Common misconceptions Science Biology Evolution
Soon after the first vertebrate  land-dwellers appeared, they split into two branches. Coven R 2000. History of life. Mammals are the only survivors of the synapsid line. Under Linnaean taxonomy reptiles are all amniotes except mammals and birds, thus including the synapsids as well as the first basal amniotes. With the rise of classification based on phylogeny, the Sauropsida excludes basal amniotes and the synapsid line. An example is 'Dimetrodon', which is often thought of as a dinosaur, but is in fact neither a dinosaur nor closely related to modern reptiles.