Amniota - BIO205

Phylum Chordates (Chordata)

  • Definition: Animals with a notochord at some stage in their life cycle.

  • Sub-phylum Vertebrates (Craniata)

    • Vertebrates are chordates with vertebrae and a cranium.

    • Clade Gnathostomata: Vertebrates with jaws.

    • Clade Osteichthyes: Bony fishes and tetrapods.

    • Clade Tetrapods: Four-limbed vertebrates.

    • Clade Amniotes: Tetrapods with embryos having extraembryonic membranes.

Classification Overview

  • Protochordata:

    • Includes lancelets and tunicates.

  • Agnatha:

    • Includes hagfishes and lampreys.

  • Chondrichthyes:

    • Includes sharks, rays, and chimaeras.

  • Actinopterygii:

    • Ray-finned fishes.

  • Lobe-finned Fishes:

    • Ancestors to tetrapods.

  • Reptilia:

    • Includes turtles, lizards, snakes, crocodiles, and birds (Aves).

  • Mammalia:

    • Mammals characterized by hair and mammary glands.

Characteristics of Amniotes

  • Adaptations for a terrestrial lifestyle:

    1. Amniotic Egg:

      • Contains four extra-embryonic membranes that support development.

    2. Rib Ventilation of the Lungs:

      • More efficient method of breathing allowing greater activity levels.

    3. High Pressure Cardiovascular System:

      • Facilitates increased metabolism via efficient oxygen delivery.

    4. Thicker and More Waterproof Skin:

      • Protects against desiccation and environmental factors.

    5. High Performance Kidneys:

      • Water-conserving kidneys to adapt to dry environments.

    6. Expanded Brain and Sensory Organs:

      • Enhanced sensory processing and motor control.

    7. Stronger Jaws:

      • Improved feeding mechanisms over ancestral forms.

Detailed Features of Amniotic Egg

  • Components of the Amniotic Egg:

    1. Chorion:

      • Surrounds the embryo, acts as a respiratory organ.

    2. Allantois:

      • Stores metabolic wastes, involved in gas exchange.

    3. Amnion:

      • Protects the embryo by providing a fluid-filled cavity.

    4. Yolk Sac:

      • Supplies nutrients to the developing embryo.

    5. Mineralized Shell:

      • Provides mechanical support, limits water loss, and allows gas exchange.

Respiratory Adaptations

  • Lungs Development:

    • Increased surface area with the development of alveoli for gas exchange.

    • Rib ventilation improves lung capacity and efficiency.

    • Evolutionary examples: Salamander, Frog, Lizard, Mammal.

Cardiovascular Adaptations

  • High Pressure System:

    • Justifies double circuit circulation

      • Completely separated (in mammals, birds, and crocodiles).

      • Partially separated (in other reptiles).

Skin Adaptations

  • Thicker and Waterproof Skin:

    • Includes keratinized structures for protection (scales, hair, feathers).

    • Adaptations for moisture retention in terrestrial environments.

Sensory and Neurological Advancements

  • Expanded Brain and Sensory Organs:

    • Significant development in the cerebrum and cerebellum.

    • Enhanced processing of sensory information and muscle control for locomotion.

Conclusion

  • Amniotes demonstrate a suite of adaptations that allow them to thrive in diverse terrestrial environments, leading to evolutionary success in reptiles, birds, and mammals.