Pachydectes Temporal range: Middle Permian, | |
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Pachydectes (above) and other burnetiamorphs | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Synapsida |
Clade: | Therapsida |
Suborder: | † Biarmosuchia |
Family: | † Burnetiidae |
Genus: | † Pachydectes Rubidge et al., 2006 |
Species: | †P. elsi |
Binomial name | |
†Pachydectes elsi Rubidge et al., 2006 | |
Pachydectes is an extinct genus of biarmosuchian therapsids from the Middle Permian of South Africa known from a single skull. [1] The etymology of the name Pachydectes is derived from the Greek word pakhus, meaning "thick" or "thickened", and dektes, meaning "biter". In conjunction this name is representative of the unique pachyostotic bone present above the maxillary canine tooth found in the skull of the specimen. [1] There is only one known species within the genus, Pachydectes elsi which is named in honor of the person who discovered the fossil.
The holotype and only known specimen was found just above the Ecca-Beaufort contact in the eastern Karoo basin, which was a fluvial depositional environment. [2] [3] As a member of the clade Biarmosuchia, Pachydectes retains many basal therapsid features, though with unique specializations one of which is the presence of adornments on the skull with horn-like protuberances. [1] Also as a member of this clade Pachydectes is thought to be carnivorous.
Pachydectes was initially discovered in 1997 during road construction being collected from just above the Ecca-Beaufort boundary in the Jansenville District of the Eastern Cape Province of South Africa, taking the form of a skull though missing the dentary. [1] The initial description of the taxon by Rudbride and Sidor based on the large maxillary caniniform teeth, a preparietal, and traces of large bosses on the skull roof took place in 2006. [1] Initially, using cladistic analysis and stratigraphic distribution Pachydectes was thought to be the sister taxon of Bullacephalus with the two collectively comprising the clade Burnetiidae. [1] With the discovery of new members of the clade by Day in 2016 and 2018, Day concluded that Pachydectes and Bullacephalus formed a different clade which they called Bullacephalidae which diverged before Burnetiamorpha entirely. [4] Subsequently Kammerer and Sidor have composed a reanalysis of the relationships between Burnetiamorphs with the discovery of Mobaceras zambeziense showing similarities to the Bullacephalus providing further evidence that Pachydectes is in fact a member of the clade Burnetiid as proposed originally. [5]
The preserved specimen is a laterally compressed skull with no lower jaw measuring 310 mm in length. [1] Pachydectes still has a great deal of ancestral therapsid traits including the convex nature of the skull roof with a deep snout as well as a wide temporal roof. Due to the extensive weathering and lateral compression, the premaxilla and septomaxilla are difficult to decipher information from; however, the portions of the skull of the surrounding area do not differ greatly. The maxilla supports a large boss with an elongate bulbous dorsal extension. There are no pre-canine maxillary teeth consistent with primitive therapsids. Pachydectes supports a knoblike thickening just below the postorbital similarly to other burnetiamorphs with a thickened boss present just above the postorbital bar, where the postorbital contacts the postfrontal. [5] Distinct tear drop shaped boss posterior to the pineal foramen ending in a pointed tip. [6] The distinguishing trait is a conspicuous pachyostotic maxillary boss that sheathes the root of the upper canine. [1]
The primary traits that have discernible ecological significance are the large caniniform teeth present on the maxilla and the previously mentioned series of large bosses and protuberance on the skull roof. [1] Pachyostosis is common both for protecting the brain during sexual displays in the case of head-butting or other forms of combat for reproductive success. [7] Conspicuous ornamentation with skull bosses, such as in Pachydectes, can be used as sexual display structures in a different capacity. Rather than combat, these "display structures" taking the form of cranial bosses can be a tool in intraspecific competition for mates. [7]
The other trait, caniniform teeth, are a key indicator that Pachydectes was carnivorous. [1] This is because of the advantage that this form of teeth have to tear through flesh rather than having a grinding surface as would be expected in an herbivore. This is contrasted with the weathering and erosion of the fossilized specimen leading to a lack of clarity in the attachment of the jaw adductor musculature which prevents from complete understanding of the closure mechanism. [1]
It is difficult to place the geographic distribution of Pachydectes as only one specimen has ever been discovered however, being that the skull was found in the Karoo Basin in South Africa, Pachydectes was at the very least found in southern Gondwana. The soil composition of shales and mudstones appears to imply a fluvial environment. [8] [9] Based on reconstructive models of the positioning of the continents at the time he latitudinal position of the current Karoo Basin is consistent with it being in a more temperate region. [10] It is thought that a series of meandering rivers and or large river deltas could be responsible for the deposition and transfer of nutrients and moisture inland creating a variety of rich habitats resulting in the tremendous diversity in the region. Pachydectes may have lived in this paleoenvironment, potentially preying upon smaller vertebrates and using its pachyostotic bosses to signal to other members of its species.
