Institutional abbreviations

DUNMG, McManus Galleries and Museum, Dundee, UK; NH, Montrose Museum, Montrose, UK; NHMUK, Natural History Museum, London, UK; NMS, National Museums of Scotland, Edinburgh, UK.

Type species

Vernicomacanthus uncinatus (Powrie) (= Climatius uncinatus Powrie, 76).

Type specimen

NMS G.1891.92.208 (Fig. 3) is the lectotype.

Remarks

Further to Miles’ description the following characters can be used to diagnose the genus Vernicomacanthus. Gnathostome symplesiomorphies: dorsoventrally closing jaws, teeth, sclerotic ring. Characters of uncertain polarity: branchial plates, dorsal fin spines, paired fin spines, tooth whorls. Shared with total-group chondrichthyans: dorsal scapular shaft, ventrolateral spines consisting of one pair of admedian and five pairs of prepelvic spines, microsquamose body integument, sensory lines pass between scales, skull roofed by polygonal tesserae. Shared with certain total-group chondrichthyans: anal fin spine, scales consisting of multiple laterally apposed odontodes, scales growing by posterior and lateral addition of elongate odontodes, ?posterolateral angle of scapulocoracoid. Shared with other climatiid acanthodians: dermal pectoral girdle integrating two paired prepectoral spines and a ventral pinnal plate, a median lorical spine-bearing plate, distinctly expanded postorbital tessera. Shared with some gyracanthids and some other stem-group chondrichthyans: fin spine ridges oblique to leading edge, row of denticles on trailing edges of pectoral fin spines.

Material

NHMUK PV P 1342a, NHMUK PV P 6960, NHMUK PV P 1342, NMS G.1891.92.208 (lectotype), NHMUK PV P 6968, NMS G.2001.7.4, counterparts NMS G.1891.92.209 and DUNMG Kinnaird 82, counterparts NMS G.1891.92.210 and NH Mitchell 57, NMS G.1885.54.69, NMS G.2018.18.1.

Occurrence

Fossils of V. uncinatus are known from Tillywhandland (‘Turin Hill’) and Canterland Den (NHMUK PV P 6967, a pectoral fin spine) near Forfar, and Balruddery Den, near Dundee, all in Angus, UK. The horizon from which the fossils come is the Arbuthnott–Garvock Group, Dundee Flagstone Formation, Lower Old Red Sandstone

Emended diagnosis

As for genus

General features

All complete specimens of V. uncinatus are between c. 70 and 85 mm in length (Figs 1, 3-6). The lengths of most incomplete specimens are consistent with this, although specimen NHMUK PV P 1342a is 80 mm long and everything posterior to its pelvic fin spines is not preserved (Fig. 4), suggesting that some animals may have reached lengths of up to 100 mm. Miles (65) reported a length of 150 mm for V. uncinatus; this is presumably a typographical error given that he later states that V. waynensis is of ‘greater size’ and ‘at least 140 mm’ in length. In overall shape V. uncinatus is similar to Climatius, with an elongate body, and a heterocercal tail with a pronounced hypochordal lobe. The pectoral fins are proportionately larger than those of Climatius or Parexus (compare Fig. 3A to Burrow et al. 20, fig. 6a, 21, fig. 1c). A reconstruction is shown in Figure 7A, B.

Head skeleton

The external head skeleton of V. uncinatus is especially well-preserved in two articulated specimens: NMS G.2001.7.4 (Fig. 1A) and DUNMG Kinnaird 82 (Fig. 5C, and see Miles 65 for specimen prior to over-preparation). The account given here is mainly based on these two, as well as on details from NMS G.1891.92.208 and NHMUK PV P 1342a (Figs 3B, 4B). In DUNMG Kinnaird 82, NMS G.2001.7.4 and NMS G.1891.92.203, the head is dorsoventrally flattened. The head's proportions are similar to those of other climatiid-grade animals such as Climatius and Parexus (Burrow et al. 20, 21). The orbits have a strongly anterior position (e.g. Figs 4B, 5C) as in numerous other stem-chondrichthyans, for example diplacanthids (Burrow et al. 22), ischnacanthids (Blais et al. 8), acanthodids (Heidtke 51), Climatius (Burrow et al. 21), Parexus (Burrow et al. 20) and Brochoadmones (Hanke & Wilson 49). Teeth are present and visible in DUNMG Kinnaird 82 and NHMUK PV P 1342a (Figs 4B, 5C), and these appear to be arranged in lateral families of tooth whorls as in other climatiid-grade fishes (e.g. Ptomacanthus; Miles 65), but there is no clear view of the cusps, and their distribution around the jaws is undeterminable.

