Athena Review Vol. 5, no. 1
Records of Life: Fossils as Original Sources
17. Middle and Late Permian Therapsids: South Africa
The best continuous fossil record from the Middle Permian through Early Triassic periods has been found in the Karoo Basin of South Africa. This occurred while the earth's continental masses were conjoined in a megacontinent called Pangaea.
Pangaea
In the Permian period, all major land masses were joined in the mega-continent Pangea, which formed from the juncture of two supercontinents, Laurasia in the north and Gondwanaland in the south. These had gradually assembled during the preceding Devonian, Mississippian, and Pennsylvanian periods. Pangea lasted through the Permian and into much of the subequent Triassic period, before the rocky plates representing the continents began to separate.
A key indicator of the connection of land masses in the Permian is the distribution of the same species in continental areas now separated by oceans. A good example of this is the conifer Glossopteris, an important Permian forest element preserved in the fossil record. Glossopteris was a woody, seed-bearing tree, growing as high as 30 meters, and interpreted to have thrived in very wet soil conditions, such as around swamps and along river banks. Fossils of Glossopteris have been found in all of the southern continents (fig.1), with over 70 species identified in India alone, and other species known from Africa, Madagascar, Australia, Antarctica, and South America. Appearing by the Early Permian period (298-280 mya), members of the Glossopterid family became the dominant elements of the southern flora through the rest of the Permian. They then disappeared during the Permian-Triassic mass extinction of 252-250 mya.
Fig.1: Distribution of Glossopteris (green area) in southern Pangea.
The zone of Glossopteris distribution (fig.1) across several, now detached, landmasses led Austrian geologist Eduard Suess (1885-1909) to infer that these areas had once been connected by a land bridge, with the continents remaining in the same position. As expressed in his major work, The Face of the Earth (1885-1909), Suess also believed that the rise and fall of sea levels were mappable across the earth through geological time, and that the periods of ocean transgression and regression could be correlated from one continent to another. He named the interconnected southern land mass Gondwanaland, after the district in India where fossils of the plant Glossopteris were abundantly found. The ancient sea that he postulated to be north of Gondwanaland he named the Tethys Sea.
Shortly thereafter, the German meterologist and polar researcher Alfred Wegener (1880-1930) more accurately interpreted that the land masses themselves had moved together by shifting continental plates. Wegener's theory of Continental Drift (1912, 1929), hypothesizing that the continents were slowly moving around the Earth, was not widely accepted for several decades. Among its most vocal opponents was the American paleontologist George Gaylord Simpson (1943). Wegener's theory began to gain wide acceptance in the early 1950s, when paleomagnetic samples taken from India showed that the country had previously been in the Southern hemisphere, as Wegener had predicted. His theory is now fully confirmed and forms the starting point for current models of plate tectonics. Suess's names Gondwanaland and the Tethys Sea have also both been retained. The name Pangea, from pan ("entire" [Gk]) and Gaia (the name of the Greek earth goddess), thus "the whole earth", was coined at a 1927 conference of geologists held in Tulsa, Oklahoma to discuss Wegener's theory of continental drift (Willem et al. 1928).
Pangea is the setting for the first appearance in the fossil record of mammal-like reptiles or theriodonts, the ancestors of mammals, during the Middle and Late Permian (268-251 mya). The clearest exposure of this lies in a portion of the southern region of Gondwanaland, centering in South Africa.
.
South Africa: Karoo Basin
The best continuous fossil record from the Middle Permian through Early Triassic periods has been found in the Karoo Basin of South Africa. This sedimentary basin is bounded on the south by the Cape Fold Mountains, which were uplifted in the Early to Middle Permian period by tectonic plates converging on those of South Africa (Rubridge 1995).
The geological formations in the Karoo Basin include a succession of five groups (Dwyka, Ecca, Beaufort, Stormbert, and Drakensberg), dating from the Late Carboniferous through Jurassic periods (fig.2). The third of these, the Beaufort Group, is the lowest terrestial formation, overlying shallow marine shales of the Ecca Group.
Beaufort
Group rocks consists of shales and sandstones that represent riverine
deposits of an ancient sedimentary basin. Its importance for
paleontology stems from its having provided a comprehensive
series of often well-preserved fossil zones, including a continuous
record of flora and fauna dating from the Middle Permian through Middle
Triassic periods (270-220 mya) (Rubridge 1995). Fig.2: Geological formations in the Karoo Basin of South Africa.
