Fig. 6.

Tooth-to-tooth attachment within an embryonic Hypacrosaurus dental battery. a wholeview image of a transverse section through a maxillary battery (MOR 559), near the occlusal surface (labial is towards the top). Illustration of Hypacrosaurus skull modified from Bailleul et al. [31]. b closeup image of maxillary teeth in the same transverse section. c closeup image of tooth-to-tooth attachment in MOR 559 (note the lack of contact between the adjacent teeth). d closeup image of (c) showing partial root resorption and attachment tissues. e closeup image of attachment sites of periodontal ligament between two teeth (Sharpey’s fibers). ab, alveolar bone (possible repair cementum between teeth); ac, acellular cementum; cc, cellular cementum; de, dentine; en, enamel; ode, dentine of older tooth; rl, reversal line; sf, Sharpey’s fibers