The skull roof in V. uncinatus is covered with tessellating tesserae (Figs 1B, 3B, 4B, 5C, 8A, B), similar to those of other climatiid acanthodians such as Climatius and Parexus (Burrow et al. 20, 21). These are irregular in shape and pattern, but most plates have one larger, roughly central stellate tubercle, surrounded by radiating rows of smaller unornamented tubercles (Fig. 8B). These tesserae cover the roof of the skull between the level of the shoulder girdle and the snout (Fig. 1B). Towards the snout, the tesserae become larger and more densely packed with tubercles. Some of these anterior tesserae have a more specialized shape, and could be something more like the circumnasal plates of Climatius (Miles 65) than tesserae, although it is difficult to make out exact borders of elements. The extreme anterior end of the snout is covered in very small stellate scales (Figs 1B, 8E), similar to those described in Obtusacanthus (Hanke & Wilson 48, fig. 6).

The position of the anteriorly placed orbits are marked by sclerotic rings (Figs 1B, 4B, 5C). The dorsalmost two plates forming the ring on both sides of the head are visible on NMS G.2001.7.4 (Fig. 1B). Both sclerotic rings are visible in NHMUK PV P 1342a (Fig. 4B); individual plates are difficult to count exactly but from their size and shape seem likely to number five as in Parexus and Climatius (Burrow et al. 20, 21). Each bone is slightly convex and ornamented with tuberculate ridges radiating outwards from the edge facing into the orbit. Posteriorly to each orbit is a large, spine-like postorbital tessera. These have a pronounced peak and are ornamented with tuberculate ridges radiating outwards from the apex (Figs 1B, 8D). Between these postorbital tesserae and the branchial plates, tesserae are slightly smaller, although still tuberculate. Although no pattern can be discerned, markedly larger tesserae appear to be present on either side anterior to the lowermost visible branchial plate.

The dermal covering of the branchial region is best visible on the left-hand side of NMS G.2001.7.4 (Figs 1B, 2A, 8C), and consists of a dermally plated hyoid operculum and smaller scales. The hyoid operculum has a similar structure to that in Climatius (Burrow et al. 21), being formed by a number of broad branchiostegal plates (Figs 1B, 8C). The most ventral visible plate is the largest and is ornamented with a large anterodorsal ridge extending along the middle two-thirds of its length. Smaller ridges extend dorsally and ventrally from this ridge. Around these ridges, particularly anteriorly, the plate is ornamented with small tubercles. The whole plate, including the main ridge, has a slight curve, giving it a convex ventral side. Other plates are similar in overall shape, but decrease in size dorsally. This makes their exact number difficult to count, but in NMS G.2001.7.4 there are at least five, and possibly as many as seven. The branchial integument posterodorsal to the plates is difficult to observe, but is made up of small scales. These are best visible in NMS G.2001.7.4, in which small scales with anteroposteriorly aligned ridges lie posterodorsally to the branchiostegal plates (Fig. 2A). These may be equivalent to the small scales fringing the gill openings in Climatius (Watson 89). However, no rod-like fringing scales, such as those in Climatius (Burrow et al. 21), Euthacanthus (Newman et al. 69, 71) and Brachyacanthus (Watson 89), are visible.

The sensory lines are particularly clearly visible in specimens DUNMG Kinnaird 82 and NMS G.1891.92.208 (Figs 3B, 5C), and are broadly similar to those of other stem-group chondrichthyans. The otic branches of the infraorbital sensory line are the most clearly visible, particularly so in DUNMG Kinnaird 82, which shows that they curve laterally as they pass posteriorly to join the lateral lines, together forming a lyre shape in dorsal view (Fig. 5C). On this specimen Miles (65) also identified preopercular canals; these are visible anterior to the branchial plates in DUNMG Kinnaird 82 and NMS G.2001.7.4, where they curve anteriorly to meet the otic branches of the infraorbital sensory line (Fig. 5C). This canal is also clearly visible on NMS G.1891.92.208 (Fig. 3). Also visible on DUNMG Kinnaird 82, but not figured by Miles, is the postorbital sensory line (Fig. 5C).