Fossil evidence of Therapsids ("beast faces"), the ancestors of mammals, first appear in the Middle Permian deposits of the Beaufort Group in South Africa. Three suborders of Therapsids will be briefly traced below in their appearance in the Beaufort faunal zones: the Anomodontia ("undefined teeth"), the Dinocephalians ("terrible heads"), and the Theriodonta ("beast teeth"). The theriodonts became one of the two synapsid survivors of the great Permian–Triassic extinction event, the other being the dicynodonts, part of the Anomodontia. Theriodonts split into two groups, Therocephalians ("beast heads") who died out after the Early Triassic; and cynodonts ("dog teeth"), whose carnivorous forms became progressively smaller during the Triassic. By the Late Triassic the first mammals evolved from small, shrew-sized cynodonts called trithelodonts.
The Beaufort group has been subdivided into eight faunal assemblage zones (A.Z.), each associated with one or more local geological formations, and each containing a number of associated taxa (fig.3). 1. Eodicynodon A.Z., Abrahamskrall Formation; 2. Tapinocephalus A.Z., Abrahamskraal Formation; 3. Pristerognathus A.Z., Koonap and Middleton Formations; 4. Tropidostoma A.Z. Middleton Formation; 5. Cistecephalus A.Z., Middleton and Balfour Formations; 6. Dicynodon A.Z., Balfour Formation; 7. Lystrosaurus A.Z, Balfour and Katberg Formations; 8. Cynognathus A.Z., Burgersdorp Formation (Rubridge 1995).
1. Eodicynodon Assemblage Zone. This dates from the Middle Permian, Wordian stage (268.8-265.9 mya), and occurs at the southwestern edge of the Abrahamskraal Formation, the lowest zone of continental rocks in the Karoo Basin. This is composed of thick layers of fluvial-deposited shale or mudstones totalling 1400-1800 m in depth, with a higher percentage of sandstone, limestone, and chert than in the overlying Teekloof Formation (Keyser and Smith 1978).
The Abrahamskraal layers,heavily folded to the south, directly overlie marine-deposited shale of the Ecca Group's Waterford Formation. The intersection of the Waterford and Abrahamskraal Formations represents the paleoshoreline at about 270-269 mya (Rubridge 2000; Modesto et al. 2001).
Fig.3:
Stratigraphy of the Beaufort Group Faunal Zones. Skulls used as
examples: 1. Eodicynodon. 2. Robertia. 3. Pristerognathus. 4. Lycaenops
5. Cistecephalus. 6. Dicynodon. 7. Lystrosaurus. 8.
Cynognathus. The zone is named for the small herbivore Eodicynodon ("dawn double dog-tooth"), the earliest known genus of dicynodont, first found as a skull at Farm Zwartskraal near Prince Albert (Barry 1974). Subsquent recovery of postcranial elements revealed that the limbs of Eodicynodon show some relatively primitive (i.e., reptilian) traits, in that they tended to sprawl in standing posture. Eodicynodon was about 15 cm tall at the shoulders, and 45 cm in total body length. It had strong forelimbs and broad paws (mani) with claws, indicating it dug frequently for food. The hind legs were longer and more gracile, which is a typical derived feature for dicynodonts (Rubridge, King, and Hanson 1994).
Eodicynodon is relatively similar to the herbivore Robertia, also commonly found in this zone, although the two genera can be distinguished by the differing forms of the humerus or upper arm bone. Other Therapsids found in this zone include Patranomodon, Tapinocaninus, and Australosyodon. The latter two genera are part of the Anteosauridae family, considered ancestral to the Dinocephalia from the Late Permian. Australosyodon is considered the most primitive Dinocephalian yet found in Gondwanaland (Rubridge 1994). Related genera of Anteosauridae include the Russian taxa Paranteosaurus, Sinophoneus and Titanophoneus.
2. Tapinocephalus Assemblage Zone (Middle Permian, Capitanien stage, 265.8 -261.2 mya). This, the thickest biozone in the Beaufort Group, was originally divided into three layers, a scheme that has subsequently been refined. The lowest division contains many dinocephalians and therocephalians, with relatively few dicynodonts. The middle division has many dicynodonts and therocephalians, but relatively few pareisaurs and dinocephalians. The topmost layer, with a scarcity of faunal elements, includes therocephalians and dicynodonts, but no dinocephalians (Boonstra 1969).
