The Chordata

Phylum of the Vertebrates

Chordates

• Phylum Chordata– Four Main Characteristics

NotochordNerve CordPharyngeal PouchesTail

Invertebrate Chordates

• Notochord persists and is never replaced by a vertebral column.– Lancets (Subphylum Cephalochordata)– Sea Squirts (Subphylum Urochordata)

Invertebrate Chordates

Vertebrates

• Subphylum Vertebrata– Vertebrate skeleton is living tissue that

grows with the animal.Main axis of internal jointed skeleton

consists of vertebral columns and a skull that encloses the brain.

Cephalization is accompanied by sense organs.

Evidence of jaws and predation. Amnion allows reproduction on land.

Vertebrate Features

• Living endoskeleton with vertebral column.• Closed circulatory system.• Paired appendages.• Efficient respiration and excretion.• High degree of cephalization.• Adapted to active lifestyles.

Fishes

• Fishes are aquatic, gill-breathing vertebrates that usually have fins and scale-covered skin.– Jawless fishes (Superclass Agnatha)

Ostracoderms - earliest vertebrate fossils.

Lampreys and hagfishes are modern-day jawless fishes that lack a bony skeleton.

Jawless Fishes

Fishes With Jaws

• Gnathostomates have jaws.– Believed to have evolved from first pair of

gill arches of agnathans.Placoderms, extinct jawed fishes of

Devonian period, are believed to be ancestral to early sharks and bony fish.

Cartilaginous Fishes

• Class Chondrichthyes have a skeleton of cartilage instead of bone.– Cartilaginous Fishes

Sharks, rays, skatesLack gill cover of bony fish.Utilize lateral line system.Filter feeders and predators.Pectoral fins can be enlarged into large,

winglike fins.

Cartilaginous Fishes

Bony Fishes

• Class Osteichthyes have a skeleton of bone.– Most are ray-finned fishes.

Lobe-finned fishes are small subgroup with fleshy fins supported by central bones.

– Bony fish have a gas-filled sac (swim bladder) whose pressure can be altered to change buoyancy.

Ray-Finned Fishes

Amphibians

• Tetrapods (Have four limbs)– Hypotheses of evolution.

Lobe-finned fishes had an evolutionary advantage due to movement capability.

Supply of food on land and the absence of predators promoted further adaptations.

Lobe-Finned Fish Versus Amphibians

Diversity of Amphibians

• Amphibians today occur in three groups:– Salamanders and newts

Salamanders practice internal fertilization.

– Frogs and toadsTailless

– CaeciliansLegless, sightless, worm-shaped

• Most return to water for reproduction.

Amphibians

Amphibian Features

• Usually tetrapods.• Lungs usually present in adults.• Metamorphosis• Smooth and moist skin.• Three-chambered heart.• Ectothermic

Vertebrate Circulatory Systems

Reptiles

• Class Reptilia is believed to have evolved from amphibian ancestors by the Permian period.

Phylogenetic Tree

Reptiles– Practice internal fertilization and lay eggs

protected by a leathery shell (amniotic egg).

Anatomy and Physiology of Reptiles

• Reptiles have a thick, scaly skin that is keratinized and impermeable to water.– Usually tetrapods.– Lungs with expandable rib cage.– Shelled amniotic egg.– Dry, scaly skin.– Ectothermic

Birds

• Characteristics of Class Aves– Feathers– Hard-shelled amniotic egg.– Four-chambered heart.– Often winged– Air sacs– Endothermic

Bird Beaks

Mammals

• Class Mammalia – Mammalian skull accommodates a larger

brain relative to body size.– Chief characteristics and hair and milk-

producing mammary glands.– Infant Dependency– Internal Development– Differentiated Teeth

Mammals

• Monotremes - Hard-shelled amniotic eggs.• Marsupials - Females contain pouch.• Placentals - Females have organ for

exchange of maternal and placental blood.

Major Orders of Mammals

• Perissodactyla– Horses

• Artiodactyla– Deer

• Carnivora– Cats

• Primates– Monkeys

• Cetacea– Whales

• Chiroptera– Bats

• Rodentia– Mice

• Proboscidea– Elephants

• Lagomorpha– Rabbits

Review

• Chordates– Invertebrate chordates– Vertebrates

FishesAmphibiansRetilesBirdsMammals

Mader: Biology 8th Ed.

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Mader: Biology 8th Ed.

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