Ib 104: Vertebrate Natural History - Reptiles

Front 1

Differences from amphibians

Back 1

- amniotic egg
- integument
- excretion
- thermal needs

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Amniotic egg

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- shared with old mammals
- mineralized shell
- smaller clutches than amphibians, large eggs require less moisture but still some
- chorion and allantois = chorioallantoic membrane

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Integument

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keratinous scales, scutes, or plates
- less subject to water loss b/c of lipids in skin
- can be diurnal, can actively self-thermoregulate
- less glandular, no toxic skin secretions
- have femoral gland secretions to mark territories

Front 4

Excretion

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Ammonia: toxic when produced, difficult out of water
urea: nontoxic, requires water and energy
uric acid: conserves more water, requires more energy to produce, used by most desert species

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Thermal regulation

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some thermoconformers, mostly ectothermic
- hemotherms = maintain constant body temp via behavioral thermoregulation

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Heat energy gained =

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= Qabs + M + R + C + LE + G

Qabs = sunlight rediation
M = metabolic heat production, easier for large reptiles
R = infrared radiation received or emitted, better with matte surface
C = consecutive exchange of heat, boundary layers around animal
LE = heat via condensation, sweating, panting, gular fluttering
G = conduction, heat exchange with substrate

Front 7

3-chambered heart

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single ventricle with 3 compartments
- blood doesn't mix despite lack of septum due to muscular ridge and AV valve
- intracardiac shunts: can resend deoxygenated blood while holding breath when diving
lungs --> LA --> cavum arteriosum --> cavum venosum --> aortic arches
body --> RA --> cavum venosum --> cavum pulmonale --> pulmonary arteries

Functions: controls O2 content of blood when holding breath
- thermoregulation (blood circulation)
- myocardial oxygenation (avascular heart)

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Lepidosauria

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Rhynchcoephalia and Squamata
- streptostylic skull
- plearodont dentition
- caudal anatomy
- skin shedding

Front 9

Streptostyly

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lost lower temporal arsh of diapsid skull
- removes strut that fixes quadtrate in place
- possibly increases bite force

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Pleurodont dentition

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teeth attached to labial side of jaw, continually shed during life
- adaptation for insectivory
- vs. acrodont dentition (teeth fused to jaw, irreplaceable)

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Tuatara

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Rhynchocephalia
- lizard-like
- once world-wide, now only 2 extant species near New Zealand
- disappeared from fossil record after KT extinction
- heterodonty, loss of streptostyly
- no copulatory organ
- Jacobsen's organ separated from oral cavity, tongue not chemoreceptive
- retained "ribs" (gastalia)
- nocturnal, insectivorous, territorial (via displays)
- slow metabolic rates, long-lived, low temp
- low respiratory rate
- temp-determined gender
- endangered due to rats

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Squamata

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- mostly insectivorous lizards
- monophyletic, many synapomorphies

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Highly kinetic squamata skull

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mesokinetic and metakinetic articulations, loss of kinesis in herbivore

Front 14

Squamata hemipenes

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out-pocketing of cloaca, covered with spines and ridges
- retractor muscles
- stored in base of tail

Front 15

Squamata vomeronasal system

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opens to oral cavity, works via tongue
- iguanids use tongue more for capture instead of chemoreception

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Squamata limb reduction

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paired with elongation and loss of axial skeleton

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Squamata Hox genes

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regulate expression for fore-limb and axial development (segmentation)
- some snakes still have hindlimb elements

Front 18

Terrestrial lizards

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runners: powerful hindlimbs, long tail
ant-specialists: tank-like body, thorny, cryptic

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Aquatic lizards

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- laterally compressed tail
- double row of keeled scales
- transparent lower eyelid
- fringes on toes for running on water

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Limbless lizards

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burrowing: small tails, reduced eyes, short ossified skulls
grass-swimmers: long tails with no skull modifications

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Saxicolous lizards

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not obvious
- body inflation in crevices, spiny tails, large hands for gripping boulders (Sauromalus)

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Arenicolous lizards

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sand dune specialist
- toe fringes, cryptic coloration
- smooth/shiny ventrals
- blunt head
- unexposed tympana

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Arboreal lizard

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not obvious
- toe pads with microscopic setae
- zygodactyly
- prehensile tail
- some gliders with skin flaps