Revision of the Tapiocephalus zone separated out this topmost layer, which now comprises the Pristerognathus A.Z. (Keyser and Smith 1978; Rubridge 1995).
Extensive deposits of this zone occur at the western side of the Karoo Basin, along the interface of the Ecca and Beaufort Groups, where the strata are often complicated by excessive folding of the shale layers, thus making it difficult to identify the sequence and chonology of fossil-bearing deposits.
In the lower part of the Tapinocephalus Zone, three main families of dinocephalians are represented: the Anteosauridae ("earlier lizards"), also found in the underlying Eodicynodon Zone; the Titanosuchidae ("Titanic crocodiles") thought to have descended from the Anteosauridae; and the Tapinocephalidae ("humble heads"), including the type genus for the zone, Tapinocephalus (Rubridge 1995).
Dinocephalians:
Anteosauridae
The huge, semiaquatic carnivore Anteosaurus magnificus ("great earlier lizard"), the type species for the Anteosauridae, was named by Watson in 1921. Up to 5 meters in length, and with a notably long skull (fig.4), it had prominent interlocking incisors, large canine teeth, and ten additional cheek teeth on each side (Boonstra 1954). Anteosaurus probably lived as a river predator, something like a modern crocodile. The giant Anteosaurus existed in South Africa at the same time that Titanophoneus and Doliosauriscus dominated riverine environments in the Isheevo region in western Russia.
Fig.4: Skull of Anteosaurus magnificus, from the Mid Permian.Anteosaurus, defined by a relatively lage sample well-preserved skulls, shows distinctive traits in both its elongated, primitive skull form, and enlarged canine teeth which were related to its carnivorous feeding habits. These traits were passed on to its later descendants such as the Titanosuchidae, many of which, however, changed their dietary habits to become omnivores or herbivores. In terms of their roles as carnivores, the family Anteosauridae were replaced in the Late Permian by large gorgonopsians (described below).
Titanosuchidae
The second family of dinocephalians from this zone are the Titanosuchidae, considered direct descendants of Anteosauridae. Titanosuchidae include the genera Titanosuchus and Jonkeria, whose skulls show close similarities, retaining the primitive form of the anteosaurs, including a thickened frontal bone at the top, with a large pineal foramen. The skeletal anatomy among the Titanosuchidae, however, often differs significantly between genera, as presumbly did their eating habits. The type species, Titanosuschus ferox ("fierce Titanic crocodile") is considered to have been a carnivore (King 1988). It measured over 2.5 meters in length, had a massive skull, and had curved, fang-like canines and sharp incisors, like those of Anteosaurus.
A second genus from the same family, Jonkeria, is thought to have been
a partial herbivore, sometimes eating plants (King 1988). Jonkeria
ingens (fig.5), defined by Broom (1929), was 4-5 m long, almost as
large as Anteosaurus, with long, stout limbs. It had a typically long,
dinocephalian snout, with large incisors and canines. A total of six
Jonkeria species have been named (Boonstra 1969).Fig.5: Skeleton of Jonkeria ingens.
Tapinocephalidae
The third family from this zone, the Tapinocephalidae, are also known in Russia, and probably had an even wider distribution in the Middle Permian, before becoming extinct at the end of the Capitanian stage. Primarily herbivores, their short, high skulls contrast significantly with the long, primitive skulls of the prevous two families (Anteosauridae and Titanosuchidae). The Tapinocephalidae were among the largest animals of their age, weighting up to 3,000 - 4,500 pounds, with large, rounded midsections, as is typical for plant-eaters. Their teeth have chisel edges, and (also in contrast to the previous two families) lack the specialized canines of carnivores. Their relatively short, sturdy forelegs extended outwards, while the longer hind legs were placed directly under the hips (similar to that of the Late Permian dicynodonts). Based on comparisons with some modern herbivores, they could stand bipedally and eat vegetation directly from lower tree branches.
Tapinocephalus atherstone (fig.6),, the type species for this family, and the only known species of the genus, was a large herbivore up to three meters long, weighing an estimated 3,300-4.400 pounds. Their skulls are characterized by massive frontal bones in the skull roof, and short snouts.
