20-627: Leucocephalus is a genus of biarmosuchian belonging to the family Burnetiidae dating to the Wuchiapingian ( Late Permian ). It was found in the Tropidostoma Assemblage Zone of the Main Karoo Basin of South Africa . It is a monotypic taxon which contains one only species, Leucocephalus wewersi . The genus name Leucocephalus is derived from Greek. Leucos, meaning white; kephalos, meaning skull, as
40-462: A cascade of biotic response. Compared to their pelycosaur ancestors, Leucocephalus and other early therapsids are distinguished by more vertical (mammal like) leg positioning beneath their bodies, larger temporal fenestra and increased jaw complexity and power. Like other burnetiids, Leucocephalus skulls exhibit numerous distinguished bony protuberances and bosses giving it a bumpy appearance. These include paired supratemporal "horns" formed by
60-547: A natural group or an assemblage that had in common only shared primitive characteristics. They thought that Phthinosuchus was too poorly known to tell if it also belonged, but considered Eotitanosuchus a more advanced form. Denise Sigogneau-Russell (1989) erected the infraorder Biarmosuchia to include the families Biarmosuchidae, Hipposauridae and Ictidorhinidae, distinct from Eotitanosuchia and Phthinosuchia. Ivakhnenko (1999) argued that Biarmosuchus tener , Eotitanosuchus olsoni , and Ivantosaurus ensifer , all known from
80-748: A partial skull roof including the dorsal margin of orbits and parietal foramen of an unnamed burnetiid from the upper Permian of Tanzania, and Sidor et al . (2014) noted the presence of a burnetiid in the middle Permian of Zambia. Other Biarmosuchia include Biarmosuchus from Russia, Hipposaurus , Herpetoskylax , Ictidorhinus and Lycaenodon from South Africa, and Wantulignathus from Zambia. Biarmosuchus Hipposaurus Ictidorhinus Herpetoskylax Lycaenodon Lemurosaurus Bullacephalus Pachydectes Lobalopex Lophorhinus Niuksenitia Proburnetia Burnetia Paraburnetia Leucocephalus Lende Biarmosuchians are typically considered
100-529: A single skull was found which was located in 2012 at a farm called Amandelboom in Northern Cape Province . It was found on a slope with strata that hosted a tetrapod fossil assemblage to the lower Tropidostoma AZ by a local sheep herder who then hung it on a fence on his farm. Although the skull was outside of its site of burial, strata stuck to it was verified to match that of the adjacent cliff section. The biostratigraphic occurrence of
120-558: A skull 60 centimetres (24 in) in length. Currently the most representative group of the Biarmosuchia, the Burnetiamorpha, comprise ten genera: Bullacephalus , Burnetia , Lemurosaurus , Lobalopex , Lophorhinus , Paraburnetia , and Pachydectes from South Africa, Niuksenitia and Proburnetia from Russia, and Lende (MAL 290) from Malawi. In addition, Sidor et al . (2010) recently described
140-543: Is an extinct clade of non-mammalian synapsids from the Permian . Biarmosuchians are the most basal group of the therapsids . They were moderately-sized, lightly built carnivores, intermediate in form between basal sphenacodont " pelycosaurs " and more advanced therapsids. Biarmosuchians were rare components of Permian ecosystems, and the majority of species belong to the clade Burnetiamorpha, which are characterized by elaborate cranial ornamentation. The biarmosuchian skull
160-573: Is known for most species. However, they were moderately diverse and there were multiple contemporary species in some ecosystems. All were predators similar to gorgonopsians and therocephalians , though they were generally not apex predators. [REDACTED] Sphenacodontia Sphenacodontia is a stem-based clade of derived synapsids . It was defined by Amson and Laurin (2011) as "the largest clade that includes Haptodus baylei , Haptodus garnettensis and Sphenacodon ferox , but not Edaphosaurus pogonias ". They first appear during
180-420: Is now southern Africa may have been the area of origin for burnetiamorphs. During the period Leucocephalus lived, what is considered the most extensive mass extinction in the history of the earth was occurring, which caused over 80% of the all Earth's species to go extinct. The cause of this end-Permian mass extinction is hypothesized to be climate change induced by volcanic CO 2 degassing which lead to
200-445: Is very similar to the sphenacodontid skull, differing only in the larger temporal fenestra (although these are still small relative to later therapsids), slightly backward-sloping occiput (the reverse of the pelycosaur condition), reduced number of teeth, and single large canine teeth in both upper and lower jaws, and other features (Carroll 1988 pp. 370, Benton 2000 p. 114). In later specialised Biarmosuchia, these resemble
