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VertebratesChapter 35



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Chordates (phylum Chordata)

-Nearest relatives are echinoderms (the

only other deuterostomes)



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The Chordates

Four features characterize chordates

1. Nerve cord

2. Notochord

3. Pharyngeal slits

4. Postanal tail



4

The Nonvertebrate Chordates

Phylum chordata can be divided into three

subphyla

1. Urochordata

2. Hemichordata

3. Cephalochordata

4. Vertebrata

Nonvertebrates



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Subphylum Urochordata

Tunicates are marine animals

-Larvae are tadpolelike and have notochord and

nerve cord

-Adults Are immobile filter-feeders

-Many secrete a tunic (cellulose sac) that

surrounds the animal



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Subphylum Cephalochordata

Lancelets are scaleless chordates

-Notochord persists throughout animal’s life

-Have no dist ingu ishable head -Feed on plankton

using cilia-

generated currents

-Closest relatives

to vertebrates



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Subphylum Vertebrata

Vertebrates: chordates with a spinal column

-Distinguished from nonvertebrates by

1. Vertebral column – Encloses andprotects the dorsal nerve cord

2. Head – Distinct and well-differentiated

possessing sensory organs



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Subphylum Vertebrata

Vertebrates also have

-Neural crest – A unique group of embryonic

cells that forms many vertebrate structures

-Internal organs – Liver, kidneys, endocrine

glands, heart and closed circulatory system

-Endoskeleton – Made of cartilage or bone-Makes possible great size and

extraordinary movement



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FishesTHE FIRST VERTEBRATES appeared in the

oceans about half a billion years ago

1. Vertebral column

2. Jaws and paired appendages

3. Internal gills

4. Single-loop blood circulation

5. Nutritional deficiencies



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History of the Fishes

The FIRST FISHES had mouths with NO

JAWS

Extant (still living) as HAGFISH (class Myxini)

and as

LAMPREYS (class Cephalaspidomorphi)



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Emergence of JAWS

Skull

Gill slit

Anterior gill arch

Jaws evolved from the anterior

gill arches that were made of cartilage

Spiny fishes (Acanthodii)

-Smaller fishes that dominated early on

Armored fishes (Placodermi)

-Larger fishes that dominated late



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Early fishes were replaced by

sharks and bony fishes Had improved jaws

Sharks (Class Chondrichthyes) became the

dominant sea predators

Among the first vertebrates to develop teeth

-Evolved from rough scales on mouth’s skin



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History of the Fishes

Bony fishes evolved at the same time assharks about 400 MYA

-However, they adopted a heavy internal

skeleton m ade completely of bone

Bony Fishes (and sharks) have a lateral line

system Sensory organs under the skin thatdetects changes in pressure waves

B Fi h Ad t ti



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Bony Fish AdaptationsSwim bladder (NOT SEEN IN SHARKS so they sink)

-A gas-filled sac that allows bony fishes to regulate

their buoyant density

-Gas addition = Gas gland

-Gas release = Oval body

Gill cover-A hard plate, the

operculum, covers gills

-Its flexing permits

water pumps over gills

without fish swimming

T M j G f B Fi h



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Two Major Groups of Bony Fishes

Ray-finned fishes

(class Actinopterygii)

-Parallel bony rays support & stiffen

each fin-There are no muscles in the fins

Lobe-finned fishes(class Sarcopterygii)

-Have paired fins that consist of a

long fleshy muscular lobe

Amphibians e ol ed



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Amphibians evolved

from lobe-finned fish

Ichthyostega was one of the first

amphibians

-Efficient limbs for land crawling

-Improved olfactory and auditory

structures



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Amphibians (class Amphibia)

are damp-skinned vertebrates

Successful INVASION OF LAND by vertebratesrequired several adaptations

1. Legs to support body’s weight

2. Lungs to extract oxygen from air

supplemented by skin

3. Redesigned heart (Partially divided) to drivelarger muscles

4. Reproduction in H2O to prevent egg drying

5. Pulmonary veins

M d A hibi



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Modern Amphibians

Descended from three Orders of the Tertiary

period (65-2 MYA)

- Anura (“without tail”)--frogs and toads

-Caudata/urodela (“visible tail”)--salamanders

- Apoda (“without legs”)--caecilians



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Reptiles (Class Reptilia)

All living reptiles exhibit three key features

1. Amniotic eggs, which are watertight 2. Dry skin, which covers body and

prevents water loss

3. Thoracic breathing, which increaseslung capacity



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ReptilesReptiles, birds and mammals are AMNIOTES

The AMNIOTIC EGG has four membranes

-Chorion –

Allows O2 entry

-Amnion –

Fluid-filled cavity

- Yolk sac –

Provides food-Allantois –

Excretes wastes



M d R til



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Modern Reptiles

Modern reptiles developed two important

characteristics:

1. Internal fertilization:

Sperm fertilizes egg

before protective

membranes are formed

2. Improved circulation:Oxygen is provided to

the body more efficiently

Bi d ( l A )



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Birds (class Aves)Birds still retain many reptilian traits

-Amniotic eggs and scales on legsTwo major traits distinguish them

1. Feathers

-Provide lift for flight and conserve heat2. Flight skeleton

-Bones are thin and hollow

-Many are fused (collarbone and keeled breastbone



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Birds evolved from theropod

dinosaurs



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Mammals (class Mammalia)

Mammals differ from other vertebrates in

TWO FUNDAMENTAL TRAITS:

1. Hair

-Long, keratin-rich filaments that extend

from hair follicles

-Insulation, camouflage, sensory structure

2. Mammary glands

-Females possess mammary glands that secrete

milk

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