''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'' fossils 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''.

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 fossils 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''. Some years later, the name ''T. microtrema'' was changed to ''Tropidostoma dubium'', and ''Tropidostoma dunni'' is now considered to be the type species.

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 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.

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, Oudenodon bainii'' due to their remarkable similarity. In addition, the type fossil of the recently discovered ''Bulbasaurus, Bulbasaurus phylloxyron'' was misidentified as a ''Tropidostoma'' fossil for several years.

References

{{Taxonbar, from=Q7846231 Dicynodonts Lopingian synapsids of Africa Fossil taxa described in 1876 Lopingian genus first appearances Lopingian genus extinctions Anomodont genera

History of discovery

Description

Classification

See also

References