Origin of Tetrapods, Amphibians and Reptiles

Chapter 34

“Never grow a wishbone where your backbone ought to be”

-Clementine Paddleford

Origin of Tetrapods First tetrapods diverged

365 million years ago (________)

________________________and shallow inland lakes with muddy bottoms likely selected for early tetrapods

Origin of Limbs Tetrapod limbs were

modification of preexisting body plan

Single appendicular bones (humerus and femur) articulate with pectoral or pelvic girdles Become larger and stronger

Mesomeres deviate from _______ _____ Diversification of limb bones

_______________ separate tetrapods from fins of lobe-finned fish

Evolution of Tetrapods Increased air breathing capabilities

More efficient lung Gill arches move to _________

Limbs with digits support tetrapod’s weight on land

Evolution of a _____________ separated head from body Allowed for head movement

Separation of ______________ form skull Supports fore limbs

Fusion of pelvic girdle to spine Transfers forces from hind legs to body

Evolution of TetrapodsEusthenopteron Prehistoric Sacopterygian Early forelimb bones

Humerus Radius and ulna

Internal nostrils Pectoral girdle bones attached to skull

Acanthostega Recognizable limbs Sturdy forelimb bones ___________________ present

Eight digits on each hand Fore limbs could not bend forward or support

weight Pectoral girdle bones ______________

Evolution of TetrapodsIchthyostega Reinforced ribcage Limbs ___________

Support weight on land Limited movement on land _____________ present

Gills used primarily for respiration

Limnoscelis Early amphibian Sturdy pelvic and pectoral girdles Sharp teeth

Terrestrial predator

Evolution of Tetrapods: Tiktaalik Mid to late Devonian (~380

mya)

Tetrapod characteristics Independent ___________________Ribs to support weightFront fin bone structure similar to

all tetrapodsLimbs bent at elbow and kneeFlat skull with eye on top of head

Fish characteristics_____ScalesFins

Class AmphibiaAmphibians (Frogs, Salamanders, Caecilians) Approximately 6,150 species Diverged in the late Devonian Most go through metamorphosis (“two lives”)

Aquatic, gill breathing larvae Terrestrial, lung breathing adults

__________ eggs: jelly like eggs with ~50% yolk Thin, highly vascularized skin

Scaleless (except Caecilians) Cutaneous respiration Poison glands

_________________ heart Ectothermic

Class Amphibia, Order AnuraFrogs and Toads “without a tail” ~ 5,400 species

Frogs = smooth skin “Toads” = rough, warty skin

Short fore limbs and long hind limbs long Modified for jumping

Head and trunk fused Tongue attached to front of mouth _______ fertilization Vocalizations in males

________ membrane

Amphibian MetamorphosisEgg development: 6-21 days

Metamorphosis: 0-7 days: tadpole feeds on yolk

then attaches to substrate, breathes through external gills

7–28 days: tadpole swims freely feeding on aquatic vegetation, breathes through internal gills

4-6 weeks: ___________, skin grows over operculum

6-9 weeks: __________ from buds 10-12 weeks: froglet with small

tail 12-16 weeks: adult frog

Class Amphibia, Order UrodelaSalamanders and Newts “bearing a tail” ~ 550 species Carnivorous Legs usually at _________ to body Prefer dark, damp terrestrial

habitats ______ fertilization

Spermatophore: packet of sperm Smooth skin, except newts Blunt nose and tails typically

flattened on sides

Class Amphibia, Order Apoda Caecilians “without legs”

Secondary adaptation ~ 170 species ___________ diggers Tropics and subtropics Scales in some Sensory tentacles on head Internal fertilization

25% oviparous 75% viviparous

Amphibians as Ecological Indicators_______________: a species whose presence, absence of abundance can be used to assess the biological condition or health of a particular ecosystem 1/3 of amphibian species are at risk of extinction

Characteristics that make amphibians good indicators Aquatic and terrestrial habitats

Metamorphosis Breathe with gills and lungs

________ Cutaneous respiration Susceptible to environmental contaminants (chemicals)

___________ lack shell Integral part of the food chain

Herbivorous tadpoles and carnivorous frogs and toads

AmniotesAmniotic egg: allowed for embryos to develop in terrestrial environment without __________________.

Two major lineagesDiapsids: Reptiles, including birds

Synapsids: _________

Amniotic EggAmnion: inner membrane filled amniotic fluid, which cushions the embryo

Yolk sac: sac containing nutrients (yolk) for the developing embryo

_______: membrane that facilitates gas exchange between the embryo and the air

Allantois: sac that collects _________ _______ produced by the embryo

Anapsids, Synapsids and DiapsidsBased on number of temporal openings (fenestra)

____________ attachment

Anapsid: no temporal openings Turtles

Synapsid: single temporal opening ___________

Diapsid: two temporal openings Reptiles including birds

Temporal fenestra

Orbit (eye socket)

Evolutionary History of Reptiles Rise in reptiles associated with

decline in __________ ~315mya (Carboniferous)

Permian dominated by parareptiles, which were large, stocky herbivores

Permian-Triassic Extinction followed by evolution of Archosaurs (crocodilians, dinosaurs, pterosaurs) and Lepidosaurs (lizards, snake, tuataras)

