Euthacanthus macnicoli Powrie 1864

• Main Authors: Newman, Michael J., Burrow, Carole J., Den Blaauwen, Jan L., Davidson, Robert G.
• Format: Text
• Language: unknown
• Published: Zenodo 2014
• Subjects: Biodiversity; Taxonomy; Animalia; Chordata; Euthacanthus; Euthacanthus macnicoli; Northwest Territories; Canada; Davidson; Nares; Elliott; Severnaya Zemlya; Midland; Woodward; Coates; Dundee; Denison; Tareya; Taimyr
• Online Access: https://dx.doi.org/10.5281/zenodo.4822661; https://zenodo.org/record/4822661

Euthacanthus macnicoli Powrie, 1864 (Figs 1-19) Euthacanthus macnicoli Powrie, 1864: 425, pl.20, fig. 2; 1870: 290, pl. 11, figs 3, 3a, 3b; 1881: 169. — Anonymous 1867: 7, fig. 1. — Barkas 1874: 550. — Traquair 1892: 33. — Dean 1907: 216, figs 23, 36. — Watson 1937: 61, figs 3, 4, pl. 7, figs 1, 2. — Adams & Eddy 1949: fig.11. — Lehman 1959: fig. 22. — Heyler 1969b: 59, figs 1, 20. — Miles 1970: 362. — Moy-Thomas & Miles 1971: figs 4.2, 4.6. — Miles 1973: 183, fig. 36, pl. 15, fig. 1. — Paton 1976: 7. — Jarvik 1977: 212, fig. 11B. — Denison 1979: 27, figs 4A, 10A, 11A, 17C. — Young 1995: 66, fig. 5. Euthacanthus grandis Powrie, 1870: 292, pl. 12, fig. 6; 1881: 169. — Barkas 1874: 550. — Traquair 1892: 33.— Gunther 1904: 312. — Miles 1970: 362. — Paton 1976: 6. Climatius grandis – Woodward & Sherborn 1890: 36, 81. — Woodward 1891: 31. — Dean 1907: 218, fig. 30. — O’Connell 1916: 90. Climatius macnicoli – Woodward & Sherborn 1890: 36, 81. — Woodward 1891: 30. — O’Connell 1916: 90. — Graham-Smith 1936: 596. Euthacanthus – Traquair 1894: 257. — Hay 1902: 274. — Heyler 1969a: 40, 42, 43, 49.— Halstead 1969: fig. 17a. — Moy-Thomas & Miles 1971: 61, 69, 70, 71. — Long 1986: 336, fig. 10. — Frickhinger 1991: 239.— Janvier 1996: 177. — Trewin & Davidson 1996: 233, 241. — Benton 1997: fig. 3.14b. — Prothero 1998: fig. 17.23.— Wilson & Anderson 2004: 171. — Hanke & Wilson 2006: 534, 535. — Miller 2007: 994. — Park & Gierlowski-Kordesch 2007: 165. — Brazeau 2009: fig.3. — Franz-Odendaal 2011: 394. — Hanke & Davis 2012: 480, fig. 7A, B.— Davis et al. 2012: fig.4. — Zhu et al. 2013: fig. 6. Euthacanthus mitchelli – Goodchild 1904: 597. — O’Connell 1916: 90, 175. Euthacanthus macnicolli [sic] – Moy-Thomas 1939: fig. 8A. — Frickhinger 1991: 239, fig. caption. Euthacanthus macnicoli – Burrow & Young 1999: 10. — Gagnier et al. 1999: 93. — Dineley 1999: 159, figs 5.6B, C, 5.8C. — Davidson & Newman 2003: 244.— Hanke & Wilson 2004: 189. — Valiukevičius & Burrow 2005: 636. — Hanke & Davis 2008: 318; 2012: 480, 482. — Newman et al. 2011: 101; 2012: 740. — Brazeau 2012: 356. TYPE SPECIMEN. — NMS G.1891.92.231 and the counterpart NHM P.1337 (near complete specimen missing the snout). REFERRED SPECIMENS. — Over 50 articulated or partial articulated specimens have been identified by the authors in public museums and private collections. The largest collection of specimens is in the National Museums of Scotland. Furthermore, many hundreds of specimens consisting of disarticulated fin spines and scales have been observed by the authors; in this state of preservation the species could be considered common. Apart from the holotype, studied specimens include: from Turin Hill, NMS G.1881.5.60, NMS G.1885.54.6B, NMS G.1887.35.6A, NMS G.1891.92.236, NMS G.1891.92.238, NMS G.1891.92.275, NMS G. 1967.12.5; from Tillywhandland, NHMP.67308, NMS G.2007.24.2, NMS G.2010.7.39, NMS G. 2010.7.41, NMS G. 2010.7.42, NMS G.2010.7.43, NMS G. 2013.8.1, QMF57175, QMF57176; from Duntrune, NMS G.2002.59.97, NMS G.2002.59.100; from Balruddery Den, NMS G.2011.33.1. TYPE LOCALITY. — Tillywhandland Quarry (National Grid reference NO 528 537) near Forfar, Scotland. Tillywhandland Quarry is part of the Turin Hill complex of quarries and it is thought that most specimens recorded as coming fromTurin Hill were collected there (Trewin & Davidson 1996). STRATIGRAPHIC HORIZON AND AGE. — Upper part of the Arbuthnott Group of the Lower Devonian (Lochkovian) of the Strathmore Region of Scotland. OCCURRENCE. — Tillywhandland; Balruddery