chapter 13

Bio1100 Chapter 13

Animal diversification

Vertebrates possess vertebrae and evolved from an ancestor that had a notochord .
- Chordates are a clade that possess:
  - a rigid but flexible notochord
  - dorsal hollow nerve cord
  - pharyngeal slits or gill pouches
  - post-anal tail
  Most chordates possess vertebrae; these vertebrates include fishes, amphibians, reptiles (including birds), and mammals.
  Note that no animal other than chordates can possess any of these traits such as a post-anal tail.
- Chordates (phylum Chordata) are a clade within kingdom Animalia defined by successively evolving these traits:
  - tissues: specialized cells to perform specific functions
  - bilateral symmetry: left and right side are mirror images
  - back to front development (or deuterostomes): the 2nd opening in the early embryo becomes the mouth
  - notochord
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.
- The evolution of jaws and fins from ancestral fish allowed for more efficient feeding and movement.
  Four of the fins are paired due to bilateral symmetry:
  - pectoral fins in front that became forelimbs,
  - pelvic fins in rear that became hindlimbs.
  These fins paved the way for tetrapods with 4 limbs.
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.
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.
Humans are primates that evolved out of Africa.
- Humans belong to a smaller clade within class Mammalia.
  - Primates possess opposable thumbs for grasping.
  - Simians include monkeys that retain long tails.
    - New world monkeys have prehensile tails.
    - Old world monkeys have less agile tails.
  - Apes have vestigial tails.
    - Chimpanzees are closest relatives to humans.