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Chapter 34
Vertebrates
Vertebrates
 These are a subphylum of the phylum
Chordata.
 They are deuterostomes
Chordates
 Bilaterally symmetrical.
 They are deuterostomes.
 Have a notochord.
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
1. Notochord
 A longitudinal, flexible rod between the
digestive tube and the nerve cord.
 It is fluid filled and provides support for
the animal.
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.
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.
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.
3. Pharyngeal Slits or Clefts
Functions:
Invertebrate Chordates:
Suspension feeding devices
Non-terrestrial
Vertebrate Chordates:
Slits and support structures become gills for gas exchange
Terrestrial (tetrapods)
Vertebrate Chordates:
Clefts don't become slits
They develop into important parts of the inner ear, head and neck
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.
Craniates
 Craniates are cordates with a head.
 They have two clusters of Hox genes.
 They have a neural crest.
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
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.
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.
Gnathostomes
 Vertebrates with jaws.
Derived Characters
 Jaws
 Duplication of Hox genes:
 Gave rise to larger brains, enhancing
smell and vision.
 Aquatic gnathostomes have a lateral
line.
Tetrapods
 Animals with four feet derived from the
lobe fins.
 Made the move to land.
 Their body changed to allow for
walking.
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.
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.
Amniotes
 Also acquired less permeable skin, a
ribcage to ventilate the lungs, and a
more upright or elevated stance.
Derived Characters of
Mammals
 Mammary glands
 Body hair
 Live young
 Endothermic
 Differentiation of teeth
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 mother’s fur.
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 mother’s pouch.
Eutherians
 These are the placental mammals.
 High metabolic rate, nipples, live young.
 Longer period of gestation.
 Embryonic development is completed
within the uterus.