220-558: Is visible in palatal view. The maxilla comprises the majority of the snout and is also larger than usual. Leucocephalus also has a more random arrangement of polygonal raised surfaces and irregular trenches on maxilla than what is observed in other burnetiamorphs. This is hypothesized to be indicators of a thickened dermis or keratinized skin. Leucocephalus exhibits a sinuous intranarial process. Intranarial processes are common in mammal like therapsids, however they are usually straight in biarmosuchians. Biarmosuchia Biarmosuchia
SECTION 10
#1732798710309240-527: The Ezhovo locality, Ocher Faunal Assemblage , are actually the same species. Even if these taxa are shown to be distinct, Ivakhnenko's paper indicates that Eotitanosuchus and Biarmosuchus are very similar animals. Ivakhnenko also relocates the family Eotitanosuchidae to the order Titanosuchia, superorder Dinocephalia . Benton 2000 and 2004 gives the Biarmosuchia the rank of suborder. Biarmosuchians were rare components of their ecosystems; only one specimen
260-562: The Late Pennsylvanian ( Upper Carboniferous ) epoch. From the end of the Carboniferous to the end of the Permian , most of them remained large, with only some secondarily becoming small in size. Basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammals ). One might say that
280-644: The Leucocephalus skull discovered was unusually pale. The species epithet wewersi comes from the farm employee who found the skull, Klaus ‘Klaasie’ Wewers. Biarmosuchians are a group of some of the earliest therapsids , a group of synapsids including mammals and their ancestors. The skull of Leucocephalus was found in the Tropidostoma Assemblage Zone (Tropidostoma) of the Main Karoo Basin of South Africa. Only
300-402: The squamosals and parietals . In lateral view, a ridge like boss on the nasal extending exteriorly to the prefrontal is present. The snout is notably tall and the supraorbital region contains large triangular bosses. Amongst other members of the burnetiid family, Leucocephalus has some distinct features unique to its genus. This includes a longer and rounder than usual vomerine process which
320-583: The enlarged canines of the Gorgonopsia . The presence of larger jaw-closing muscles (and hence a stronger bite) is indicated by the flaring of the rear of the skull where these muscles were attached. Burnetiamorphs, which made up the majority of biarmosuchian diversity, were characterized by elaborate cranial ornamentation consisting of bumps and bosses. Some burnetiids have a thick domed skull reminiscent of dinocephalians and pachycephalosaur dinosaurs. The vertebrae are also sphenacodontid-like (but lack
340-578: The long neural spines that distinguish Dimetrodon and its kin), but the shoulder and pelvic girdles and the limbs indicate a much more advanced posture. The feet are more symmetrical, indicating that they faced forward throughout the stride, and the phalanges (fingers/toes) are reduced in length so that they are more like that of later synapsids (therapsids and mammals ) (Carroll 1988 pp. 370–1). Biarmosuchians ranged in size from relatively small species with skulls 10–15 cm in length to large species such as Biarmosuchus , which may have had
360-634: The most basal major lineage of therapsids. Biarmosuchia consists of a paraphyletic series of basal biarmosuchians that are fairly typical early therapsids, and the derived clade Burnetiamorpha, characterized by skulls ornamented by horns and bosses. Biarmosuchians were the last of the six major therapsid lineages to be recognized. The majority of biarmosuchians were once considered gorgonopsians. James Hopson and Herbert Richard Barghusen (1986 p. 88) tentatively united Biarmosuchidae and Ictidorhinidae (including Hipposauridae and Rubidginidae) as "Biarmosuchia", but were undecided as to whether they constituted
380-454: The skull was in the lowermost Tropidostoma Assemblage Zone. Based on previous dating of the surrounding strata, the Leucocephalus skull is estimated to be around 259 Ma. Other Late Permian therapsids have been collected from the same interval and vicinity including dicynodonts ( Pristerodon mackay , Tropidostoma dubium , Diictodon feliceps ), a gorgonopsian, and a pareiasaur. Based on discoveries of early therapsids and biarmosuchians, what
400-704: The sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record). The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front ( caniniform ) teeth; and the premaxillary teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets. The following taxonomy follows Fröbisch et al. (2011), Benson (2012) and Spinder (2016) unless otherwise noted. Class Synapsida Sphenacodontia in
#308691