Cheiracanthus murchisoni Agassiz, 1835
|
publication ID |
https://doi.org/ 10.26879/1035 |
|
persistent identifier |
https://treatment.plazi.org/id/039D87FE-FFDB-FFB6-3186-2CCDFA9DFA84 |
|
treatment provided by |
Felipe |
|
scientific name |
Cheiracanthus murchisoni Agassiz, 1835 |
| status |
|
Cheiracanthus murchisoni Agassiz, 1835
Figure 1 View FIGURE 1 , Figure 2 View FIGURE 2 , Figure 6.1, 6.2 View FIGURE 6 , Figures 7-14 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 View FIGURE 14
1835 Cheiracanthus murchisoni Agass. ; Agassiz, vol. 2 p. 126-127, pl. 1c, figs. 3-4.
1835 Cheiracanthus minor Agass. ; Agassiz, 127-128, pl. 1c, fig. 5.
1841 Cheiracanthus ; Miller, p. 86, 88-93, pl. 7, figs. 1- 2.
1844 Cheiracanthus microlepidotus Agass. ; Agassiz, 38-39, pl. 15, figs. 1-3.
1847 Cheiracanthus microlepidotus Ag. ; Miller, p. 119, 122-126, pl. 7, figs. 1-2.
1848 Chiracanthus pulverulentus (M’Coy) ; M’Coy, p. 299.
1848 C. murchisoni (Ag.) ; M’Coy, p. 299.
1848 Chiracanthus lateralis (M’Coy) ; M’Coy, p. 300.
1855 Chiracanthus lateralis (M’Coy) ; M’Coy, p. 582.
1855 Chiracanthus microlepidotus (M’Coy) ; M’Coy, p. 583.
1855 Chiracanthus minor (M’Coy) ; M’Coy, p. 583.
1855 Chiracanthus murchisoni (Ag.) ; M’Coy, p. 583.
1855 Chiracanthus pulverulentus (M’Coy) ; M’Coy, p. 583, pl. 2B, fig. 2.
1860 Cheiracanthus lateralis ; Egerton, p. 123.
1860 Cheiracanthus minor ; Egerton, p. 123.
1860 Cheiracanthus pulverulentus ; Egerton, p. 123.
1861 Cheiracanthus murchisoni ; Egerton, p. 73.
1861 Cheiracanthus microlepidotus ; Egerton, p. 73- 74.
1861 Cheiracanthus minor ; Egerton, p. 73.
1861 Cheiracanthus pulverulentus ; Egerton, p. 73.
1888 Ch. murchisoni, Ag. ; Traquair, p. 512.
1890 Cheiracanthus murchisoni ; Woodward and Sherborn, p. 29-30.
1891 Cheiracanthus murchisoni, Agassiz ; Woodward, p. 16-18.
1907 Cheiracanthus murchisoni ; Dean, p. 213.
1927 Cheiracanthus murchisoni Ag. 1835 (t.), 1836 (p.); Jeannet, p. 106.
1927 Cheiracanthus microlepidotus Ag. 1844 ; Jeannet, p. 106.
1935 Cheiracanthus murchisoni Agassiz ; Watson, p. 158, fig. 22.
1937 Cheiracanthus murchisoni Ag. ; Watson, p. 84- 88, fig. 12, pl. 12, figs. 1-3.
1940 Cheiracanthus murchisoni Agassiz ; Berg, p. 129, fig. 21B.
1947 Cheiracanthus murchisoni AG ; Gross, p. 124- 125, fig. 13A-F, pl. 25, fig. 5.
1951 Cheiracanthus murchisoni ; Ørvig, p. 414.
1966 Cheiracanthus murchisoni Ag. ; Miles, p. 159, 161, fig. 8F.
1970 Cheiracanthus murchisoni Agassiz ; Miles, p.
362.
