Gorgonopsia
Inostrancevia skeleton
from Gondwana Studios
The Gorgonopsia were the "sabre tooth tigers" of the Permian, medium-sized to large therapsids equiped with huge canine teeth, used to bring down large prey. These theriodonts, typified by animals like the dog-sized Lycaenops (below) and the bear-sized Inostrancevia (above), initiated many of the trends that were to culminate in the later theriodonts. In all respects they were more primitive then, and in a sense ancestral to, later forms. Thus the dentary bone in the jaw was large, but not as large as in Cynognathus (in mammals the jaw consists only of the dentary); the teeth, although differentiated, were not highly specialized; there was as yet no hard secondary palate (bony roof of the mouth, enabling the animal to eat and breath at the same time); the occipital condyle which connects the skull to the backbone was single; and so on.
Yet these were efficient, very capable hunters, the dominant predators of the Late Permian terrestrial ecosystem. They may have hunted singularily or in packs, and probably preyed on large, plant-eating animals like Pareiasaurs, Tapinocephalians, and large Dicynodonts. The canines were particularly long, giving the mouth a distinctly "sabre-toothed" appearance, and the front part of the skull was deeper than normal to accommodate their roots.
A medium-sized form like Lycaenops, represented by several species from the Late Permian (Cistecephalus and Daptocephalus zones) of South Africa, averaged about a meter in length. It was a lightly built carnivore, with long running legs, that almost certainly fed on the abundant dicynodont herbivores that shared its envioronment. Larger forms, like Dinogorgon and Inostrancevia, grew to be lion to bear sized, and prayed upon the ox- and hippo-like megaherbivores like the Pareiasaurs and the biggest Dicynodonts, both of which attained weights of a tonne. Gorgonopsids and Pareiasaurs in particular seemed to have formed a co-adaptive relationship (like mammoths and sabre-tooth cats), and significantly both became extinct at the same time (at the end of the epoch)
The Gorgonopsia are generally considered the most primitive members of the suborder Theriodontia of order Therapsida. It is also conceivably possible that the characters they share with those more advanced mammal-like reptiles could perhaps be explained as convergences (parallel evolution) rather than as shared traits inherited from a common ancestor, and the Gorgonopsia have also been grouped (by the South African Palaeontologist Boonstra) with the Dinocephalia and other very primitive forms (Bairmosuchia etc), under the heading "alphatherapsida". However there is no certain evidence for close relationships between advanced Gorgonopsids and Dinocephalia, especially since many primitive forms (Hipposauridae/Ictidorhinidae) previously considered Gorgonopsids are now generally accepted not to belong to this group at all. The most likely hypothesis at present is that they represent a distinct lineage of Theriodonts, as Christian Kammerer explains in an informative reply to my query on this subject.
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some Links and References |  |
L. D. Boonstra, "The Fauna of the Tapinocephalus Zone (Beaufort Beds of the Karoo)", Annals of the South African Museum, 56 (1) 1969, pp. 1-73
Carroll, R. L. Vertebrate paleontology and evolution. -W. H. Freeman and company, New York, 1988
Edwin H. Colbert, Evolution of the Vertebrates, 2nd edition, 1969, John Wiley & Sons
Illustrated Encyclopaedia of Dinosaurs and Prehistoric Animals, Barry Cox, R.J.G.Savage, Brian Gardiner, Dougal Dixon)
The morphology and behaviour of gorgonopsids, and a new use for computers in palaeontology - Undergraduate Project (1994/5) - Alexandra Freeman - excellent and highly recommended
James A. Hopson, "The Origin and Adaptive Radiation of Mammal-Like Reptiles and Non-Therian Mammals, Annals of the New York Academy of Sciences 167:199-216, 1969
James A. Hopson and Herbert R. Barghusen, "An Analysis of Therapsid Relationships", in The Ecology and Biology of Mammal-Like Reptiles ed. by Nocholas Hotton III, Paul D. MacLean, Jan J. Roth and E. Carol Roth, Smithsonian Institute Press, Washington and London, 1986, pp.83-106
Gorgonopsia - cladogram and genus list - Mikko K. Haaramo
Gorgonopsia - Palaeos Vertebrate Notes - Toby White's excellent technical summary, heaps of links. Incorporates material from these pages.
Inostrancevia alexandri - same content as preceeding page, but bigger photo
Stars of the Show - includes Inostrancevia
| Permian Period | Therapsida | Theriodontia |
Palaeos Page (incorporates some of this material, plus a lot of additional material)
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