Amniotes

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Amniotes

• Vertebrate Anatomy
• Notes

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What Are Amniotes?

• Tetrapods
• The vertebrates that are NOT fish
• Amphibians
• Reptiles
• Birds
• mammals
• Amniotes
• The tetrapods that are TOTALLY independent from
  water living (need water only to drink)
• Have important adaptations for terrestrial life
• Include all tetrapods EXCEPT amphibians
• Reptiles
• Birds
• mammals

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Why Move to Land?

• Fewer Predators (at least at the start)
• Lots of available resources
• Food
• shelter
• Less competition for resources (at least at the
  start)

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Amniote Adaptations for Terrestrial Life

• Amniotic Egg
• Allows life cycle to be completed on LAND
• Shell retains WATER and can be laid in a dry
  place without dessicating
• Most mammals have dispensed with the shell, but
  retain other key features of the amniote egg.
• The extraembryonic membranes
• It is from these membranes that the placenta is
  derived

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Specialized Membranes of the Amniotic Egg

• Extraembryonic membranes develop from tissue
  that grows out from the embryo but is NOT part of
  the embryos body
• Amnion
• Fluid filled sac
• Protects embryo from drying out
• Yolk sac
• Food source
• Allantois
• Waste sac
• Chorion
• Responsible (with the allantois) for gas exchange

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Amniotic Egg Diagram
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Amniotic Egg Diagram
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Amniotic Egg Shell

• Composed of Calcium
• Waterproof, but porous
• Water cannot leave the egg, BUT
• Gases (CO2 and O2) can move in and out of the egg.

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Fertilization in Amniotes

• For ALL amniotes, fertilization MUST be INTERNAL
• If youre going to have an egg protected with a
  hard shell, youd better get sperm to that egg
  before that hard shell gets laid down around it.
• Hence, sperm must get to egg in the females
  reproductive tract well before the shell is made.

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Other Adaptations for Life on Land found in
Amniotes

• Waterproofing of the integument
• Epidermal scales (keratinized skin) vs. dermal
  scales (in fish, made of bone)
• Allow for more elaborate skin related structures
  like feathers, fur, horns, etc.
• Also ultimately leads to thermoregulation in
  higher vertebrates

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Other Adaptations for Life on Land found in
Amniotes

• Thermoregulation
• The regulation of body temperature

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Thermoregulation

• Ectothermy
• Cold blooded
• Body temperature is the same as environment
• Only way to control body temperature is to change
  location, body position, etc.
• PROS doesnt require much energy
• CONS doesnt allow for much activity,
  especially in cool temps

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Thermoregulation

• Endothermy
• Warm blooded
• Body temperature is relatively constant
  regardless of environment
• Ways to control body temperature involve
• Body coverings fur, feathers, etc.
• Metabolism body temp is maintained from heat
  generated by the bodys own chemical reactions
• Shivering
• Sweating
• PROS
• Allows for a high degree of activity and complex
  behaviors
• Activity is not so dependent on environmental
  temperature
• CONS
• Requires LOTS of ENERGY
• Animals must be seeking out food almost
  constantly.

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Other Adaptations for Life on Land found in
Amniotes

• Increase in Locomotor efficiency
• Limbs are placed UNDER the body in the higher
  amniotes (birds and mammals)
• Weight is supported by bone as opposed to muscle

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Other Adaptations for Life on Land found in
Amniotes

• Increased feeding efficiency
• Lighter skulls
• Improved jaws

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Other Adaptations for Life on Land found in
Amniotes

• Increased metabolic efficiency
• Lungs improved
• Somewhat in reptiles
• LOTS improved in birds and mammals
• Move to four chambered heart in birds and
  mammals.
• More efficient and moving oxygen into and through
  the body therefore more energy available for
  activities

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Result of Amniote Improvements

• Increased ecological diversity
• Increased activity levels