Fig. 1

Odontode diversity of the pre-hatchling Catshark (S. canicula). Samples a–i are cleared and stained for calcium-rich tissue using alizarin red dye. Samples j–k are computerised tomography (CT) scans of a Stage 32 whole embryo, and samples l–m are light sheet fluorescence microscopy (LSFM) images of caudal denticles of a Stage 31 embryo, stained with alizarin red. The pre-hatchling (a) possesses three major external denticle types. The caudal denticles are the first to emerge, appearing on either side of the tip of the tail in dorsal and ventral rows (b, c, j–m) [23]. These denticles are not strongly polarised, although cusps generally point towards the posterior [27]. Next, the dorsal denticles emerge along the trunk of the embryo in two polarised rows (d, e). Finally, general body denticles emerge just before hatching, covering the whole body (f, g). These denticles are also highly polarised. Teeth emerge in the jaws at a similar stage to general body denticles (h, i). The scale bar for a = 1000 µm, b, c, g and i = 200 µm, d and h = 2500 µm, e and f = 500 µm