Fig.6: Skull of Tapinocephalus atherstonei, shown in overhead and lateral views (after Smith and Keyser 1995,
fig.12a).Another large herbivore from the same family was Moschops capiensis (Broom 1911). Moschops ranged from 2.5 - 5.0 m in length, with a large, rounded midsection. They had a high, short skull, with short jaws and chisel-shaped teeth. There are two widely-accepted species, M. capensis and M. koupensis, both found within the same stratigraphic range of the Beaumont Formation.
The pareisaurs are represented in this zone by Bradysaurus (figs.7,14), another large herbivore. Bradysaurus had heavily armored scales on its head and neck for protection against gorgonopsians and other predators.
Fig.7: Skeleton of Bradysaurus (Berlin Mus. Nat. Hist.)
3. Pristerognathus Assemblage Zone (late Middle Permian). This narrow zone, skirting the eastern edge of the much larger Tapinocephalus zone contains the first evidence of the carnivorous Gorgonpsida ("gorgon faces"), the most primitive group of theriodonts ("beast teeth"). The other two groups, Therocephalia ("beast heads") and Cynodontia ("dog teeth") are grouped as Eutheriodonts, "true beast teeth". The Eutheriodonts have larger skulls, with larger brains related to improved hearing and vision, and improved jaw muscles related to enlarged lower jaw bones (dentaries), a mammal-like trait which enabled more effective chewing. The early theriodonts were carnivorous; later, during the Triassic, several groups became herbivorous.
The zone is named for Pristerognathus, a medium sized therocephalian carnivore discovered by Broom in 1904, growing up to 1.5 meters in body length. These otter-sized animals had long, narrow skulls with large canines, and probably hunted smaller therapsids and reptiles. Three species include P. baini, P. polyodon, and P. platyrhinus.
At this point, another major change was occurring in the theriodonts, in the miniaturization of several smaller bones in the rear of the lower jaw (the reptilian quadrate, articular, and surangular bones), and their transformation into the tiny ossicle bones of the mammalian middle ear (stapes, incus, and malleus). This process, completed by the Late Triassic, led to the much improved hearing of mammals, as compared to reptiles who have only the stapes in the middle ear to amplify airborne sounds. Improved hearing helped make the theriodonts the most successful group of synapsids. The two diagnostic traits of the middle ear with three ossicles, and the related changes in the lower jaw joint, are the two most commonly used guides in the fossil record to distinguish early mammals from non-mammal synapsids as well as reptiles.
4. Tropidostoma Assemblage Zone (Late Permian). This zone, dating from the Late Permian (Tatarian stage) is named for the early dicynodont, Tropidostoma ("keel mouth"), first reported by Seeley (1889) and Broom (1915) from Tafelberg in the Beaufort West District of South Africa. One species is known, T. micrtotrema, with various earlier names (Keyser and Smith 1978). The Tropidostoma zone sees an increase in gorgonopsians as a primary predator.
5. Cistecephalus Assemblage Zone (Late Permian). This zone is named for the small dicynodont Cistecephalus, one of the first known dicynodonts (Owens 1876, 1879). Cistecephalus was a small, burrowing animal up to 60 cm long. It had a flattened and wedge-shaped skull, slightly convex as in present day burrowers, for the attachment of powerful neck and shoulder muscles. Its strong forelimbs show structural similarities to those of modern burrowing mammals (King, 1990), such as the mole (Talpidae family). The Cistecephalus Zone shows a peak in dicynodont diversity, including about 35 genera. By this time in the Late Permian, the larger dicynodonts have radiated to other parts of Gondwanaland (King 1990). This genus has also been identified in India (Bandyopadhyay 1988) and Zambia. A very similar genus, Kawingasaurus, is also known from the Kawinga Formation of Tanzania, considered equivalent to the Cistecephalus zone.
In this zone, the gorgonopsians show their largest presence, with the greatest number of their species identified.