Den (National Grid reference NO 314 325) and Duntrune Quarry (National Grid reference NO 438 352) both just north of Dundee, Scotland. REVISED DIAGNOSIS. — Euthacanthus with large polygonal tesserae covering the dorsal surface of the head forward of the hyoid region; five circumorbital plates with the uppermost plate being largest, and ornamented with sinuous radiating nodose ridges; at least two external nares surrounded by small plates; small scales cover the cheek region; at least seven closeset branchiostegal plates above the angle of the jaw and five or more closeset branchiostegal plates below the angle of the jaw that cover the anterior branchial region; branchiostegal plates have an ornament comprising both short inclined or conical tubercles and long subparallel sinuous ridges; three subsidiary gill covers posterodorsal to these plates; scapula shaped like an inverted letter T with a smooth and straight lower edge; paired ventral postbranchial plates spine-shaped, ornamented with apically-directed nodose ridges on the lateral side and irregular tubercles medially; posterior dorsal fin spine is approximately opposite the anal fin spine; leading edge ridge on fin spines is fully rounded, with lateral ridges having a gently curving upper surface separated by a sharp edge from a lower/posterior surface curving steeply down into the groove; scales have subparallel deep grooves and ridges at the anterior end of the crown with the number of grooves ranging between five to twenty depending on the size of the scale; scales along the lateral line are the same size as normal flank scales; scale crowns comprise superposed growth zones with wide radial, ascending and circular vascular canals, Stranggewebe filling the primordial and posterior parts of the crown growth zones, and simple mesodentine filling the anterior parts of the growth zones; scale bases are slightly convex and formed of cellular bone with simple Sharpey’s fibres extending from the base apex to the lower surface of the base. DESCRIPTION General features Of the fifty or more articulated specimens known, nearly all are laterally compressed apart from NMS G.1891.92.275 (only the front third is preserved) and NMS G.2007.24.2, which are dorsoventrally compressed, and NMS G.1891.92.238, which is ventrodorsally compressed. NMSG.2002.59.100 is compressed laterally although the head has twisted to show it in a ventral view. Collection specimens vary in size from 100 mm to an estimated 450 mm long (based on isolated large fin spines and an articulated specimen c. 430 mm long in the private collection of Roger Jones of Geneva). The holotype (NMS G.1891.92.231; Fig. 3A) differs slightly from most other specimens in being more slender, with Duntrune specimen NMS G.2002.59.97 (Fig. 3B) representing the average body shape. The species is fusiform with a maximum depth to length ratio of about 0.2. There are four (e.g., NMS G.2002.59.97) or five prepelvic fin spines (e.g., NMS G.1891.92.231). Watson (1937: 65) stated that one specimen he observed (he did not say which one) had six prepelvic fin spines on one side of the fish, but we have not seen any such specimens and suspect this is a misinterpretation or a pathological aberration rather than a general character. The posterior dorsal fin spine is oppo- site or nearly opposite the anal fin spine, and the anterior dorsal fin spine is positioned far behind the level of the pectoral fin spines, opposite the midpoint of the prepelvic fin spine series. Head and branchial region Many specimens show elements of the head but they are usually disarticulated and poorly preserved. Some of the best preserved examples are the holotype NMS G.1891.92.231 (Fig. 4A) and NMS G.1891.92.236 (Fig. 4B) from Turin Hill, NMS G.2002.59.97 (Fig. 4C) from Duntrune and NMS G.2011.33.1 (Fig. 4D) from Balruddery. The ventral surface of the body is exposed on NMS G.1891.92.238 (Fig. 5A), but the jaws appear to have been lost exposing the inner surface of the tectal squamation and sclerotic