Chordates

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Chordates

• There are four distinct characteristics of
  chordates, many of which only appear during
  embryonic development of various chordate species
• Notochord becomes the discs between the
  vertebrae in humans and other mammals
• Dorsal, hollow nerve cord becomes the spinal
  cord
• Pharyngeal clefts/gill slits remain in the lower
  chordates (fish) for breathing, disappear in the
  higher chordates
• Tail disappears in humans
• The two invertebrate and one craniate chordate
  phyla
• Subphylum Urochordata (tunicates)
• Subphylum Cephalochordata (lancelets)
• Subphylum Myxini (hagfish) - have a skull but no
  vertebrae

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Chordate characteristics
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A tunicate - a urochordate
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The lancelet Branchiostoma, a cephalochordate
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A hagfish a cephalochordate
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Subphylum Vertebrata

• Class Agnatha jawless fish (lamprey), most
  primitive vertebrate group

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Class Agnatha sea lamprey
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Subphylum Vertebrata

• Gnathostomes have jaws
• Class Chondrichthyes cartilaginous fish (sharks,
  skates, rays)
• Class Osteichthyes bony fish (salmon, trout)

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Coelacanth (Latimeria) oldest living order of
jawed fish
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Class Chondrichthyes
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Class Osteichthyes
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Subphylum Vertebrata

• Tetrapods are gnathostomes with limbs feet
• Class Amphibia maintain close ties with water,
  rely on their skin for gas exchange (frogs,
  salamanders)

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Amphibians
(a) Order Urodela. Urodeles (salamanders) retain
their tail as adults.
(b) Order Anura. Anurans, such as this poison
arrow frog, lack a tail as adults.
(c) Order Apoda. Apodans, or caecilians, are
legless, mainly burrowing amphibians.
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The dual life of a frog (Rana temporaria)
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Subphylum Vertebrata

• Amniotes are tetrapods that have an egg adapted
  to land survival (shell retains water, has
  extraembryonic membranes for gas exchange, waste
  storage and nutrient transport)
• Class Reptilia have scales containing keratin,
  use lungs for oxygen, lay their eggs on land and
  undergo internal fertilization most are
  ectothermic (turtles, lizards, snakes,
  alligators, crocodiles)
• Class Aves lay eggs, are endothermic, have
  keratin scales on their legs, have wings and
  feathers, and a four-chambered heart (penguins,
  crows, emus)

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Extant reptiles
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A small sample of living birds
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Diversity of form and function in bird feet
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Subphylum Vertebrata

• Class Mammalia
• Mammals are amniotes that have hair and produce
  milk
• All mammals have mammary glands, have hair, are
  endothermic, have teeth and use internal
  fertilization most are born rather than hatched
• Monotremes are egg-laying mammals (platypus,
  spiny anteater)
• Marsupials complete their development in a
  marsupium (pouch) while nursing (opossum,
  kangaroo)
• Placental mammals (eutherians) have longer
  pregnancy and complete development in the uterus
  (dogs, cats, horses, deer, humans)

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Short-beaked echidna (Tachyglossus aculeatus), an
Australian monotreme
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Australian marsupials
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Coquerels sifakas (Propithecus vereauxi
coquereli), a type of lemur
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New World monkeys and Old World monkeys
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Hominoids (apes)