View source for Tropidostoma

{{Short description|Extinct genus of dicynodonts}}
{{Speciesbox
|fossil_range=[[Late Permian]], [[Lopingian]]<br />~{{fossil range|260|258}}
|image=Tropidostoma.png
|image_caption=''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.
|parent_authority=Owen, 1876
|genus=Tropidostoma
|species=dubium
|authority=Seeley, [[1876 in paleontology|1876]]
|synonyms=
*''Cteniosaurus platyceps''
*''Dicynodon acutirostris''
*''Dicynodon cavifrons''
*''Dicynodon dunnii''
*''Dicynodon rogersi''
*''Dicynodon validus''
*''Tropidostoma microtrema''
|synonyms_ref=
}}
'''''Tropidostoma''''' is a medium-sized [[Herbivore|herbivorous]] oudenodontid [[dicynodont]] [[therapsid]] that lived during the Late [[Permian]] ([[Lopingian]]) period in [[South Africa]]. The first ''Tropidostoma'' fossil was described by [[Harry Seeley|Harry Govier Seeley]] in 1889. Later two [[subspecies]] were identified. ''Tropidostoma'' [[fossil]]s are an [[List of index fossils|index fossil]] in a [[biozone]] of the [[Karoo Supergroup|Karoo Basin]] known as the [[Tropidostoma Assemblage Zone|''Tropidostoma'' Assemblage Zone]]. This [[biozone]] is characterized by the presence of this species in association with another [[dicynodont]] species, ''[[Endothiodon|Endothiodon uniseries]]''.<ref>{{cite book|last1=Smith|first1=R.M.H.|last2=Keyser|first2=A.W.|chapter=Biostratigraphy of the ''Tropidostoma'' Assemblage Zone|editor-last=Rubidge|editor-first=B.S.|title=Biostratigraphy of the Beaufort Group (Karoo Supergroup)|series=South African Committee for Stratigraphy Biostratigraphic Series|volume=1|publisher=Council for Geoscience|location=Pretoria|pages=18-22}}</ref><ref>{{cite journal|last1=Day|first1=M.O.|last2=Smith|first2=R.M.H.|year=2020|title=Biostatigraphy of the ''Endothiodon'' Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa|journal=South African Journal of Geology|volume=123|issue=2|pages=165-180|doi=10.25131/sajg.123.0011|url=https://pubs.geoscienceworld.org/gssa/sajg/article/123/2/165/587460/Biostratigraphy-of-the-Endothiodon-Assemblage-Zone}}</ref>
==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 [[Harry Seeley|Seeley]] (1889) in a study in which he described two [[fossil]]s which had been named ''Dicynodon microtrema'' and ''Tropidostoma dunni''. In 1915, several years after [[Harry Seeley|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''.<ref>{{cite journal|last=Broom|first=Robert|year=1915|title=On the anomodont genera, ''Pristerodon'' and ''Tropidostoma''|journal=Proceedings of the Zoological Society of London|volume=1915|pages=355-361|url=https://www.biodiversitylibrary.org/page/31547348#page/99/mode/1up}}</ref> Some years later, the name ''T. microtrema'' was changed to ''Tropidostoma dubium'', and ''Tropidostoma dunni'' is now considered to be the type species.<ref>{{Cite journal|last=Keyser|first=A. W.|date=1973|title=A RE-EVALUATION OF THE GENUS TROPIDOSTOMA SEELEY|journal=Palaeontologia Africana |url=http://wiredspace.wits.ac.za/handle/10539/16045|language=en|issn=0078-8554}}</ref><ref>{{cite journal|last1=Keyser|first1=A.W.|last2=Smith|first2=R.M.H.|year=1978|title=Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin|journal=Annals of the Geological Survey of South Africa|volume=12|pages=1-36}}</ref><ref>{{cite book|last=Keyser|first=A.W.|year=1981|chapter=The stratigraphic distribution of the Dicynodontia of Africa reviewed in a Gondwana context|editor-last1=Creswell|editor-first1=M.M.|editor-last2=Vella|editor-first2=P.|title=Gondwana five|pages=61-63|publisher=A.A. Balkema|location=Rotterdam}}</ref><ref name="BA07">{{Cite journal|last1=Botha|first1=J.|last2=Angielczyk|first2=K. D.|date=2007-09-01|title=An Integrative Approach to Distinguishing the Late Permian Dicynodont Species Oudenodon Bainii and Tropidostoma Microtrema (therapsida: Anomodontia)|journal=Palaeontology|language=en|volume=50|issue=5|pages=1175–1209|doi=10.1111/j.1475-4983.2007.00697.x|bibcode=2007Palgy..50.1175B |issn=1475-4983|doi-access=free}}</ref>
==Description==
Two [[subspecies]] exist among the specimens referred to as ''Tropidostoma dubium'' and ''Tropidostoma dunni'' . ''T. dubium'' is observed to have two [[Skull|cranial]] morphs, one being robust form with a tall snout and large [[tusk]]s 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.<ref>{{Cite journal|last1=Smith|first1=Roger M. H.|last2=Kammerer|first2=Christian F.|date=2017-01-31|title=An early geikiid dicynodont from the Tropidostoma Assemblage Zone (late Permian) of South Africa|journal=PeerJ|language=en|volume=5|pages=e2913|doi=10.7717/peerj.2913|pmid=28168104|pmc=5289114|issn=2167-8359 |doi-access=free }}</ref>
==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 [[maxilla]]ry [[tusk]]s being intact. However, many species in this [[clade]] sporadically lack tusks completely and their [[fossil]]s only hold evidence that they retained their [[keratin]]ous beaks.<ref name=KA09>{{cite journal |last=Kammerer |first=C.F. |author2=Angielczyk, K.D.  |year=2009 |title=A proposed higher taxonomy of anomodont therapsids |journal=Zootaxa |volume=2018 |pages=1–24 |url=http://www.mapress.com/zootaxa/2009/f/z02018p024f.pdf}}</ref> Many ''Tropidostoma'' fossils previously collected have been misidentified as other species, such as of ''[[Oudenodon|Oudenodon bainii]]'' due to their remarkable similarity.<ref name="BA07"/> In addition, the type fossil of the recently discovered ''[[Bulbasaurus|Bulbasaurus phylloxyron]]'' was misidentified as a ''Tropidostoma'' [[fossil]] for several years.<ref>{{Cite journal|last1=Abdala|first1=F.|last2=Botha-Brink|first2=J.|date=2008-04-01|title=A new cynodont record from the Tropidostoma Assemblage Zone of the Beaufort Group: implications for the early evolution of cynodonts in South Africa|journal=Palaeontologia Africana |url=http://wiredspace.wits.ac.za/handle/10539/13803|language=en|issn=0078-8554}}</ref><ref>{{Cite journal|last1=van der Walt|first1=Merrill|last2=Day|first2=Michael|last3=Rubidge|first3=Bruce|last4=Cooper|first4=Antony|last5=Netterberg|first5=Inge|date=2010-12-31|title=A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa|url=https://www.researchgate.net/publication/239521002|journal=Palaeontologia Africana|volume=45|pages=1–6}}</ref>
==See also==
{{Portal|Geology|Paleontology}}
* [[List of therapsids]]
==References==
{{Reflist}}
{{Anomodontia|O.}}
{{Taxonbar|from=Q7846231}}
[[Category:Bidentalians]]
[[Category:Lopingian synapsids of Africa]]
[[Category:Fossil taxa described in 1876]]
[[Category:Lopingian genus first appearances]]
[[Category:Lopingian genus extinctions]]