The sensory lines of the head are edged by rectangular scales, best seen in the infraorbital canal of DUNMG Kinnaird 82 (Fig. 5C; Miles 65, pl. 7) and the preopercular canal of NMS G.1891.92.208 (Fig. 3B). These scales are smaller than the tesserae of the skull roof, and each is offset from its opposite number along the course of the sensory line. This offset suggests that the sensory line passed between paired scales, rather than being carried in c-shaped scales as in Acanthodes (Zidek 96). In NMS G.2001.7.4 the sensory line is almost invisible (also see DUNMG Kinnaird 82 in Miles 65, pl. 7), whereas in the more heavily worn NMS G.1891.92.208 a clear space is present (Fig. 3B). This suggests that the crowns of the scales arched over the sensory line to some extent, as in Cheiracanthus (Burrow et al. 25) and Ischnacanthus (Burrow et al. 24).

Shoulder girdle

The ventral dermal pectoral girdle has been described in detail by Miles (65). Our specimen observations largely confirm his account that the dermal shoulder girdle consists of paired pinnal plates each with two prepectoral spines, and a median prepectoral spine (Fig. 9). A new observation is that the squamation dorsal to the pectoral fin spines is formed from small tesserae with smooth rounded crowns. These are visible in NMS G.2001.7.4, and a patch is clearly visible immediately dorsal to the right pectoral fin spine in NMS G.1885.54.69 (Fig. 10C), showing that in life it would have overlain the lateral face of the scapulocoracoid.

The scapulocoracoid is best preserved in NMS G.1885.54.69, split between the part and counterpart (Fig. 10A, D). The fish has been dorsoventrally flattened, and the scapulocoracoid is split down the middle, with the inside of the medial face preserved in one part, NMS G.1885.54.69a, and the scapulocoracoid in medial view with the medial face removed in the other, NMS G.1885.54.69b. Miles (65) described the scapulocoracoid of Vernicomacanthus as perichondrally ossified. We have no additional data to confirm this, but the surface of the element is uniform, lacks tesserae, and lacks the granular texture of endoskeletal tissues interpreted as mineralized cartilage in some other acanthodians (Hanke & Wilson 50), consistent with it being perichondral bone (Fig. 10D). This would be in keeping with sectioned acanthodian scapulocoracoids, which are formed from laminar bone (e.g. Burrow et al. 21, 22, 24). However, we note that some stem-chondrichthyans have endoskeletal structures that outwardly could be perichondral but are in fact cartilaginous, for example the jaws of Ischnacanthus (Burrow et al. 24) and the visceral skeleton of Diplacanthus NMS G.1891.92.334 (Brazeau et al. 12).

The scapulocoracoid is L-shaped, with a pronounced dorsal scapular shaft, and is laterally flattened (Fig. 10). The scapular shaft is slender with anterior and posterior margins that taper towards a rounded-off dorsal tip. It meets the ventral part of the scapulocoracoid at a 135° angle around the frontal axis. This ventral section is triangular and tapers to an anterior point where it meets the anterior margin of the fin spine insertion. The ventral margin of the scapulocoracoid is flat, rising posteriorly to meet the scapular shaft. On the posterior edge of the scapular shaft is a pronounced process, clearly visible in NMS G.1885.54.69 (Fig. 10D), which can also faintly be seen in NHMUK PV P 1342a (Fig. 10B) and NHMUK PV P 1342 (Fig. 10C). This bears a similarity to the posterolateral angle observed in many conventional chondrichthyans (Coates & Gess 27), although its position on the scapular shaft is low by comparison. Another possible identity is a fin articulation as in Gogoselachus (Long et al. 60). However, the location of the process in NMS G.1885.54.69 is dorsal to the level of the fin spine insertion. This is topologically out of place for a pectoral glenoid, which is normally situated within the sulcus of the spine itself (Miles 65; Maisey et al. 62). Further preparation of NMS G.1885.54.69 will be carried out to better resolve its morphology.

