Dimetrodon basically evolved itself into extinction. It was the first in a long line of non-mammalian synapsids. It was an ancestor to other more derived synapsids like cynodonts and gorgonopsids. A good technical paper on its evolution is called:

EVOLUTIONARY PATTERNS IN THE HISTORY OF
PERMO-TRIASSIC AND CENOZOIC SYNAPSID PREDATORS

by Blaire Van Valkenburgh and Ian Jenkins

You can find it on google scholar it you're interested.