1973 C. murchisoni Agassiz ; Miles, p. 157, pl. 20.2
1976 Cheiracanthus murchisoni Agassiz 1835 ; Paton, p. 18.
1976 Cheiracanthus murchisoni ; Zidek, p. 23.
1979 Cheiracanthus murchisoni ; Denison, figs. 9E, 10J, 31D.
1979 C. murchisoni Agassiz 1835 ; Denison, p. 47.
1995 Cheiracanthus murchisoni ; Young, p. 68, fig. 9.
1996 Cheiracanthus murchisoni ; Gagnier, p. 162.
1997 C. murchisoni ; Young, p. 48.
1999 Cheiracanthus murchisoni ; Dineley and Metcalf, ch. 6, Den of Findon p. 1, 3; Cruaday Quarry fig. 6.12E, F; Tynet Burn fig. 6.20B.
1999 Cheiracanthus murchisoni Agassiz, 1835 ; Dineley and Metcalf, ch. 6, Den of Findon p. 3; Achanarras Quarry p. 3; Cruaday Quarry p. 3; Black Park p. 3.
1999 C. murchisoni Agassiz, 1835 ; Dineley and Metcalf, ch. 6, Tynet Burn p. 3.
2005 Cheiracanthus ; Davidson and Trewin, p. 131, table 1, fig. 2A, 2B.
2005 Cheiracanthus murchisoni ; Newman and Dean, p. 4.
2005 C. murchisoni ; Newman and Dean, p. 4.
2005 Cheiracanthus murchisoni Agassiz, 1835 ; Burrow and Young, p. 13.
2010 Cheiracanthus murchisoni ; Sallan and Coates, p. 24.
2015 Cheiracanthus murchisoni ; Taylor and O’Dea, p. 51, 216, fig. on pp. 50-51.
2018 Cheiracanthus murchisoni Agassiz, 1835 ; Glinskiy and Pinakhina, p. 83.
2019 Cheiracanthus murchisoni Agassiz, 1835 ; Newman, Burrow and den Blaauwen, p. 5.
Holotype. MHNN FOS 39 from Lethen Bar.
Material examined. From Lethen Bar: MHNN FOS
40, 41; NHMUK PV P544; NMS G.1891.92.323;
NMS G.1966.40.23; NMS G. 1972.23.1; NMS
G.1973.12.106; NMS G.1973.12.109; NMS
G.1973.12.120; NMS G.1973.12.116; NMS
G.1973.12.130; NMV P30172. From Tynet Burn:
NMS G.1877.30.2; NMS G.1884.60.3; NMS
G.2000.65.1; NMS G.2000.65.2; NMS G.2019.14.1;
NMS G.2019.14.2; NRM P1638; NRM P1654;
QMF60005. From Gamrie: NMS G.1891.92.8.1;
NMS G.1891.92.306; NMS G.1891.92.307; NMS
G. 1975.12.8; NMS G. 2019.3.6; NMV P29277 About NMV ; NMV
P29286; NMV P29287; NRM P1650. From Geanies Point, Tarbat Ness Peninsula: NMS
G.2019.14.3. From Cromarty: NMS G. 1953.4.2; NMS G. 2019.9.25; NMS G. 2019.9.29; NMS G.2019.9.32. From Jessie Port, Tarbat Ness Peninsula : NMS G.2019.14.6; NMS G.2019.9.33. From Edderton, Ross and Cromarty : NRM P4260 View Materials ; NMS G. 2019.9.27; NMS G. 2019.9.28; NMS G. 2019.9.30. From Tarbat Ness: NMS G. 2019.9.26 (this is from below the Achanarras horizon). From Den of Findon : NMS G. 2019.9.31. From the Moray Firth area : NMS G.1870.14.171; NMS G.1882.16.13; NMS G.1981.39.36. From Cruaday Quarry : NMS G. 2019.9.24. From Hooveth, Orkney: NMS G.1899.83.5; From Instabillie, Orkney: NMS G.1898.163.4. From Orkney: SM H 4424 ; SM H 4425 .
Distribution. Nodule beds stratigraphically equivalent to the Achanarras Fish Bed Member, Moray Firth; Sandwick Fish Bed Member and Upper Stromness Flagstone Formation (Eifelian), Orkney;?undetermined levels in the Narva Regional Stage (R.S.), Baltic countries.
