Tropidostoma

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Tropidostoma
Temporal range: Late Permian, Lopingian
~260–258  Ma
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Tropidostoma.png
Tropidostoma dubium (SAM-PK-K11238) in (A) dorsal, (D) ventral, (G) right lateral, and (J) anterior views. Bulbasaurus phylloxyron (CGP/1/938) in (B) dorsal, (E) ventral, (H) right lateral, and (K) anterior views. Specimen has suffered some lateral compression. Scale bars equal 5 cm.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Suborder: Anomodontia
Clade: Dicynodontia
Family: Oudenodontidae
Genus: Tropidostoma
Owen, 1876
Species:
T. dunnii
Binomial name
Tropidostoma dunnii
Seeley, 1876
Synonyms
  • Tropidostoma microtrema
  • Tropidostoma dubium

Tropidostoma is a medium-sized herbivorous oudenodontid dicynodont therapsid that lived during the Late Permian (Lopingian) period in South Africa. The first Tropidostoma fossil was described by Harry Govier Seeley in 1889. Later two subspecies were identified. Tropidostoma fossils are an index fossil in a biozone of the Karoo Basin known as the Tropidostoma Assemblage Zone. This biozone is characterized by the presence of this species in association with another dicynodont species, Endothiodon uniseries . [1]

Contents

History of discovery

The first Tropidostoma fossil material was found during a field expedition in the Upper Permian-aged Teekloof Formation of the Beaufort Group. This material was later described by Seeley (1889) in a study in which he described two fossils which had been named Dicynodon microtrema and Tropidostoma dunni. In 1915, several years after Seeley's death, the paleontologist, Robert Broom, reexamined the same material and discovered that the fossil material in question was of the same species. This new single species was renamed Tropidostoma microtrema. [2] Some years later, the name T. microtrema was changed to Tropidostoma dubium, and Tropidostoma dunni is now considered to be the type species. [3] [4] [5] [6]

Description

Two subspecies exist among the specimens referred to as Tropidostoma dubium and Tropidostoma dunni . T. dubium is observed to have two cranial morphs, one being robust form with a tall snout and large tusks and the other more gracile with a low snout and small or no tusks. The robust and gracile forms are considered to either represent sexual dimorphism or individual variation. [7]

Classification

Tropidostoma is currently classified as an oudenodontid within the larger dicynodont clade Bidentalia. This clade is characterized collectively by their reduced dentition with only their maxillary tusks being intact. However, many species in this clade sporadically lack tusks completely and their fossils only hold evidence that they retained their keratinous beaks. Many Tropidostoma fossils previously collected have been misidentified as other species, such as of Oudenodon bainii due to their remarkable similarity. In addition, the type fossil of the recently discovered Bulbasaurus phylloxyron was misidentified as a Tropidostoma fossil for several years. [8] [9]

See also

Related Research Articles

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<i>Emydops</i> Extinct genus of dicynodonts

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<i>Dinogorgon</i> Extinct genus of therapsids

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.

<i>Tapinocephalus</i> Assemblage Zone

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<i>Cistecephalus</i> Assemblage Zone

The Cistecephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important geological group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the Teekloof Formation north-west of Beaufort West in the Western Cape, in the upper Middleton and lower Balfour Formations respectively from Colesberg of the Northern Cape to east of Graaff-Reinet in the Eastern Cape. The Cistecephalus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Late Permian in age.

<i>Daptocephalus</i> Assemblage Zone

The Daptocephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the upper Teekloof Formation west of 24°E, the majority of the Balfour Formation east of 24°E, and the Normandien Formation in the north. It has numerous localities which are spread out from Colesberg in the Northern Cape, Graaff-Reniet to Mthatha in the Eastern Cape, and from Bloemfontein to Harrismith in the Free State. The Daptocephalus Assemblage Zone is one of eight biozones found in the Beaufort Group and is considered Late Permian (Lopingian) in age. Its contact with the overlying Lystrosaurus Assemblage Zone marks the Permian-Triassic boundary.

