A line of ancient amphibians, called the Anthracosaurs have skulls which are very similar to those of early reptiles, and it is difficult to know whether these animals should be called reptiles or amphibians.
Some authorities consider it to be a reptile, and others an amphibian.
Unfortunately we do not know what type of egg animals like Seymouria laid because eggs are rarely found as fossils, and it is really the method of reproduction which is an important distinguishing feature between reptiles and amphibians. Most amphibians produce eggs which require water for the development of the aquatic larvae, while the reptiles were the first animals to lay an egg which could develop on land - an EGG with a shell. Further structural adaptations led to reptiles being the dominant animals on land, in the air and sea for over 120 million years and after an explanation of these we will consider the main reptile groups.