Diagnosis. Cheiracanthus with more than 20 contiguous long, robust, branchiostegal rays with straight posterior ends; several fine thin rays above the main branchial cover; fine thin gular rays below the jaws; slender, dorsally-tapering scapular shaft, height 10 times its minimum width; spiracle with pair of comma shaped valves; pectoral spine with low sharp-crested ridges along lateral faces; scale crowns ornamented with non-branching subparallel ridges extending from the anterior edge and terminating before mid-crown; some scales with a posterior median pit on the crown; scale crown growth zones with straight posterolateral edges.
Description. General features: The dorsal fin spine is positioned halfway between the pelvic and anal spines. On all fish, the pelvic spines are always the shortest, about 60 percent of the length of the dorsal spine. The anal spine is intermediate in length between that of the dorsal and pelvics, about 70 to 75 percent the length of the dorsal spine. The pectoral spine is variable in length, and can be shorter than, equal in length, or longer than the dorsal spine.
Head and branchial region: Watson (1937, figure 12) detailed the main morphological features of these regions, so we only present an overview and describe new observations ( Figure 7 View FIGURE 7 ). The lower jaw Meckel’s cartilages are always mineralised as a single unit as are the palatoquadrates, but these are less frequently mineralised, and are also often not preserved intact but as scattered patches. We note that the fossa for insertion of the adductor muscle on the lateral side of the Meckel’s cartilage ( Figure 7.1-3 View FIGURE 7 ) extends about half the length of the jaw. The ventral margin of the cartilage is thickened to form a ridge along this edge. The small preglenoid process is quite rounded, and the articular cotylus is a shallow embayment, slightly longer than wide. Tooth-like structures are present in the mouth ( Figure 7.1-3 View FIGURE 7 ). These are possibly eqivalent to similar elements in Homalacanthus concinnus , where they are distributed in rows near the upper edge of the Meckel’s cartilage and the lower edge of the palatoquadrate (Schultze, 1972, figure 2).
The two main dermal elements of the head and branchial region are the orbital bones and the branchiostegal rays. The former comprise 4-6 sclerotic plates ( Figure 7.4, 7.5 View FIGURE 7 ), not circumorbital bones as described by Watson (1937); see Burrow et al. (2011). Disarticulated sclerotic plates ( Figure 7.1, 7.2 View FIGURE 7 : shaded grey) show that they are short, curved, and mesially concave. In articulation they are close-set ( Figure 7.4 View FIGURE 7 ). The internal surface is smooth, but the external surface on at least some specimens was ornamented with fine, sinuously radiating ridges ( Figure 7.5 View FIGURE 7 ). The ornament layer appears very thin and is rarely preserved intact ( Figure 7.4 View FIGURE 7 ).
The dermal branchiostegal rays are as Watson (1937) described them ( Figure 7.6, 7.7 View FIGURE 7 ), with c. eight below the angle of the jaw and 16 or more above the jaw angle; some of the larger rays have an ornamentation of two ridges running parallel to their long edges ( Figure 7.8 View FIGURE 7 ). As noted by Watson (1937), the most dorsal branchiostegal rays of the main cover are fairly flat with no abrupt bends to the ventral on the posterior ends of the individual rays ( Figure 7.6 View FIGURE 7 ). We observe that there are also long thin rays above the main branchial cover ( Figure 7.7 View FIGURE 7 ). These are much more fragile than the branchiostegal rays and are rarely preserved. Short delicate rays are present between the dorsal area of main branchial cover and the shoulder girdle ( Figure 7.7 View FIGURE 7 ). Watson (1937, p. 87, figure 12; plate 12, figure 3) described “two small sickleshaped bones” above the main branchial cover on NHMUK PVP.43273 that he identified as the upper end of the hyoid arch. Based on their position and circular arrangement, we interpret these elements as the dermal spiracular valve (Burrow et al., 2020). The internal pseudobranch is also seen as an impression on NRM P1650 ( Figure 7.9 View FIGURE 7 ) and in thin section on NMS G.2019.3.6.15 (see next section). Thin gular rays are also present below the jaws ( Figure 7.7 View FIGURE 7 ). Elements not previously identified are denticles in the branchial region, presumed to have been borne on the branchial arches ( Figure 7.1, 7.2 View FIGURE 7 ; see next section).
