Synapsid
The trend towards differentiation is found in some labyrinthodonts and early anapsid reptilians. They have enlarged first teeth on the maxilla, forming a form of proto-canines. This trait was subsequently lost in the sauropsid line, but developed further in the synapsids. Early synapsids could have 2 or even 3 enlarged 'canines', but in the therapsids, the pattern had settled to one canine in each upper jaw half. The lower canines developed later.