Athena Review Vol. 5, no. 1
Records of Life: Fossils as Original Sources
18. Gorgonopsians
Gorgonopsians
Gorgonopsidae ("gorgon faces") are a family of medium to large-size carnivores in the Therapsid order from the Late Permian with many advanced, mammal-like features. A number of genera have been found in the Karoo Basin of South Africa, where the group was first identified by Owen in 1876.
Gorgonopsians are the most primitive of the three groups of theriodonts found in the Karoo Basin, the other two being therocephalians and cynodonts. During the Late Permian, the gorgonopsians were a highly successful group, becoming the main predators of their regions. They include a total of 25 genera and 41 species, from South Africa, Tanzania, Zambia, and Malawi, as well as from Russia (Sigogneau-Russell 1989; Ivokonenko 2005; Gebauer 2007).
In the Beaufort Group of South Africa’s Karoo Basin, the earliest significant finds of gorganopsians are in the Middle Permian, Tapinocephalus Zone (266-260 mya), representing the three genera Gorgonops, Eoarctops, and Galesuchus. Colbert (1948) proposed Galesuchus as the most primitive of the known gorgonopsians from South Africa.
Fig.13: Skeleton of Sauroctonus, a Late Permian gorgonopsian found in Russia and Africa (Gebauer 2007)
During the Late Permian, gorgonopsians became much more common, with the genera Gorgonops, Eoarctops, Lycaenops, Sauractonus (figs.13,16) Arctognathus, Njalila, Clelandina, and Rubidgea being found in the Tropidostoma and Cistecephalus Zones dated at 260-255 mya (Rubidge 1999; Smith and Keyser 1995). In the Dicynodont Zone (2
55-252
mya) occur the latest forms of Gorgonopsians, including Cynosaurus,
Prorubidgea, and Rubidgea, the latter with extremely enlarged canines.
Gorgonopsians then became extinct as part of the mass extinction at the
end of the Permian (251 mya), with the other two theriodont groups
continuing into the Triassic (Rubidge et al. 1995; Gebauer 2007).Gorgonopsians are thought to have evolved in the Middle Permian (ca. 272-265 mya) from a reptile-like therapsid. The early gorgonopsians were small, dog-sized therapsids. The extinction of dinocephalians around the end of the Middle Permian, however, enabled gorgonopsians to become the dominant Late Permian predators. Their success as hunters was partly due to their large canines, and to changes in their limbs allowing more efficient movement. Their saber-like teeth, which grew larger in later species, could penetrate the tough, scaly skin of some slow-moving herbivores, including pareiasaurs and other therapsids. The legs of gorgonopsians, importantly, supported their bodies from below rather than sprawling out to the sides in the reptilian mode, and enabled speed as well as strength. This provided a decisive advantage over animals they hunted, such as the armored pareiasaur Bradysaurus (fig.14).
Fig. 14: Skull of Bradysaurus seen from above and from the side, showing the rough, scaly armor used as a defense against predators (after Smith and Keyser 1995).
Gorgonopsians were among the largest carnivores of the Late Permian. Most of the known forms, such as the type genus Gorgonops, were 1.5 - 2 meters in length, about the size of lions and other large felids. The largest known genus was Inostrancevia, found in Late Permian deposits in the Northern Dvina Valley in Russia, in the Sokolki assemblage (Efremov 1937; Ivakhnenko 1990). Inostrancevia was over 3 meters long, about the size of the largest modern bears, with a skull length of 45 cm, and saber-like canine teeth up to 12 cm long.
The mammal-like traits of gorgonopsians include differentiated or heterodont teeth, with incisors, canines, and cheek teeth or molars; a large, fully developed temporal fenestra for strong jaw m
uscle
attachment; and vertically-aligned rear legs for faster movement.
Gorgonopsids also had a vaulted palate that may have facilitated
breathing while holding prey in their jaws; and early stages of the
hearing ossicles that later developed in the mammalian middle ear.The type species, Gorgonops torvus, was first identified on the basis of an incomplete and flattened skull found in South Africa at Mildenhalls, Fort Beaufort. Among the first of the therapsids to be described (Owen 1876), G. torvus was also used as the type genus both for the Gorgonopsidae family (Lydekker 1890),and the suborder Gorgonopsia (Seeley 1895). Seeley's grouping, however, was based on a mistaken notion that gorgonopsians lacked temporal openings for muscle attachments, as opposed to theriodonta (Gebauer 2007). This was corrected by Broom in 1913, who established the subfamily of gorgonopsia as distinct from the theriocephalians (Broom 1913b). From then onward, continued fossil discoveries in South Africa, Tanzania, Zambia, Malawi, and Russia, and South America are described in a long series of publications, beginning with Broom (1912, 1913a, 1925, 1930, 1932, 1940) and Watson (1914, 1921), along with numerous other authors cited below.