<i>Lystrosaurus</i> Assemblage Zone

The Lystrosaurus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the upper Adelaide and lower Tarkastad Subgroups of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. This biozone has outcrops in the south central Eastern Cape and in the southern and northeastern Free State. The Lystrosaurus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Early Triassic in age.

<i>Cynognathus</i> Assemblage Zone Biozone which correlates to the Burgersdorp Formation of the Beaufort Group

The Cynognathus Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The Cynognathus Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age. The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid which occurs throughout the entire biozone.

<i>Pristerognathus</i> Assemblage Zone

The Pristerognathus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the upper Abrahamskraal Formation and lowermost Teekloof Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching not more than 300 metres (980 ft), occur just east of Sutherland through to Beaufort West in the south and Victoria West in the north. Exposures are also found west of Colesberg and south of Graaff-Reinet. The Pristerognathus Assemblage Zone is the third biozone of the Beaufort Group.

<i>Tropidostoma</i> Assemblage Zone

The Tropidostoma Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the lower Teekloof Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching approximately 240 metres (790 ft), occur from east of Sutherland through to Beaufort West and Victoria West, to areas south of Graaff-Reinet. Its northernmost exposures occur west/north-west of Colesberg. The Tropidostoma Assemblage Zone is the fourth biozone of the Beaufort Group.

<i>Eodicynodon</i> Assemblage Zone

The Eodicynodon Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching approximately 620 metres (2,030 ft), occur south-east of Sutherland, north of Prince Albert, and south-east of Beaufort West. The Eodicynodon Assemblage Zone is the lowermost biozone of the Beaufort Group.

<i>Paraburnetia</i> Extinct genus of therapsids

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.

Cynosaurus is an extinct genus of cynodonts. Remains have been found from the Dicynodon Assemblage Zone in South Africa. Cynosaurus was first described by Richard Owen in 1876 as Cynosuchus suppostus. Cynosaurus has been found in the late Permian period. Cyno- is derived from the Greek word kyon for dog and –sauros in Greek meaning lizard.

<i>Oudenodon</i> Extinct genus of dicynodonts

Oudenodon is an extinct genus of dicynodont. It was common throughout southern Africa during the Late Permian. Several species of Oudenodon are known. Both O. bainii, the type species, and O. grandis are known from South Africa. Specimens of O. luangwensis have been found from Zambia. One species, O. sakamenensis, is the only Permian therapsid yet described from Madagascar. It is the type genus of the family Oudenodontidae, which includes members such as Tropidostoma.

<i>Aulacephalodon</i> Extinct genus of dicynodonts

Aulacephalodon is an extinct genus of medium-sized dicynodonts, or non-mammalian synapsids, that lived during late Permian period. Individuals of Aulacephalodon are commonly found in the Lower Beaufort Group of the Karoo Supergroup of South Africa. Rising to dominance during the Late Permian, Aulacephalodon was among the largest terrestrial vertebrate herbivores until its extinction at the end of the Permian. Two species have been named, the type species, A. bainii, and a second species, A. peavoti. However, debate exists among paleontologists if A. peavoti is a true member of the genus Aulacephalodon. Aulacephalodon belongs to the family Geikiidae, a family of dicynodonts generally characterized by their short, broad skulls and large nasal bosses. Sexual dimorphism has been identified in A. bainii.

<span class="mw-page-title-main">Abrahamskraal Formation</span> Geological formation of the Beaufort Group in South Africa

The Abrahamskraal Formation is a geological formation and is found in numerous localities in the Northern Cape, Western Cape, and the Eastern Cape of South Africa. It is the lowermost formation of the Adelaide Subgroup of the Beaufort Group, a major geological group that forms part of the greater Karoo Supergroup. It represents the first fully terrestrial geological deposits of the Karoo Basin. Outcrops of the Abrahamskraal Formation are found from the small town Middelpos in its westernmost localities, then around Sutherland, the Moordenaarskaroo north of Laingsburg, Williston, Fraserburg, Leeu-Gamka, Loxton, and Victoria West in the Western Cape and Northern Cape. In the Eastern Cape outcrops are known from Rietbron, north of Klipplaat and Grahamstown, and also southwest of East London.

