The Sakmarian

Eryops megacephalus [Cope]

Horizon and Locality: Witchita Series (Wolfcampian age), Texas Red Beds
Locality:
Specimens:
Length (skull):
Length (total): 1.5 to 2 meters
Weight: about 130 kg
Diet: other stem tetrapods
Comments: a large carnivorous aquatic tetrapod, which seems to have persisted with no change for some 20 million years or so

Sphenacodon ferocior

Horizon and Locality: from the Abo/Cutler Formation, New Mexico, USA
Adult Length: 225 cm
Adult Mass: 129 kg
Diet: other stem tetrapods
Comments: Almost identical to Dimetrodon, except that it lacks the famous "sail". Sphenacodon lived in a different region (separated by an expanse of sea) from most species of Dimetrodon (apart from the small contemporary D. occidentalis), and was the size of larger and later species of the latter.
References: Romer and Price 1940, Reisz 1986

Dimetrodon milleri Romer 1937

Horizon: from the Putnam Formation, Wichita Group, Texas, USA
Specimens: one nearly complete and two partial skeletons
Adult Length: 174 cm
Adult Mass: 47 kg
Diet: smaller Tetrapods
Comments: a small, rare form, this is the stratigraphically earliest of the many Dimetrodon species recovered from Texas.
References: Romer and Price 1940, Reisz 1986

Ophiacodon retroversus [Cope]

Horizon and Locality: Admiral Formation, Witchita Series (Wolfcampian age), Texas Red Beds
Adult Length: 2.5 meters
Adult Mass: 120 kg
Diet: mostly fish, perhaps also small aquatic tetrapods
Comments: a large species of the Ophaicodontid lineage. These creatures apparently grew progressively bigger through time.
The skull is very deep and long, not unlike phytosaurs such as Nicrosaurus. It has been suggested that Ophiacodon was a fish-eating form that lived largely along the shores of streams and ponds.
References: Romer and Price 1940, Reisz 1986

Dimetrodon limbatus [Cope]

Horizon: Admiral and Bell Plains Formations, Wichita Group,
Locality: Texas, USA
Specimens: Skull and skeletal elements
Adult Length: 256 cm
Adult Mass: 146 kg
Diet: other Tetrapods
Comments: a large animal, representing the trend in increase in size of successive Dimetrodon species. It seems to be less common than smaller contemporary species
References: Romer and Price 1940, Reisz 1986