Spines

The pectoral fin spines are about one-quarter of the length of the body, measured in a straight line from base to tip, have a broad base, and curve posteriorly (Figs 1, 3, 5, 6). They are ornamented with ridges formed of flat, overlapping nodes (Fig. 8G), oriented obliquely towards the leading edge of the fin spine. This ornament occurs uniformly along the length of the spine. Posteriorly the fin spine is ornamented with large, pointed denticles (Figs 3A, 8F). They are slightly curved inwardly, pointing towards the insertion of the fin spine. These posterior denticles occur along the entire length of the fin spine's trailing edge, from tip to insertion. Burrow et al. (19) reported a double row of trailing edge denticles, interpreting the pectoral fin spine of NHMUK PV P 6960 as preserving one row along the spine's distal tip and another in the impression of its middle part. Based on observations of this and other material we interpret there to be only a single row, with NHMUK PV P 6960 preserving a dorsal and ventral view of this same row. The pelvic fin spines are slightly curved, and ornamented with oblique rows of denticles, but are shorter than the pectoral fin spines, about one-tenth of total body length, and lack posterior denticles.

Two dorsal fin spines are present; these are longer relative to body length than those of Climatius and Brachyacanthus and are slightly curved and laterally flattened (Figs 1, 3-6). The anterior dorsal fin spine is about one-quarter of total body length, slightly longer than the posterior, which is about one-fifth of total body length. They are ornamented with oblique rows of rounded nodes borne on ridges, converging on the leading edge of the spine (Fig. 8H), and no trailing-edge denticles are present. The anal fin spine is also ornamented with noded ridges, slightly curved, and is about one-quarter of the total body length.

Vernicomacanthus uncinatus has six pairs of ventrolateral spines: five pairs of prepelvic and one pair of admedian spines. These are countable in all three examples positioned with an extended abdomen: NMS G.1891.92.208 (Fig. 3), DUNMG Kinnaird 82 and NMS G.1891.92.209 (Fig. 5), and NH Mitchell 57 and NMS G.1891.92.210 (Fig. 6). In other specimens it is difficult to perform a full count due to missing pieces of matrix or the specimen's position. The admedian spine is located ventral to the shoulder girdle, between the pinnal plate and the insertion of the pectoral fin spine (Fig. 9). The prepelvic spines series continue posteriorly, in line with the admedian spine, with the posteriormost prepelvic spine situated close to the pelvic girdle, but displaced slightly laterally relative to the pelvic fin spines. More posterior prepelvic spines become progressively larger. In NMS G.2001.7.4 the ventrolateral spines were pushed together during preservation, making it difficult to perform a count (Fig. 1A). However, this specimen shows the best view of the individual spines themselves. The spines are short, elliptical in cross-section, and the inserting end is open (Fig. 8I). They are ornamented with oblique rows of small nodes, as with the other spines. Proximally these nodes are smaller and more pointed than those on the fin spines; distally they become more rounded, and more organized into ridges.

The histological structure of the sectioned pectoral fin spine NMS G.2018.18.1 is similar to that of other climatiid acanthodian fin spines such as Climatius and Parexus (Burrow et al. 20, 21) (Fig. 11). The pulp cavity is large, becoming relatively smaller towards the distal end of the spine (Fig. 11A). The outside of the cavity is bordered by a thin layer of lamellar tissue; this is so thin as to be invisible in some sections, and is possibly present only intermittently, but can be best seen in section 5 (Fig. 11C). Outside this lamellar layer is a thick layer of osteodentine (trabecular dentine), punctured by large, presumably vascular, canals (Fig. 11C, D). No osteons are visible. The spine becomes progressively more compact as the canals diminish in size towards the tip (Fig. 11A, F), and vascular canals towards the surface of the spine are smaller in diameter, with some present inside the ornament ridges (Fig. 11C). The surface of the ornament is formed from a dentine with branching tubules extending outwards from the vascular canals and intersecting with cell spaces (Fig. 11C, E), identical to tissue identified as mesodentine in other fin spines such as those of Parexus (Burrow et al. 20). Enameloid is absent. Osteocyte lacunae are present throughout the tissues, including in the lamellar layer (Fig. 11D, F).

