Vertebrates

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Chapter 34

• Vertebrates

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Vertebrates

• These are a subphylum of the phylum Chordata.
• They are deuterostomes

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Chordates

• Bilaterally symmetrical.
• They are deuterostomes.
• Have a notochord.

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Derived Characters of Chordates

• 4 key characters of chordates
• 1. A notochord
• 2. A dorsal, hollow nerve cord
• 3. Pharyngeal slits or clefts
• 4. A muscular, post-anal tail

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1. Notochord

• A longitudinal, flexible rod between the
  digestive tube and the nerve cord.
• It is fluid filled and provides support for the
  animal.

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1. Notochord

• Larvae and adults that retain it
• The muscles can work against it.
• In animals that develop a skeleton, the remnants
  of the notochord are disks.

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2. Dorsal Hollow Nerve Cord

• Develops from a plate of ectoderm.
• It rolls into a tube dorsal to the notochord.
• Dorsal hollow nerve cords are unique to
  chordates.
• The nerve cord develops into a CNS.

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3. Pharyngeal Slits or Clefts

• The region just posterior to the mouth is the
  pharynx.
• All chordates have a series of pouches separated
  by grooves that allow water to pass in and out
  without having to go through the entire digestive
  tube.

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3. Pharyngeal Slits or Clefts
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4. Muscular, Post-Anal Tail

• Many species of chordates lose their tail during
  embryonic development.
• For aquatic animals that retain it, it provides a
  propelling force for the animal.

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Craniates

• Craniates are cordates with a head.
• They have two clusters of Hox genes.
• They have a neural crest.

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Neural Crest

• These are the cells that appear as the neural
  tube closes.
• These cells get dispersed throughout the body.
• They give rise to many structures
• Teeth, bones and cartilage of the skull, the
  dermis of the face, neurons, sensory organs

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Craniates

• In aquatic craniates, the pharyngeal clefts
  evolved into gill slits.
• In terrestrial craniates, the slits develop into
  important parts of the inner ear and neck.

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Vertebrates

• Dlx gene duplication gave rise to increased
  nervous system complexity, more extensive skull
  and a backbone with vertebrae.
• The vertebrae enclosed the spinal cord.
• Dorsal, ventral, and anal fins stiffened with fin
  rays enhanced swimming.

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Gnathostomes

• Vertebrates with jaws.

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Derived Characters

• Jaws
• Duplication of Hox genes
• Gave rise to larger brains, enhancing smell and
  vision.
• Aquatic gnathostomes have a lateral line.

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Tetrapods

• Animals with four feet derived from the lobe
  fins.
• Made the move to land.
• Their body changed to allow for walking.

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Amniotes

• Tetrapods (mammals and reptiles, including birds)
  with adaptations for land.
• Amniotic egg.
• Contains extraembryonic membranes that protect
  the embryo.
• Function in gas exchange, waste storage, and
  nutrient exchange.

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The Amnion

• Bathes the embryo and acts as a shock absorber.
• Eggs contain either a calcareous shell or a
  leathery shell to protect against dehydration.
• Expanded habitat choices.

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Amniotes

• Also acquired less permeable skin, a ribcage to
  ventilate the lungs, and a more upright or
  elevated stance.

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Derived Characters of Mammals

• Mammary glands
• Body hair
• Live young
• Endothermic
• Differentiation of teeth

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Monotremes

• Platypus, ant eaters.
• Found only in Australia and New Guinea.
• Lay eggs that hatch.
• The mom secrets milk from a gland in the belly.
• No nipples, the hatchlings suck milk from the
  mothers fur.

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Marsupials

• Opossum, kangaroos, and koalas.
• High metabolic rate, nipples, live young.
• Embryo partially develops in the uterus.
• When born, it completes its development in the
  mothers pouch.

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Eutherians

• These are the placental mammals.
• High metabolic rate, nipples, live young.
• Longer period of gestation.
• Embryonic development is completed within the
  uterus.