Fig. 1.

Daily growth lines in embryonic dinosaur teeth and CT rendering of a P. andrewsi jaw and tooth family. (A) Von Ebner’s growth lines (alternating dark and light bands) in the orthodentine surrounding the pulp cavity (at top of graphic) of an embryonic H. stebingeri tooth (polarized microscopy, transverse view). (B) Von Ebner’s growth lines surrounding the pulp cavity (at top of the graphic) in an embryonic tooth of P. andrewsi (polarized microscopy, transverse view). (C) High-resolution CT rendition of a P. andrewsi tooth family within the jaw used to determine tooth-formation times in embryonic teeth.