Figure 1.
The phylogenetic framework showing the alternative positions of Psarolepis romeri.
Based on references [3], [6], [7], [8]. Icons of representative fishes after reference [9].
Figure 2.
SEM photos of scales that probably constitute the squamation of Psarolepis romeri.
A. IVPP V17913.6, subtype 1. B. IVPP V17913.7, subtype 2. C. IVPP V17913.8, subtype 3. D. IVPP V17913.9, subtype 4. E. IVPP V17913.10, subtype 5. F. IVPP V17913.11, subtype 6, note that this image has been mirrored in order to match the orientation of other scales. G. IVPP V17913.12, subtype 7. All scales in crown view and anterior to the right. Hypothetical outline of Psarolepis is adopted from Guiyu [11] with the squamation scheme from Esin [33]. Scales in A, B, C, E, and F come from the right side of the fish. Scale bar = 0.5 mm.
Figure 9.
Horizontal ground sections of scales (subtypes 1 and 3) of Psarolepis romeri.
A. IVPP V17757.29, subtype 1, horizontal ground section, light microscope photo, note that the dorso-ventrally and antero-posteriorly oriented horizontal canals join to form a horizontal canal network, where the pore cavities ascend from. B. IVPP V17757.30, subtype 3, horizontal ground section, light microscope photo. Scale bar = 200 µm. hc, horizontal canal; hc.dv, dorso-ventrally oriented horizontal canal; hc.ap, antero-posteriorly oriented horizontal canal; vc, vascular canal.
Figure 3.
Gross anatomy of trunk scales (subtype 1) of Psarolepis romeri in surface view and ground sections.
A–C. IVPP V17913.6 in crown view (A), basal views (B) and antero-lateral view (C); scale bar = 0.5 mm. D. IVPP V17757.16, light microscope photo, antero-posterior vertical ground section showing anatomical structures indicated in A–C; scale bar = 0.1 mm. E. IVPP V17757.17, light microscope photo, dorso-ventral vertical ground section cutting through the keel; scale bar = 0.1 mm. F. Reconstruction of the anterior squamation in basal view, showing the peg-and-socket structure in situ. cob, canal opening on the base; con, canal opening on the neck; g.a, anterior groove of the base; g.p, posterior groove of the base; k, keel; l.a, anterior ledge; l.p, posterior ledge; n, neck; nr, neck ridge; n.a, anterior neck; n.p, posterior neck; p, peg; po, pore opening on the crown; s, socket.
Figure 4.
Selected scales displaying the neck structures.
A. Antero-lateral view of IVPP V17913. 13, a subtype 1 scale with lateral-line canal, showing the lateral-line canal penetrating the neck in antero-posterior direction; B. Antero-lateral view of IVPP V17913.8, subtype 3; C. Lateral view of IVPP V17913.12, subtype 7. scale bar = 0.5 mm. con, canal opening on the neck; k, keel; l.a, anterior ledge; lco, lateral-line canal opening on the neck; n, neck; nr, neck ridge; n.a, anterior neck; p, peg; po, pore opening on the crown.
Figure 5.
IVPP V17757.19, subtype 1, light microscope photos of a dorso-ventral vertical ground section.
A. Full view of the ground section, the red insets are detailed in higher magnification in B–E, scale bar = 200 µm. B. The close-up of inset 1 in A, showing the odontode overlap pattern in the most ventral part of the crown, note that the pulp cavity is recrystallized and can only be recognizable according to the radiating dentine tubules; scale bar = 100 µm. C. The close-up of inset 2 in A, showing the odontode overlap pattern in the middle region of the crown, note the well-developed pore-canal system and the vascular canals connecting with the horizontal canals, the same scale bar as in B; D. The close-up of inset 3 in A, showing the odontode overlap pattern in the most dorsal part of the crown, the same scale bar as in B; E. The close-up of inset 4 in A, showing the boundary between the keel and the ledge, marked by the end of Sharpey's fibers, pink arrows indicate the osteocyte lacunae, note that only the keel shows the plywood-like pattern, the same scale bar as in B. cob, canal opening on the base; con, canal opening on the neck; d, dentine; e1–e3, enamel layers of first to third generations of odontodes; hc, horizontal canal; k, keel; l, ledge; n, neck; p, peg; pc, pore cavity; puc?, probable recrystallized pulp cavity; s, socket; vc, vascular canal.
Figure 6.
Comparison of the plywood-like tissues in Psarolepis, osteostracans and galeaspids.