6. Dicynodon Assemblage Zone (Latest Permian, 257-252 mya). This extensive, ring-shaped zone is
named
for Dicynodon ("Two Dog-teeth"), the type species of the dicynodonts,
first described in the mid 19th century. It is a medium-sized,
herbivorous therapsid about 1.2 meters long, with no teeth except for
two prominent, tusk-like canines (fig.8). It probably cropped
vegetation with a horny beak, much like a tortoise, while the tusks may
have been used for digging up roots and tubers. The type species is
Dicynodon lacerticeps, named by Owen (1845). Although over 160 species
of Dicynodon have since been named from various Late Permian formations
in Russia , China, India, and elsewhere, these have recently been
reclassified. A recent study of the genus determined the only valid
members of the genus to be D. lacerticeps from South Africa, and
D. huenei from Tanzania, with nine other species from other regions
assigned to the infraorder Dicynodontia (Kammerer and Angielczyk 2009).Fig. 8: Skull of Dicynodon.
7. Lystrosaurus Assemblage Zone (Early Triassic; 252-247 mya). While most of the Permian species described from the previous six faunal zones were eliminated by the massive extinction event at the end of the Permian, some dicynodonts and cynodonts from the Karoo Basin survived, and their fossils are found in Early Triassic layers of the Beaufort Group. The first faunal zone of the Early Triassic in South Africa (fig.6) is named for the small dicynodont Lystrosaurus, a widely dispersed genus who is by far the most commonly found terrestial animal during the Early Triassic. Lystrosaurus will be further discussed in later sections on the Triassic period.
8. Cynognathus Assemblage Zone (Early Triassic, 247-242 mya). This zone, located on the inner edge of the Beaufort Group (fig.6), will likewise be discussed in later sections.
.
Glossary
.
References:
Amson, E. and M. Laurin 2011 . "On the affinities of Tetraceratops insignis, an Early Permian synapsid." Acta Palaeontologica Polonica 56: 301–312.
Anderson, J.M., and A.R. Cruikshank 1978. "The Biostratigraphy of the Permian and Triassic. Part 5: A review of the classification and distribution of Permo-Triassic tetrapods." Palaeontologia Africana 21, pp. 15-44.
Bain, A.G. 1845. "On the discovery of fossil remains of bidental and other reptiles in South Africa". Transactions of the Geological Society of London, pp. 53–59.
Bandyopadhyay, S. 1999. "Gondwana Vertebrate Faunas of India." PINSA 65, pp. 285-313.
Barberena, M.C., D.C. Araujo, and E.L. Lavina 1985. "The evidence for close paleofaunistic affinity between South America and Africa as indicated by Late Permian and Early Triassic tetrapods." In Ulbick, H.Y. and A. Rocha-Campos (eds.), Gondwana Proceedings, 7th International Gondwana Symposium, San Pablo, pp. 454-467.
Barry, T.H. 1974. "A new dicynodont ancestor from the Upper Ecca." Annals of the South African Museum 64, pp.117-136.
Boonstra, L.D. 1938. "A report of some Karoo reptiles from the Luangwa Valley, Northern Rhodesia" Quaternary Journal of the Geological Society of London 94, pp. 371-384.
Boonstra, L.D. 1953 "A report on a collection of fossil reptilian bones from Tanganyika Territory." Ann. S. Afr. Mus.,42, pp.5-18
Boonstra, L.D. 1954."The cranial structure of the Titanosuchian Anteosaurus." Ann. S. Afr. Mus., 42, pp.108-148.
Boonstra, L.D. 1969."The fauna of the Tapinocephalus Zone (Beaufort Beds of the Karoo)." Ann S. Afr. Mus. 56: 1-73.
Boos, A. D. S.; Schultz, C. L.; Vega, C. S.; Aumond, J. S. J. 2013. "On the presence of the Late Permian dicynodont Endothiodon in Brazil". In Angielczyk, Kenneth.
Broom, R. 1912. "On some new fossil reptiles from the Permian and Triassic beds of South Africa." Proc. zool. Soc. London, pp. 859-876.
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.
Broom, R. 1940. "On some new genera and species of fossil reptiles from the Karroo beds of Graaff-Reinet." Ann. Transvaal Mus., 20, pp. 157-192.
Chowdhury. T.R. 1970. "Two new dicynodonts from the Triassic Yerrapalli Formation of central India." Palaeontology 13, pp.133-144.
Colbert, E.H. 1948. "The mammal-like reptile Lycaenops." Bull. Am. Mus. Nat. Hist., 89, pp. 357-404.
