bio 108 topic 31: Clade Amniotes

Clade amniotes characteristics

• tetrapods

• Living members are reptiles ( and birds, mammals)

• Adaptions for terrestrial life

• Amniotic egg

Amniotes shared derived traits

• amniotic egg

• Internal fertilization via specialized intromittent organs

• Direct development

Explain the amniotic egg

• 4 extra-embryonic membranes

• Enable reproduction on land

  • gas exchange done by chorion and allantois

  • Nutrient supply (provided by yolk sac and albumen

  • Protection

    • from desiccation (amnion, chorion, external shell)

    • Mechanical shock (cushioned by amniotic fluid)

  • Waste removal (allantois)

• Eggs lay in land

• Reproduction not in water

Explain internal fertilization via intromittent organs

• external genitalia of males specialized for sperm delivery during copulation

• Intromittent organs are traits of internal fertilization

What is direct development

• amniotes dev directly into terrestrial adults without aquatic larvae stage

Amniotes adaptations for land life

• relatively impermeable skin

• Use rib cage to ventilate lungs

Temporal fenestrae

Classification of amniotes partially based on major skull openings

Three types of temporal fenestrae

1. Anapsid: lack temporal fenestrae (ex: turtles)

2. Synapsid: one pair of temporal fenestra (mammals)

3. Diapsid: 2 pairs of temporal fenestrae behind eye sockets (reptiles)