Figure 1.
A simplified phylogeny of jawed vertebrates modified from Brazeau [14].
‘Placoderms’ and ‘Acanthodians’ are extinct, probably paraphyletic, groups. Representative scales of osteichthyans (Cheirolepis), acanthodians (Nostolepis), stem chondrichthyans (Cladoselache) and ‘placoderms’ (Ohiolepis) are modified from [52], [53], [44] and [54] respectively.
Figure 2.
The scanned scale of Andreolepis hedei Gross, 1968.
A. Scanned part of the scale (PMU 24786) rendered in VG Studio 2.1, crown view, red line marking the position of the slice in B. B. Longitudinal virtual thin section from the synchrotron scanning data, the red rectangle marking the region in C. C. Close-up of B, showing the segmentation of odontodes and the tissue composition of the crown (picture exported from VG Studio 2.1). The numbers in circles correspond to the odontodes in following Figures 3 and 4. D. A real thin section (PMU 24784) from an Andreolepis body scale made in the anteroposterior plane for comparison (DIC, optical microscopy); the scale is slender and comes from the posterior region of the body [28]. Abbreviations: e, enamel; d, dentine; hc, horizontal vascular canal, O1-O5, odontodes 1–5, Shb, Sharpey’s fibers.
Figure 3.
The reconstructed growth pattern of odontodes in the scanned scale of Andreolepis, crown view.
A–J. The referred sequential addition of odontodes –
in the crown of the scale. The first generation odontodes (odontodes
–
, see text) form a growth series, but the other younger odontodes (
–
) do not necessarily fall neatly into the same sequence even though they generally continue to get larger; the yellow horizontal vascular canal system is used as landmark to show the positions of the odontodes K. Crown view of the scale with buried odontodes, showing the actual surface composition of the scale. Note that the most dorsal denticles compose the enamel layers from both odontode
and
, odontode
is partially overlapped by
; odontode
is only overlapped by
and
posteriorly and exposed to the surface otherwise.
Figure 4.
The reconstructed growth pattern of odontodes in the scanned scale of Andreolepis, anterolateral view.
For explanations see Figure 3.
Figure 5.
The reconstructed odontodes –
showing the consistent morphology and overlap relationships.
A–D. Odontodes –
in ventral view. E. Odontodes
–
in anterodorsal view, in original relative positions showing the overlap mode of odontodes
–
.
Figure 6.
Two acanthodian tooth whorls (SEM photos with line drawings).
A–C, GIT 658-1; D–F, GIT 658-2. A,D. Oral views, labial to the right. B,E. Sketch interpretations of A,D. C,F. Lateral views, labial to the right. Abbreviations: t1-t3, tooth element 1–3 belonging to the linear growth serial; t0?, possible origination element of the linear growth serial; o, disorganized odontodes on the labial base.