Cheiracanthus latus Egerton, 1861

Burrow, Carole & Newman, Michael, 2020, A redescription of the three longest-known species of the acanthodian Cheiracanthus from the Middle Devonian of Scotland, Palaeontologia Electronica (a 15) 23 (1), pp. 1-43 : 28-38

Cheiracanthus latus Egerton, 1861

Figure 4 , Figure 6.5-6.8 , Figures 24-32

1861 Cheiracanthus latus ; Egerton, 73-75, pl. 10.

1888 Ch. latus, Egerton ; Traquair, p. 512.

1890 Cheiracanthus latus ; Woodward and Sherborn, p. 29.

1891 Cheiracanthus latus, Egerton : Woodward, p. 19

1937 Cheiracanthus latus Eg. ; Watson, p. 88, fig. 13, pl. 12, figs. 4-6.

1947 Cheiracanthus latus Egerton ; Gross, p. 125- 126, fig. 13G, pl. 25, fig. 4.

1966 Cheiracanthus latus Egerton ; Miles, p. 157, 159, fig. 6A, 8E.

1970 Cheiracanthus latus Egerton ; Miles, p. 349, 358, 362.

1973 Cheiracanthus latus Egerton ; Miles, p. 157, text-fig. 22.

1973 Cheiracanthus longicostatus ; Gross, p. 69, figs. 33E, 34A-C, pl. 28.16-20.

? 1973 Cheiracanthus brevicostatus in part; Gross, pl.

28.12.

1976 Cheiracanthus latus ; Zidek, p. 23.

1976 Cheiracanthus spp. in part; Paton, p. 18.

1979 Cheiracanthus latus ; Denison, figs. 29F, 30B,

31A-C.

1979 C. latus Egerton 1861 B; Denison, p. 47.

1985 Cheiracanthus longicostatus ; Valiukevičius, p.

35, figs. 12-14, plates 2.1-10, 4.10-11, 8.7-8,

10, 11.10.

1988 C. longicostatus ; Valiukevičius, p. 75.

1995 Cheiracanthus longicostatus ; Valiukevičius, Talimaa and Kruchek, figs. 1-5.

1995 Cheiracanthus latus ; Young, p. 68, fig. 8.

1996 Cheiracanthus latus ; Gagnier, p. 162.

1997 C. latus ; Young, p. 48.

1999 C. latus Egerton, 1861 ; Dineley and Metcalf, ch. 6, Den of Findon p. 3.

1999 Cheiracanthus latus Egerton, 1861 ; Dineley and Metcalf, ch. 6, Tynet Burn p. 4, fig. 6.20A.

2000 Cheiracanthus longicostatus Gross ; Valiukevičius, figs. 1, 4, 5.

2002 Cheiacanthus longicostatus [sic]; Valiukevičius, table 1.

2002 Cheiracanthus longicostatus ; Valiukevičius, p.

37.

2005 C. latus Egerton, 1861 ; Burrow and Young, p.

13.

2005 Cheiracanthus latus ; Burrow and Young, p. 15.

2009 Cheiracanthus latus ; Albert et al., app. 1 p. 371. 2010 Cheiracanthus longicostatus ; Sallan and Coates, p. 24.

2011 Cheiracanthus latus ; Retallack, fig. 1C.

2014 Cheiracanthus longicostatus ; Ivanov and Märss, p. 158.

? 2015 Cheiracanthus longicostatus ; Plax, pl. 4, figs. 3, 4.

2018 C. latus Egerton ; Glinskiy and Pinakhina, p. 84. 2018 Cheiracanthus latus? Egerton ; Pinakhina and Märss, p. 99, table 1, fig. 4R.

2019 Cheiracanthus latus Egerton, 1861 ; Newman, Burrow and den Blaauwen, p. 13, figs. 13, 14.

Holotype. NHM UK PV P3253 from Tynet Burn.

Remarks. Egerton (1861, pl. 10) states that the type specimen figured by him was forwarded to him by the then recently deceased Duke of Richmond, from his quarries at Tynet Burn. This specimen is not part of the Egerton collection now in the Natural History Museum and therefore must be considered lost. However, it is known that Egerton and his good friend William Cole, 3 rd Earl of Enniskillen, used to swap parts and counterparts with one another (E. Bernard, pers. comm.) As NHM UK PV P3253 is part of the Enniskillen collection (also housed in the NHMUK) and is a mirror image of Egerton’s (1861, pl. 10) figure, it is certain that it is the counterpart of Egerton’s (1861) type specimen and is therefore one half of the holotype.

