Jan A. van Dam, Mikael Fortelius, Oyvind Hammer, John P. Hunter, Han-Sung Jung, Merja Mäkinen, Qiu Zhuding, Riikka Santalahti and Irma Thesleff are gratefully acknowledged for their suggestions and help. We thank Helena Vihinen for helping with the confocal microscope and three anonymous referees. This work was supported by grants 39486 and 38355 from the Academy of Finland. This is a contribution from the Valio Armas Korvenkontio Unit of Dental Anatomy in Relation to Evolutionary Theory.