bones, and a visceral view of the pectoral region. NMS G.1891.92.275 (Fig. 5B) from Turin Hill shows the head and branchial region preserved in dorsal view, and on NMS G.2007.24.2 (Fig. 5C) from Tillywhandland, the head is exposed in dorsal view. NMS G.2002.59.100 (Fig. 5D) from Duntrune is a rare specimen showing the branchial region and some of the head preserved in ventral view. Whereas Watson (1937) stated that the neurocranium and visceral skeleton were unossified and never preserved, we note that at least some elements of the endocranium and visceral skeleton were composed of globular calcified cartilage globules, preserved in situ on rare articulated specimens (e.g., NMS G 1967.12.7) and as patches visible in some thin sections and scattered amongst the dermal structures (e.g., NMS G.2010.7.39). On NMS G. 1967.12.7 (Fig. 6A), the upper and lower jaws are preserved by granular mineralization of the cartilages. The lower jaws have dropped off most specimens before burial, as is common with most LORS acanthodians (Burrow et al. 2013). Teeth are absent from both the upper and lower jaw. Large dermal bones are only present in the orbital and branchial regions. The eyes are very far forward, with a ring of five robust bones of which the most dorsal one is markedly larger than the others (Figs 4A, D; 5C). The bones are convex radially as well as laterally and ornamented with noded sinuous ridges that sometimes bifurcate. There are no sensory lines present on any of the orbital bones and, contra Watson (1937), these are interpreted as sclerotic rather than circumorbital bones (see Burrow et al. 2011). Euthacanthus macnicoli has a very blunt snout terminating just in front of the orbits (Fig. 5A, C). Two circular objects preserved as impressions behind the eyes on NMS G.1891.92.238 (Fig. 5A) could represent the otic capsules. Th e dorsal surface of the head is covered with dermal tesserae circa 0.5 mm wide in between the main lateral lines, and larger, more polygonal tesserae c. 1.0 mm anteriorly as shown in NMS G.1881.5.60 (Fig. 7) from Turin Hill. In the cheek region between the orbits and the branchial chamber are small scales that progressively decrease in size from the ventral anterior to the posterior dorsal. Th is area is particularly well preserved in NMS G.2007.24.2 (Fig. 5C), with scales aligned in posteroventral to anterodorsal rows. Th e posterior dorsal cheek region abuts the subcircular mandibular operculum (sensu Watson 1937), which is covered with small rod like scales that are larger than the scales of the cheek region. Th e rest of the relatively long branchial region is well preserved on a number of specimens, and was described in detail by Watson (1937). Th e anterior branchial region has a dermal cover comprising up to 25 slender plates. Following the designation of Hanke & Wilson (2004), these are divisible into a series above the angle of the jaw and another series below the angle of the jaw; the widest and longest rays are those near the jaw articulation. Th ese robust dermal plates appear smooth on the holotype; Watson (1937) described these elements as unornamented, but we suggest that his description was based on specimens in which the outer layer was lost when the specimen was split and/or he was looking at the smooth internal surfaces, as ornament is visible on several other articulated specimens (e.g., Fig. 5D). Th e ornament consists of tubercles and long sinuous ridges running subparallel to the edges of the branchiostegal plates, giving them a rugose surface. Th e tubercles are irregular in form, with some being conical and forming short rows such as on QMF57175 and QMF57176 (Fig. 6B, C), and others short and inclined as on disassociated plates in the acidprepared regurgitate/coprolite NHM P.67308 (Fig. 6D). Th e branchiostegal rays become much thinner on the ventral side of the fish in the gular region, as exemplified on NMS G.1891.92.238 (Fig. 5A) which is preserved ventral side up. Th is specimen also shows separate areas of