Body squamation

The body scales are organized into diagonal lines, and become gradually smaller posteriorly on the body (Fig. 1A). Scale crowns consists of several elongate, anteroposteriorly oriented cusps, with a large central cusp flanked by two pairs of smaller cusps on the majority of scales (Figs 2B, 12). Most body scale crowns have this symmetrical organization, with five parallel cusps. However in some areas of the squamation, such as in an area immediately anterior to the first dorsal fin and on parts of the flank, scales are asymmetrical with six parallel cusps (Fig. 2A). These are organized as in symmetrical scales, but with three, rather than two, smaller cusps on the side of the crown facing the fish's ventral side. Below the anterior dorsal fin spine is a region of scales that are more tessera-like, with horizontal ridges connecting the longitudinal cusps (Fig. 2C). A similar condition was described in the midline of Dobunnacanthus waynensis gen. nov. (Miles 65). The right pectoral fin of NMS G. 2001.7.4 also preserves scales; these are much like the body scales in all aspects except that they are smaller and possess only three or four cusps (Fig. 2A, D). In an area at or above the fin insertion are large scales with numerous short, unaligned cusps (Fig. 2A, ‘multicusped scale’). These appear superficially similar to the artichoke-shaped scales in the shoulder girdle of Kathemacanthus (Hanke & Wilson 50), isolated scales found in association with Parexus (Burrow et al. 20, fig. 11M), and the pinnal plate of Parexus and Sevyacanthus (Burrow 13; Burrow et al. 20). The arrangement of cusps in these scales is also similar to that in gyracanthid scales (e.g. Owen 74, ‘Mitrodus quadricornis’; Snyder et al. 81, ‘Gyracanthus’ sherwoodi), although the cusps are much shorter.

The transition between the head tesserae and the body scales is gradual rather than an abrupt boundary. At the rear of the skull roof the tubercles ornamenting the tesserae become progressively more anteroposteriorly oriented (Figs 1B, 2E) in more posteriorly located tesserae, but remain joined by ridglets perpendicular to the cusps. These ridglets are gradually lost in more posterior tesserae, giving way to the anteroposteriorly oriented cusps of the body squamation. A similar condition was reported in D. waynensis gen. nov. (Miles 65).

The body scales of V. uncinatus consists of a polyodontode crown on a thin, concave base (Fig. 12). This base is polygonal, and wider than it is long (Fig. 12A, D), with a slight anterior lamina beyond the anterior margin of the crown, resembling an overlap surface (Fig. 12A). The crowns of the body scales of V. uncinatus are formed from multiple anteroposteriorly elongate odontodes. Each odontode except for the posteriormost one (see below) corresponds to a single scale cusp, consisting of an underlying leaf-shaped lateral lamina topped by a sharply defined, wedge-shaped crest that tapers posteriorly. Although the base of each odontode is firmly attached to the scale base, they extend posteriorly well past the scale base and in articulation the crown overlies the anterior laminae of the bases of the posterior two scales (Figs 1A, 2B, 12). The large middle odontode is linked to its lateral counterparts by the fusion of their lateral laminae (Fig. 12B, E). Anteriorly to the large odontode, on the central axis of the scale, is a smaller odontode (Fig. 12A–C, E). Like its larger fellows it has a pronounced dorsal ridge, but its underlying lamina is shaped into two posterior points flanking the dorsal ridge. Underlying the largest odontode is an additional odontode of similar size to it (Fig. 12E). The crest of this basal odontode is obscured by the growth of the overlying central odontode, but its lamina can be seen projecting laterally. Cell spaces visible in section show that the scale base is made from cellular bone (Fig. 12K, M, N) like that in other stem-chondrichthyans such as Gladbachus (Burrow & Turner 17, fig. 2). The crown of the scale is formed from a dentinous tissue with branching tubules intersecting with cell spaces (Fig. 12L, N), as in tissues identified as mesodentine in other stem-chondrichthyan scales such as Diplacanthus (Burrow et al. 22, fig. 21).

Internally each odontode has a separate pulp cavity (Fig. 12H, I). This cavity comprises an anteroposteriorly elongate void that runs most of the length of the odontode (Fig. 12H–J). The pulp cavity is restricted to the centre of the odontode, and does not extend into the dorsal ridge, although this is likely to vary with the scale's age (Fig. 12J). The pulp cavities of the two lateralmost odontodes are far broader than those in the more medial odontodes, filling almost the entire odontode (Fig. 12H), probably a result of their relatively younger age. Branching off the pulp cavity laterally are several neck canals of similar lumen size to the pulp cavity, which extend ventrolaterally out of the odontode (Fig. 12H–J). These canals are inconsistent in number in individual odontodes, but each odontode has at least two pairs of neck canals. Because of the growth of the scale some of these neck canals end in dead ends within the crown, although many remain open on the surface of the scales (Fig. 12F, G). Most are visible on the posterior neck of the scale, fewer open between odontodes or anteriorly. Although the pulp cavities are separate, some of them communicate within the scale via neck canals; this can particularly be seen between the central large odontode and the large odontode underlying it (Fig. 12H–J). Canals penetrating the base are absent in the scanned specimen, and canal openings appear to be absent on exposed bases of scales on the surface of specimen NMS G.2001.7.4 (Fig. 2F).