The type genus Gorgonops, like most members of the family gorgonopsidae, has a body length of 1.2-2 meters and a skull length of 22-35 cm. Its formidable array of teeth included the large canines, which had serrated edges, and five incisors. Besides G. torvus, among the earlier species to be described were the larger Gorgonops whaitsi (Broom, 1912), found in the Tropidostoma and Cistecephalus Zones in the Beaufort West area. Sigogneau-Russell (1989) considered this a more primitive form than G. torvus. A third and still larger species, which may be descended from G. whaitsi, is Gorgonops longifrons (Haughton 1915), known from an incomplete and flattened skull about 35 cm long, with larger eye orbits and a longer snout.
Fig.15: Skeleton of Lycaenops, a Late Permian gorgonopsian found in the Beaufort Group (photo: after Gebauer 2007)
Lycaenops ("Wolf-face"), found in the Late Permian Endothiodon Zone,
was another medium-sized gorgonopsian, with more enlarged canines. The
first named species of this genus was Lycaenops ornatus (fig.15), whose
type specimen was a nearly complete skeleton found by Broom in 1920 on
a weathering shale slope near a railway line, two miles south of the
railway station at Biejespoort, South Africa. Stratigraphically,
it was at the very top of the Endothiodon zone, within the Teekloof
Formation of the Karoo Basin. Some carpal bones of the hands and
feet had weathered away along with most of the tail and cervical
region, but otherwise the skeleton was intact, a rarity for Gorgonopsia
fossils (Broom 1930, pp.349-50; Colbert
1948).
Broom published descriptions of L. ornatus in 1925, 1930, and 1932. The fossil, obtained by the American Museum of Natural History (AMNH No. 2240), was cleaned of all stone matrix and fully restored, with a number of new new details found in the skull and skeleton reported by Colbert (1948). This provided insights for more efficient classification of gorgonopsians. The species Symnognathus angusticeps, previously described by Broom (1915) was later reclassified as Lycaenops angusticeps. It has a longer, more narrow snout than L. ornatus, but is otherwise quite similar in its skull anatomy.
Regarding the undoubted identity of gorgonopsians as Late Permian
"saber-toothed" carnivores, Colbert observed that the condition of
hypertrophy of the canines, accompanied by a deepening of the anterior
part of the lower jaw, is well represented in Lycaenops ornatus, but is
seen at its most advanced form in the late gorgonopsians Inostrancecia
and Rubidgea (Colbert 1948, pp.373-375). Eva Gebauer (2007) reevaluated the relationships between various Gorgonopsid taxa, based on finds in the Ruhuhu Valley of Tanzania in the 1930s by Nowack (Von Huene 1950). A main concentration is on Sauroctonus parringtoni, which shows close similarities the Russian genus Sauroctonus, establishing for the first time a link between Tanzania and Russia in the Late Permian Pangaea. Sauroctonus appears to have been a highly efficient predator, with surprisingly close analogies to the Pleistocene saber-toothed cat, Smilodon (who postdated Sauroctonus by 250 million years.)More recently, Gebauer (2007) has made a detailed comparison between the gorgonopsian Sauroctonus (figs.13,16), first described from the Northern Dvina region in Russia (Tatarinov 1974), and the saber-toothed cat Smilodon fatalis (fig.17), which had similar body lengths of about 2 meters.
Fig.16: Skull and anterior portion of the skeleton of Sauroctonus parringtoni, from the Upper Permian in the Ruhuhu Valley, Tanzania; image reversed (Staatliches Museum für Naturkunde, Karlsruhe, Germany).
In spite of the fact that they are separated by at least 230 million years, and that Sauroctonus still retained some reptilian features in its lower jaw, skull, and skeleton, while Smilodon was an advanced mammal, there are some intriguingly close functional parallels between these two extinct carnivores, both in teeth and jaw forms, and the musculature of jaw movements used in catching and eating prey.
The lower jaws of gorgonopsians, for example, had a thicker front portion than the rear portion, protecting the enlarged canine teeth; a similar function was performed by bone flanges of saber-toothed cats. After a detailed analysis, Gebauer concludes that "it can be well imagined that Sauroctonus in all probability occupied the same ecological niche [as] its mammalian relative 230 million years later" (Gebauer 2007).
Fig.17: Skeleton of the saber-toothed cat Smilodon fatalis (after Gebaur 2007).Gorgonopsians in Tanzania, Malawi, and Zambia
Haughton (1927) later described two gorgonopsian genera found in Malawi, Gorgonops and Aelurognathus (fig.18), the latter genus previously named by Owen (1881). Boonstra (1934), based on analysis of post-cranial anatomy, described two species of the genus Aleruognathus, and one of the genus Arctognathus.