A–D. IVPP V17757.16, subtype 1, antero-posterior vertical ground section, showing light microscope photo of the crown (A) and the base (B), polarized light microscope photo of the base (C) and Nomarski interference light microscope photo of the keel (D), pink arrows indicating the osteocyte lacunae; scale bar = 100 µm in A–C, scale bar = 40 µm in D. E. IVPP V18540, vertical ground section through the dermal fragment of polybranchiaspid indet., showing the similar laminated pattern in galeaspidin but with less fiber layers in each ply; scale bar = 40 µm. F. Vertical ground section through the dermoskeleton of Tremataspis mammilata after Wang et al. [59], showing only one thick fiber-bundle in each ply; scale bar = 40 µm. G. Schematic models to compare the lamellated structures in osteostracans (G1) and keel of Psarolepis scales (G2), G1 is modified from Gross [13], note that the Sharpey's fibers are not incorporated; galeaspids have less fibril layers than Psarolepis in each ply, but more than osteostracans. bka, boundary between keel and anterior ledge; bkp, boundary between keel and posterior ledge; d, dentine; e1–e4, enamel layers of first to fourth generations of odontodes; hc, horizontal canal; k, keel; l.a, anterior ledge; l.p, posterior ledge; p, peg; pc, pore cavity; shb, Sharpey's fibers; t, tubercle on the top of galeaspid dermal skeleton; vc, vascular canal.
Figure 7.
Scales (subtypes 2 and 4) of Psarolepis romeri.
A–C. IVPP V17757.26, subtype 4, vertical ground section; A. Light microscope photo, full view; scale bar = 100 µm. B. Light microscope photo, close-up of A in the crown showing the overlap pattern of enamel layers; scale bar = 50 µm. C. Nomarski interference light microscope photo, close-up of A in the keel showing the plywood-like structure and Sharpey's fibers; scale bar = 50 µm. D–F. IVPP V17757.27, subtype 2, antero-posterior vertical ground section; D. Light microscope photo, full view; scale bar = 100 µm. E. Nomarski interference light microscope photo, close-up of D in the crown showing the overlap pattern of enamel layers; scale bar = 20 µm. F. Nomarski interference light microscope photo, close-up of D in the keel showing the plywood-like structure and Sharpey's fibers; scale bar = 20 µm. d, dentine; e1–e4, enamel layers of first to fourth generations of odontodes; hc, horizontal canal; o, osteocyte lacuna; pc, pore cavity; rt, recrystallized tissue; shf, Sharpey's fibers; vc, vascular canal.
Figure 8.
Scales (subtypes 3 and 7) of Psarolepis romeri.
A–C. IVPP V17757.4, subtype 3, antero-posterior vertical ground section; A. Light microscope photo, full view; scale bar = 100 µm. B. Light microscope photo, close-up of A in the crown showing the overlap pattern of enamel layers; scale bar = 20 µm. C. Nomarski interference light microscope photo, close-up of A in the keel showing the plywood-like structure and Sharpey's fibers, note an air bulb on the central left; scale bar = 20 µm. D–F. IVPP V17757.28, subtype 7, antero-posterior vertical ground section; D. light microscope photo, full view; scale bar = 100 µm. E. Nomarski interference light microscope photo, close-up of D in the crown showing the overlap pattern of enamel layers; scale bar = 50 µm. F. Nomarski interference light microscope photo, close-up of D in the keel showing the plywood-like structure and Sharpey's fibers; scale bar = 20 µm. d, dentine; e1–e2, enamel layers of first to second generations of odontodes; hc, horizontal canal; pc, pore cavity; shf, Sharpey's fibers.
Figure 10.
SEM picture of the etched ground section made from IVPP V17758, a subtype 1 scale.
A. The full view of an etched ground section in antero-posterior direction; scale bar = 200 µm. B. The close-up of (A) showing the enamel crystallites and growth lines at the anterior margin of the scale, arrows marking the growth lines; scale bar = 5 µm. C. The close-up of (A) showing that the enamel dippers into a pore cavity; scale bar = 10 µm. d, dentine; e, enamel; hc, horizontal canal; pc, pore cavity; shb, Sharpey's fibers.
Figure 11.
IVPP V17756, antero-posterior vertical ground sections of Psarolepis skull roof.
A. Light microscope photo, showing three generations of odontodes on the bony tissue and the cylindrical pore cavity, note the vascular bone almost absent at this region, scale bar = 100 µm in all four figures; B. Nomarski interference light microscope photo of the same region in (A); C. Light microscope photo, showing two generations of odontodes and a thin vascularized layer below; D. Light microscope, showing three generations of odontodes with both superpositional growth and areal growth, the vascular bone well developed than in (A). bb, basal compact bone layer; d, dentine; e1–e3, enamel layers of first to third generations of odontodes; hc, horizontal canal; pc, pore cavity; puc?, probable recrystallized pulp cavity; vc, vascular canal.
Figure 12.
Comparison of rhombic trunk scales of three early bony fishes, in illustrative drawings.
A. Ligulalepis toombsi, modified from Burrow [35]; B. Psarolepis romeri; C. Andreolepis hedei, adopted from Gross [50]. The second keel (k′) in Schultze [49] is explained as the posterior ledge that has the same tissue composition as the anterior ledge, but is different from the keel. Scale bar = 0.5 mm in A1–A2, B1–B2 and C1–C2; scale bar = 0.1 mm in A3, B3 and C3. df, depressed field; e, enamel; k, keel; l.a, anterior ledge; l.p, posterior ledge; n.a, anterior neck; n.p, posterior neck; po, pore opening; shb, Sharpey's fibers.