Protuberum was a large traversodontid, with the holotype subadult specimen weighting about , and other, probably adult specimens being 40% larger. On the upper jaw,
Protuberum had four
incisors, one
canine, and
postcanines on each side. The incisors are large and point slightly forward, and have a thick coat of
enamel on the
labial surface (= the side touching the lips), with the largest being the third incisor. The canines are not preserved, with only a single scrap of a tooth remaining, although the fourth incisor was originally misinterpreted as a canine. The paracanine fossa (a depression on the upper jaw to accommodate the canines of the
mandible when the mouth is closed) is larger than that of other traversodontids, and was originally interpreted a being so extensive it would create a uniquely long
diastema (gap) between the canine and postcanine teeth, although this was later rejected. The postcanine teeth possess two cusps connected by a sharp transverse process. Unlike
Massetognathus, Exaeretodon and some other
gomphodonts, they lack a shouldering pattern. They are worn sequentially from the front of the mouth back, indicating that the postcanines erupted from the back of the mouth over time. However they likely did not move as new teeth grew, as indicated by a straight root.
Postcranial skeleton Protuberum is most striking for its neural spines, presacral ribs and
illium which are covered in bumps. Analogous rib ornaments are found in the
ankylosaur Spicomellus and the
pseudosuchian Euscolosuchus, although in the former they are epidermal.
Thrinaxodon had a similar condition with a series of tubercules on the proximal ribs.
Kayentatherium was another cynodont with bump-like vertebral processes. On the illium they are present on the iliac blade, above the hips, and are aligned with the bumps of the ribs. These bumps are made of compact bone tissue, possibly
pachyostotic, and were most likely not covered in
cartilaginous tissue. Like with other cynodonts, the ribcage can be separated into two distinct regions,
thoracic and
lumbar, based on the presence of costal plates. The thoracic region bears overlapping costal plates, where the proximal half of each rib is widened. Each rib is lined with a single row of bumps, which decrease in size
distally (away from the midline), so that the largest are the near the spine. The longest middle thoracic ribs bear up to eight of these processes, and their number generally decreases with the length of the rib. == Classification ==