HAVE EGGSHELL, WILL TRAVEL

The image below is a photo of the exhibit panel. Following it is a transcript of the panel.

Photo of the panel from the exhibit.

Some vertebrates became land-dwellers when a new kind of egg with special membranes evolved.

The amnion is a membrane that encloses the embryo in a fluid-filled cavity. The amnion keeps the embryo wet and cushioned; other membranes hold food, store waste, and assist breathing.

amniotes ( AM -nee-otes): animals with an amnion, including reptiles and mammals

New features:

  • internal fertilization: the male's sperm fertilizes egg within the female's body
  • amniotic egg
      amnion: a membranous sac that surrounds the embryo with fluid
      allantois: a membranous sac that holds waste; assists breathing when fused with chorion
      chorion: a membranous sac that enclosed amnion and allantois; lets oxygen in, carbon dioxide out
      shell: a durable casing for eggs that are laid on land

When? 300 million years ago to present

Early amniote eggs were deposited on land, where the embryo developed within a hard or leathery outer membranes, or shell. In some later amniotes, the eggs develop within the mother's body.

PICTURE CAPTIONS:

  • Hylonomus is the first known amniote. Clutches of this early reptile's fossil eggs have been found, safely nestled in tree stumps, in 300-million-year-old Coal Forest deposits.
  • Diagram showing common ancestry and evolution of Ichthyostega , amphibians, and amniotes from organisms with four limbs. Evolution of amphibians and amniotes is where fully developed shoulder girdles branch off.