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Fig. 6 | BMC Evolutionary Biology

Fig. 6

From: Synchrotron imaging of dentition provides insights into the biology of Hesperornis and Ichthyornis, the “last” toothed birds

Fig. 6

Enamel microstructure of the teeth of Hesperornis and Ichthyornis. All SEM micrographs. Low-angle views show sections of enamel down to EDJ, visible due to diagenetic fissuring and breakage. No etching was performed. These views reveal the thin Basal Unit Layer formed by parallel columns (of near-polygonal section) orthogonal to the EDJ and enamel surface. Each column is formed by assembled divergent parallel crystallites. a, c Hesperornis regalis (isolated tooth YPM.1206.b). b d e f g Ichthyornis dispar (third tooth in YPM.1775). in e, thick black lines are drawn to highlight some columns, whereas thin black lines highlight some of the divergent crystallites forming a column. f, g magnifications of regions in e. Crystallites are not all obvious since the surface has undergone no etching. Scale bars 5 μm

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