thinner rays oriented obliquely across each side between the branchiostegal series. Possibly when the jaws fell off the specimen, the skin and gular rays remained behind but were flipped backwards. As noted by Watson (1937), there are three well-defined postopercular branchial arches. In NMS G.1891.92.231 (Fig. 4A) and NMS G.1891.92.236 (Fig. 4B) the gill septa are covered by a series of moderately long, narrow rods that curve posteriorly at their ventral ends. Additional rods are inserted between the upper ends of these rods before the curvature, creating a narrow gill cover. Th ese subsidiary gill covers are better preserved in NMS G 1891.92.238 (Fig.5A), NMS G.2011.33.1 (Fig.4D) and NMS G.2002.59.100 (Fig. 5D). In these specimens the rods are positioned more horizontally and are closer packed, forming a continuous covering. On NMS G.2002.59.100 (Fig. 5D), the small specimen with ventral surface exposed, both the pectoral fin spines and the postbranchial spinose plates are preserved in position. Th e rods and plates of the first and second subsidiary gill covers extend down to the edge of the postbranchial plate; all three posterior gill slits are of equal length, but the posteriormost subsidiary gill cover is shallower than the other two. Th e sensory lines on the head are preserved as a gap between rows of rod-like scales or plates (Fig. 5B, 5C), and their layout was well described by Watson (1937: fig.3, pl. 7, fig. 2). However, we consider that the structures that Watson labelled as mandibular canal, oral canal and supramaxillary are probably not sensory lines, but the outlines of the jaw cartilages (Fig. 6A). We still recognize a preopercular canal that more or less follows the upper edge of the palatoquadrate. Pectoral region A pair of robust triangular plates with a spinose projection are positioned anteromedially to each of the pectoral fin spines (Fig. 5C, D). Watson (1937: fig. 4B) referred to these structures as antero-lateral pectoral dermal bones. Their lateral ornamentation comprises broad tubercles that run in rows to the apex and coalesce in places into ridges, with these ridges becoming finer towards the spine tip (Figs 4B; 8A). The medial surfaces of these “plates” are also ornamented, with more irregularly placed tubercles (Fig. 8B). Miles (1973) described the structures as pinnal plates and interpreted the spine projection as prepectoral spine three, and also stated that the posterolateral edge of the plate was bevelled as in Parexus Agassiz, 1845 and Vernicomacanthus . Although characterized as a spine-bearing plate, its preservation in the dorsoventrally compressed specimens (Figs 5A, D) and ornamentation on both sides show that it was more spine-like than plate-like in life, projecting down from the body of the fish. Their preservation sometimes between the pectoral fin spines suggests that these plates could be admedian rather than prepectoral structures, but as the plates are usually displaced we are not certain of their homology and continue referring to them as prepectoral plates. The scapulocoracoid is a simple structure comprising a columnar scapular shaft expanding sharply to a triangular area with a flat lower edge articulating with the base of the pectoral fin spine (Fig.8C, D). Figure 9 is a new reconstruction of the head, branchial and pectoral regions of Euthacanthus macnicoli in lateral view, based on Watson (1937: fig. 4) and incorporating our reinterpretation of some of the morphological features. Fin spines In general the fin spines are of moderate length and thickness with short bases. From splitting of the fish-bearing blocks, the fin spines are often fractured lengthwise showing the cores rather than the surface ornament. Where the ornament is preserved, it consists of smooth, longitudinal ridges and deep grooves (Fig.10A, B). The grooves terminate along the leading edge toward the tip of the spine. The posterior dorsal fin spine (Fig. 10A) is longest, with c. seven ridges and grooves on each The Early Devonian acanthodian