Microstructural variation in conodont enamel is a functional adaptation

Recognition that conodonts were the earliest vertebrate group to experiment with skeletal biomineralization provides a window in which to study the origin and early evolution of this developmental system. It has been contended that the conodont skeleton comprised a classic suite of vertebrate hard tissues, while others suggest that conodont hard tissues represent divergent specializations within the early diversification of vertebrate hard tissues, supporting a view that the hard tissues of conodonts, particularly enamel, exhibit a range of microstructural variation beyond that seen in vertebrates. New evidence reveals that, although variable, conodont enamel microstructure is consistent between homologous portions of homologous dentitions. Although there is a correlation between morphology and microstructure, this belies a stronger correlation between the commonality of microstructure and dental function. The enamel of conodonts evolved in response to changes in dental function and differentiation of the microstructural layer into a number of enamel types and can be linked to dental occlusion, heterodonty, a permanent dentition, enamel thickness and, probably above all, the small size of the dental elements.