Similarly to the geographic distribution, the stratigraphic range is difficult to determine as there is one known location that the species has been found that being just above the Ecca-Beaufort contact in the eastern Karoo basin. This means that the stratigraphic distribution is partially determined with the use of a strict consensus tree of therapsids. Being specifically from the Beaufort group means that the Pachydectes was present solely during the Guadalupian, specifically during the Wordian and Capitanian without being found anywhere else. [1]
Pachydectes is a genus in the family Burnetiidae as well as a sub clade Burnetiinae. The family Burnettidae falls into the suborder Burnetiamorph which was initially described in 1923 by Broom and is from the Middle Permian exclusively. The sister taxa of Pachydectes are Bullacephalus , Mobaceras , Burnetia , and Niuksenitia all of which are in a polytomy and are part of the clade Burnetiinae which diverged from Proburnetiinae, both of which form Burnetiidae. [5]
Burnetiamorpha |
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This cladogram is based on the phylogeny described in Kammerer 2021 in which the most recent analysis of Burnetiamoph relationships has come to the conclusion of the figure above. [5]
Robertia is an extinct genus of small herbivorous dicynodonts from the Middle to Late Permian of South Africa, between 260 and 265 million years ago. It is a monospecific genus, consisting of the type-species R. broomiana, which was classified by Lieuwe Dirk Boonstra in 1948 and named in honor of Robert Broom for his study of South African mammal-like reptiles.
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 "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.
Dinogorgon is a genus of gorgonopsid from the Late Permian of South Africa and Tanzania. The generic name Dinogorgon is derived from Greek, meaning "terrible gorgon", while its species name rubidgei is taken from the surname of renowned Karoo paleontologist, Professor Bruce Rubidge, who has contributed to much of the research conducted on therapsids of the Karoo Basin. The type species of the genus is D. rubidgei.
Anteosaurus is an extinct genus of large carnivorous dinocephalian synapsid. It lived at the end of the Guadalupian during the Capitanian stage, about 265 to 260 million years ago in what is now South Africa. It is mainly known by cranial remains and few postcranial bones. Measuring 5–6 m (16–20 ft) long and weighing about 600 kg (1,300 lb), Anteosaurus was the largest known carnivorous non-mammalian synapsid and the largest terrestrial predator of the Permian period. Occupying the top of the food chain in the Middle Permian, its skull, jaws and teeth show adaptations to capture large prey like the giants titanosuchids and tapinocephalids dinocephalians and large pareiasaurs.
Tapinocaninus is an extinct genus of therapsids in the family Tapinocephalidae, of which it is the most basal member. Only one species is known, Tapinocaninus pamelae. The species is named in honor of Rubidge's mother, Pam. Fossils have been found dating from the Middle Permian.
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 easily identifiable by its prominent eye crests, and large eyes. The name Lemurosaurus pricei was coined by paleontologist Robert Broom in 1949, based on a single small crushed skull, measured at approximately 86 millimeters in length, found on the Dorsfontein farm in Graaff-Reinet. To date, only two skulls of the Lemurosaurus have been discovered, so body size is unknown. The second larger, more intact, skull was found in 1974 by a team from the National Museum, Bloemfontein.
