Origin of dental occlusion in tetrapods: signal for terrestrial vertebrate evolution?

Evolutionary changes of the dentition in tetrapods can be associated with major events in the history of terrestrial vertebrates. Dental occlusion, the process by which teeth from the upper jaw come in contact with those in the lower jaw, appears first in the fossil record in amniotes and their close relatives near the Permo-Carboniferous boundary approximately 300 million years ago. This evolutionary innovation permitted a dramatic increase in the level of oral processing of food in these early tetrapods, and has been generally associated with herbivory. Whereas herbivory in extinct vertebrates is based on circumstantial evidence, dental occlusion provides direct evidence about feeding strategies because jaw movements can be reconstructed from the wear patterns of the teeth. Examination of the evolution of dental occlusion in Paleozoic tetrapods within a phylogenetic framework reveals that this innovation developed independently in several lineages of amniotes, and is represented by a wide range of dental and mandibular morphologies. Dental occlusion also developed within diadectomorphs, the sister taxon of amniotes. The independent, multiple acquisition of this feeding strategy represents an important signal in the evolution of complex terrestrial vertebrate communities, and the first steps in the profound changes in the pattern of trophic interactions in terrestrial ecosystems.