Fig 1.
Development of the squamation pattern in Triazeugacanthus affinis.
A-E: Ontogenetic stages with the corresponding squamation pattern schematically represented in F (1 to 5), respectively. A: Early juvenile MHNM 03-401. B: Early juvenile MHNM 03-2684. C: Late juvenile MHNM 03-259. D: Late juvenile MHNM 03-435. E: Adult MHNM 03-1497. F: Development of the squamation (grey zones) in relation to size ranges (not to scale). Dashed lines indicate the presence of median ridge scales. Arrows indicate the direction of the squamation progression along the body and in the fin webs. Dashed lines indicate the development of the median ridge scales. Arrows indicate the direction of the squamation progression along the body and fin webs. Scale bars: A-D = 1 mm; E = 10 mm.
Table 1.
Characteristics of the ontogenetic stages of the acanthodian Triazeugacanthus affinis based on [14].
Fig 2.
Variation of squamation along the body of Triazeugacanthus affinis.
A: Schematic representation of an adult Triazeugacanthus affinis with position of the four body regions. Regions outlined in squares are detailed in B, C and D. B: MHNM 03-1550, detail of ventral scales. C: MHNM 03-1819, SEM showing scale alignment in the region below the dorsal fin (2). D: MHNM 03-1497, scale alignment in the caudal region whiten with ammonium chloride. E: juvenile MHNM 03-2631, SEM showing the organic layer (“epidermal cover”) covering the trunk scale ornamentation. F: juvenile MHNM 03-1819, SEM of a trunk scale. Arrows point forward. l.l, lateral line; body region 1, trunk; 2, dorsal-anal; 3, post-dorsal; 4, caudal. Scale bars: A = 5 mm; C = 500 μm; D = 1 mm; E = 250 μm; E (close-up), F = 100 μm.
Fig 3.
Transverse ground sections of Triazeugacanthus affinis scales in natural light.
A-B: MHNM 03-2620, scale arrangement on both sides of the specimen showing the antero-posterior and lateral overlapping of the scales. B: MHNM 03-2620, interpretative drawing of A. The grey dashed line indicates the boundary between both sides; dark dotted lines indicate dentine tubules; dashed lines indicate the boundary between the crown and the basal plate. C: Diagram showing position of ground sections D-G in a body scale. D-F: Ground sections through the anterior, middle, and posterior levels of the scale and their interpretative drawings. D: MHNM 03-1817, the anterior region of the scale is mostly composed of acellular bone with embedded Sharpey’s fibers, a small, centrally located mesodentine layer, and thin layers of well-mineralised ganoine. E: MHNM 03-2620, the central region of the scale shows a basal plate of acellular bone, a thick middle region housing numerous ascending tubules and branched tubules, characteristic of the mesodentine, and a ganoine covering best visible in lateral regions, showing the growth zones. F: MHNM 03-1817, the posterior region of the scale is organised similarly to the anterior region of the scale. G: MHNM 03-2620, central region of the scale showing three dentine layers delimited by odontocyte cavities and tubules; each layer corresponds to a growth zone. H: juvenile MHNM 03-701, transverse section through the scales of a juvenile specimen showing a homogeneous histological composition. bb, bony base; dt. t, dentine ascending canals and tubules; g, ganoine layer; GZ, growth zone; m, mesodentine; odont., odontocytic cavities; Sh. f, Sharpey’s fibers. Scale bars: A-G, I = 100 μm; G = 20 μm; H = 10 μm.
Fig 4.
Superficial hypermineralised tissue of Trizeugacanthus affinis scales.
A, C: MHNM 03-1817, ground section in natural (A) and polarised (C) light. B: MHNM 03-1817, close-up of the superficial multi-layered ganoine. D, F: MHNM 03-1460, SEM of the microtubercles of the ganoine surface. E: MHNM 03-1699, SEM showing the ganoine crystallites (arrows). Sl, superficial layer. Scale bars: A-C = 100 μm; D and F = 20 μm; E = 2 μm.
Fig 5.
Individual and species ontogeny of Triazeugacanthus affinis.
A: adult MHNM 03-1817, scale section of an adult specimen with superimposition (white lines) of the contours of a sectioned scale from a juvenile specimen (MHNM 03-701) [S2 Table for measurements (grey and white arrows)]. B: Scale thickness/width relationship in juvenile and adult specimens. C: Side-by-side boxplot showing thickness to width scale ratio in juvenile and adult specimens. D, E: Side-by-side boxplot showing thickness to width scale ratio in various body regions of juvenile D and adult E specimens. F: Number of growth zones per scale in function of the total length in various body regions of adult specimens. The regions from which measurements were taken are shown in Fig 2A. Asterisks refer to significant differences between two groups. Scale bar: A = 100 μm.
Fig 6.
Phylogenetic relationships among early gnathostomes.
50% majority rule consensus tree based on 10,000 trees at 711 steps (79 taxa, 267 characters). Numbers on branches show percentage bootstrap support.
Fig 7.
Development of the squamation pattern in various acanthodiformes (A-F) and actinopterygians (G-H).
A: Triazeugacanthus affinis. B: Lodeacanthus gaujicus [modified from [18]]. C: Acanthodes bronni [modified from [20]]. D: Acanthodes ovensi [modified from [23]]. E: Acanthodes gracilis [modified from [21]. F: Acanthodes bridgei [modified from [8]]. G: Elonichthys peltigerus [modified from [1]]. H: Danio rerio [modified from [104]]. Estimated total length is given in A to G, whereas standard length is given in H.