| Biarmosuchia | |
|---|---|
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| Mounted skeleton ofBiarmosuchus tener | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Biarmosuchia Sigogneau-Russell,1989 |
| Subgroups | |
Biarmosuchia is an extinct clade of non-mammaliansynapsids from thePermian. Biarmosuchians are the most basal group of thetherapsids. They were moderately-sized, lightly built carnivores, intermediate in form between basalsphenacodont "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 biarmosuchianskull is very similar to the sphenacodontid skull, differing only in the largertemporal fenestra (although these are still small relative to later therapsids), slightly backward-slopingocciput (the reverse of the pelycosaur condition), reduced number of teeth, and single largecanine teeth 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 theGorgonopsia. 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.[1] Some burnetiids have a thick domed skull reminiscent ofdinocephalians andpachycephalosaur dinosaurs.[2]
Thevertebrae are also sphenacodontid-like (but lack the long neural spines that distinguishDimetrodon and its kin), but theshoulder andpelvic girdles and the limbs indicate a much more advanced posture. The feet are more symmetrical, indicating that they faced forward throughout the stride, and thephalanges (fingers/toes) are reduced in length so that they are more like that of latersynapsids (therapsids andmammals) (Carroll 1988 pp. 370–1).
Biarmosuchians ranged in size from relatively small species with skulls 10–15 cm in length to large species such asBiarmosuchus, which may have had a skull 60 centimetres (24 in) in length.[2]
Currently the most representative group of the Biarmosuchia, the Burnetiamorpha, comprise ten genera:Bullacephalus,Burnetia,Lemurosaurus,Lobalopex,Lophorhinus,Paraburnetia, andPachydectes from South Africa,Niuksenitia andProburnetia from Russia, andLende (MAL 290) from Malawi.[3] In addition, Sidoret al. (2010)[4] 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 Sidoret al. (2014)[5] noted the presence of a burnetiid in the middlePermian of Zambia. Other Biarmosuchia includeBiarmosuchus from Russia,Hipposaurus,Herpetoskylax,Ictidorhinus andLycaenodon from South Africa, andWantulignathus from Zambia.[1]
| Phylogeny of Biarmosuchia from Dayet al., 2018[6] |
Biarmosuchians are typically considered the most basal major lineage of therapsids.[2] 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.[2] The majority of biarmosuchians were once considered gorgonopsians. James Hopson and Herbert Richard Barghusen (1986 p. 88) tentatively unitedBiarmosuchidae andIctidorhinidae (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 thatPhthinosuchus was too poorly known to tell if it also belonged, but consideredEotitanosuchus a more advanced form.[7]
Denise Sigogneau-Russell (1989) erected the infraorder Biarmosuchia to include the families Biarmosuchidae, Hipposauridae and Ictidorhinidae, distinct from Eotitanosuchia and Phthinosuchia.
Ivakhnenko (1999) argued thatBiarmosuchus tener,Eotitanosuchus olsoni, andIvantosaurus ensifer, all known from theEzhovo locality,Ocher Faunal Assemblage, are actually the same species. Even if these taxa are shown to be distinct, Ivakhnenko's paper indicates thatEotitanosuchus andBiarmosuchus are very similar animals. Ivakhnenko also relocates the family Eotitanosuchidae to the order Titanosuchia, superorderDinocephalia.
Benton 2000 and 2004[8] gives the Biarmosuchia the rank of suborder.
Biarmosuchians were rare components of their ecosystems; only one specimen is known for most species.[2] However, they were moderately diverse and there were multiple contemporary species in some ecosystems.[9] All were predators similar togorgonopsians andtherocephalians, though they were generally not apex predators.
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