Tropidostoma is a medium-sized Herbivore oudenodontid dicynodont therapsid that lived during the Late Permian (Lopingian) period in South Africa. The first Tropidostoma fossil was described by Harry Seeley in 1889. Later two subspecies were identified. Tropidostoma are an index fossil in a biozone of the Karoo Supergroup known as the Tropidostoma Assemblage Zone. This biozone is characterized by the presence of this species in association with another dicynodont species, Endothiodon.
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 (1889) in a study in which he described two
which had been named
Dicynodon microtrema and
Tropidostoma dunni. In 1915, several years after
Harry Seeley 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 morphs, one being robust form with a tall snout and large
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
being intact. However, many species in this
clade sporadically lack tusks completely and their
only hold evidence that they retained their
beaks.
Many
Tropidostoma fossils previously collected have been misidentified as other species, such as of
Oudenodon due to their remarkable similarity.
In addition, the type fossil of the recently discovered
Bulbasaurus was misidentified as a
Tropidostoma fossil for several years.
See also
