359-299 million years ago
The first amphibians evolved in the Devonian Period. During the Early to Mid-Carboniferous Period, the first reptiles evolved which possessed a mix of primitive ancestral features and derived reptilian characteristics.
The first reptiles are known from the Carboniferous Period: Westlothiana and another fossil are known from the early Carboniferous (Gee, 1988) and Hylonomus and Paleothyris are known from the Middle Carboniferous. These earliest reptiles possessed a number of primitive features in common with anthracosaur amphibians which were not present in later reptiles.
The bones in the back of their braincases (in the occipital region)
were still not firmly attached to each other and the stapes was still
a large bone, rather than the small structure in modern reptiles which
is modified for hearing. The first two vertebrae (the atlas and axis)
retained the primitive amphibian condition, the vertebrae retained intercentra
components which would be lost in later reptiles, and the notochord still
passed unrestricted through the vertebral column. There were still small
dermal scales on their undersides between their arms and legs and the
number of bones in the digits were the same as those of anthracosaurs.