The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the <answer>Carboniferous period</answer>, this group diverged from the sauropsid line that led to today's reptiles and birds. The line following the stem group Sphenacodontia split-off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals (Therapsida) in the early Mesozoic era. The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of the non-avian dinosaurs 66 million years ago.
From which time period did birds and reptiles began to appear from?
Carboniferous period