Ophiacodon was a large synapsid predator that lived during the Early Permian and competed for food with the likes of Dimetrodon. While it didn’t have a sail on its back it was clearly related in some way, a distant cousin to DImetrodon. It seems to have mostly preyed on fish and lived in or near water most of its life, but any animal nearly the size of a Komodo Dragon was not to be trifled with.
Ctenospondylus is yet another Early Permian predator, that shared its world with Ophiacodon and Dimetrodon. It had a back spine but it was much shorter than the Dimetrodons and its head was very large and most likely had a very powerful bite.
Diplocaulus was a roughly three-four foot long salamander-like amphibian with a strange boomerang shaped head. It lived during the Permian and spent a large majority fo its life in the water. It was likely preyed upon by various predators such as Dimetrodon, Ophiacodon and Ctenospondylus as well as other aquatic animals. Its head is a bit of a mystery as to what it was for. Theories suggest use as camouflage, helping it to hide at the muddy bottom, or perhaps it was packed with sensitive nerves to help sense food under the mud. Another suggestion is that its wide head made it difficult to swallow whole by chasing fish.