Styracocephalus platyrhynchus (Greek for "spiked-head") is an extinct genus of dinocephalian therapsid that existed during the mid-Permian throughout South Africa, but mainly in the Karoo Basin. It is often referred to by its single known species Styracocephalus platyrhynchus. The Dinocephalia clade consisted of the largest land vertebrates and herbivores during the early to mid-Permian. This period is often also referred to as the Guadalupian epoch, approximately 270 to 260 million years ago.
Paraburnetia is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. It is known for its species P. sneeubergensis and belongs to the family Burnetiidae. Paraburnetia lived just before the Permian–Triassic mass extinction event.
Lobalopex is an extinct genus of biarmosuchian therapsids. It was alive during the Late Permian and has only been found in the Teekloof Formation in South Africa. The only known species of the genus is Lobalopex mordax. Lobalopex is part of the clade of Burnetiamorpha, which have fossil specimens located in multiple areas of Africa and Russia.
Angonisaurus is an extinct genus of kannemeyeriiform dicynodont from the Middle Triassic of Africa between 247 and 242 million years ago. Only one species, Angonisaurus cruickshanki has been assigned to this genus. This genus is thought to have been widely spread but rare in southern Gondwana. Though few in number, the fossil record of Angonisaurus cruickshanki contains multiple specimens giving it a measurable stratigraphic range. Sexually dimorphic features are found in Angonisaurus which include presence or absence of tusks and difference is size and robustness of the temporal arch and the rostral.
Bullacephalus is an extinct genus of biarmosuchian therapsids belonging to the family Burnetiidae. The type species B. jacksoni was named in 2003. It is known from a relatively complete skull and lower jaw, discovered in the Late Permian Tapinocephalus Assemblage Zone of the Beaufort Group of South Africa. This genus of therapsida lived during the Late Permian period, approximately 250 million years ago. The name Bullacephalus comes from the Latin words "bullatus," meaning "bossed" or "knobbed," and "cephalus," meaning "head." This name refers to the distinctive bony knob on the top of the therapsid's skull, which contributes to the history of this genus. This stem based taxon includes Ictidorhinus or Hippasaurs. Bullacephalus can even be characterized as having a, “skull moderately to greatly pachyostotic; swollen boss present above the postorbital bar formed by the postfrontal and postorbital; deep linear sculpturing of the snout; exclusion of the jugal from the lateral temporal fenestra”. These Therapsids have spongy bone skull roof, palatal process of premaxilla are long, diverticulum of naris adding them to the Burnetiamorph. Furthermore, the discovery of Bullacephalus has helped to refine the taxonomic classification of therapsids. Prior to its discovery, there was uncertainty regarding the relationship between different groups of therapsids, particularly the Burnetiamorpha and the Biarmosuchia. However, the distinctive features of Bullacephalus suggest that it is a member of the Burnetiamorpha, and provides a bridge between this group and the Biarmosuchia. The discovery of Bullacephalus has also highlighted the importance of continued exploration and excavation in areas that have yielded few therapsid fossils. The Beaufort Group of South Africa, where Bullacephalus was discovered, has been an important site for therapsid fossils, but much of the area remains unexplored. Further discoveries in this region and other areas around the world may provide new insights into the evolution and diversification of therapsids, as well as other groups of extinct animals. These discoveries will also help to refine our understanding of the history of life on Earth and the processes that have shaped the diversity of organisms that exist today.
Biseridens is an extinct genus of anomodont therapsid, and one of the most basal anomodont genera known. Originally known from a partial skull misidentified as an eotitanosuchian in 1997, another well-preserved skull was found in the Qingtoushan Formation in the Qilian Mountains of Gansu, China, in 2009 that clarified its relationships to anomodonts, such as the dicynodonts.
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 small-bodied biarmosuchians. Two specimens are known, and both preserve only the front portions of the skull. These specimens come from the Cistecephalus Assemblage Zone of the Karoo Basin. Broom attributed the back portion of a third skull to Lycaenodon, but subsequent examiners considered it to belong to a gorgonopsian or dinocephalian and not a biarmosuchian. Most of the distinguishing features of Lycaenodon come from its palate. As a member of Biarmosuchia, the most basal group of therapsids, Lycaenodon shares many features with earlier and less mammal-like synapsids like Dimetrodon.
