Reptiles and mammals did not evolve in a sequential manner, with one group preceding the other. Instead, both groups emerged around the same time from a common ancestor, which was a fish that transitioned from water to land.

This fish-like ancestor eventually gave rise to animals resembling modern amphibians, displaying cold-blooded characteristics. They likely possessed traits similar to those depicted in the illustration.

Subsequently, these amphibian-like creatures further evolved, leading to the ancestors of reptiles and mammals during the Carboniferous era. The chart provided illustrates the branching paths of evolution, with the leftmost branch representing our ancestors and the right branches depicting the ancestors of reptiles and birds.

At that time, our ancestors belonged to a group called synapsids. While they were referred to as “mammal-like reptiles” due to their cold-blooded nature and reptilian appearance, they are distinct from true reptiles. Some synapsids, such as Moschops, did not resemble reptiles at all. They are actually more closely related to us, humans, than to true reptiles.

Meanwhile, true reptiles, known as diapsids, were also in the early stages of their evolution during the same era. The diapsids displayed a variety of forms, as shown in the image provided.

As diapsids continued to evolve, their descendants retained features like scaly skin and cold-bloodedness inherited from their amphibian ancestors. These lineages eventually led to the animals we now recognize as crocodiles, turtles, snakes, and lizards. On the other hand, some diapsids evolved feathers and warm-bloodedness, giving rise to the lineage we now refer to as birds.