Breeding mechanisms of the ancestral reptile
The ability to breed under dry conditions is achieved by a gland located in the lower part of the oviduct and secretes a parchment-like shell which prevents desiccation of the shell. However, the shell still needs to be supplied with sufficient yolk to support the development of the embryo and the shell needs to be porous to enable oxygen to diffuse through. Clearly fertilization of eggs needs to be internal (male reptiles therefore evolved a penis) and to be completed before the shell is deposited. TheTuatara Sphenodon punctatus (Order Rhynchocephalia) an ancient lizard that occurs on New Zealand has no penis and males and females press their genital openings close together in order to achieve internal fertilization in a way similar to amphibians. These lizards have another amphibian feature that is an ability to be active down to 7ºC, a much lower temperature than for any other reptile. Fossilized bones of these creature have be dated to 200 million years ago and may represent one of the most basic four-legged (tetrapod), tough skinned, egg-laying ectotherm that was a predecessor to the great dinosaurs that conquered all parts of the earth (except the polar region). The diversity of dinosaurs also included forms that returned to the sea (ichthyosaurs and plesiosaurs).