Material examined. From Cromarty: NMS G.1870.14.145. From Cushnie Burn: NMS G.1965.59.38. From Gamrie: NMS G.1870.14.173; NMS G.1882.60.14; NMS G.1891.92.320; NMS G. 1892.8.3; NMS G.1891.92.320; NMS G. 2019.3.7; NMS G. 2019.9.19; NMS G.22019.9.22; NMS G.2019.14.7; NMS G.2019.14.8. From Tynet Burn : NHM UK PV P3253a [note: not the counterpart of the holotype]; NHM UK PV P43273a, b; NMS G.1968.19.18; NMV P29280 ; NMV P203744 ; NMV P204033 ; QMF60004 From Jessie Port , Tarbat Ness Peninsula: NMS G. 2019.3.3. From Geanies Point , Tarbat Ness Peninsula: NMS G. 2019.9.17; NMS G. 2019.9.18; NMS G.2019.14.9; NMS G. 2019.9.20; NMS G. 2019.9.23; NMS G.2019.14.4. From Hilton of Cadboll (below the Achanarras horizon): NMS G.2019.14.10. From Eathie, Black Isle: NMS G. 2019.9.21. From Tarrel Bay , Tarbat Ness Peninsula: NMS G.2018.28.26.

Distribution. Nodule beds stratigraphically equivalent to the Achanarras Fish Bed Member (Eifelian), Moray Firth; Narva (Narova) Formation (Eifelian), Estonia, Latvia, and Narva R.S. Russia, possibly ranging from the Rezekne R.S. (upper Emsian) to the top of the Burtnieki R.S. (upper Givetian) in the Baltic countries and Belarus (Valiukevičius, 2000; Plax, 2015).

Diagnosis. Cheiracanthus with large deep tail, its greatest depth c. one-third the length of the fish; deep palatoquadrate with maximum depth c. 2.5 times maximum depth of Meckel’s cartilage; Lunate dorsal circumorbital bone; dorsal branchiostegal rays very short and slender with a distinct bend downwards on their anterior ends; long, thin rays above the main branchial cover; scale crowns with two broad median ridges edging median longitudinal sulcus with an oval pit in the posterior half; posterior crown with serrated margin.

Description. General features: The body shape and relative proportions of the fins were described by Watson (1937). The most obvious feature distinguishing C. latus from C. murchisoni and C. grandispinus is the large caudal fin. The dorsal spine is slender and straight, positioned midway between the levels of the pelvic and anal spines. The anal spine is also slender and straight, and c. 80% the length of the dorsal spine. The pelvic spines show a very slight curvature, and are c. 65% the length of the dorsal spine. The pectoral spines are a similar length to the dorsal spine and slightly curved.

Head and branchial region: The head of Cheiracanthus latus is very similar to that of Cheiracanthus murchisoni . The only difference Watson (1937) noted was that the dorsalmost branchiostegal rays in C. latus are shorter, slenderer, and the anterior ends turn sharply ventrally ( Figure 24.1, 24.2 ). We note that the main branchiostegal rays are ornamented with thin parallel longitudinal ridges, however, this ornament is rarely seen as the rays usually fracture centrally when nodules are split. NHM P43273 is a rare specimen where it is visible ( Figure 24.4 ). We also note that C. latus has distinct circumorbital bones ( Figure 24.3 ) with the most dorsal one extending about one-fifth the circumference of the orbit.

Thin sections ( Figure 25 ) show that the jaws and most other endoskeletal structures in these regions are mineralised as calcified cartilage (cc) with the same basic varieties as in C. murchisoni . The jaws are mostly a single layer of contiguous calcified cartilage blocks ( Figure 25.1-3 ), and the branchial arches comprise a more irregular consolidated globular calcified cartilage forming cylinders filled with calcite that has presumably replaced the uncalcified cartilage core. The endoskeletal branchial arches show a similar structure as in C. murchisoni , but the walls are thinner and appear to comprise only one layer ( Figure 25.3, 25.4 ). As the C. latus fish sacrificed for thin sectioning was larger than the C. murchisoni one, it is unlikely that the difference in thickness is related to the size of the fish. The dermal branchiostegal plates and smaller gular rays are formed of a dense lamellar bone ( Figure 25.5-7 ); the ornament layer on the branchiostegal rays comprises sharp crested ridges. Small mono- and multicuspid denticles are preserved around the branchiostegal rays ( Figure 25.5, 25.7 ). Blocks of short, thin mineralised elements within the branchial regions are interpreted as the endoskeletal gill bars ( Figure 25.6, 25.7 ); some show short projections ( Figure 25.6 ). Flat or concave based dermal tesserae from the head region have a lamellar base and areal-growth odontodes formed of acellular layered dentine ( Figure 25.7, 25.8 ).