Efremov, I.A. 1937. "On the stratigraphic division of the continental Permian and Triassic USSR on the basis of the terrestrial vertebrate fauna." – Dokl. Akad. Nauk SSSR, Nov. Ser., 16(2), pp.125-132.
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.
Gregory, W.T. 1926. "The skeleton of Moschops capensis Broom, a dinocephalian reptile from the Permian of South Africa." Bull. Amer. Mus. Nat. Hist. 56: 179-251
Haughton, S.H. 1915. "Investigations in South African fossil reptiles and Amphibia, 7. On some new gorgonopsians." Ann. S. Afr. Mus.,12: 82-90.
Haughton, S. H. 1917. "Investigations in South African fossil reptiles and Amphibia. Part 10. Descriptive catalogue of the Dicynodontia." Annals of the South African Museum 12, pp.127-174.
Haughton, S.H. 1927. "On Karroo vertebrates from Nyasaland." Trans. Geol. Soc. S. Afr., 29, pp. 69-83.
Haughton, S. H. 1932 . "On the collection of Karoo vertebrate fossils from Tanganyika Territory." Quarterly Journal of the Geological Society of London 84, pp. 634-668.
Ivakhnenko, M.F. 1990. "The late Palaeozoic faunal assemblage of tetrapods from deposits of the basin of the Mezen River." Paleont. J. 24, pp.104-112.
Ivakhnenko, M.F. 2005. "Comparative survey of Lower Permian tetrapod faunas of Eastern Europe and South Africa." Paleont. J., 39, pp.66-71.
Jacobs, L. L., Winkler, D. A., Newman, K. D., Gomani, E. M. & Deino, A., 2005, "Therapsids from the Permian Chiweta Beds and the age of the Karoo Supergroup in Malawi." Palaeontologia Electronica. Vol. 8, #1, pp. 28A: 21-23.
Kammerer, C.F. and K.D. Angielczyk 2009. "A proposed higher taxonomy of anomodont therapsids". Zootaxa 20, pp. 1–24
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.
Keyser, A. W. 1975 . "A re-evaluation of the cranial morphology and systematics of some tuskless Anomodontia." Memoir of the Geological Society of South Africa 67, pp.1-110.
King, G.M. 1988. "Anomodontia. Encyclopedia of Paleoherpetology, Part 17c, Gutsav Fischer Verlag, Stuttgart & New York.
King, G.M. 1990. The Dicynodonts: A Study in Palaeobiology. Chapman & Hall.
King, G.M. 1992. "The paleobiogeography of Permian anomodonts." Terra Nova 4, pp.633-640.
Kutty, T.S. 1972. "Permian reptile fauna from India." Nature 237, pp.462-463.
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.
Mazin, J. M. and King, G. M. 1991. "The first dicynodont from the Late Permian of Malagasy." Palaeontology 34, pp.837–842.
Ochev, V.G., 2001. Zonal stratigraphic correlations of the Upper Permian from the Cis-Urals and South Africa according to tetrapods. 6th European Workshop on Vertebrate Palaeontology - Florence and Montevarchi.
Olson, E. C. 1937. "The cranial morphology of a new gorgonopsian." J. Geol., 45, pp.511-527.
Owen, R. 1860. "On some reptilian fossils from South Africa." Quaternary Journal of the Geological Assotiation of South Africa 67, pp.1-110.
Owen, R. 1876a. "Evidences of theriodonts in Permian deposits elsewhere than in South Africa." Quat. J. Geol. Soc. London, 27, pp.352-363.
Owen, R. 1876b Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum.
Owen, R. 1881. "On the order Theriodontia with a description of a new genus and species (Aelurognathus fel. ow.)." Quat. Jour. Geol. Soc. London, 37, pp. 261-265.
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.
Ray, S. 1999. "Permian Reptilian Fauna from the Kundaram Formation, Pranhita-Godavari Valley, India." Journal of African Earth Sciences, 29 (1), pp.211-218.
Rubidge, B.S. 1990 "A new vertebrate biozone at the base of the Beaufort group, Karoo Sequence, South Africa." – Pal. Africana., 27, pp.17-20.
Rubridge, B.S. (ed.) 1995. "Biostratigraphy of the Beaufort Group." South African Commission on Stratigraphy, Biostratigraphic Series 1, pp.1-45.
