A group of tetrapods that bear embryos enveloped in extra-embryonic membranes. These membranes are called the amnion (this is what the group is named for), the chorion, and the allantois. The embryo together with these membranes is usualy packaged in a calcareous (mineralised) or leathery shell. .<\p>

The oldest known amniote fossile is thought to be from the upper carboniferous, about 310 million years ago.

Reptiles (including turtles, crocodylians, Sphenodon, and the extinct Dinosaurs), birds and mammals all belong in the group of the amniotes, which therefore comprises most of the terrestrial vertebrates (including of course us...).<\p>

Looking at the fossile records of the early amniotes, fossils indicate that amniotes first diverged into two lines. One line (Synapsida) culminated in mammals and another line (Sauropsida, which compromise anapsids and Diapsids) that to which all living reptiles and birds belong.

The amniotic egg, together with a penis for internal fertilization and the loss of a free-living larval stage in the life cycle, allowed the amniote ancestors become truly free of the need for watery surrounds (even during reproduction), and thus truly terrestrial.

Personal note from the author: The importance of this group cannot be stressed enough when looking at our world today. Without it, the reign of dinosaurs would never have been. Instead we might have had 10 foot insects (not likely, as the amount of available oxygen was too low by this time, but who knows what kind of effect such a drastic change might have had) buzzing about these days. Vertebrates might never have gotten free from water, remaining in a amphibian situation. Perhaps crustations would have taken over. Or perhaps a different water-proof amphibian adaptation might have come along, making the difference much smaller. But consider one day, when you walk though nature, when you ride down the street, when you stare out of the window or when you're watching TV: How many of the things around you are or need vertabrate life to exist or to come into existance??

Interesting though, isnt it (and now to really have fun, do the same for any other group of animals.... honeybees perhaps??)