The only known specimen of
Bocaconodon (IGM 6617) is a partial right
dentary bone, which preserves most of the last two
molar teeth and the rear portion of a third molar. The preserved part of the dentary was quite thin from top to bottom, with the thinnest part being beneath the last molar. Behind the tooth row there was a facet that may have housed the
coronoid bone. At the rear end of the dentary, there was a depression known as the
postdentary trough, where the postdentary bones (homologous to some of the
middle ear bones of modern mammals) would have been attached. Since the postdentary bones were attached to the dentary,
Bocaconodon may have retained the primitive
quadrate-
articular jaw joint found in most non-mammalian
synapsids, in addition to the newer dentary-
squamosal joint found in mammals and other
mammaliaforms. The molars had a "triconodont" shape, with three main
cusps aligned in a straight line. In both of the well-preserved teeth, the middle cusp (cusp a) was the largest, the cusp behind it (cusp c) was smaller, and the front cusp (cusp b) was smaller still. Cusp a had an asymmetrical, backwards-curved shape, while cusps b and c were more symmetrical. Cusp b pointed upwards while cusp c was more backwards-pointing. Behind cusp c there was another, smaller cusp (cusp d). The molars bore a narrow ridge on the lingual (inner) side known as the
cingulum. The lingual cingulum differed from those of most
morganucodonts in lacking any distinct cusps. == Classification ==