Bulbasaurus (meaning "bulbous reptile") 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.

Other distinguishing characteristics of Bulbasaurus among the geikiids include the hook-like beak, very large tusks, and absence of bossing on the prefrontal bone.

Smith in the Vredelus locality, which is located at an altitude of 1,445 metres (4,741 ft), in the district of Fraserburg, Northern Cape, South Africa.

This locality is part of what is known as the Tropidostoma Assemblage Zone, which belongs to the Lopingian (upper Permian) Hoedemaker Member of the Middle Teekloof Formation.

[1] "Head-only" preservation is common in therapsid fossils of the Hoedemaker Member, because the specimens were probably left out in the open and became disarticulated before being rapidly buried by flash floods.

The description states that the generic name combines the Latin bulbus, referring to the very large and bulbous nasal bosses, with the common suffix -saurus.

As for the specific name phylloxyron, meaning literally "leaf razor", it is derived from the Greek phyllos and xyron, and apparently refers to the keratinous covering on the premaxilla, maxilla, and palate that would have been used to shear plant material.

The pterygoid bones are robust in contrast to Tropidostoma, and bear ridges that converge into a tall, blade-like process known as the crista oesophagea.

At the back of the bosses, a slight indentation wrapping around the top and sides of the skull separates them from the eye socket, typical of cryptodontians except for Odontocyclops.

Near the back, the postorbitals curve and converge to form a somewhat pinched intertemporal bar that overlaps the parietal bones to varying extents.

Projections of the squamosal bones partially surround the posttemporal fenestrae on the rear of the skull, like Aulacephalodon, Pelanomodon, Oudenodon, and Tropidostoma.

In front of the parietals are the small midline preparietal bones, which are relatively broad and have a rounded tip, as in Aulacephalodon and Pelanomodon but in contrast to Tropidostoma.

The contribution of the supraoccipital bones to the back of the skull is unusually extensive and occupies much of the area not part of the squamosals above the level of the foramen magnum.

[1] In 2017, Bulbasaurus was assigned to the Geikiidae clade of dicynodonts on account of its prominent nasal-frontal ridge, its relatively wide interorbital region, and its twisted squamosal on the postorbital bar.

This assignment was supported by a phylogenetic analysis based on that conducted by Kammerer et al. in 2011,[5][11] which found it as the closest relative of Aulacephalodon on the basis of it lacking a ridge behind its tusk (which is ontogenetically influenced).

However, this assignment is somewhat questionable, and forcing Bulbasaurus as a basal geikiid outside of the Geikiinae (Aulacephalodon, Geikia, and Pelanomodon) only requires one additional evolutionary step.

Keyseria Daqingshanodon Odontocyclops Oudenodon Tropidostoma Australobarbarus Idelesaurus Syops Rhachiocephalus Kitchinganomodon Aulacephalodon Bulbasaurus Pelanomodon Geikia locusticeps Geikia elginensis Tropidostoma, the genus Bulbasaurus was originally assigned to, exhibits two distinct morphologies - a robust morph with short snout and large tusks, and a gracile morph with long snout and small tusks, which probably represents sexual dimorphism as in other dicynodonts.

Additionally, even the holotype of Tropidostoma (which is probably immature judging by the unerupted tusks) is larger than adult specimens of Bulbasaurus, which further warrants their separation.

[16] Rarer members of the Tropidostoma AZ assemblage include the burnetiamorphs Lobalopex[17] and Lophorhinus;[18] parareptiles Pareiasaurus and Saurorictus; the archosauromorph Younginia; and the temnospondyl Rhinesuchus.

[14] Bulbasaurus was probably buried on floodplains surrounding a meandering river up to 350 metres (1,150 ft) wide and with point bars up to 3 kilometres (1.9 mi) in diameter.