Most Archosaurs extinct by end of Cretaceous

Squamata radiation during Cenozoic

Testudines origin __________

Class Reptilia Diverged ~ 310 mya (Carboniferous) Scales made of ________ Internal fertilization Most oviparous

Lay eggs on land Ectothermic, poikilotherms Incomplete ________

Four orders Testudinata (turtles) Squamata (snakes and lizards) Crocodillia (crocodiles and allies) Rhynchocephalia (tuataras)

Characteristics of Amphibians and Reptiles

Characteristics Amphibians Reptiles

Metabolism Ectothermic Ectothermic

Skin texture Smooth, thin, permeable skin Tough, scaly skin

Breathing Gills and lungs Well developed lungs (thoracic breathing)

Reproduction Internal and external fertilization Internal fertilization with copulatory organs

Egg Jelly-like egg with no shell Amniotic egg with shell

Circulatory system Three-chambered heartThree-chambered heart with

chambered ventricle, 4 chambered heart in crocodilians

Jaws Weak, used for gripping Strong, used for crushing or gripping

Class Reptilia, Order TestudinesTurtles and Tortoises Origin remains uncertain _______ skull Bony or cartilaginous shell from fusion of

vertebrae and ribs Carapace, Plastron, Scutes

Tortoise = terrestrial Turtles = live in or near water Herbivorous and carnivorous

Beaks (no teeth)

Two groups Cryptodira Pluerodira

Scutes

Carapace

Fused vertebraeRibs

Neck

Plastron

Class Reptilia, Order TestudinesCryptodira Retract head __________ into shells 12 scutes on plastron Includes most extant turtles

Sea turtles Tortoises Pond turtles

Class Reptilia, Order TestudinesPluerodira Retract head by __________

to the side 13 scutes on plastron

Class Reptilia, Order SphenodontiaTuataras Two extant species Endemic to New Zealand _______ skull preserved No ears or eardrums ________ of teeth on upper

jaw __________ Slow growing, long lived

>100 years Temperature of eggs

influences sex

Parietal eye

Class Reptilia, Order SquamataLizards and Snakes Largest order of reptiles, second

largest order of vertebrates ~ 9,000

Diverged in the Triassic period Snakes evolved from _______ _____ their skin/scales Flexible upper jaw with movable

quadrate bone Forked tongue in some

Chemical reception __________: paired copulatory organ

Quadrate bone

Worm lizards ~ 180 species ________: adapted for

burrowing and life underground Usually legless Elongate bodies Rudimentary eyes No outer ears

Carnivorous

Class Reptilia, Order Squamata

Class Reptilia, Order SquamataLizards ~6,000 species

All continents except Antarctica Terrestrial, burrowing, aquatic,

arboreal Legs and external ears Movable _______ Herbivorous and carnivorous Range from 16mm to 3m _________: detach tails

Regeneration Good vision

Communication and locating Parthogenesis in some

Class Reptilia, Order SquamataSnakes ~2,900 species

All continents except Antarctica Terrestrial, burrowing, aquatic, arboreal

Diverged from lizards _______________ (anal spurs) Lack movable _______ Lack external _______________

Carnivorous Constrictors or venomous

Jacobson’s Organ Loreal pits

Highly mobile jaws >200 vertebrae

Feeding Adaptations in Snakes Teeth curved and pointed

inward Hinged ___________ Bones of lower jaw are

attached by muscles and ligaments

Moveable palate Elastic skin No ________

Sensory Adaptations in SnakesJacobson’s organ (Vomeronasel organ): olfactory sense organ used to detect _______________ Present in many amphibians, reptiles and mammals Snakes deliver odorants to organ with tongue

Heat sensing organs: facial pits lines with thermoreceptors capable of sensing minute changes in temperature _________: pit vipers Labial pits: some boas and pythons

Lower jaw transmits ground vibrations to cochlea

Nostril

Nostril

Labial pits

Loreal pit

Poisonous vs. VenomousPoisonous: toxins that are absorbed or ingested, often secreted by the animal

Venomous: toxins that are ________ _______, usually with stingers, or fangs Three families of snakes

Vipers, Elapsids, Colubrids Two venomous lizards

Gila monster and komodo dragon

Toxins ___________: disrupt nerve function Hemotoxin: hemolytic enzymes cause

blood clotting

Families of Venomous SnakesViperidae: Puff adders, rattlesnakes, cooperheads, cottonmouths Hollow, ______________ Ellipitcal pupils Hemotoxin venom

Elapsidae: Seas snakes, taipans, coral snakes, death adders, mambas, cobras Hollow, fixed fangs Round pupils Neurotoxic venom

Colubridae: Boomslang, mangrove snake, vine snake ___________ Most are mildly venomous

Class Reptilia, Order CrocodiliaCrocodiles, Alligators, Cayman, Gharials Diverged around 85 mya Closely related to birds and dinosaurs

Archosaur lineage 5 unwebbed digits front, 4 webbed back Complete ______________ Four chambered heart

Foramen of Panizza _________ membrane: transparent third

eyelid used for protection or to moisten eye

Nest temperature influences sex

Alligators vs. Crocodiles

Crocodile Lower teeth ______ Narrow, pointed snout

Alligator Lower teeth ________ Blunt, rounded snout