Pectoral region and fin spines: The scapulocoracoid of Cheiracanthus latus closely resembles that of C. murchisoni , with a slender tapering scapular shaft ( Figures 24.1-4 , 26.1 ). Miles (1973, text-figure 22) described the pectoral region of C. latus , correcting some of the observations made by Watson (1937). We note that there is a marked delineation between the scapula and the coracoid ossifications ( Figure 26.1-2 ).

None of the fin spines are deeply inserted, contra Watson (1937). As noted by Watson (1937), the dorsal fin spine has a basal bone ( Figure 26.3 ); this is a short D-shaped mineralised cartilage. The pulp cavity is open for about half the length of the spine. The pectoral spines have a smooth leading edge ridge, deep lateral groove, and thin longitudinal ridges along the side, usually best developed more proximally ( Figure 26.4-5 ). A single row of pores opens out in the groove. They have a short insertion, and a strip lacking dentine extending along the upper side of the spine, where the scapulocoracoid abutted ( Figure 26.6 ). Like the dorsal spine, the anal and pelvic spines have a smooth leading edge ridge separated from the smooth sides by a deep groove ( Figure 26.7 ).

The scapulocoracoid is formed of a dense lamellar bone around a central cavity ( Figure 27.1- 2 ). The histological structure of the fin spines is very similar to that of C. murchisoni and C. grandispinus , the main difference being that the lateral groove is not as deeply incised ( Figures 27.3-9, 27.11-13 , 28 ). The pectoral spines have a very thin enameloid layer on the leading edge ridge and the ‘shoulders’, with most of the spine formed of osteodentine. Spines lack an accessory pulp canal. Pores leading from the vascular canals open out into the lateral groove ( Figure 27.3-4, 27.13 ). Dentine tubules of the osteodentine layer are usually only visible near the surface of the anterior ridge ( Figure 27.5 ), oriented perpendicular to the surface and running in to the more or less radially arranged vascular canals. The inner lamellar layer is very thin proximally, thickening distally ( Figure 27.6, 27.9 ), and is penetrated by fine branching dentine tubules ( Figure 27.10 ). The vascular canals and the central pulp cavity become almost closed by lamellar infilling towards the tip of the spine ( Figure 27.6, 27.9-10 ), but canals still extend from the cavity through the dentine ( Figure 27.7, 27.9-10 ). The inserted part of the spine lacks an outer enameloid cover and dentine tubules, and is composed of a vacuous osteodentine or bone ( Figures 27.12 , 28.1.12 , 28.2.6). The thin longitudinal ridges on the sides of the spines are low, sharp-crested, and best visible in the proximal part of the spine ( Figure 27.13-14 ).

Body scales: The mid-flank scales of Cheiracanthus latus range in size from 0.25 mm wide on small fish c. 130 mm long ( Figure 29.1-2 ), c. 0.5 mm wide on medium sized fish ( Figure 29.3-7 ), to 1.0 mm wide ( Figure 29.8 ) on large fish. The scale crown has a marked smooth rim along the anterior edge ( Figures 29.4-8 , 30.1-3, 30.5-10 ). The ornament over the rest of the crown comprises two prominent, broad ridges ("Groszrippen" of Gross, 1947, p. 125) extending back on either side of a median sulcus, and narrower, sharp-crested ridges on both sides of the median ridges extending back towards the serrated posterolateral edges of the crown ( Figures 29.8 , 30 ). A few short ridges are developed in the anterior part of the median sulcus, and an oval pit is developed in the posterior half of the scale within the sulcus ( Figures 29.4, 29.5, 29.7-10 , 30 ). The neck and base of the scales ( Figure 30.3, 30.6, 30.10 ) closely resemble those of C. murchisoni in general profile and relative heights.

