FIGURE 7 in Holocephalan (Chondrichthyes) dental plates with hypermineralized dentine as a substitute for missing teeth through developmental plasticity

FIGURE 7 Hydrolagus mirabilis. (a)–(c) Photomicrographs in incident light of upper and lower dental plates, (c) in situ, surrounded by soft tissue). (a) Anterior upper plate shows ridges on the lingual surface (arrows), extent of worn tissue fossa (double arrow) and translucent grey rods. (b) Lower dental plate tissue shows the transparency of most mineralized tissues as in outer dentine (double arrow) surrounding trabecular dentine. Ovoid stack not fully mineralized. (c) Upper dentition in situ with soft tissue, plates lined by epithelium, rostral snout present. (d) Close-up of virtual section through anterior upper plate as in Figure 4d,e, coloured red to show whitlockin as mineralized ovoids. Red rings show the preformed capsular spaces in the trabecular dentine, the newest ridge forming aborally, and coincidence of ridges with new whitlockin forming (double arrows). (e) Callorhinchus milii Bory de Saint-Vincent, 1823, schematic drawing of section through lower jaw embryonic plate (Kemp 1984). Red indicates whitlockin formation (ple = pleromin) under an epithelium, with modified trabecular dentine (mt), condensed mesenchyme (md), cartilage (c). Scale bar = 1 mm. (f) Callorhinchus milii, adult lower jaw, μCT rendered with whitlockin segmented, coloured red (Drishti), showing low ridges on the surface that form deep into the trabecular dentine, above a cartilage furrow. Abbreviations as in previous figures. car, cartilage furrow; ep, epithelium; nrdg, newest ridge; ov st, ovoid stack; ros, rostral snout