Introduction%20to

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Introduction to Vertebrates
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Four anatomical features that characterize the
phylum Chordata
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1.  Embryos all have a common skeletal structure
called a notochord.  The notochord is a flexible
rod located between the digestive tube and nerve
chord.                                     a. 
Provides skeletal support. b.  In most
vertebrates, its replaced by a jointed
skeleton. c.  Remains of the notochord exist as
disks between the vertebrae.   2.  Dorsal, hollow
nerve cord                                    
a.  Develops into the brain and spinal cord of
the adult.
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3.  Pharyngeal slits                             
        Water enters through the mouth and
passes out through the slits in the pharynx,
without going through the digestive system. i. 
Slits function as suspension-feeding devices in
many invertebrate chordates ii.  Slits have been
modified in more evolved vertebrates for      
                  - Gas exchange                  
       - Hearing                         - Jaw
support  4.  Postanal tail              Provides
propulsion for swimming
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Invertebrate chordates provide clues to the
origin of vertebrates.                        
1.  Subphylum Urochordata                        
             Adult is sessile and feeds via
pharyngeal slits.  
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Subphylum Urochordata  a tunicate
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2.  Subphylum Cephalochordata                     
                a.  Adult form shows chordate
features. b.  Adults feed and swim.  
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Subphylum Cephalochordata  the lancelet
Branchiostoma
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II.  Introduction to the vertebrates A.  Neural
crest, enhanced cephalization, vertebral column,
and a closed circulatory system characterize the
subphylum Vertebrata                         1. 
Neural crest                                    
a.  Embryonic feature that allows for many
unique vertebrate characteristics, e.g. bones and
cartilage are formed from the neural crest cells
throughout the body. b.  Forms along the dorsal
side of the embryo.   Figure 34.6 (p. 683) The
neural crest, embryonic source of many unique
vertebrate characters.
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2.  Skeletal elements, such as the cranium
(braincase), allow for the big evolutionary
feature of vertebrates, cephalization. This
gives us the term Craniates   3.  Vertebral
column is the main support for the body axis.  It
allows for large size, fast movement, and
protection of the nerve cord.   4.  The closed
circulatory system pumps oxygenated blood to
cells and allows rapid metabolism, rapid movement
to search for food, escape predators.
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B.  Overview of vertebrate diversity              
           Figure 34.7 (p. 684) Phylogeny of
the major groups of extant vertebrates.   Note
the three super groups Gnathostomes,
Tetrapods, Amniotes
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III.  Jawless vertebrates             A.  These
are the most primitive vertebrates.              
B.  Groups include hagfish (no skeleton, no
notochord in adult) lamprey (early version of a
vertebral column).               Figure 34.8 (p.
685) A hagfish.               Figure 34.9 (p.
685) A sea lamprey.
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Lamprey on trout
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IV.  Fishes and amphibians             A. 
Vertebrate jaws evolved from skeletal supports of
pharyngeal slits 1.  Animals that replaced
jawless vertebrates, and are Gnathostomes.        
     2.  Members of group have two pairs of
fins.   3.  Jaws and fins allowed fish to become
active in pursuit of food and in biting off
chunks of flesh. 4.  Jaws evolved from
modifications of skeletal elements of anterior
pharyngeal gill slits.  
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Hypothesis for the evolution of vertebrate jaws
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 5.  Fishes were prevalent about 360 to 400
million years ago- the Age of Fishes     6. 
Two groups are alive today                       
              a.  Class Chondricthyes  Sharks
and rays have cartilaginous skeletons   Figure
34.11 (p. 688) Cartilaginous fishes.
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Osteichthyes  Extant classes of bony fishes
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Lake trout
Whitefish
Sturgeon
Great Lakes
Walleye
Some of the natives
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Rainbow trout/brown trout
Alewife
Smelt
Great Lakes
Some Exotics
Ruffe
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Bluegill
Yellow perch
Great Lakes
Some successors
Largemouth bass
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D.  Tetrapods evolved from specialized fishes
that inhabited shallow water ? Figure 34.15 (p.
690) The origin of tetrapods. 1.  The first
tetrapods to spend much time on land were
amphibians.          Figure 34.17 (p. 691)
Amphibian orders. Order Urodela Salamanders,
retain tails as adults Order Anura Frogs, lack
tails as adults Order Apoda Caecilians, lack
legs
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• 2.  There were earlier tetrapods.  These were
  specialized fish that
• occupied shallow ponds,
• breathed air by gulping, and
• developed lobed walking fins for moving from one
  pond to another.
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• 3.  Why go on dry land? There were no other
  competitors for plants and insects that serve as
  food.

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            4.  Amphibians need to return to
water to lay eggs and for development of
larvae.   Figure 34.18 (p. 692) The dual life
of a frog.
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V.  Amniotes (includes reptiles, mammals, and
birds)             A.  Evolution of the amniotic
egg expanded the success of vertebrates on
land   Figure 34.19 (p. 693) The amniotic egg.
                        
