REISZ, R.R.; University of Torontoa at Mississauga: Origin of dental occlusion in tetrapods, signals for terrestrial vertebrate evolution

Among terrestrial vertebrates, the general primitive dental condition is the presence of simple conical teeth arranged in a single row along the edges of the upper and lower jaw. The upper and lower teeth do not occlude (come together) and there is little or no oral processing. This condition is seen not only Paleozoic tetrapods, but is also retained in living amphibians, crocodiles and most lizards. A survey of the fossil record within a phylogenetic framework, extending over 300 million years of history, reveals that dental occlusion and oral processing have multiple origins spread out throughout synapsids (mammals and their relatives) and reptiles (extant taxa, their fossil relatives, including dinosaurs). Moreover, there is clear evidence that these multiple origins have had a fundamental effect on the evolution of terrestrial ecosystems, both in terms of the origin and maintenance of the modern type of trophic structure. The diversity of dental occlusion revealed by the fossil record permits reconstruction of some overall patterns, with the primitive condition represented by the use of dental wear to develop precise occlusion. This pattern occurs widely within higher vertebrates, both among synapsids and reptiles. Only within mammals is there evidence for an evolutionary transformation to a system of genetically programmed precise occlusion that is fully developed at the time of dental eruption.