Procerberus enamel: a missing link.

In a fossil tooth of Procerberus (a Late Cretaceous palaeoryctid insectivore), there is a unique, clear and simultaneous expression of all three known forms of enamel: prismatic, pseudoprismatic and aprismatic. The pseudoprismatic domain, generally regarded as the more primitive unit compared to the prismatic domain, may be interpreted in this material as that morphological territory in which the prism appears, or evolves, as an additional structural unit. It is possible to construct a three-dimensional, developmental scheme for Procerberus enamel on the basis of known principles and to use it to help build a conceptual bridge between synapsid and mammalian enamel.