The Chordates

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The Chordates
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The Chordates

• All chordates have
• Dorsal nerve (Spinal) cord
• Notochord or backbone/vertebrae
• Tail (at some stage of the life cycle)
• Gill Slits (at some stage of the life cycle)

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General Chordate Body Plan
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• Vertebrata
• Some of the 5 chordate features are evident only
  during development
• - Embryonic vertebrates have
• - a notochord
• - dorsal nerve chord
• - gill slits/pouches
• (pharyngeal clefts)

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• Compared to the Invertebrates, the Chordates are
• Smarter
• Larger
• Faster
• More coordinated

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Why a spinal cord?

• Allows for better nerve conduction to the brain
  from a longer body.
• Messages can travel faster
• Organisms can grow larger and still be able to
  send nerve signals effectively.

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Why a backbone (Vertebrae)?

• Added strength and rigidity for an elongated
  body,
• Protection for the spinal cord
• Muscle attachment sites
• Organisms can grow larger and have larger muscles.

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Why a Tail?

• An adaptation for locomotion,
• Improves balance
• Improves forward movement (propulsion)

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Why Gill Slits?

• Greater exchange of respiratory gases is needed
  for larger organisms.
• Also thought to be the structures from which jaws
  evolved.

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7 Classes of Chordata

• Agnatha
• Chondrichthyes (cartilaginous fish)
• Osteichthyes (boney fish)
• Amphibia
• Reptilia
• Aves (bird)
• Mammalia

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The Fish

• Common Features
• Skull
• Bones (either cartilaginous or calcified)
• Jaws (which evolved from gill slits)
• Fins (paired appendages, different from the
  appendages of the invertebrates)

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The first 3 classes are often grouped under the
heading Fish

• Agnathans
• Chondrichthyes
• Osteichthyes

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Agnathans

• Jawless
• Cartilaginous skeletons
• E.g - Lampreys and hagfish

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Why Jaws Evolved

• Gill openings in the head became enlarged and
  fitted with teeth
• Allowed organisms to consume huge chunks of food,
  allowing fish to grow to enormous size.

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Other Interesting Facts about Fish

• Have a 2 chambered heart a closed circulatory
  system
• Are cold blooded (ectotherms)
• Sexually reproduce, but use external
  fertilization
• Sharks have 2 penises
• Produce jelly-like eggs that must be laid in water

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Chondrichthyes

• Skulls smaller lighter weight
• Skeletons of cartilage very flexible and light
  weight for greater agility and speed
• Sharks
• and Rays

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Osteichthyes

• The Bony Fishes
• Two types
• 1) Lobe Finned Fish
• 
  2)Teleosts

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Lobe Finned Fish

• Fins in the shape of lobes,
• allowing them to walk on
• pond bottom or even on land
• Also had primitive lungs for
• breathing did not have to rely on gills,
  could be out of water for short periods of time
• Modern day lung fish and coelocanthes evolved
  from the lobe finned fish
• Amphibians likely evolved from lobe finned fish
  too

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Teleosts Spiny Finned Fish

• Modern fish - name a fish and its
• probably a teleost !!
• Fins have spines in them for support
• Have a swim bladder to help them be buoyant at
  any depth

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Amphibians

• Frogs, toads, newts and salamanders
• In addition to the innovations accomplished
  by fish, amphibians have
• Legs that extend sideways awkward for both
  swimming and walking but better
• than lobes
• Lungs (though the lobe finned
• lung fish also had lungs)
• 3 chambered heart

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Crocodiles Snakes
Reptiles
Turtles Lizards
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And Dont Forget

• Dinosaurs were reptiles too!!

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• Reptile Evolution
• Dry scaly skin (prevented drying out of skin, but
  also prevented breathing through skin)
• Expandable rib cage (allowed them to inflate
  their lungs to a large volume)
• Leather shelled amniote eggs (allowed them to lay
  their eggs away from water)

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• Copulatory organs (i.e. a penis - for internal
  fertilization the only way for sperms to get to
  eggs when animals are living on land !!)
• Legs extending beneath the body (for better
  locomotion supporting more weight)
• 3 ½ chamber heart (for better separation of
  oxygenated and deoxygenated blood richer blood
  more energy)

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Birds

• Improvements over
• reptiles include
• Feathers
• (for insulation and flight)
• Hollow bones
• (lighter weight for flight)

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• Warm blooded
• (allowing for greater energy production)
• Air sacs
• (for greater surface area and gas exchange)
• 4 chamber heart
• (for complete separation of oxygenated and
  deoxyg. blood richer blood more energy)
• Hard shelled amniote egg
• (more protection from drying out and
  from predators)

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Mammals

• In addition to warm blood and a 4 chambered
  heart, mammals also possess
• Milk and Mammary glands
• (to nourish young)
• Body hair
• (for insulation)
• 3 groups placentals, monotremes, and marsupials

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Placentals

• Possess a placenta which supports the growth of
  the embryo until birth better chance of survival

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Monotremes

• Lay leathery eggs (like reptiles)

Echidna (spiny ant-eater)
platypus
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Marsupials

• Give birth to an immature live young - no larger
  than a kidney bean
• Wombats, opossums, kangaroos, koalas

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How well do you know your classes of Chordates?
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• The End!