In most histological features the scales of C. latus resemble those of C. murchisoni , other than the development of a wide midline channel extending the length of the crown, which usually deepens to form an oval pit just posterior to the centre of the scale. The ridges extending back from the anterior edge are sharp-crested near this edge ( Figure 31.1 ), becoming rounded more posteriorly ( Figure 31.2 ), and often fading out past the posterior median pit ( Figure 31.3-8 ). The crown is formed of up to 10 growth zones, which show that the wide central pit/channel was present at all stages from the embryonic/primordial scale ( Figure 31.3-7 ). As in C. murchisoni , the primordial scale (c. 60 μm long and 70 μm wide) contains wide lacunae connected by short canals ( Figure 31.8 ) with offshoots extending down into the top of the basal cone. Each growth zone has its own system of anastomizing ascending canals, building an intricate network especially in the posterior side of the scales ( Figure 31.7-9 ). The anterior areas of the crown growth zones are developed similarly to those of C. murchisoni , but differ in that the horizontal canals in the upper crown leading back from the semicircular ring canal are arranged much less regularly, and the lateral canals are better developed than the central canals ( Figure 31.10, 31.11 ). This central area is delimited by two strongly developed horizontal canals, which extend further posteriorly than the other canals, in the larger ribs that flank the central pit. The horizontal canals are always situated in the grooves between crown ridges ( Figure 31.1 ). In the posterior half of the crown, the ascending networks of canals gradually turn from a vertical into a more horizontal direction ( Figure 31.8-10 ). The enameloid layers in the crown growth zones fill most of the depth of each zone in the ridges flanking the central pit, diminishing in depth laterally and disappear about halfway between the midline and the lateral edge. In the midline of the crown, enameloid layers are only developed anterior to the central channel and are completely lacking along most of the length ( Figure 31.3-7 ). Fin web scales distal to the fin base differ markedly to the flank scales in their general shape, having a flat or concave base, deep neck, and crown plane that is concave both anteroposteriorly and side to side ( Figure 31.12, 31.13 ).

Scale Comparisons

Cheiracanthus scales are common elements in microvertebrate assemblages from the Middle Devonian of the Baltic countries. Gross (1973) erected three new species, C. brevicostatus , C. longicostatus , and C. splendens , based on isolated scales mainly from the Eifelian Narva Formation, Estonia. The scale morphology of C. longicostatus Gross, 1973 appears identical to that of C. latus . Although Gross (1973, plate 28.16-20) differentiated the crown of C. longicostatus as relatively long and narrow, the figured scales do not corroborate this feature, as all have a width that is equal to or wider than the length, even when broken posterior ends are taken into account. One of the scales that Gross (1973, plate 28.12) assigned to his newly erected species C. brevicostatus should also be assigned to C. latus . At least some C. brevicostatus scales show features distinguishing them from other species – serrated posterior margins of crown growth zones and interconnections of horizontal canals in the upper crown. The main feature determined by Gross (1973) to distinguish them from C. murchisoni is crown ridges of unequal width, but the crown on the holotype of C. brevicostatus (Gross, 1973, pl. 28.10) is similar to some C. murchisoni scale crowns ( Figures 11 , 12 ). We surmise that at least some of the records of C. brevicostatus from the Baltic countries are likely to be C. murchisoni , but are as yet unable to verify this determination. We have only identified one published illustration of a scale possibly assignable to C. grandispinus from the Baltic countries. Valiukevičius (1985, pl. 13.8) labelled the specimen from the Narva Formation as Diplacanthus ? carinatus, but the crown closely resembles the distinctive C. grandispinus scale in Figure 20.10 . Den Blaauwen et al. (2019) assigned the Narva Formation scale to C. peachi , as one of the scale morphotypes of the latter species (den Blaauwen et al., 2019, figure 7e-j) shows similarity to scales of C. grandispinus . Certainly in crown ornament, C. peachi most closely resembles C. grandispinus . C. splendens does not appear similar to scales on any of the Scottish Cheiracanthus specimens that we have examined. As we have noted, however, other newly identified Scottish cheiracanthid species are still to be described, one or more of which belong to taxa erected based on isolated scales from the Baltic countries.

