17'1 Common Traits of Vertebrates

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17.1 Common Traits of Vertebrates
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Objectives

• Describe the characteristics vertebrates have in
  common.
• Distinguish between endothermic and ectothermic
  animals.
• Discuss the evolutionary development of
  vertebrates.

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• Up and down the middle of your back are bones
  that make up your vertebrae (VUR tuh BRAY).
• Your vertebrae are joined together with cartilage
  to form a flexible but supportive column called
  the backbone.

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• Humans aren't the only organisms with backbones.
• Fishes, amphibians, reptiles, birds, and other
  mammals also have backbones.
• Recall that animals with backbones are called
  vertebrates.

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Characteristics of Vertebrates

• All vertebrates belong to a single phylum called
  Chordata.
• Animals in this phylum are called chordates (KOR
  dayts).
• Among the chordates are several types of animals
  that do not have a backbone.

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• One chordate trait is the presence of gill slits
  at some stage of development.
• Chordates also have a flexible skeletal rod
  called a notochord (NOHT oh KORD).
• The notochord forms the body axis in embryos and
  is the only skeletal element in some chordates.

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• In vertebrates, the notochord is present only in
  the embryo stage.
• As a vertebrate develops, its notochord is
  replaced by a backbone that surrounds and
  protects the spinal cord.
• The backbone is the central part of an internal
  support structure called an endoskeleton.

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• Even though vertebrates share many traits, they
  have important differences, too.
• Birds and mammals are endotherms (EHN doh
  THURMS), animals with constant internal body
  temperatures.
• Their body cells produce enough heat to keep
  their bodies warm despite the changing
  temperature outside their bodies.
• Endotherms are commonly described as
  warm-blooded.

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• Most fishes, amphibians, and reptiles, in
  contrast, don't keep their body temperatures
  constant internally.
• Their body temperatures depend on the temperature
  of their environment.
• Animals with bodies that receive heat from the
  outside are called ectotherms (EHK toh THURMS).

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• Ectotherms are sometimes described as
  coldblooded.
• Most of the animals you will read about in this
  chapter are ectotherms.

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Origin of Vertebrates

• The first vertebrates appeared on the earth about
  500 million years ago.

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• They were water-dwelling, fishlike animals.
• Over time they evolved into many different kinds
  of fishes.
• Fishes are still one of the most successful life
  forms on the earth.

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• Gradually, some fishes developed adaptations that
  permitted them to move from the water onto the
  land.
• One of these adaptations was strong, lobelike
  fins that could be used like limbs to crawl
  across land.

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• Once out of the water, another adaptation-lungs-he
  lped these animals survive on land.
• Lungs allowed the organisms to exchange gases
  with the atmosphere.
• These early land-dwelling vertebrates were the
  first amphibians.

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• Some amphibians evolved into reptiles, and some
  reptiles gave rise to mammals and others to
  birds.
• Each of these types of vertebrates is considered
  a separate class.
• There are seven classes of vertebrates because
  the fishes are divided into three classes.

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