Euthacanthus macnicoli Powrie, 1864 from the Midland Valley of Scotland inner lamellar bone layer; I , thin section towards the distal end of the spine, showing tissues between the small central cavity and groove on the outer surface, with vascular canals and bone cell lacunae with cell processes of middle osteodentine layer. Abbrevia- tions: ad.fs , anterior dorsal fin spine; cc , central cavity; p.fs , pectoral fin spine; pd.fs , posterior dorsal fin spine; ppv.fs , prepelvic fin spine; pv.fs , pelvic fin spine. Scale bars: A-C, 10 mm; D, E, I, 0.05 mm; F, G, 0.25 mm; H, 0.1 mm. side of the straight fin spine. The anterior dorsal fin spine is only slightly shorter, with c. five ridges and grooves on each side of the spine. The anal fin spine (Fig. 10B) is slightly shorter than the anterior dorsal fin spine, straight, and quite thin, with four or five ridges and grooves on each side of the fin spine. The pectoral fin spine (Fig. 10C) is slightly curved, shorter than the anal fin spine, with a rela- tively long base compared with the other fin spines, and usually having six ridges and grooves on each side of the spine. The pelvic fin spines (Fig. 10C) have four ridges per side, are a similar length to the pectoral spines, and are about twice as long as the largest prepelvic fin spine. The prepelvic spines (Fig. 10C) decrease in length towards the anterior. Four ridges and grooves on each side of the spine converge at the tip, and the spines are strongly laterally compressed and slightly curved. Thin sections through the anal and posterior dorsal fin spines on NMS G.2010.7.42 (Figs 10 D-I; 11) show variations in the cross-sectional shape of the ridges and infilling of the central pulp cavity between the base and the tip. Near the tip, the ridges are sharp-crested (Fig.10D), becoming more rounded toward the base (Fig. 10F); the pulp cavity is wholly infilled by bone (Figs 10D, I; 11) at the distal end, and wide open toward the spine base. Through most of the length of the spine, a dense lamellar layer lines the inner surface (Fig. 10E), overlain by thick osteodentine that extends into the ridges (Figs 10H; 11). Only a thin outer layer is devoid of the wide vascular canal network penetrating the spine. Squamation The caudal fin shows a similar pattern to that of Acanthodes described by Heyler (1969a, b) and expanded on by Miles (1970). The notch on the tail of Watson’s (1937: fig. 4A) reconstruction is a preservational artifact caused by the separation of zone Z2 from Zone Z2”. The only difference between Miles’s (1970: fig. 7) reconstruction of the tail zonation of Acanthodes and that of Euthacanthus macnicoli (Fig. 12) is a further subdivision being present in the latter at the anterior end of the hypochordal lobe, which has scales which are notably larger than the surrounding scales. Miles (1970) also noted this feature in the Early Devonian acanthodians Ischnacanthus gracilis (Egerton, 1861) and Mesacanthus mitchelli (Egerton, 1860), as did Dean (1907) in the Early Devonian acanthodian Parexus recurvus Agassiz 1844. Later, Miles (1973: text-fig. 3) described the same condition in Early Devonian acanthodian Ptomacanthus anglicus Miles, 1 : Published as part of Newman, Michael J., Burrow, Carole J., Den Blaauwen, Jan L. & Davidson, Robert G., 2014, The Early Devonian acanthodian Euthacanthus macnicoli Powrie, 1864 from the Midland Valley of Scotland, pp. 321-348 in Geodiversitas 36 (3) on pages 326-346, DOI: 10.5252/g2014n3a1, http://zenodo.org/record/4538455 : {"references": ["POWRIE J. 1864. - On the fossiliferous rocks of Forfarshire and their contents. Quarterly Journal of the Geological Society of London 47: 413 - 429.", "ANONYMOUS 1867. - Report of the Directors for 1866. Montrose Museum, Scotland: 3 - 11.", "BARKAS W. J. 1874. - II. List of Palaeozoic Fishes. Geological Magazine (Decade II) 1: 542 - 553.", "TRAQUAIR R. H. 1892. - List of the Type and Figured specimens in the \" Powrie Collection \" of fossils. 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