''Scylacops'' (meaning "face that tears") is an extinct genus of

Gorgonopsia Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of sabre-toothed therapsids from the Middle to Upper Permian roughly 265 to 252 million years ago. They are characterised by a long and narrow skull, a ...

. It was first named by Broom in 1913,Broom, R. "On the Gorgonopsia, a Sub-order of the Mammal-like Reptiles." ''Proceedings of the general meetings for scientific business of the Zoological Society of London''. (1913): 225-230. and contains two species, ''S. bigendens'', and ''S. capensis''. Its fossils have been found in

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

and

Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...

. It is believed to be closely related to the Gorgonopsian ''

Sauroctonus ''Sauroctonus'' (from el, σαῦρος , 'lizard' and el, κτόνος , 'murderer') is an extinct genus of therapsids. ''Sauroctonus progressus'' was a large (2 m long) gorgonopsid that lived in the Late Permian epoch before the Permian-Tri ...

progressus''. ''Scylacops'' was a moderately sized Gorgonopsid. Scylacops is an carnivorous

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

, existing from 259.0 to 254.0 Ma. ''S. bigendens'' was first described by Brink and James Kitching in 1953, although its original description was ''Sycocephalus bigendens''.Brink, A. S., and J. W. Kitching. "Studies on new specimens of the Gorgonopsia." ''Palaeontologia africana'' 1 (1953): 1-28. According to the paleobiology database ''Scylacops'' specimens have been found in the following locations in South Africa; Uitsspansfontein at Beaufort West, Dunedin, Wellwood, and Sondagsriviershoek. ''Scylacops'' is also known from Zambia.Battail, Bernard, and Mikhail V. Surkov. "Mammal-like reptiles from Russia." The age of dinosaurs in Russia and Mongolia (2000): 86-119.

Systematics

Although there have been multiple alignments for ''Scylacops'' within Gorgonopsidae starting with Broom's original declaration that ''Scylacops'' is “allied with ''Gorgonops torous'',” morphological similarities point to it as a close relative of ''Sauroctonus progressus''. Battail & Surkov described Gorgonopsinae a subfamily of Gorgonopsidae. However, now only

Rubidgeinae Rubidgeinae is an extinct subfamily of gorgonopsid therapsids known only from Africa. They were among the largest gorgonopsians, and their fossils are common in the Cistecephalus and Daptocephalus assemblage zones of the Karoo Basin. They lived ...

is recognized as a sub-family of Gorgonopsidae. Because Battail & Surkov diagnosed ''Scylacops'' as Gorgonopsinae, a description of Gorgonopsinae is warranted. Gorgonopsinae is diagnosed by a thin zygomatic arch, a ventrally extended edge of posterior cranial roof, an often present preparietal and a post temporal fossa oriented horizontally. Because of the research and analysis of Battail & Surkov, a phylogeny which includes ''Scylacops'' as sister ''Sauroctonus'' to can be inferred. Because of ''Scylacops’'' relationships in the Therapsid clade. Broom describes the key morphological differences between Gorgonopsia and

Therocephalia Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their te ...

. Gorgonopsia have a broad parietal region vs a narrow one in Therocephalians. Gorgonopsians have a preparietal while Therocephalians do not. Gorgonopsians have a large post frontal while Therocephalians have a small one. Gorgonopsians have a single true vomer while Therocephalians have a pair of prevomers. Gorgonopsians have strong mandible symphysis while Therocephalians have loosely articulated jaws. Gorgonopsians have an angular with a deep grove while they are perforated in Therocephalians. Analysis showing cyclical growth in cortical fibrolamellar bone tissue in ''Scylacops'' and gorgonopsians as a whole is one reason they are considered more distantly related to crown Mammilla. Early–Middle Triassic non-mammalian cynodonts ''Cynognathus'' and Early Jurassic ''Tritylodon'' exhibit rapid, sustained growth and are placed closer to crown Mammilla.

Description/morphology

A Lateral view diagnoses include a large septomaxilla, a large prefrontal which meets the post- frontal and shuts out the frontal from the orbital margin, and the increased forward extension of the zygomatic portion of the squamosal. Dorsal view diagnoses include a large frontal which does not reach the orbital margins, behind the frontal is a large postfrontal bounded by the prefrontal, the frontal, the parietal, and the postorbital. ''Scylacops'' has 5 incisors 1 canine and 3 molars. ''Scylacops'' has a similar occipital region to ''Lycaenops ornatus'', another gorgonopsian discovered by Broom in 1920. Its occipital region is described with the following characteristics. The interparietal is a large broad bone between the parietal and supraoccipital. The interparietal is entirely on the occipital face. Below it lies a large broad supraoccipital forming the upper margin of the foramen magnum. The interparietal articulates inferiorly with the exoccipital and the opisthotic with the tabular forming the outer portion of the occiput. Above the interparietal is articulation with the parietal and the squamosal. As part of the articulation with the quadrate is a long process lying against the squamosal externally and the opisthotic internally. The exoccipitals are small and form the lateral walls of the foramen magnum. Sauroctonus progressus09