Thin sections ( Figure 8 View FIGURE 8 ) show that the jaws and at least some other endoskeletal structures in these regions are preserved as a layer of calcified cartilage (cc), often formed of contiguous blocks which are sub-rectangular in vertical section ( Figure 8.1 View FIGURE 8 ). In other areas, the cartilage layer is formed of separated irregularly shaped blocks ( Figure 8.2-6 View FIGURE 8 ). Rings and lines of Liesegang are sometimes visible within the cc blocks ( Figure 8.2 View FIGURE 8 ). The jaw cartilages are preserved as a single-layer of cc blocks enclosing a calcitic core, presumed to have originally been unmineralised cartilage. Both dorsal and ventral edges of the jaws are thickened, but still encased with just a single layer of cc blocks ( Figure 8.6 View FIGURE 8 ).
Flat or slightly concave based dermal tesserae are borne directly on the cartilage blocks ( Figure 8.3, 8.5 View FIGURE 8 ). The sensory lines on the head are enclosed by paired specialised scales with thin flat bases and thin crowns that arch over and meet along the median line between the two rows of scales ( Figure 8.7, 8.9 View FIGURE 8 ). The scale crowns are formed of superposed growth zones. Tesserae above the jaws have a thick base penetrated by Sharpey’s fibres and a dentinous crown showing apposed growth zones ( Figure 8.8 View FIGURE 8 ).
The anteriormost branchial arches are formed of a two-layered, consolidated cc, with the outer layer appearing denser than the inner layer ( Figure 8.10, 8.11 View FIGURE 8 ). This two-layered structure perhaps equates with a mesodermal and neural crest derived origin for the outer and inner layers respectively, based on comparison with the development of the gill arches in skate embryos (see Gillis and Tidswell, 2017, figure 2c).
Some of the branchial arches (e.g., Figure 8.10 View FIGURE 8 ) are surrounded by small plates with a long inclined pointed crown, which we identify as branchial denticles. Other larger elements in the branchial region show a vertical section similar to that of the branchial denticles, but have a large pulp cavity and a dentine crown ( Figure 8.12, 8.13 View FIGURE 8 ). We identify these elements as equivalent to the supposed gill rakers of the cheiracanthid Homalacanthus concinnus . Schultze (1972, figure 4) described these as teeth, but Zidek (1985) subsequently suggested that they were gill rakers, agreeing with Schultze that the outer layer was dentine and so, like teeth, they were dermal structures. We are unable to determine the exact distribution of the elements in C. murchisoni , but refer to them as tooth-like elements as it seems likely that, as in H. concinnus , they are only found near the edges of the palatoquadrate and Meckel’s cartilage rather than being associated with the branchial arches. The dermal branchiostegal plates and smaller gular rays are formed of a dense bone; the ornament layer on the branchiostegal plates is formed of superposed dentine layers ( Figure 8.14-16 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 View FIGURE 16 ). As noted in the previous section, we have also identified spiracular valves, shown in vertical cross section in Figure 8.17 View FIGURE 8 , formed of dense mineralised tissues (Burrow et al., 2020).
Pectoral region and fin spines: The scapulocoracoid has a slender tapering scapular shaft ( Figure 9.1-3 View FIGURE 9 ) with a circular cross section ( Figure 10.1 View FIGURE 10 ). Minimum diameter of the shaft increases very slightly between the smallest and largest fish, being 0.9 mm in the 100 mm long NMS G.1965.59.34 and 2.0 mm in the 205 mm long NMS G.1972.23.1. The height of the scapulocoracoid, however, increases more dramatically, being 6.0 mm in the smallest and 19.0 mm in the largest fish ( Table 1). Contra Watson (1937), the ventral edge of the scapulocoracoid is contiguous with the upper surface of the pectoral fin spine, as described by Miles (1973). The line of fusion between the scapula and coracoid is convex upwards ( Figure 9.3 View FIGURE 9 ). Miles (1973) noted that the element sometimes mineralised in front of the fin spine, that Watson (1937) referred to as the coracoid, is in fact the procoracoid.