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1.  Amniotic eggs allowed vertebrates to sever
the link with water and live their whole lives on
land.   2.  Specialized membranes, called
extra-embryonic membranes that function in gas
exchange, waste storage, and transfer of
nutrients. a.  Membranes develop from tissues
derived from the embryo. b.  One membrane, the
amnion, gives the name for the amniotic egg.
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B.  Reptilian heritage is evident in all
amniotes                         1.  Scales of
keratin, waterproof skin - prevent dehydration. -
Reptiles cannot breathe through skin, so all gas
exchange occurs via lungs.   2.  Shelled amniotic
eggs require internal fertilization.  Shell forms
around fertilized egg in the reproductive
tract.   3.  Reptiles dont use metabolism to
regulate body temperature they are ectotherms. 
Ectotherms absorb external heat (i.e. sunlight) ?
Reptiles are able to survive on about 10 of
calories required by mammals.   4.  Oldest
reptiles are from the late Carboniferous (about
300 million years ago) à dinosaurs and pterosaurs.
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5.  Modern reptiles include 6,500 species that
are in four groups                             a.
  Testudines Turtles      - Some species
returned to water all lay eggs on land.   b. 
Sphenodontia Tuataras                          
           c.  Squamata Lizards,
snakes       - Lizards are the most numerous
group.      - Snakes are descendants of lizards
and have vestigial pelvic and limb bones.    d. 
Crocodilia Crocodiles, alligators       - This
is the group most closely related to
dinosaurs    Figure 34.24 (p. 697) Extant
reptiles.
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 C.  Birds began as feathered reptiles, evolved
to fly                         1.  Honeycombed
skeletons are light and strong à good for flight.
Figure 34.25 (p. 698) Form fits function  the
avian wing and feather. 2.  Toothless for weight
reduction.   3.  Endothermic use metabolic
energy to generate heat.       - Feathers
provide insulation.      - Efficient circulatory
system supports high rate of metabolism necessary
for flying.   4.  Acute vision à Large brains
that allow complex behavior.   5.  Wings - Flight
enhanced the ability to hunt and scavenge, escape
predators, and move with changing seasons.
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6.  Theropods were the closest dinosaur relative
of birds.  Example  Velociraptor ? Archeopteryx
is an example of a Mesozoic bird that shows
reptilian features.    Figure 34.27 (p. 699)
Archaeopteryx, a Jurassic bird-reptile.
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7.  Modern birds include about 8,600 species. 
Some are flightless ratites.    Figure 34.29
(p. 701) A small sample of birds.
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D.  Mammals diversified extensively in the wake
of the Cretaceous extinctions                     
    1.  Radiation of mammals occurred during two
events                                     a. 
Extinction of dinosaurs                           
          b.  Fragmentation of continents   2. 
There are about 4,500 species of extant mammals
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 3.  Features of mammals                         
            a.  Defined by Linnaeus as having
mammary glands, which produce milk rich in fats,
sugars, proteins, minerals, and vitamins. b. 
Hair and subcutaneous fat help retain metabolic
heat. c.  Most embryos develop in a uterus.  In
placental mammals, the lining of the uterus and
extraembryonic membranes form the placenta. d. 
Large brains and long period of parental care. à
Ability to learn. e.  Differentiation of teeth
for efficient eating.
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4.  The earliest mammals evolved from reptiles
about 220 million years ago.  Therapsids gave
rise to mammals. Early example is the
Morganucodon in previous figure.   5.  Major
groups of mammals                                
     a.  Monotremes lay eggs and produce milk,
but have no nipples. - Platypus,
echidna             b.  Marsupials born early
in embryonic development climb to mothers pouch
and attach to a nipple. - Opossum,
kangaroo  Figure 34.31 (p. 703) Australian
monotremes and marsupials.  
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                                    c. 
Eutherians long pregnancy with embryonic
attachment to mother in uterus via
placenta.                                         
        - Human, Wolf Figure 34.32 (p. 704)
Evolutionary convergence of marsupial and
eutherian (placental) mammals.     Table 34.1
(p. 705) Major Orders of Mammals
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VI.  Primates and the evolution of Homo
sapiens             A.  Primate evolution
provides context for understanding human
origins                         1.  Hands and
feet adapted for grasping. Possess opposable
thumb.                         2.  Large brains
allow complex social behavior.  Figure 34.35 (p.
708) A phylogenetic tree of primates.
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B.  Hominid lineage diverged from other primates
about 7 million years ago. Humans compared to
other hominids                                   
  a.  Brain size large size allows development
of language and social behavior.   b.  Jaw shape
shortened to give a flatter face.    
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c.  Bipedalism walking on two legs.         -
Frees hands to do other things.         - Eyes
set higher can see farther.  
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d.  Females smaller than males   e.  Extended
parental care changes family structure and
enhances learning and social behavior.
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