The amniotes are those organisms united by the egg type described last week. This includes all of the non-amphibian land dwellers, and as seen below, their lineages are characterized by different skull types. Two atria, right and left. Incompletely divided ventricle, and no more of the spiral valves seen in amphibians.
Lungs work by negative pressure in reptiles, in contrast to amphibians.
The diaphragm as a muscle of respiration is seen only in mammals. Most reptiles have Jacobson's organs as accessory olfactory organs. Water balance . Reptiles excrete uric acid , which is semisolid and nontoxic. Reptiles are well represented by the fossil record.