A comparative odontologic study was conducted on teeth and their supporting tissues from extant sharks, fossil sharks, and living lungfishes using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) X-ray microprobe to investigate evolutionary changes in tooth structure of the fishes.
No histological differences between the extant and fossil teeth of lamnoid sharks were observed. The weight percent of calcium in osteodentin of the fossil shark was higher than that in the extant shark. The weight percents of both P and Ca of tooth tissues in the giant extinct shark showed comparatively low values.
Both the upper and lower jaws of the African lungfish possessed a pair of tooth plates composed of a very thin enamel, and layers of petrodentin and osteodentin. The radical osteodentin of the plates changed gradually, fusing with the jaw bones without distinct boundaries. SEM and EDS indicated the petrodentin contained bundles of fibers impregnated with hydroxyapatite crystals, and the enamel had plate-like crystals running at right angles to the tooth surfaces; no tubules were observed in this enamel. The total content of both P and Ca in the lungfish enamel is lower than those in the petrodentin and shark enameloid.
Iwai-Liao, Yasutomo; Higashi, Yoshikage; and Tamada, Yoshitaka
"Tooth Tissues of Certain Sharks and Lungfishes,"
Scanning Microscopy: Vol. 6
, Article 17.
Available at: https://digitalcommons.usu.edu/microscopy/vol6/iss1/17