
  retention during colder periods
 Squamates are found world wide. Terrestrial, Arboreal,
  Aquatic and Marine species are found
 Squamate skulls are kinetic, lower jaw can unhinge and
  head plates are pliable to allow for expanded gape
             Lacertilia (Lizards)
 ~3300 species with wide distribution
 Most are terrestrial or arboreal
 Eyelids are movable, eyes generally well
  developed with rods, cones, pecten. Geckos are
  without cones (nocturnal)
 External ear is present, however except in
  Geckos, hearing is not thought to play a major role
 Many lizards can change colour to blend into
  background (camouflage)
 Some (e.g. Skinks) will drop a portion of their tail
  to distract predators. Gila monsters store water
  rich fat in their tails
Some living lizards. CW from
upper left: Marine Iguana (New
World); Chameleon (Old World)
snaring a dragonfly; Tokay (Old
World) Gecko
SSSSSerpents
               Serpentes (Snakes)
 ~ 2300 species of snakes have been ID’d
 Elongate body, limbless (boas, pythons have spurs)
 No external ear or middle ear, hearing poor although
  vibrations and low frequency sound can be detected
 Eyelids fused into transparent spectacle, eyes have little
  motion, vertical pupils-covered by a transparent scale
  (brille)
 Tongue is used in olfaction in conjunction with the
  Jacobsen’s organ (found inside the mouth)
 Lower jaw halves not fused, allowing for incredible
  gape. Snakes eat live prey, headfirst. Prey can be
  immobilized by constriction or by envenomation
 GSD only
                                            C




    Four principal forms of locomotion in
    snakes. A and C are seen in arboreal
    snakes. B common in terrestrial snakes and
    D in some terrestrial snakes (sidewinders)



D
                 Serpentes (Snakes)
 Snake saliva - many species have evolved highly toxic venom – all
  somewhat toxic
 Venom may be neurotoxic; blocking nerve transmission (eg.
  Cobras and sea snakes), or hemotoxic (hemorragic); breakdown
  RBCs and BVs (eg. Rattlesnakes)
 Venomous snakes are divided into 4 groups, based on the design of
  their fangs. Colubrids have rear fangs and must chew on the prey
  to envenomate. Elapids have short, fixed fangs in front and must
  strike repeatedly (e.g.. Cobras). Vipers have tubular fangs located
  in front, that can be erected by muscle contraction. They are
  considered to be the most advanced. New world vipers
  (Rattlesnakes, Copperheads and Cottonmouths) have heat sensing
  pits. Old world vipers (Adders, Puff adders) lack this feature. The
  fourth classification is Hydrophiidae (sea snakes) which have the
  most neurotoxic venom of any snakes
Life imitates art – 2m alligator inside a 4m invasive python
Archaosaurs:
The
Crocodilians
                Crocodilians
 Crocodiles, Alligators, Caimans and Gavials. 25
  species are extant
 Diapsid—Have 2 pairs of temporal openings
 Most closely related to birds and extinct dinosaurs
 Have 4 chambered hearts
 In all species, sex is determined by the
  temperature at which the eggs incubate (TSD-
  FMF)
 Males larger than females, have harems, territories
 Many crocodilians show maternal nesting
  behaviour
 Vocalizations are common
        Sex Determining Mechanisms

 Genetic Sex Determination occurs in all reptilian groups
  except Crocodilians
 Temperature Dependent Sex Determination occurs in
  some lizards, some turtles and all Crocodilians (not
  snakes)
 TSD has allowed Crocodilians to survive highly skewed
  sex ratio of 10:1 F:M caused by over hunting—GSD
  species would not have survived
 Tuatara, sea turtles and other TSD species may be
  endangered by global warming:
       skewed sex ratios due to changes in incubation temps
       beach erosion and habitat destruction
         Examples of TSD and of How a single nest can produce 2 sexes




                    % Male
% Male