Reconstruction of Cheiracanthus

The lateral reconstructions of Cheiracanthus latus ( Figures 32 , 33 ) closely follows Watson’s (1937, figure 13) reconstruction except for details of the head, as described earlier, and the angle of the pectoral fin spine. The shallower angle of the pectoral fin spine is based on the alignment of the upper edge of pectoral fin spine with the base of the scapula as described above. We speculate that these spines projected markedly laterally; when the fish were compressed during burial the spines were dislocated. All three species of Cheiracanthus described here have similar body shapes, with C. latus having a slightly larger and deeper caudal fin.

Figures

FIGURE 4. Cheiracanthus latus Egerton, 1861 holotype from Tynet Burn. 1, NHMUK PV P3253, half of specimen not previously figured; 2, half of the holotype specimen illustrated by Egerton (1861, plate 10, figure 1, 2), now lost. Scale bar equals 20 mm.

FIGURE 6. Specimens sacrificed for thin sectioning; numbered slices are vertical unless indicated. 1, 2, Cheiracanthus murchisoni NMS G.2019.3.6 from Gamrie; slices 36-38 horizontal. 3, 4, Cheiracanthus grandispinus, NMS G.2019.9.7 from Achanarras. 5, 6, Cheiracanthus latus NMS G.2019.3.3 from Jessie Port; slices 18, 19 horizontal. 7, 8. Cheiracanthus latus NMS G.2019.3.7 from Gamrie. Scale bars equal 20 mm. a.fs, anal fin spine; d.fs, dorsal fin spine; gr, gular rays; Mc, Meckel’s cartilage; pect.fs, pectoral fin spine; pelv.fs, pelvic fin spines; sc, scapulocoracoid; SEM, area where scales were removed for scanning electron microscopy; small numbers indicate suffix on NMS G specimen number for each thin section.

FIGURE 11. Cheiracanthus murchisoni squamation: light microscope images, all mid-body scales except 9. 1, NMS G.1892.8.1 from Gamrie. 2, NMS G.1891.92.323 from Lethen Bar. 3, NMS G.2019.9.25 from Cromarty, Sutors. 4, NMS G.2019.9.26 from Tarbat. 5, NMS G.1882.16.13 from Cromarty. 6, NMS G.1899.83.5 from Hooveth, Orkney. 7, NMS G.1877.30.2 from Tynet Burn. 8, NMS G.1968.5.3 from Edderton. 9, NMS G.2019.9.27 from Blackpark, tail. 10, NMS G.2019.9.28 from Blackpark, scales with crown pits. Scale bars equal 1.0 mm in 1, 2, 7, 8; 0.5 mm in 3-6, 9, 10. p, pit on posterior scale crown.

FIGURE 12. Cheiracanthus murchisoni scale morphology. 1-11, NMS G.2019.3.6 from Gamrie: 1-6, SEM images of scale patch NMS G.2019.3.6.35 removed from midflank of counterpart; 7-11, drawings of scale crowns from: 7, behind the head; 8, midbody; 9, near the dorsal fin spine; 10, in front of the tail; 11, on the tail. 12-15, SEM images of detached midbody? scales of NMS G.2019.9.29 from Cromarty Sutors: 12, NMS G.2019.9.29.11.5, crown view; 13, NMS G.2019.9.29.11.2, laterocrown view; 14, NMS G.2019.9.29.11.19, lateral view; 15, NMS G.2019.9.29.11.1, anterolateral view. 16, 17, NMS G.2019.9.29.12 from Cromarty Sutors: 16, NMS G.2019.9.29.12.3, base showing concentric lines of Sharpey’s fibre bundles; 17, NMS G.2019.9.29.12.2, patch of articulated scales, crown view. 18, 19, ventral mid-body squamation patches of NMS G.2019.9.31.2 from Den of Findon. 20, NMS G.2019.9.30.2 from Edderton, scale in squamation patch. Scale bars equal 1.0 mm in 1-3, 0.3 mm in 4-11 (7-11 all at same scale), 17, 18, 20; 0.1 mm in 12-16, 20.

