A Toothy Problem: Large mammalian herbivores such as horses and bison are well known to possess a complex, grinding dentition that facilitates processing of their tough, cellulose-rich plant diet. Hadrosaurid, or duck-billed, dinosaurs also possessed complex teeth, but how this was achieved has been unknown because reptiles typically possess simple teeth. Erickson et al. (p. 98 ) show how Hadrosaurs evolved teeth composed of six tissues, which allowed for the development of tooth complexity rivaling, or exceeding, that of modern herbivorous mammals.