Evolution of the

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Comparative Anatomy of the Vertebrates

• Evolution of the
• Phylum Chordata

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THE PHYLUM CHORDATA
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• I. Unifying Features of Vertebrates
• A. Generalized body plan
• 1. Diagnostic features - present sometime during
  the development or life of all Chordates.
• a. Dorsal, hollow nerve cord
• b. Pharyngeal gill slits
• c. Notochord - originally a cord of living
  cells becomes part of the centrum of vertebrates
  up through primitive reptiles incorporated into
  intervertebral discs in birds and mammals.

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Other Features of Chordates
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• B. Pharynx - gill slits develop as outgrowths of
  pharyngeal endoderm and are paired
• C. Fate of gill slits
• 1. 8 is the largest number formed in vertebrates
  15 in lampreys
• 2. 1-3 retained in gilled salamanders
• 3. 4 slits in frog tadpoles
• 4. 3 rupture through in birds and then close
  except 1 becomes Eustachian tube

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C. Fate of Gill Slits (cont.)
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• 5. 1 or 2 rupture through in mammals 1 becomes
  the Eustachian tube
• 6. Original function of gill slits is for filter
  feeding - not respiration
• 7. Most gill pouches contribute to other organs

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Still Other Features
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• D. Pharyngeal arches - four basic structures
• 1. Pharyngeal skeletal element
• 2. Branchiomeric muscle element
• 3. Branches of nerves
• 4. Aortic arches - arteries that contribute to
  other arterial structures

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And Still More
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• E. Dorsal-hollow nerve cord
• 1. Formation - forms from neural folds of
  ectoderm on dorsal surface of the embryo.
• F. Other basic features
• 1. Integument - skin protective covering that
  can serve for respiration sweat and mammary
  glands form here other structures such as nails,
  horns, feathers, hair, scales
• 2. Respiration - can occur through skin, via
  gills, or via lungs

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Plus More Yet
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• 3. Coelom - internal body cavity whose lining
  forms entirely from mesoderm
• Pericardial cavity surrounds the heart
• Pleuroperitoneal cavity surrounds the lungs
• Parietalperitoneal cavity surrounds abdominal
  viscera

Coelom
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And Finally . . .
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• 4. Digestive system - complete digestive system
  with mouth and anus
• 5. Urogenital system - comprised of excretory and
  reproductive systems which form in unison and
  share common ducts.
• 6. Circulatory system - closed system usually
  with a pumping heart and differentiation of
  arteries and veins.
• 7. Sense Organs - more numerous and often more
  developed than in invertebrates

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II. Origin of the Phylum Chordata
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• A. Echinoderm theory - theory that Echinoderms
  and Chordates had a common ancestor.
• 1. Mesoderm formation - forms by pouching of
  solid masses of tissues in Echinoderms and
  Chordates

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• 2. Larval forms - Some Echinoderms and primitive
  relatives of Chordates (protochordates) have a
  free-living tornaria larva

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• 3. Biochemical similarity - Echinoderms and
  Chordates have similar amino acid sequences for
  blood proteins and both utilize creatine
  phosphate as a storage compound for P that is
  released to make ATP in muscle all other animals
  utilize argenine phosphate
• 4. Developmental similarity
• In both Echinoderms and Chordates,
• the blastopore of the developing embryo becomes
  the anus
• among other animals the blastopore becomes the
  mouth.

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Relationship to Classification of Animals
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• Echinoderms and Chordates are referred to as
  Deuterostomes
• All other animal phyla are referred to as
  Proterostomes.

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C. Evolution of the Vertebrata
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SURVEY OF PHYLUM CHORDATA
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• I. Evolutionary History
• A. Subphylum Urochordata - sessile tunicates
  that have a free-living tadpole larva
• B. Subphylum Cephalochordata - filter-feeding
  Amphioxus or lancets

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C. Evolution of Vertebrata
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• II. Class Cyclostomata (Agnatha)
• A. General features of modern agnathans
• 1. no scales
• 2. notochord large in adult - only skeletal
  component
• 3. single nostril located dorsally - both
  nostrils fused into one
• 4. lack paired fins

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Early Fishes
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• B. Ostracoderms
• 1. Extinct armored, jawless fishes of the
  Ordivician
• 2. poorly developed paired fins
• 3. eyes located dorsally
• 4. bony armor in skin

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First Jawed Fishes
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• III. Class Placodermi
• A. General features
• 1. Extinct, jawed fishes of the Devonian
• 2. boney skeleton
• 3. paired fins
• 4. along direct line to modern fishes

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Cartilagenous Fishes
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• V. Class Chondrichthyes
• A. General features
• 1. skeleton of cartilage - secondary loss of
  ossification
• 2. teeth derived from scales
• 3. placoid scales
• 4. both egg-laying and live- bearing, with
  2-chambered ht.

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Bony Fishes
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• V. Class Osteichthyes
• A. General features
• l. Jawed fishes with paired fins
• 2. 2-chambered ht.
• 3. scales of various types
• 4. ectothermic
• 5.represent modern fishes

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Terrestrial Vertebrates
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• VI. Class Amphibia
• A. General features
• 1. semi-terrestrial tetrapods- return to water to
  breed
• 2. respire by lungs or the integument
• 3. ectothermic
• 4. 3-chambered ht.
• 5. frogs, toads, salamanders, caecelians

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Complete Invasion of Land
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• VII. Class Reptilia
• A. General features
• 1. first amniotes and fully terrestrial
• 2. incomplete 4-chambered ht.
• 3. ectothermic
• 4. scales
• 5. dominant during the Mesozoic Era

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Aerial Vertebrates
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• VIII. Class Aves
• A. General features
• 1. Endothermic
• 2. lack teeth (some extinct forms had teeth)
• 3. feathers for flight surface and temperature
  regulation
• 4. 4-chambered ht.
• 5. all oviparous

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Furry Things
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• IX. Class Mammalia
• A. General features
• 1. Endothermic
• 2. Hair for thermoregulation
• 3. Mammary glands
• 4. 4-chambered ht.
• 5. viviparous (except for
• monotremes which lay eggs)

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CHORDATE PHYLOGENY
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Ancestral Deuterostome
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Class Agnatha
Class Chondrichthyes
Class Osteichthyes
Class Sarcopterygiipterygii
Class Mammalia
Class Amphibia
Class Reptilia
Subclass Aves
Reptilia
Subclass Crossopterygii
Subclass Teleostei
Subclass Dipnoi
Class Reptilia
Holostei
Class Amphibia
Crossopterygii
Chondrostei
Class Osteichthyes
Placodermi
Ostracodermae
Urochordata
Cephalochordata
Hemichordata
Echinodermata
Ancestral Deuterostome
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