main idea. A. Alfred Romer's hypothesis was that early amphibians started evolving reptilian skeletal features long before they started laying eggs on land. B. Alfred Romer theorized that early reptiles developed protective membranes around the egg in response to the dangers to young amphibians in water and threats to the egg on land. C. In Rolf Kohring's view, early reptiles developed protective membranes around the large eggs that were produced in harsh water conditions, making it possible for the egg to be laid on land. D. Gary and Mary Packard claimed that reptiles developed the hard-shelled egg in order to reduce the rate at which eggs were destroyed by predatory insects and microbes. E. Rolf Kohring argued that egg development was poor during the Mississippian epoch due to nutrient-poor waters. F. According to Mary Packard and Roger Seymour, reptiles could not successively develop very large eggs because of the elimination of the gelatin coat.