<i>Bulbasaurus</i> Extinct genus of dicynodonts

Bulbasaurus is an extinct genus of dicynodont that is known from the Lopingian epoch of the Late Permian period of what is now South Africa, containing the type and only species B. phylloxyron. It was formerly considered as belonging to Tropidostoma; however, due to numerous differences from Tropidostoma in terms of skull morphology and size, it has been reclassified the earliest known member of the family Geikiidae, and the only member of the group known from the Tropidostoma Assemblage Zone. Within the Geikiidae, it has been placed close to Aulacocephalodon, although a more basal position is not implausible.

<i>Abdalodon</i> Extinct genus of cynodonts

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.

<span class="mw-page-title-main">Teekloof Formation</span> Late Permian geological formation that forms part of the Beaufort Group of South Africa

The Teekloof Formation is a geological formation that forms part of the Beaufort Group, one of the five geological groups that comprises the Karoo Supergroup in South Africa. The Teekloof Formation is the uppermost formation of Adelaide Subgroup deposits West of 24ºE and contains Middle to Late Permian-aged deposits and four biozones of the Beaufort Group. It overlies the Abrahamskraal Formation. The Teekloof Formation does not underlie other units other than the younger Karoo dolerites and sills that relate to the emplacement of the Early Jurassic Drakensberg Group to the east. Outcrops and exposures of the Teekloof Formation range from Sutherland through the mountain escarpments between Fraserburg and Beaufort West. The northernmost localities of the Teekloof Formation are found by Loxton, Victoria West and Richmond.

<i>Thliptosaurus</i> Extinct genus of dicynodonts

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.

References

  1. Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
  2. Broom, R., 1915. On the anomodont genera, Pristerodon and Tropidostoma. In Proceedings of the Zoological Society of London (Vol. 1915, pp. 355-361).
  3. Keyser, A. W. (1973). "A RE-EVALUATION OF THE GENUS TROPIDOSTOMA SEELEY". Palaeontologia Africana. ISSN   0078-8554.
  4. Keyser, A. W., & Smith, R. M. H. (1978). Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin. Geological Survey, Department of Mineral And Energy Affairs, Republic of South Africa.
  5. Keyser, A.W., 1981. The stratigraphic distribution of the Dicynodontia of Africa reviewed in a Gondwana context. Gondwana five, pp.61-63.
  6. Botha, J.; Angielczyk, K. D. (2007-09-01). "An Integrative Approach to Distinguishing the Late Permian Dicynodont Species Oudenodon Bainii and Tropidostoma Microtrema (therapsida: Anomodontia)". Palaeontology. 50 (5): 1175–1209. Bibcode:2007Palgy..50.1175B. doi: 10.1111/j.1475-4983.2007.00697.x . ISSN   1475-4983.
  7. Smith, Roger M. H.; Kammerer, Christian F. (2017-01-31). "An early geikiid dicynodont from the Tropidostoma Assemblage Zone (late Permian) of South Africa". PeerJ. 5: e2913. doi: 10.7717/peerj.2913 . ISSN   2167-8359. PMC   5289114 . PMID   28168104.
  8. Abdala, F.; Botha-Brink, J. (2008-04-01). "A new cynodont record from the Tropidostoma Assemblage Zone of the Beaufort Group: implications for the early evolution of cynodonts in South Africa". Palaeontologia Africana. ISSN   0078-8554.
  9. van der Walt, Merrill; Day, Michael; Rubidge, Bruce; Cooper, Antony; Netterberg, Inge (2010-12-31). "A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa". Palaeontologia Africana. 45: 1–6.