All the fin spines have only one groove on each side, separating the leading edge ridge from the ‘shoulder’ (i.e., rounded upper corner) of the sides ( Figure 9.1, 9.2, 9.4-6 View FIGURE 9 ). Towards the base of the spine, the groove becomes deep and narrow. The pectoral fin spine has low, sharp-crested lateral ridges ( Figure 9.4, 9.5 View FIGURE 9 ), which are sometimes also present on the dorsal fin spines. In all spines the inserted part is short, contra Watson (1937, p. 84). The pulp or central cavity of the spines is open posteriorly/along the trailing edge for a considerable distance, up to half the total length on the dorsal spine.
The dorsal fin spine ( Figure 9.1, 9.7, 9.8 View FIGURE 9 ) is almost straight, laterally compressed, with a broadly rounded leading edge ridge; the sides of the ridge are in line with the shoulders and the flanks. The height of the spine increases relative to the width from proximal to distal. The anal fin spine ( Figure 9.6 View FIGURE 9 ) is slightly recurved and also has a broadly rounded anterior rib; the sides are more rounded than on the dorsal spine. Both dorsal and anal spines sometimes have a mineralised basal cartilage preserved ( Figure 9.6-8 View FIGURE 9 ); its presence or absence appears independent of locality.
On the paired pelvic fin spines, the anterior ridge has a more or less triangular shape, and the height to width ratio increases from proximal to distal. The spines are notably asymmetric.
The pectoral spine ( Figure 9.1, 9.2, 9.4 View FIGURE 9 ) is strongly curved lengthwise, relative to the other spines. Like the pelvic spines, the spines are slightly asymmetric in cross section, and the anterior ridge has a sharply pointed triangular shape in cross section. The sides are straight, in line with the sides of the anterior ridge.The height:width ratio increases dramatically from proximal to distal, and the spines are more robust than the other spines.
All spines (exemplified here by the pectoral fin spine, Figure 10.2-7 View FIGURE 10 ), like those of all Cheiracanthus species, have a thin enameloid outer layer on the leading edge and ‘shoulders’ of the spine, preserved best towards the proximal end, as are the thin sharp-crested lateral ridges. Spines have a wide central cavity, and all spines lack an accessory pulp canal above the central cavity. Osteodentine forms most of the width of the spine proximally. In the leading edge ridge, dentine tubules run perpendicular from the outer surface towards vascular canals running longitudinally. These canals are arranged in concentric, interconnected series, more or less parallel to the outer surface of the spines. Longitudinal and interconnecting canals extend the length and breadth of the whole spine, with smaller canals leading off to open out in the sulcus between the leading edge ridge and the ‘shoulders’ of the spines, as well as into the central cavity. Denteons are formed around the canals in the exserted part, but not in the inserted part; they increase in thickness distally, with the canals subsequently becoming narrower or almost closed. An inner lamellar layer is present proximal to the closure of the central cavity, and increases in thickness distally. A very thin, dense layer lines the central cavity proximally, and separates the osteodentine layer from the inner lamellar layer through the whole spine. Short dentine tubules extend through each of the lamellar layers, perpendicular to the inner surface. Towards the tip of the spine, the central cavity is almost filled by the centripetal growth of the inner layers of dentine.
Body scales: Watson (1937) and Gross (1947) described the scales as being relatively uniform over the body, but we note some variation. In the anterior half of the body the width of the scales sometimes slightly exceeds the length, whereas posterior to the anal fin spine the length of the scales often considerably exceeds the width, with the maximum length to width ratio about 2:1. On most flank scales, the crown ornament comprises fine subparallel ridges extending back from the anterior margin ( Figures 11.1-8, 11.10 View FIGURE 11 , 12.1-6, 12.12-20 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 View FIGURE 16 View FIGURE 17 View FIGURE 18 View FIGURE 19 View FIGURE 20 ), which often has a smooth rim on scales of larger fish. The ridges have a rounded surface, do not branch, and terminate in the anterior half of the crown. The length of the ridges varies depending on the area of the body ( Figure 11.7-10 View FIGURE 11 ), with scales above the lateral line tending to have longer ribs than those below (Young, 1995, figure 9). Ridge length also depends on the age of the fish, with larger/older fish having relatively longer ridges than smaller/juvenile fish. Many scales have a median depression longitudinally on the crown surface ( Figures 11.3, 11.4, 11.10 View FIGURE 11 , 12.5, 12.6, 12.13 View FIGURE 12 , and 12.15).
