Aloposaurus gracilis (Broom 1910; 10cm skull length; AMNH FARB 5317) is a generalized taxon that nests as the last common ancestor of the theriodonts (gorgonopsids + therocephalians + cynodonts).

Scymnognathus parringtoni (text to come, certain authorities consider this taxon congeneric with Gorgonops)

Gorgonops torvus (Owen 1876, BMNH 1647; Lat Permian, 260-255) mya; 22-30cm skull length, 1.2-2m long). This top predator was derived from a sister to Eotitanosuchus and was a terminal taxon. Aelurognathus (below) was another gorgon.

Distinct from therocephalians, gorgonopsians had a wider cranium and a complete retroarticular process of the angular.

Aelurognathus tigriceps (Haughton 1924, von Huene 1950, SAM 2343) skull length 30 cm, total length: 1.5 m. 250 mya Late Permian represents a subset of the therapsids, a gorgonopsian, a group derived from Biarmosuchus and leading toward Procynosuchus.

Reptiles have two skulls. One to protect their brain and another to house their jaw muscles. Mammals essentially lose the outer skull. Only the cheekbone and the back of the skull remain. The transition from one to another occurred with gorgonopsians such as Aelurognathus in which the primitively small synapsid opening (lateral temporal fenestra) became progressively larger and larger.

The dentary (tooth-bearing jawbone) was larger and developed a posterior elevated area (the coronoid process) for muscle attachment.

Aelurognathus had a shorter tail. Caudofemoral muscles that had once pulled the femora while walking were moving forward, becoming rump muscles.

Araujo RM, Fernandez V, Polycyn MJ, Fröbisch J and Martins RMS 2016. Aspects of the gorgonopsian paleobiology: insights from the basicranium, occiput, osseous labyrinth and neuroanatomy of the immature gorgonopsian skull of Aloposaurus gracilis (Therapsida: Theriodontia: Gorgonopsia). PeerJ Preprints https://doi.org/10.7287/peerj.preprints.2313v1

Gebaur EVI 2007. Phylogeny and Evolution of the Gorgonopsia with a Special Reference to the Skull and Skeleton of GPIT/RE/7113 ('Aelurognathus?' parringtoni) PhD dissertation.

Haughton SH 1924. On some Gorgonpsian skulls in the collection of the South African Museum: Annals of the South African Museum 12: 499-517.

Olson E C 1937. The cranial morphology of a new gorgonopsian. Journal of Geology 45: 511–527.

Owen R 1876a. Evidenves of theriodonts in Permian deposits elsewhere than in South Africa. – Quat. J. Geol. Soc. London, 27: 352-363.

Owen R 1876b. Descriptive and illustrated catalogue of the fossil Reptilia of South Africa in the collection of the British Museum. London, XII + 88 pp.

wiki/Aelurognathus
wiki/Cyonosaurus
wiki/Gorgonops