Fig. 2

Harriotta raleighana (Rhinochimeridae; Holocephali; Chondrichthyes). Microstructure of hard tissue sections in dental plate of a lower jaw alongside virtual μCT. a–c Optical microscopy, d–e μCT scans: a Nomarsky optics of tritoral labial margin without ovoids, worn surface of sclerotic osteodentine (sod); translucent tissue is hypermineralized, for outer dentine layer (od), and most of osteodentine (os) with strong birefringence of organized collagen fibres of trabecular dentine framework (see C), brown colour is partially infilled vascular tissue, and odontoblast tubules. b surface illumination of hypermineralized ovoids (grey, ov), region just below oral surface (field in Fig. 1a), sclerotic osteodentine white (see Fig. 1a, sod), trabecular dentine (td) is less mineralized (see D, E for comparable X-ray density), white arrows, deep sclerodentine forming front. c field in Fig. 5a, polarized light with a gypsum plate shows opposite orientation of collagen fibre bundles as colours in sclerotic dentine matrix (gypsum plate at -ve 45° to polarizer at 90° gives direction of birefringent tissue components as blue or yellow, not red; see also Fig. 3b, c, Fig. 11e), note the birefringent capsular fibres (cap) enclosing the ovoids, but none inside, only HD tubules. d, e adult, μCT virtual section through dental plate of tissue arrangement (see Fig. 18b for interpretive drawing), oral surface worn ovoids (ov, top) to aboral (bottom) with sequence of ovoids as mineralized with HD (white) to empty capsules (ov.s) as forming spaces in the trabecular dentine aborally, also tritor spaces organized around the special blood vessels, in parallel tubes (vt, tri.s), e close up of aboral margin in Fig. 1d, developing ovoid and tritor spaces between the vascular tubes within the tritor (vt). Scale bar D = 0.25 cm, E = 0 .1cm