Rows of scales near the lateral lines and also some in other areas have a median pit in the posterior half of the crown (Gross, 1947). Some of these pitted scales have a crown that is otherwise identical to the majority of scales, whereas others have a relatively narrow crown with thicker subparallel ribs extending to the posterior of the crown, around a relatively large pit ( Figure 12.19 View FIGURE 12 ). Scales on the front edge of the tail are larger than body scales and have a totally smooth crown (Gross, 1947). The neck is concave and smooth all round, with a pair of protuberances posteriorly, just above the base-neck rim ( Figure 12.13, 12.14 View FIGURE 12 ). The neck height is almost equal to the height of the base, which is well rounded and penetrated by bundles of Sharpey’s fibres aligned in concentric circles over the base surface ( Figure 12.16 View FIGURE 12 ).
The histological structure of the scales of C. murchisoni was described and illustrated by Gross (1947). The main features he noted were that there are up to 14 crown growth zones; the oldest growth zones lack ridges; the embryonic zone has wide semicircular canals and lacunae from which the dentine tubules radiate obliquely upwards and backwards, passing radially into the centre of each neck lamella; and arch-like connections extend between tubules in the upper neck posteriorly.
Our observations indicate that all growth zones, except the embryonic one, show ridges ( Figure 13.1-3 View FIGURE 13 ). As in all acanthodiforms, crown growth zones are superposed. Each zone is slightly wider in the neck than in the upper crown plane ( Figure 13.1, 13.4 View FIGURE 13 ), and all zones outside the embryonic one are of similar width ( Figure 13.1, 13.2 View FIGURE 13 ). Canals extend upwards and down into the base from the lacunae in the embryonic zone ( Figure 13.6, 13.7 View FIGURE 13 ). Eight radial canals extend from openings close to the neck-base rim towards the embryonic zone, with ascending canals rising up in the middle of each growth zone ( Figure 13.4, 13.6, 13.8 View FIGURE 13 ). The four posterior canals open out through small calibre canals on each side of the two neck protuberances ( Figure 13.5 View FIGURE 13 ). Ascending canals branch and form an irregular anastomizing network ( Figure 13.7 View FIGURE 13 ). Near the anterior edge of the scales, canals from the network in the neck turn sharply back horizontally, and are interconnected by a horizontal ring canal completely encircling each growth zone in the inner zones, and only along the anterior edge in the outer growth zones. Lacunae are formed at the junction of the canals. The horizontal canals lie under the grooves on the crown surface. Along the posterior sides of scales, the anastomizing networks forming the ascending canals gradually turn posteriorly and peter out into delicate dentine tubules reaching towards the surface of each growth zone. The central depression in the posterior surface of the crown of some scales appears to be related to a lower density of the networks of canals in this area of the scale. The central area of the upper plane in each crown growth zone is enameloid, with no dentine tubules visible. The base is formed of acellular bone lamellae. Sharpey’s fibre bundles and canals of Williamson extend through the base ( Figure 13.1-4 View FIGURE 13 ). Scales in the proximal area of fin webs have a similar profile to the body scales, decreasing in size distally to scales with a low flat base with a thin elongate crown ( Figure 13.9, 13.10 View FIGURE 13 ). Thin fin rays, the ‘ceratotrichia’ of Miles (1970), underly the fin scales of each side of the web, apparently correlated one to one with the scales ( Figure 13.10, 13.11 View FIGURE 13 ). Being clearly overlain by normal scales, they are surely directly comparable with the endoskeletal ceratotrichia of chondrichthyans rather than the dermal lepidotrichia of actinopterygians.
Reconstruction: Our new observations on structures in the head and branchial regions of Cheiracanthus murchisoni are shown in Figure 14 View FIGURE 14 .
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.