Boonstra (1953) later described gorgonopsians from Tanzania, as did Parrington (1955, 1972), including those found by the German engineer Nowack in the 1930s. Identified taxa from Tanzania now include
Aloposaurus, Leontocephalus, Dinogorgan, Sauroctonius, and possibly Arctognathus (Gebauer 2007). Including the Tanzanian materials, Kemp (1982, 2005) has made detailed comparisons of gorgonopsian skull and skeletal anatomy with other synapsids. More recently, Gebauer (2007) reanalyzed one of the best preserved of the Tanzanian specimens, a nearly complete skeleton originally described as Aelurognathus, now identified as a variant of the Russian genus Sauroctonius (Tatarinov 1974).
Fig.18:
Skull of Aelurognathus, a Late Permian gorgonopsian found iin Tanzania,
Malwai, and Zambia, as well as South Africa.From Zambia, specimens have been identified as Aelurognathus by Sigogeneu (1970). In general for the gorgonopsians, many problems in redundant classifications (such as addressed by Colbert in 1948) were sorted out by Sigogneau-Russell (1989), although some difficulties remain, given the number of gorgonopsian taxa and the wide geographical range of their presence.
The most primitive known gorgonopsians are pelycosaur-like forms in Late Permian Russia, including Biarmosuchus and Eotitanosuchus from Ezhevo. They are contemporary with more advanced forms from South Africa, and thus can provide no simple answers to the origins of gorgonopsians. Other, more derived Russian forms include Sauroctonius, Viatkogorgon, and Suchogorgon (Tatarinov 1974, 1999, 2000; Ivakhnenko 1990). These and other Russian taxa are discussed in the following section.
References:
.
Broom, R. 1913a. "On a nearly perfect skull of a new species of the Gorgonopsia." Ann. S. Afr. Mus., 12, pp. 8-10.
Broom, R 1913b. "On the Gorgonopsia, a sub-order of the mammal-like reptiles." Proc. zool. Soc. London, 1, p.. 225
Broom, R. 1925. "On some carnivorous therapsids." Rec. Albany Mus., 3. pp. 309-326.
Broom, R. 1930. "On the structure of the mammal-like reptiles of the sub-order Gorgonopsia" Phil. Trans. Roy. Soc.
London, Ser. B, 218, pp. 345-371.
Colbert, E.H. 1948. "The mammal-like reptile Lycaenops." Bull. Am. Mus. Nat. Hist., 89, pp. 357-404.
Gebauer, E.V.I. 2007 . "Phylogeny and evolution of the Gorgonopsia with a special reference to the skull and skeleton of GPIT/RE/7113 ('Aelurognathus?' parringtoni)" Ph.D. thesis, Tübingen: Eberhard-Karls Universität Tübingen. pp. 1–316.
Kemp, T.S. 1982. Mammal-like reptiles and the origin of mammals. Academic Press., London, xiv + 363 pp.
Kemp, T.S. 2005. The Origin and Evolution of Mammals. Oxford University Press, pp.331.
Laurin, M. 1998 . "New data on the cranial anatomy of Lycaenops (Synapsida, Gorgonopsidae), and reflections on the possible presence of streptostyly in gorgonopsians." Journal of Vertebrate Paleontology 18: 765-776.
Olson, E. C. 1937. "The cranial morphology of a new gorgonopsian." J. Geol., 45, pp.511-527.
Owen, R. 1876b Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum.
Parrington, F.R. 1955. "On the cranial anatomy of some gorgonopsids and the synapsid middle ear." Proc. Zool. Soc. London, 125, pp.1-40.
Parrington, F.R. 1974. "A new genus of gorgonopsid from East Africa." Ann. S. Afr. Mus., 64:, pp. 47-52.
Rubridge, B.S. (ed.) 1995. "Biostratigraphy of the Beaufort Group." South African Commission on Stratigraphy, Biostratigraphic Series 1, pp.1-45.
Sigogneau D. 1970 "Révision systématique des gorgonopsiens sud-africains." Cah. Paléont., Paris, XII + 414 pp
Sigogneau-Russell, D., 1989. "Theriodontia I - Phthinosuchia, Biarmosuchia, Eotitanosuchia, Gorgonopsia" Part 17 B I, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York
Tatarinov, I. P. 2000. "A new Gorgonopid (Reptilia, Theriodontia) from the Upper Permian of the Volgoda Region." Paleont. J., 34: 64-72.
Watson, D.M.S. 1914. "Notes on some carnivorous reptiles." Proc. Zool. Soc. London, 4, pp.1021-1038.
Glossary