Rubridge, B.S., G.M. King, and P.J. Hancock 1994. "The postcranial skeleton of the earliest dicynodont synapsid Eodicynadon from the Upper Permian of South Africa." Palaeontology 37 (2), pp.397-408.
Seeley, H.G. 1895. "Researches on the structure, organization and classification of the fossil Reptilia. IX, section 1. On the Therosuchia." Phil. Trans. Roy. Soc. London, B, 185, pp. 987-1018.
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
Simpson, G.G. 1943 . "Mammals and the Nature of Continents". American Journal of Science 241, pp.1–31.
Smith, R.H.M. and Keyser, A.W. 1995. Biostratigraphy of the Tropidostoma Assemblage Zone. Geological Survey of South Africa, South African Committee for Stratigraphy, Biostratigraphic Series, 1:18-22.
Suess, Eduard 1885-1909. Das Antlitz der Erde [The Face of the Earth]. F. Tempsky, Vienna.
Tatarinov, I. P. 1974. Theriodonts of the USSR. Tr. Paleont. Inst. Akad. Nauk SSSR, 143: 1-240.
Tatarinov, I. P. 1999. "New Theriodonts (Reptilia) from the late Permian Fauna of the town of Kotelnich, Kirov region." Paleont. J., 33, pp. 540-546.
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.
Watson, D.M.S. 1921. "The bases of classification of the Theriodonta" Proc. Zool. Soc. London, 1, pp. 34-98.
Watson, D.M.S. 1948. "Dicynodon and its allies." Proc. Zool. Soc. London, 118, pp.823-877.
Wegener, Alfred 1912. "Die Entstehung der Kontinente" [The formation of continents] Geologische Rundschau, Zeitschrift für allgemeine Geologie , dritter Band, pp. 276-292
Wegener, Alfred 1929 . Die Entstehung der Kontinente und Ozeane [The Origin of Continents and Oceans] (4th ed.). Braunschweig: Friedrich Vieweg & Sohn Akt.
Wegener, Alfred 1966. The Origin of Continents and Oceans. New York: Dover. (Translated from the 4th revised German edition by John Biram.)
Willem A. J. M. et al. 1928. Theory of Continental Drift: a Symposium of the Origin and Movements of Land-masses of both Inter-Continental and Intra-Continental, as proposed by Alfred Wegener. Tulsa, Oklahoma, The American Association of Petroleum Geologists & London, Thomas Murby & Co.
In 1937, Alfred S. Romer described a second species from New Mexico named Sphenacodon ferocior ("fiercer") that was larger and more robust, with proportionately longer neural spines. Romer and Price (1940) provided detailed descriptions of both S. ferox and S. ferocior with skeletal reconstructions.
Dimetrodon is mainly known from Texas and Oklahoma in ancient deltaic and riverine environments, although the species Dimetrodon occidentalis is found in New Mexico (Berman 1977; Lucas et al 2009) During the Early Permian, Dimetrodon and Sphenocodon were mainly separated by the ancient Hueco Seaway. Each of the two genera, in its respective region, would have been a major terrestial predator, probably hunting amphibians, diadectids, and early synapsid and diapsid reptiles. Sphenacodon appears to have died out before about 280 mya during the Wolfcampian phase of the Permian, while Dimetrodon survived until about 270 mya.
The skull of Sphenacodon is very similar to that of Dimetrodon, with the same array of skull bones (Romer and Prince 1940) It is narrow from side to side and vertically deep, with an indented notch at the front of the maxillary bone in the upper jaw. The upper and lower jaws are equipped with an array of powerful teeth, divided into large “canines" (called caniniforms), with sharp pointed "incisors" (precaniniforms) in front, and smaller slicing back teeth (postcaniniforms). The eye orbit is set high and far back, with a single aperture or temporal fenestra behind and partly below the eye.
Body proportions are also similar to Dimetrodon, with a very large head, short neck, robust trunk, relatively short front and hind limbs, and a tapering tail that makes up about half the animal's entire length. However, the tops of the neural spines along the back bone are strikingly shorter than in the sailback Dimetrodon. In Sphenacodon, the neural spines are enlarged but retain a flat-tipped, blade-like shape along the back and tail, and form a crest rather than a tall sail. In both Sphenacodon and Dimetrodon, there is evidence for strong epaxial muscles along the base of the raised neural spine, which likely helping to stiffen and strengthen the backbone for walking and for lunging at prey by restricting side-to-side flexing motion.
