1966 — Alfred S. Romer, Vertebrate Paleontology, 3rd ed.; ch 14, p 173
The mammal-like reptiles, constituting the subclass Synapsida, were among the earliest to appear of known reptilian groups and had passed the peak of their career before the first dinosaur appeared on the earth.
1997 — Michael J. Benton, Vertebrate Paleontology, 2nd ed.; ch 5, p 109
Synapsida: amniotes with one lower temporal fenestra, surrounded by the postorbital, jugal and squamosal. Includes the extinct mammal-like reptiles and the mammals.