Biarmosuchians are an extinct clade of non-mammalian synapsids from the

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 ...

. They are the most basal group of the

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 ...

s. All of them were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont "

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...

s" 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.

Characteristics

The biarmosuchian

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

is very similar to the sphenacodontid skull, differing only in the larger

temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...

(although these are still small relative to later therapsids), slightly backward-sloping

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...

(the reverse of the pelycosaur condition), reduced number of teeth, and single large

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened howeve ...

in both upper and lower jaws, and other features (Carroll 1988 pp. 370, Benton 2000 p. 114). In later specialised Biarmosuchia, these resemble the enlarged canines of the

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 ...

. 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 The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

are also sphenacodontid-like (but lack the long neural spines that distinguish '' Dimetrodon'' and its kin), but the

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...

and

pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The p ...

s and the limbs indicate a much more advanced posture. The feet are more symmetrical, indicating that they faced forward throughout the stride, and the

phalange The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

s (fingers/toes) are reduced in length so that they are more like that of later synapsids (therapsids and

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

) (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 a skull in length.

Distribution

Currently the most representative group of the Biarmosuchia, the Burnetiamorpha, comprise ten genera: '' Bullacephalus'', '' Burnetia'', ''

Lemurosaurus ''Lemurosaurus'' is a genus of extinct biarmosuchian therapsids from the Late Permian of South Africa. The generic epithet ''Lemursaurus'' is a mix of Latin, lemures “ghosts, spirits”, and Greek, sauros, “lizard”. ''Lemurosaurus'' is easi ...

'', '' Lobalopex'', ''

Lophorhinus ''Lophorhinus'' is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. The type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or sub ...

'', '' 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 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

of Zambia. Other Biarmosuchia include '' Biarmosuchus'' from Russia, '' Hipposaurus'', ''

Herpetoskylax ''Herpetoskylax'' is an extinct genus of biarmosuchians which existed 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 s ...

'', ''

Ictidorhinus ''Ictidorhinus'' is an extinct genus of biarmosuchian therapsids. Fossils have been found from the ''Dicynodon'' Assemblage Zone of the Beaufort Group in the Karoo Basin, South Africa and are of Late Permian age. It had a short snout and proport ...

'' and ''

Lycaenodon ''Lycaenodon'' is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. It is known from a single species, ''Lycaenodon longiceps'', which was named by South African paleontologist Robert Broom in 1925. Both are smal ...

'' from South Africa, and ''

Wantulignathus ''Wantulignathus'' is genus of biarmosuchian therapsid from the Madumabisa Mudstone Formation, Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central, Southern and East Africa, altho ...

'' from Zambia.

Classification

Biarmosuchians are typically considered 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.

Taxonomic history

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 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.Hopson, J.A. and H.R. Barghusen. 1986. "An analysis of therapsid relationships". In: ''The Ecology and Biology of Mammal-like reptiles'' (eds. by N. Hotton III, P.D. MacLean, J.J. Roth, & E.C. Roth) pp. 83-106. Washington, DC: Smithsonian Institution Press 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 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 Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinocephal ...

. Benton 2000 an
2004
gives the Biarmosuchia the rank of suborder.

Paleoecology

Biarmosuchians were rare components of their ecosystems; only one specimen 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 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 ...

and therocephalians, though they were generally not apex predators.

References

External links

Therapsida: Biarmosuchia
at Palaeos {{Taxonbar, from=Q855488 Fossil taxa described in 1989 Guadalupian first appearances Lopingian extinctions Animal suborders Taxa named by Denise Sigogneau‐Russell