''Burnetia'' is an extinct genus of
biarmosuchia
Biarmosuchia 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 " pel ...
n
therapsids in the family
Burnetiidae
Burnetiidae is an extinct family of biarmosuchian therapsids that lived in the Permian period whose fossils are found in South Africa, Zambia and Russia. It contains ''Bondoceras'', ''Bullacephalus'', ''Burnetia'', ''Mobaceras'', ''Niuksenitia'' ...
, from the
Late Permian
Late or LATE may refer to:
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* Tardy, or late, not being on time
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* ''Late'' (The 77s album), 2000
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of
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
. ''Burnetia'' is known so far from a single
holotype
A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
skull lacking the lower jaws described by South African paleontologist
Robert Broom
Robert Broom Fellow of the Royal Society, FRS FRSE (30 November 1866 6 April 1951) was a British- South African medical doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University ...
in 1923. Due to erosion and dorsoventral crushing, features of the skull are hard to interpret. Stutural lines are further distorted by the unusual shape of the skull roof, including many bosses and protuberances.
Description
When broadly looking at the skull, there are well-developed "cheeks", bosses and pits that resemble
Pareiasaur
Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Per ...
ians'. However, the small
temporal fossa
The temporal fossa is a fossa (shallow depression) on the side of the skull bounded by the temporal lines above, and the zygomatic arch below. Its floor is formed by the outer surfaces of four bones of the skull. The fossa is filled by the te ...
distinguishes it from the
Cotylosaur.
The overall shape resembles a triangle. In the nasals, there is a bulging expansion of bone. Unlike proburnetia's median nasal bridge being long, narrow and raised, ''Burnetia'' is splindle-shaped.
The median nasal boss is spindle-shaped. The snout is wide and blunt. The large preorbital pits on the lachrymal are significant.
Over the
orbit
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
there are notable ridges on the prefrontal and frontal. The supra-orbital ridges make the orbits face distally and posteriorly.
The suborbital eminence is subdivided into distinguished portions.
The small
pineal foramen
A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...
sits dorsally on a boss.
''Burnetia'' palate is similar to
Gorgonopsia
Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of Saber-toothed predator, sabre-toothed therapsids from the Middle Permian, Middle to the Upper Permian, roughly between 270 and 252 million years ago. ...
ns'. Anteriorly, the internal
nares have the lower
canines. The
maxilla
In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
is adjacent to the palatine, and posterior to the palatine is the long prevomer that meets the
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
. The palatine is tooth bearing, as well as the pterygoid that is just posterior to the palatine.
The
vomer
The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...
is held by the surrounding vomerine processes that form the
choana
The choanae (: choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the pharynx, in humans and other mammals (as well as crocodilians and most skinks). They ...
e's middle border.
Unlike the rest of burnetiamorphs, ''Burnetia'' interchoanal part of the vomer is not narrow.
The concave
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 lies over the occipital lobes of the ...
is tilted up, which is shown when it is aligned vertically, the snout faces downward.
The supraoccipital sits anterior to the paraoccipital. The size of the basioccipital is considered to be small. The majority of the occipital surface, posterior "horn", and posterior lateral margins are made from the squamosal.
The basisphenoid in ''Burnetia'' differs from Gorgonopsians'. In ''Burnetia'', their basisphenoid is round and shallow. In the middle of the basisphenoid, it is separated by a groove. Gorgonopsians' basisphenoid contrasts ''Burnetia'' by having a "single sharp median keel".
Discovery
Broom found ''Burnetia mirabilis'' in the Dicynodon Assemblage Zone near
Graaff-Reinet
Graaff-Reinet (; Xhosa: eRhafu) is a town in the Eastern Cape Province of South Africa. It is the oldest town in the province and the fourth oldest town in South Africa, after Cape Town, Stellenbosch, Simon's Town, Paarl and Swellendam. The to ...
, South Africa.
Broom concluded that ''Burnetia'' was related closest to the group of Gorgonopsians.
However, Broom made observations based on the skull when it was covered by matrix and no underlying bone was visible.
Lieuwe Boonstra removed this matrix and found that ''Burnetia'' and Gorgonopsians differed mainly by the thickening of dermal bones, bosses and their basisphenoids.
Paleoenvironment
Phylogenetic
In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analysis done by Ashley Kruger suggests that a likely origin for burnetiamorphs could be southern Africa. The base and oldest burnetiamorphs are found in South Africa.
Classification and related taxa
The family Burnetiidae came from the discovery of ''Burnetia'', but new discoveries led to the studies of burnetiamorphs.
Burnetiamorphs only have about two taxa that represent each genus. It was previously believed that the Burnetiidae clade only contained two taxa, ''Burnetia mirabilis'' and ''Proburnetia viatkensis'', but later ''Pachydectes'' and ''Bullacephalus'' were found to be included in the clade, as well.
It was unable to be confirmed if ''Pachydectes'' shared the feature of nasal the nasal supporting a middle boss like ''Burnetia''. However, like ''Burnetia'', above the postorbital bar they have a significant boss.
''Lycaenodon longiceps'' is in the clade Biarmosuchia and has some similarities to ''Burnetia''.
Both ''Lycaenodon'' and ''Burnetia'' likely had a large foramen, surrounded by the vomer and vomerine process. This foramen implies that in biarmosuchians, the vomeronasal organ may have communicated with the oral cavity. They also share the trait of having a long vomerine process.
The first burnetiid therapsid found in Tanzania's
Usili Formation was found to most resemble ''Burnetia''. The Usili burnetiid and ''Burnetia'' both had bosses above their orbits that were "S"-like.
References
Burnetiamorpha
Prehistoric therapsid genera
Lopingian synapsids of Africa
Fossil taxa described in 1923
Taxa named by Robert Broom
Lopingian genus first appearances
Lopingian genus extinctions
{{Paleo-therapsid-stub