Battail & Surkov describe ''Scylacops'' as the closest overall morphological relative to the Russian gorgonopsine ''Sauroctonus progressus''. Battail & Surkov diagnose ''S. progressus'' by small orbits, a skull narrow posteriorly, infraorbital and temporal widths are very narrow, the postorbital bar widens ventrally with transverse flanges of pterygoids, and has 4-6 upper post canine teeth. Like ''Scylacops'' it is considered a medium-sized gorgonopsid. ''Scylacops'' SAM-PK-10188 from the Iziko South African Museum has measurements as follows; Humerus 100 mm, Radii 83.25 mm, Ulna 99 mm, Femur 174.8 mm, Fibula, 96.67 mm.Ray, Sanghamitra, Jennifer Botha & Anusuya Chinsamy. “Bone histology and growth patterns of some nonmammalian therapsids.” ''Journal of Vertebrate Paleontology'', 24.3 (2004): 634-648.

Histology

Therapsids have quick osteogenesis in the cortical fibrolamellar bone tissue. Analysis of ''Scylacops'' sp. specimen SAM-PK-10188 from Dunedin shows a cyclical and zonal growth pattern. This cyclical growth is a strong effect of ''Scylacops''’ environment. ''Scylacops’'' cortical fibrolamellar bone tissue shows a phylogenic relationship between ''Scylacops'' and the gorgonopsid from the Rubidgeinae sub-family ''

Aelurognathus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontologists Rober ...

''. However, there is a clear distinction between the two. ''Scylacops'' was distinctly cyclical with intermediate growth, where periods of fast growth were interrupted by periods of slow growth or halting of growth. ''

'' sustained fast growth early in ontogeny only to be interrupted at a later stage of growth. Aelur tigriceps1DB

SAM-PK-10188’s histology shows wide zones separated by annuli and LAGs. These wide zones are composed of a woven-fibered bone matrix with mainly longitudinally oriented channels and osteonal deposits forming primary osteons and fibrolamellar bone tissue. The outer cortical periphery is irregular with few channels opening subperiosteally. The longitudinally oriented channels in this region show few osteonal deposits and are larger than well-developed primary osteons. Organization of primary osteons varies depending on the element and even locally within the same section. The medullary cavity in all the elements are lined by endosteally lamellated bone the extent of which varies depending on the position and type of element. Secondary reconstruction is prevalent in the inner cortex resulting in enlarged resorption cavities.

Stratigraphy

The ''Cistecephalus'' zone is regarding the

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...

of a genus of burrowing

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...

from the late

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

of South Africa. The strata assigned to the zone is made from gray-green, bluish-green, purple and reddish mudstone with lenticular sandstone and siltstone beds. Fossils mostly are found in mudstone horizons lasting several miles. The Uitsspansfontein locality in Beaufort west is characterized by a low relief and small exposures covering strata immediately below the ''Cistecephalus'' band.Kitching, James W. ''The distribution of the Karroo vertebrate fauna: with special reference to certain genera and the bearing of this distribution on the zoning of the Beaufort Beds.'' University of the Witwatersrand, 1977. Beaufort biostratigraphy is made up of five zones, the ''Daptocephalus, Cistecephalus, Tropidostoma, Pristerognathus'' and ''Tapinocephalus''. The ''Cistecephalus'' zone has an age range of around 257 to 255 ma. Beaufort West is lithographically siliciclastic. The Geologic age in which ''Scylacops'' lived across all sites, is the Wuchiapingian, Late Permian. Parts of the upper ''Cistecephalus'' zone may be referenced as ''Endothiodon'' zone due to many endothiodont specimens found by Broom and Von Huene directly above the recognized ''Cistecephalus'' zone. However, there is no lithological distinction between the two rock beds. They both consist of the same identical gray-green and bluish-green and purple mudstone and shale sediments, interbedded with lenticular sandstone and siltstones. Kitching proposes that the varied color of mudstones and lenticular sandstones are not reliable markers of separation as they do not follow a consistent stratigraphical plane but are sporadic across the Beaufort series. The only location outside of South Africa where ''Scylacops'' has been found is the Madumabisa Mudstone formation in the Drysdall and Kitching locality 3–4, Upper Luangwa Valley, Zambia. It has a mudstone Lithography, and is geologically in the Wuchiapingian.Boonstra, L, D,. “A report on some Karroo reptiles from the Luangwa Valley, Northern Rhodesia.” ''Quarterly Journal of the Geological Society'' 94.1-4 (1938): 371-384.

References

External links

paleodb.orgwww.paleofile.com - Alphabetical list, S Section.www.bioone.orgwww.washington.edu
{{Taxonbar, from=Q150998 Gorgonopsia Prehistoric therapsid genera Lopingian synapsids of Africa Fossil taxa described in 1913 Taxa named by Robert Broom Lopingian genus first appearances Lopingian genus extinctions