Scymnosaurus is a dubious genus of therocephalian therapsids based upon various fossils of large early therocephalians. The genus was described by Robert Broom in 1903 with S. ferox, followed by S. watsoni in 1915 and a third, S. major, by Lieuwe Dirk Boonstra in 1954. Each of these species are considered nomen dubia today and based upon specimens belonging to two separate families of therocephalians. S. ferox and S. major represent specimens of Lycosuchidae incertae sedis, while S. watsoni is Scylacosauridae incertae sedis. Broom named a fourth species in 1907 from KwaZulu-Natal, S. warreni, though he later referred it to Moschorhinus as a valid species in 1932 but now is recognised as being synonymous with M. kitchingi.
Herpetoskylax is an extinct genus of biarmosuchians which existed in South Africa. The type species is Herpetoskylax hopsoni. It lived in the Late Permian Period.
Anomocephaloidea is a clade of basal anomodont therapsids related to the dicynodonts known from what is now South Africa and Brazil during the Middle Permian. It includes only two species, Anomocephalus africanus from the Karoo Basin of South Africa and Tiarajudens eccentricus from the Paraná Basin of Brazil. Anomocephaloidea was named in 2011 with the discovery of Tiarajudens, although Anomocephalus itself has been known since 1999.
Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.
Thliptosaurus is an extinct genus of small kingoriid dicynodont from the latest Permian period of the Karoo Basin in KwaZulu-Natal, South Africa. It contains the type and only known species T. imperforatus. Thliptosaurus is from the upper Daptocephalus Assemblage Zone, making it one of the youngest Permian dicynodonts known, living just prior to the Permian mass extinction. It also represents one of the few small bodied dicynodonts to exist at this time, when most other dicynodonts had large body sizes and many small dicynodonts had gone extinct. The unexpected discovery of Thliptosaurus in a region of the Karoo outside of the historically sampled localities suggests that it may have been part of an endemic local fauna not found in these historic sites. Such under-sampled localities may contain 'hidden diversities' of Permian faunas that are unknown from traditional samples. Thliptosaurus is also unusual for dicynodonts as it lacks a pineal foramen, suggesting that it played a much less important role in thermoregulation than it did for other dicynodonts.
Ufudocyclops is an extinct genus of stahleckeriid dicynodont from the Middle Triassic of South Africa. It was found in the Burgersdorp Formation, part of the uppermost Cynognathus Assemblage Zone of the Beaufort Group in the Karoo Basin. The type and only known species is U. mukanelai. It was a large, beaked herbivore like other Triassic dicynodonts, lacking tusks, and is mostly characterised by unique features of the skull. It is known from three specimens, two of which were previously referred to the Tanzanian dicynodont Angonisaurus. The separation of Ufudocyclops from Angonisaurus indicates that the Middle Triassic fauna of the Beaufort Group in South Africa was not part of a larger shared fauna with those of the Manda Beds in Tanzania, as was previously supposed, and suggests that they were separated as more localised faunas, possibly by geographic barriers or in time. Ufudocyclops then would have been a unique part of the uppermost Cynognathus Assemblage Zone in South Africa. It is also the oldest known member of the family Stahleckeriidae, and implies that the family was already diversifying in the Middle Triassic alongside other kannemeyeriiforms, not just in the Late Triassic after other families died out.
Phorcys is an extinct genus of gorgonopsian that lived during the Middle Permian period (Guadalupian) of what is now South Africa. It is known from two specimens, both portions from the back of the skull, that were described and named in 2022 as a new genus and species P. dubei by Christian Kammerer and Bruce Rubidge. The generic name is from Phorcys of Greek mythology, the father of the Gorgons from which the gorgonopsians are named after, and refers to its status as one of the oldest representatives of the group in the fossil record. Phorcys was recovered from the lowest strata of the Tapinocephalus Assemblage Zone (AZ) of the Beaufort Group, making it one of the oldest known gorgonopsians in the fossil record—second only to fragmentary remains of an indeterminate gorgonopsian from the older underlying Eodicynodon Assemblage Zone.
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