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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
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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
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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