Biolo1100 Chapter 11 Animal Diversification
  1. Vertebrates possess vertebrae   and evolved from an ancestor that had a notochord   .
    • Vertebrates are chordates with

      • a rigid but flexible notochord
      • dorsal hollow nerve cord
      • pharyngeal slits or gill pouches
      • post-anal tail

      Most chordates possess vertebrae and include fishes, amphibians, reptiles (including birds), and mammals.

      Note that no other animal can possess any of these traits such as a post-anal tail.


  2. Important evolutionary adaptations in fish include fins   that evolved into limbs.
    • Terrestrial vertebrates are tetrapods that evolved from lobe-finned fish.

      The jointed bones within paired fins became adapted to support weight on land.

      The fins evolved into limbs: 4 limbs.

      Most modern fishes are ray-finned and do not possess these bones.


    • Ancestral fish possessed air sacs that were adapted for

      • swim bladders in ray-finned fish,

      • lungs in terrestrial vertebrates.

      Thus human lungs and fish swim bladders are homologous structures.

  3. Most terrestrial vertebrates develop from amniotic   eggs that can be laid on dry land.
    • Amniotic egg

      Most terrestrial vertebrates produce an amniotic egg with an amnion: a watertight membrane that prevents the egg from drying out.

      The fluid within the amnion (amniotic fluid) surrounds and protects the embryo.


    • Terrestrial vertebrates that can lay eggs on land are amniotes: the amnion prevents their eggs from drying out.

      There are 2 groups of amniotes.

      • Reptiles include birds, which are most closely related to crocodiles rather than to turtles, lizards, or snakes.

      • Mammals possess mammary glands that can produce milk.


  4. Mammals are amniotes that produce milk   to nourish their young.
    • Mammals are amniotes and possess mammary glands that produce milk, and have hair that cover parts of their bodies.

      Modern mammals include

      1. Monotremes, such as the Platypus, lay eggs.

      2. Marsupials, such as Kangaroos, are pouched mammals.

      3. Placental mammals have a placenta that nourishes the embryo.


    • The hair (or fur) that covers mammals allow them to trap body heat and be endothermic: maintaining a high internal body temperature.

      This includes whales.

      • Why do whales have hair?
        • They inherited the hair from their mammal ancestors.