Forbidden seal morphologies did not occur in Jernvall's sample. This evidence suggests that cusp number is under control of allometric development. The surrounding epithelium and mesenchyme differentiate into ameloblasts and odontoblasts, respectively. Possible model fro seal cusp formation. Yellow circles are the larger enamel knot inhibitory fields.
Blue circles are the smaller fields.
Enamel knots are in red. Thus a small difference in the inhibitory field for the enamel knot can have large affects on cusp number. Many familiar molecules are active in tooth development and recent reports have further explored the role sonic hedgehog. A conditional knockout of shh was created which may tell us about shh 's role in enamel knot initiation and by extension, cusp development variability. In other words, shh expression variation may be allowing the 'easy' evolution of the hypocone.