FIGURE 20. Cheiracanthus grandispinus scale morphology. 1-3, 5-9, light microscope images; 4, 10-18, SEM images; midbody scales unless detailed otherwise. 1, NMS G.1891.92.317 from Lethen Bar. 2, NMS G.2019.9.8 from Jessie Port, Ross and Cromarty. 3, 4, USCP F00115b from Edderton. 5, NMS G.2019.9.9 from Achanarras, primordial scale revealed after abrasion/flaking of overlying crown growth zones. 6-9, NMS G.2019.9.10.1 from Cromarty: 6, mid-body scales; 7-9, pectoral fin web: spine and web; 8, distal scales; 9, scales near fin base. 10-12, NMS G.2019.9.11 from Marwick: 10, view of crown before removal of scale from matrix; 11, anterocrown view; 12, posterior view. 13, NMS G.2019.9.3.27.1 from Gamrie Den of Findon, laterocrown view. 14-18, NMS G.2019.9.13.8 from Cromarty, Eathie to Navity: 14, NMS G.2019.9.13.8.16, anterocrown view; 15, NMS G.2019.9.13.8.2 pair of scales in posterocrown view; 16, NMS G.2019.9.13.8.8, laterocrown view; 17, NMS G.2019.9.13.8.6, lateral view; 18, NMS G.2019.9.13.8.17, posterobasal view. Scale bars equal 0.5 mm in 1-9, 0.2 mm in 10-18. p, neck protuberance; ps, primordial scale. Arrows indicate anterior.

FIGURE 24. Cheiracanthus latus head and branchial region, morphology. 1-2, NHM PV P 3253 from Tynet Burn. 3, NMS G.1891.92.320 from Gamrie. 4, NHMUK PVP43273 from Tynet Burn, branchial region with ridges visible on lowest branchiostegal plates. Abbreviations: br.l, left branchiostegal plates; br.r, right branchiostegal plates; cop, circumorbital plate; gr, gular rays; Mc.l, left Meckel’s cartilage; Mc.r, right Meckel’s cartilage; pect.fs, pectoral fin spines; pq.l, mineralised cartilage along ventral edge of left palatoquadrate; proc, procoracoid; sc, scapulocoracoids; tess, head tesserae. Scale bars equal 10 mm.

FIGURE 25. Cheiracanthus latus head and branchial region, histology, NMS G.2019.3.3; position of sections shown in Figure 6.6. 1, 2, thin section NMS G.2019.3.3.3: 1,?Meckel’s cartilage; 2, closeup of calcified cartilage blocks; 3, 4, NMS G.2019.3.3.5, indet. jaw cartilage and branchial arches; 5, NMS G.2019.3.3.2, branchiostegal plate in oblique section, body scales, branchial denticles, indet. cartilage; 6, NMS G.2019.3.3.4, body scales, gill bars; 7, 8, NMS G.2019.3.3.17: 7, jaw cartilage, head tesserae, gill bars, branchiostegal plates; 8, head tessera vertical section, stellate mineralisation artifacts. Scale bars equal 1.0 mm in 1, 3, 5, 7, 0.1 mm in 2, 4, 6, 8. ba, branchial arch; br, branchiostegal plate; ccb, calcified cartilage blocks; d, denticle; gb, gill bar; gcc, globular calcified cartilage; gz, growth zones in crown; s, body scale; t, tessera.

FIGURE 26. Cheiracanthus latus pectoral region and spines, morphology. 1-3, QMF60004 from Tynet Burn: 1, left and right scapulocoracoids, white arrows indicate separation between scapula and coracoid; 2, close up of right coracoid shape (dotted line); 3, dorsal fin spine insertion and basal cartilage, white arrow indicates insertion/exertion boundary. 4-6, NMS G.2018.28.26 from Tarrel Bay: 4, left and right pectoral spines as collected; 5, closeup of thin ridges on lateral or medial? side of right spine; 6, insertion area of right spine. 7, NMS G.1968.19.18, anal and pelvic spines. Scale bars equal 5.0 mm in 1-3, 6, 20 mm in 4, 7, 0.5 mm in 5. a.fs, anal fin spine; bc, basal cartilage; calc, calcite infill; pelv.fs, pelvic fin spines.

