Chapter 34B: Tetrapods (Amphibia and Amniotes)

Tetrapods

Gnathostomes (jawed animals)

four limbs

Evidence = evolved from lobe-finned fish

Ex: amphibians, reptiles, birds, mammals

Specific adaptations of Tetrapods

4 Limbs, feet with digits

A neck

Absence of gills

Ears for detecting airborne sounds

Class Amphibia

Tetrapods;

able to live on land and water (“both ways of life”)

first vertebrates to walk on land

direct descendants of fishes

Ichthyostega

word meaning “fish” + “roof”

earliest amphibians

fish with legs

Eggs of Class Amphibia

fertilized in water

no shell

covered with gelatin

Aquatic larva

Class Amphibia;

tail

lateral line

gills

no legs

Metamorphosis

Class Amphibia;

tadpole larva → terrestrial adult

Modern Amphibians

gills usually lost by adulthood

lungs function

breathe through skin

3-chambered heart

Orders of Class Amphibia

Anura — frogs and toads

Urodela — Salamanders

Apoda — Apodans (burrowing amphibians)

Order Urodela

Orders of Class Amphibia;

retain their tail as adults

Ex: Urodeles/Salamanders

Order Anura

Orders of Class Amphibia;

lack a tail as adults

Ex: Anurans (frogs and toads)

Order Apoda

Orders of Class Amphibia;

legless

burrowing

Ex: Apodans, caecilians

Amniotes

Tetrapods;

free of life cycle dependent on aquatic environments

adapted to life on land (waterproof outer layer; thoracic/pulmonary breathing)

Amniotic Egg

Amniotic Egg

Amniotes;

“Extraembryonic Membranes”

Allantois, Chorion, Amnion, Yolk Sac

Egg Shell

Allantois

Amniotic Egg;

disposal sac for certain metabolic wastes produced by the embryo

Chorion

Amniotic Egg;

exchange gases between the embryo and the air, along with the allantois membrane

Amnion

Amniotic Egg;

protects the embryo in a fluid-filled cavity that cushions against mechanical shock

Yolk Sac

Amniotic Egg;

contains the yolk

a stockpile of nutrients

other nutrients = stored in albumen (“egg white'“)

Egg Shell

Amniotic Egg;

prevents desiccation

allows complete life on land

Class Reptilia

Amniotes;

first true land animals

no feathers

shelled egg

internal fertilization

Ectothermic

Improved heart

Keratin scales

Keratin scales

Class Reptilia;

prevent desiccation and abrasion

Ectothermic

Class Reptilia;

absorb heat form the environment as main source of body heat

lower energy requirement (10% less than similar size mammal)

Improved heart

Class Reptilia;

Right and Left Atria

1 ventricle

Anapsids

Turtles

Lepidosaurs

Class Reptilia;

Tuataras

Lizards: iguanas, geckos, chameleons, Komodo dragons

Snakes

Snakes

Lepidosaurs;

descended from lizard with legs

vestigial pelvic and limb bones seen in some species

“legless lizards”

carnivorous, venomous teeth

Crocodilians

Class Reptilia;

True, 4-chambered heart

found only in warmer regions of the globes

little change over millions of years of evolutions

Ex: crocodiles, alligators

Class Aves: Birds

Amniotes;

Adaptations that facilitate flight

wings (keratin feathers)

flight skeleton (thin, hollow bones; keeled sternum)

4-chambered heart

Endothermic

Super-efficient respiration

no urinary bladder

Females = one ovary; Males = small gonads

Endothermic

Class Aves;

maintains a relatively constant body temperature, regardless of the surrounding temperature

Benefits of flight and feathers

Class Aves;

enhanced scavenging and hunting

feeding on flying insects

escaping from predators

migration

Ratites

Class Aves;

flightless birds

Ex: Emu, Ostrich

Passeriformes

Class Aves;

perching birds

60% of birds

Ex: songbirds