.
Therapsids
Sphenacodonts were ancestral to the order of Therapsids (“beast-faces”), a term considered synonymous with “mammal-like reptiles.” The Therapsids comprised six synapsid families or sister taxawhich had evolved during the middle and Late Permian, after the decline of the Sphenacodonts and the large “sailback” carnivore taxa of the Early Permian. Three of these, the Dinocephalia, Eotitanosuchids and Gorgonopsids (“gorgon-faces”), did not survive the massive end-of Permian extinction; a fourth, the Therocephalids, lasted into the Early Triassic. Only two of the Therapsid groups, the Dicynodonts and the Cynodonts, survived through the Triassic.
One of these, the Cynodonts (“dog-teeth”), provided the next, and final, ancestral link between synapsids and mammals during the Late Triassic and early Jurassic The Dicynodonts, meanwhile, seem to have become extinct by the end of the Triassic.
Biarmosuchia (class Synapsida; order Therapsida; suborder Biarmosuchia)
Biarmosuchians, considered as one of the earliest, most basal groups of therapsids, lived during the Middle and Late Permian. Biarmosuchians were moderately sized, lightly built carnivores, intermediate in form between the sphendacodont pelycosaurs, and more advanced therapsids. The type species, Biarmosuchus tener, was found in the Russian Urals. Biarmosuchia is known from both Russia (as Phthinosuchus, Biarmosuchus, and Eotitanosuchus) and South Africa (as Ictidorhinidae, Burnetiidae, and related forms).
The biarmosuchian skull is very similar to the sphenacodont skull. Among the retained, primitive, sphenacodontid features were jaw muscles inside the skull, and a slightly backward-sloping, platelike occiput at the base of the skull, the reverse of the pelycosaur condition where the occipital plate slanted forwards. Here it is attached still more strongly to the braincase. New features include larger temporal fenestra which occupy virtually all of the cheek, with the supratemporal bone completely gone (although these fenestra are still small relative to later therapsids). There is a reduced number of teeth, and single large canine teeth in both upper and lower jaws. In later specialised Biarmosuchia, these resemble the enlarged canines of the Gorgonopsia (Carroll 1988, p.370, Benton 2000, p.114). Tooth replacement was variable: some therocephalians (e.g Scylacosaurus) had just one canine, like mammals, and stopped replacing the canine after reaching adult size.
The jaw hinge is more mammalian in position and shape, with mammalian-like jaw-closing muscle stronger, resulting in a stronger bite, as indicated by the flaring of the rear of the skull where these muscles were attached. The old amphibian-like hinged upper jaw has now been replaced by a fixed or immovable maxilla. Related new features include expansion of the maxilla to separate lacrymal from nasal bones, an intermediate trait between early reptiles and later mammals. There is still no secondary palate, but the vomer bones of the palate have developed a backward extension below the palatine bones. This is the first step toward a secondary palate, with exactly the same pattern seen in cynodonts.
The vertebrae of Biarmosuchus remained like those of sphenacodontid, although they lacked the long neural spines that distinguish Dimetrodon and its kin. Alterations in the shoulder and pelvic girdles and the limbs, meanwhile, are highly significant. All indicate a much more advanced posture and a radical alteration in the method of locomotion, with a much more mobile forelimb, more upright hindlimb, and more mammalian femur & pelvis. Primitive sphenacodontid humerus. The feet are more symmetrical, indicating that they faced forward throughout the stride, and the phalanges (toes) are reduced in length so that they are more like that of later synapsids, including both therapsids and mammals (Carroll 1988, pp. 370–1).The toes were approaching equal length, as in mammals, with the number of toe bones varying from reptilian to mammalian. The neck and tail vertebrae became distinctly different from trunk vertebrae. Finally, Biarmasuchia probably had a primitive eardrum in the lower jaw, located by the jaw hinge (the quadrate bone, which contained the stapes or columella).
Gorgonopsidae (class Synapsida; order Therapsida; family Gorgonopsidae)
Gorgonopsidae are medium to large-size therapsid carnivores 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. 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.)
Glossary