FIGURE 27. Cheiracanthus latus pectoral region and spines, histology. 1-6, NMS G.2019.3.31 (see Figure 6.6 for map of sections): 1, slice II before grinding (corresponds to sections 6, 7), arrow indicates dorsal direction; 2, NMS G.2019.3.3.7, scapulocoracoid, long section mid-shaft; 3, NMS G.2019.3.3.12, TS pectoral spine at insertion/exertion boundary; 4, NMS G.2019.3.3.10, TS of spine close to insertion; 5, NMS G.2019.3.3.6, close up of leading edge ridge structure of pectoral spine, midspine; 6, NMS G.2019.3.3.2, TS pectoral spine near the tip. 7-10, NMS G.2018.28.26, TS pectoral spines: 7, 2018.28.26.9, close to insertion; 8, 2018.28.26.7, midspine; 9, 10, 2018.28.26.5, towards tip, with closeup of infilling dentine. 11-14, NMS G.2019.3.7 TS pectoral spine, near insertion, and flange of scapulocoracoid: 11, NMS G.2019.3.7.8; 12, NMS G.2019.3.7.9; 13-14, NMS G.2019.3.7.10, outer side of spine with thin sharp ridges. Scale bars equal 10 mm in 1; 0.1 mm in 2, 5, 10; 0.5 mm in 3, 4, 6, 7-9, 11-14. c.cav, central cavity; ccb, calcified cartilage blocks; dt, dentine tubules; en, enameloid; l.pect.fs, left pectoral fin spine; min, stellate mineralisation; ost, osteodenteon; pect.fs, pectoral fin spine; r, ridges; s, scale; sc, scapulocoracoid.

FIGURE 28. Cheiracanthus latus pectoral spines, serial transverse section drawings. 1, NMS G.2018.28.26 (see Figure 27): sketch map and drawings of each section. 2, NMS G.2019.3.7 (see Figure 6.7, 8): sections NMS G.2019.3.7.6-12 through pectoral spines and scapulocoracoid.

FIGURE 29. Cheiracanthus latus squamation, light microscope images. 1, 2, QMF60004 from Tynet Burn: 1, midflank scales; 2, caudal peduncle, scale impressions. 3, 4, NMS G.2018.28.26 from Tarrel Bay. 5-7, NMS G.2019.3.7 from Den of Findon, Banffshire 8, NMS G.2019.3.3 from Jessie Port. 9, NMS G.1870.14.145 from Cromarty. 10, NMS G.2019.9.17 from Geanies Point. Scale bars equal 0.5 mm. p, pit. Arrows indicate anterior.

FIGURE 30. Cheiracanthus latus squamation, SEM images. 1-5, NMS G. 2019.3.7.21 from Den of Findon: 1, NMS G. 2019.3.7.21.2, crown view; 2, NMS G. 2019.3.7.21.5, crown view; 3, NMS G. 2019.3.7.21.13, anterior view; 4, NMS G. 2019.3.7.21.7, laterocrown view; 5, NMS G. 2019.3.7.21.14, laterocrown view. 6-7: NMS G.2019.14.9.2 from Geanies Point: 6, NMS G.2019.14.9.2.8, anterocrown view; 7, NMS G.2019.14.9.2.5, crown view. 8-10: NMS G.2019.14.4.2 from Hilton or Cadboll: 8, NMS G.2019.14.4.2.15, crown view; 9, NMS G.2019.14.4.2.5, crown view; 10, NMS G.2019.14.4.2.16, laterocrown view. Scale bars equal 0.2 mm. p, pit; pr, neck protuberance.

FIGURE 31. Cheiracanthus latus scale histology. 1, NMS G.2019.9.21.5, vertical transverse section, anterior half of scale. 2, NMS G.2019.9.19.2, vertical transverse section, anterior half of scale. 3, NMS G.2019.9.20.3, vertical transverse section, midscale. 4, 5, NMS G.2019.3.3.14, vertical transverse section, midscale, with closeup of central region. 6, NMS G.2019.9.21.3, vertical transverse sections of two scales, posterior half of scale. 7, NMS G.2019.3.3.12, vertical transverse section towards posterior end of scale. 8, NMS G.2019.3.7.6, subhorizontal section through anterior base and posterior crown. 9, NMS G.2019.3.7.6, vertical oblique section through posterior crown and base. 10, NMS G.2019.9.19.7, horizontal section low in crown. 11, NMS G.2019.9.22.5, horizontal section high in crown. 12, 13, NMS G.2019.9.23.7, section through fin web scales including tiny distal scales with a deep neck and flat base, closeup of distal fin web scales in 13. Scale bars equal 0.1 mm in 1-11,13, 0.5 mm in 12. Arrows indicate anterior.

FIGURE 32. Cheiracanthus latus head and branchial region reconstruction.

FIGURE 33. Reconstruction of a whole Cheiracanthus latus in lateral view.