Lecture 9: Amniotes: Cutting ties with Water

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17 Terms

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Amniota

Reptilomorphs that lay amniotic eggs, with thick keratinous skin, and costal lung ventilation

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Characteristics of Amniota

  1. Amniotic Egg

    • An egg with elaborate extraembyronic membranes, surrounded by a shell

  2. Relatively Impermeable Skin

    • Amniotes have a much thicker epidermis with elaborate keratinous structures (scales, feathers and hair) made of the protein keratin

  3. Costal ventilation of Lungs

    • Have an advanced method of lung ventilation that involves the rib cage

  4. Temporal Fenestration

    • Skulls are characterized by openings (temporal fenestrae) posterior to the orbit - which vary between and within groups of amniotes; may have evolved independently within Amniota

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The Amniotic Egg differs from the egg of non-amniotic vertebrates by the presence of

  1. Three additional extraembyronic membranes develop from the embryo

    1. Amnion

    2. Allantois

    3. Chorion

  2. Shell

    • Provides mechanical protection but is porous enough to allow movement of respiratory gases and water vapor

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Amnion

  • Extraembryonic membrane that only surrounds the embryo

  • Cavity formed between the embryo and the amnion is referred to as the amniotic cavity - filled with amniotic fluid

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Allantois

  • An extraembryonic membrane that develops as an extension of the hind gut

  • Acts as storage area for nitrogenous waste produced by the metabolism of the embryo - base of allantois contributes to the formation of the urinary bladder in adult stage

  • Highly vascularized and serves as a respiratory organ during later development

  • Left behind upon hatching

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Chorion

  • An extraembryonic membrane that surrounds the other extraembryonic membranes (the chorion is the outermost membrane)

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Amniotic egg shell

  • Shell gland in female reproductive system tract - produces outer shell

  • Offers mechanical protection

  • Have different properties, some are hard, some are soft

  • All are porous

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Whats the advantage of the amniotic egg?

Allows amniotes to (1) dispense with the larval stage entirely, and (2) have larger offspring upon hatching

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Stratum Corneum

Outermost layer of the epidermis, which is composed of dead keratin-rich cells

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Stratum Corneum

Outermost layer of the epidermis, which is composed of dead keratin-rich cells

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Costal Ventilation

Mode of lung ventilation that utilizes the rib cage to expand and contract lungs.

Expansion of rib cage creates negative pressure which draws air into the lungs - relaxation of rib cage forces air back out (referred to as tidal flow)

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Temporal Fenestration

openings in the skull that allow lower jaw musculature to expand onto the skull roof

three different conditions

  1. Anapsid Condition

  2. Synapsid Condition

  3. Diapsid Condition

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Anapsid Condition

  • No fenestra

  • Early amniotes (primary) and turtles (secondary condition)

<ul><li><p>No fenestra</p></li><li><p>Early amniotes (primary) and turtles (secondary condition)</p></li></ul><p></p>
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Synapsid Condition

  • Single fenestra (lower) behind orbit

  • Synapsids (mammals and mammal-like reptiles)

<ul><li><p>Single fenestra (lower) behind orbit</p></li><li><p>Synapsids (mammals and mammal-like reptiles)</p></li></ul><p></p>
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Diapsid Condition

  • Two fenestrae (upper and lower) behind orbit

  • Lepidosaurs (tuataras, lizards and snakes) and archosaurs (crocodiles, dinosaurs and birds)

<ul><li><p>Two fenestrae (upper and lower) behind orbit</p></li><li><p>Lepidosaurs (tuataras, lizards and snakes) and archosaurs (crocodiles, dinosaurs and birds)</p></li></ul><p></p>
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Synapsida

Synapsid condition animals

Have an alveolar lung - air flows over alveoli twice

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Sauropsida

Anapsid and Diapsid Condition animals.

Have a faveolar flow-through system lung where oxygenated air flows across the respiratory surface (faveoli)