Amniote
After the egg developed these structures, further sophistication allowed amniotes to lay much bigger eggs in much drier habitats. Bigger eggs allowed for bigger offspring, and bigger adults could produce bigger eggs, so amniotes grew bigger than their ancestors. Real growth was not possible, however, until they stopped relying on small invertebrates as their main food source and started to eat plants or other vertebrates, or returned to the water. New habits and heavier bodies meant further evolution for the amniotes, both in behavior and anatomy.