Front 24

Lizard locomotion

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lateral undulation: breathing muscles, must hold breath while running
- longer hindlimbs to run bipedally
- need heavy tails for sprinting
- walk on water via bubbles = Basiliscus

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Lizard feeding

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mostly insects and arthropods
- some eat vertebrates (komoto dragon)
- some eat verts whole
- some molluscivores - powerful crushing jaws
- some herbivores - in warm environments, symbiotic intestinal microorganisms to break down cellulose, enlarged colons, polycuspate teeth

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Lizard finding prey

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- iguanids and geckos use sight
- rest use chemosensation

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Lizard catching prey

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- mostly use jaws
Tongue: iguanids, chameleons (also have gret sight via accommodation)
- circular muscles, stable hyoid and tongue skeleton
- uses elastic energy storage; collagen sheaths compressed, forces them to stretch

Front 28

Lizard Reproduction

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- defend food resources or female territories
- often sexually dimorphic
- usually only threat displays, no fighting
- Uta stansburiana colors
- furcifer labordi

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Parthenogenesis

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female clonal species, results from hybridization (Aspidoscelis)
- needs pseudocopulation to initiate egg production
benefits: higher reproduction rate, can outcompete sexual species
cost: lack of recombination, doesn't allow deleterious mutations

Front 30

Snake origin theories

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1. Fossorial ancestor: no ears, eyes derived from degenerated material --> better theory
2. aquatic ancestor, derived form mosasaurs, snake eyes share similarities with aquatic organisms

Front 31

Snake feeding

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Large prey: small number, usually eat elongated animals, use constriction or envenomation

Smalls prey: large number, some blind snakes, have anal secretions to protect from ants/termites
- mandibular raking vs. maxillary raking

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Snake Envenomation

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Duvernoy's gland: secondary use for defense
- initiates digestion
- move fast
- front-fang = evolved 4 times, required shorter maxilla
- rear-fang = tube-like

Viperidae = longer fang attached to rotatable maxilla
Elapidae = shorter fang with less mobile maxilla

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Snake venom

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- cocktail of protein fractions, some from digestive enzymes
- neurotoxins attack synaptic junctions, leads to organ failure
- hemotoxic fractions destroy tissues
- some stop blood form clotting

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Snake skull

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- modified for large prey
- palatal complex suspended form brain case by ligaments
- mandibular symphyses unfused
- sides of jaw unfused, swings out when jaw opens
- pterygoid walk for large prey

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Limbless locomotion

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lateral undulation: pressure waves, pivot points
sidewinding: on sand, fling head forward
concertine: posterior body anchored, anterior moves forward
rectilinear: large-bodied snakes, ventral scales lift forward, then pulled down and back
- need friction with substrate

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Infrared detection

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sensing pits in head
- rattlesnakes cool head for thermal differentiation
- perceive visual image

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Testudines

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- aquatic/marine, some terrestrial
- omnivorous or herbivorous
- powerful jaws (middle ear leaves little room for adductor muscles, no fenestrae)
- shell: carapace and plastron
- internal girdles
- pattern of scutes and underlying bones that don't match to add structural support via misalignment

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Turtle respiration

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lungs attached to carapace and viscera
- breathing involves expansion of visceral cavity, contract muscles to expand lungs

Front 39

Testudines clades

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Pleurodirans: bend neck to side, process on pterygoid bone for pully system jaw

Cryptodirans: retract head vertically, process on quadrate/prootic bones for jaw

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Turtle reproduction

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all egg laying
elaborate courtship displays
- rare parental care
- genotypic or temp gender dependent (males need lower temp, global warming ahh!)

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Sea turtles

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Cheloniidae: hydrodynamic shell, reduced plastron
Dermochelyidae: endothermic functionally

females go on land only to lay eggs
- long time to maturity
- return to natal beaches using earth's magnetic field
- Lepidochelys = only diurnal nesting, all come ashore at once
- all endangered, shrimp trawl drowning

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Crocodylia

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fossil record = Deinosuchus and Sarchosuchus
- paddle-like tail, webbing, transparent membrane over eye
- skin covers tympanum, valved nostrils
- secondary palate separates oral cavity form resp/esoph
- bellowing and postures for communication
- head rubbing for courtship
- internal fertilization in water, lay eggs on land, much parental care
- kill/drown prey, must dismember food first b/c no mastication
- pyloric gizzard
- most powerful bite force ever measured, can crush turtles