Class Amphibia

• First chordates/vertebrates on land

• About 375mya

• Evolved from Dipnoian ancestors

• Swim AND walk sinusoidally

• Not totally adapted for life on land

• Must return to water or very moist place, at least for reproduction

• Skin not well-waterproofed

Class Amphibia

• Dioecious

• Three-chambered heart

• Lungs often aided by considerable cutaneous gas exchange

• Most oviparous

• Some ovoviviparous or viviparous

• Cloaca present

• 3 Orders: Urodella, Anura, Apoda

Tetrapod Limb Origin

Order Urodella

• Salamanders and newts (400 species)

• Some totally aquatic

• Aquatic species usually have gills in the immature stage

• Some aquatic species retain gills as adults (Paedogenesis)

• Some found in damp places on land

• Adults can regenerate limbs!

Redbacked Salamander

Necturus (mudpuppy)

Order Anura

• Frogs and toads (~3,500 species)

• Tadpoles aquatic (gills and tails)

• Adults lose gills and tail

• Enlarged hindlegs for jumping

• Tongue is attached anteriorly

• Some have camouflage coloration

• Others are brightly colored and often produce a toxic or distasteful mucus

Tadpole

Bull Frog

Order Apoda

• The caecilians

• Legless

• Almost blind

• Wormlike and appear to be segmented

• Some burrow in moist tropical soils

• Others are aquatic (freshwater)

Order Apoda (caecilians)

Class Reptilia• 8,000+ species• 300+ million year history• Dioecious• Most are oviparous• Cloaca present• Adapted to live on land

– Keratinized scales– Gas exchange via lungs– Internal fertilization– Amniotic egg (cleidoic)

Amniotic Egg

Reptilian Diversity• Many extinct groups

• Gave rise to mammals

• Gave rise to birds

• Should birds be in the same class as reptiles?

• Three main groups of reptiles:– Lizards and snakes– Turtles and tortoises– Crocodiles and alligators

Order Squamata• Lizards and snakes (~7,900 species)

• Three-chambered heart

• Snakes evolved from burrowing lizards

• Some snakes (boas) have vestigial pelvic bones

• Good sensory structures (heat, odor, ground vibrations)

• Snakes have jaws that are very loosely articulated

Carolina Anole

Python Eating a Wallaby

Order Chelonia

• Turtles and tortoises (~300 species)

• Three-chambered heart

• Protected by hard shell

• Aquatic turtles lay eggs on land

• Long-lived

Eastern Box Turtle

Order Crocodilia• Crocodiles, alligators, caimens (20 species)

• Four-chambered heart!!!!

• Confined to warm regions of the globe

Class (???) Aves• 8,600+ species in 28 orders

• Dioecious

• Sexual reproduction, oviparous

• Reptilian traits– Amniote egg– Keratinized scales on legs– Feathers are modified scales

• Birds fly – flightless birds came from ancestors that could fly

Modifications for Flight• Honeycombed bones• Reduced systems (no teeth, no bladder, one ovary

in females)• Endothermic!!!• Efficient circulatory system• Four-chambered heart!!!• Efficient lungs connecting to air sacs• Acute vision• Large pectoral muscles anchored to a keeled

sternum

Additional Information• Cloaca present• Parental care

– Incubating eggs– Feeding young

• Often have complex mating rituals• Originated at least 130 mya• Archaeopteryx not the ancestor of modern

birds (reptilian side branch?)• Flying birds (carinates) (includes penguins)• Flightless birds (ratites)

Archaeopteryx lithographica

Class Mammalia

• Hair composed of keratin (did NOT evolve from reptilian scales

• Endothermic

• 4-chambered heart

• Mammary glands produce milk for young

• Internal fertilization

• MOST are viviparous with a placenta that delivers nourishment to the developing embryo

Class Mammalia• Large brains; capable of considerable

learning

• Parental care of young

• Evolved from a reptiliam ancestor about 200 mya

• 1st mammals small and insectivorous

• Efficient respiratory system (diaphragm aids ventilation of lungs)

Mammalian Evolutionary “Tree”

Monotremata

• Platypus and Echidnas (5 species)

• Oviparous (lay reptilian type eggs)

• Cloaca

• Found in Australia & New Guinea

Marsupalia

• ~325 species

• Marsupials are therians

• Rudimentary placenta

• Young born very premature and must complete development in the marsupium (pouch)

• Convergent evolution of marsupials and Eutherians

• First evolved in what is now North America

Eutheria• ‘True’ placental mammals

• ~5,025 species

• Embryonic development completed within the uterus

• Diverged from common ancestor with marsupials about 100mya

• We are a Primate

• What other two groups are in our clade? (see p. 724)

Evolutionary Convergence(Marsupials & Eutherians)

Convergence (Concluded)

Primates