At the front of the upper jaw of Bulbasaurus, the tips of the fused premaxillae are strongly hook-like, much more so than Tropidostoma and other dicynodonts but not as much as Dinanomodon.
Also unlike Tropidostoma, the flattened front face of the premaxillae bear a tall, narrow, prominent ridge; Aulacephalodon also has a similar ridge, albeit broader and not as sharp.
The back of the premaxillae narrow and extend between the roughened bosses on the nasal bones.
Viewed from underneath, the bone is roughly pentagonal; the bottom surface bears two ridges near the front, as well as an additional ridge extending backward from where the two forward ridges end, which gradually becomes taller and wider.
These ridges are separated by depressions in the bone of roughly equal depth, which is like other geikiids but unlike Tropidostoma.
At the outer extremities of the premaxillae, low and roughened ridges are located near the base of the tusks.

Further back on the interior of the upper jaw, the palatine bones are exposed as a palatine pad, which is very roughened and would have been covered in keratin, although the portion where they contact the premaxillae is smooth and sloping.
The back portion of the palatines are thinner than the rest of the bone, but it is still thicker than that of either Tropidostoma or Oudenodon, instead resembling Aulacephalodon more closely.
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.
The pterygoids also project outwards in rod-like structures to meet the quadrate bones.

Compared to other dicynodonts, the maxillary tusk of Bulbasaurus was massive; the holotype skull, which is 14 cm (5.5 in) long, has a 1.9 cm (0.75 in) tusk diameter.
Only Aulacephalodon has comparably large tusks proportionally, but these belong to adult specimens much larger than Bulbasaurus (in juveniles the size of Bulbasaurus, the tusks are still erupting).
The root of the tusk bulges outwards from the surface of the maxilla due to its large size.
Extensive pitting on the surface of the maxilla is suggestive of some kind of keratinous covering, which has also been inferred for other dicynodonts.
Unlike other geikiids and most other cryptodontian dicynodonts, there is no ridge behind the tusk, although mature Aulacephalodon also lack this ridge.
At the front of the upper jaw of Bulbasaurus, the tips of the fused premaxillae are strongly hook-like, much more so than Tropidostoma and other dicynodonts but not as much as Dinanomodon. Also unlike Tropidostoma, the flattened front face of the premaxillae bear a tall, narrow, prominent ridge; Aulacephalodon also has a similar ridge, albeit broader and not as sharp. The back of the premaxillae narrow and extend between the roughened bosses on the nasal bones. Viewed from underneath, the bone is roughly pentagonal; the bottom surface bears two ridges near the front, as well as an additional ridge extending backward from where the two forward ridges end, which gradually becomes taller and wider. These ridges are separated by depressions in the bone of roughly equal depth, which is like other geikiids but unlike Tropidostoma. At the outer extremities of the premaxillae, low and roughened ridges are located near the base of the tusks.
Further back on the interior of the upper jaw, the palatine bones are exposed as a palatine pad, which is very roughened and would have been covered in keratin, although the portion where they contact the premaxillae is smooth and sloping. The back portion of the palatines are thinner than the rest of the bone, but it is still thicker than that of either Tropidostoma or Oudenodon, instead resembling Aulacephalodon more closely. 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. The pterygoids also project outwards in rod-like structures to meet the quadrate bones.
Compared to other dicynodonts, the maxillary tusk of Bulbasaurus was massive; the holotype skull, which is 14 cm (5.5 in) long, has a 1.9 cm (0.75 in) tusk diameter. Only Aulacephalodon has comparably large tusks proportionally, but these belong to adult specimens much larger than Bulbasaurus (in juveniles the size of Bulbasaurus, the tusks are still erupting). The root of the tusk bulges outwards from the surface of the maxilla due to its large size. Extensive pitting on the surface of the maxilla is suggestive of some kind of keratinous covering, which has also been inferred for other dicynodonts. Unlike other geikiids and most other cryptodontian dicynodonts, there is no ridge behind the tusk, although mature Aulacephalodon also lack this ridge.
Bulbasaurus