Vertebrate Evolution and Diversity

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Chapter 34 Vertebrate Evolution and Diversity
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I.  Invertebrate chordates and the origin of
vertebrates             A.  Four anatomical
features that characterize the phylum
Chordata   Figure 34.2 (p. 680, ed. 6 Fig. 34.3,
p. 673, ed. 7) Chordate characteristics.
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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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B.  Invertebrate chordates provide clues to the
origin of vertebrates                        
1.  Subphylum Urochordata                        
             Adult is sessile and feeds via
pharyngeal slits.   Figure 34.3 (p. 681, ed. 6
Fig. 34.4, p. 674, ed. 7) Subphylum
Urochordata  a tunicate
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  2.  Subphylum Cephalochordata                   
                  a.  Adult form shows chordate
features. b.  Adults feed and swim.   Figure 34.4
(p. 681, ed. 6 Fig. 34.5, p. 675, ed. 7)
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, ed. 6 Fig. 34.7,
p. 676, ed. 7) 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 à
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 à 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.                                      

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III.  Jawless vertebrates             A.  These
are the most primitive vertebrates.              
B.  Groups include hagfish (no skeleton, no
notochord in adult. Thus, it is a craniate, but
not a vertebrate) lamprey (early version of a
vertebral column, which makes it a
vertebrate).               Figure 34.8 (p. 685)
A hagfish.               Figure 34.9 (p. 685) A
sea lamprey.
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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
(jaw-mouth hinged mouths).             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.   Figure 34.10 (p. 687, ed. 6 Fig. 34.13,
p. 680, ed. 7) Hypothesis for the evolution of
vertebrate jaws.
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 5.  Fishes were prevalent about 360 to 400
million years ago à 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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    b.  Osteichthyes  Extant classes of bony
fishes (Ray-finned and lobe-fin fishes)   Figure
34.13 (p. 689, ed. 6 Fig. 34.16, p. 682, ed. 7)
Anatomy of a trout, a representative ray-finned
fish. Fig. 34.18, p. 683, ed. 7 - Lobe-fin fish
Coelocanth
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 D.  Tetrapods evolved from specialized fishes
that inhabited shallow water ? Figure 34.15 (p.
690, ed. 6 Fig. 34.20, p. 683, ed. 7) The
origin of tetrapods. 1.  The first tetrapods to
spend much time on land were amphibians.          
Figure 34.21 (p. 691, ed. 6 Fig. 34.21, p. 685,
ed. 7) 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.   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, ed. 6 Fig.
34.22, p. 686, ed. 7) 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 -
no longer a need to return to water for
reproduction.   Figure 34.19 (p. 693, ed. 6 fig.
34.24, p. 688, ed. 7) 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
extraembryonic 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 and 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, ed. 6)
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, ed. 6) 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, ed.
6) 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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