The configuration of the odontodes in Vernicomacanthus is identical to that of Altholepis (Fig. 11) (Karatajūtė-Talimaa 56). Karatajūtė-Talimaa interpreted scale growth in Altholepis as involving the addition of odontodes ‘laterally and behind the primordial [odontode]’. In Vernicomacanthus the equivalent to the primordial odontode in Karatajūtė-Talimaa's Altholepis description is the central odontode, and the posterior odontode's morphology is consistent with having been added after it. The lateral odontodes were added laterally in symmetry around the central odontode, with the relatively large size of the pulp cavities in the lateralmost two odontodes probably reflecting their relatively young age. However, the Altholepis specimens upon which Karatajūtė-Talimaa's account was based lacked a small anterior odontode present in Vernicomacanthus (and Altholepis salopensis Burrow & Turner, 18). This was probably added to the scale after the large central odontode, given that it overhangs it considerably, which is even more pronounced in some isolated Altholepis scales (e.g. Burrow & Turner 18, fig. 1a, b).

LSID

urn:lsid:zoobank.org:act:A3668266-52A8-4B79-896D-BD560AAC03AF

Derivation of name

After the Dobunni, a tribe of ancient Britons whose territory extended into Southern Herefordshire (Allen 1; Van Arsdell 87), and akantha, Greek for ‘thorn’.

Holotype specimen

NHMUK PV P 24938a,b

Type species

Dobunnacanthus waynensis gen. nov. (= Vernicomacanthus waynensis Miles, 65).

Diagnosis

Further to Miles’ description these characters can be used to diagnose the genus Dobunnacanthus. gen. nov. Autapomorphies: ascending pinnal lamina over half as high as scapulocoracoid. Gnathostome symplesiomorphies: dorsoventrally closing jaws, teeth, sclerotic ring, ventral lateral line on flank. Characters of uncertain polarity: branchial plates, dorsal fin spines, paired fin spines, tooth whorls. Shared with total-group chondrichthyans: dorsal scapular shaft, anal fin spine, ventrolateral spines consisting of one pair of admedian and five pairs of prepelvic spines, microsquamose body integument, sensory lines pass between scales. Shared with other climatiid acanthodians: dermal pectoral girdle with two prepectoral spines and a median spine, dermal head skeleton formed from interlocking tesserae, scales with multiple laterally apposed odontodes. Shared with gyracanthids and some other stem-group chondrichthyans: fin spine ornament oblique to leading edge. Differs from Vernicomacanthus in that it is larger in size (at least 140 mm in length), the dermal shoulder girdle lacks a pinnal plate, the anterior lorical plate does not contact the dermal complex carrying the prepectoral spines, the scapular shaft of the scapulocoracoid lacks a posterolateral angle, and pectoral spines are not posteriorly denticulated.

Remarks

Miles (65) erected the genus Vernicomacanthus on the basis of a collection of traits, none of which is obviously autapomorphic. Beyond general observations on proportions he highlighted that the genus shared an ‘anterior dorsal fin spine slightly curved and longer than pectoral fin spine, but not as elongated as in Parexus; dermal shoulder-girdle reduced to anterior lorical, and ascending pinnal lamina of a compound pinnal plate, and with at least one paired prepectoral spine’. We judge it unclear that the anterior dorsal spine is longer than the pectoral in Dobunnacanthus waynensis gen. nov. (Fig. 13; Miles 65), and in any case it is also present outside the proposed genus across an anatomically disparate range of stem-group chondrichthyans, for example Euthacanthus, Diplacanthus and Brochoadmones (Hanke & Wilson 49; Newman et al. 71; Burrow et al. 22). Regarding the dermal shoulder girdle there is no evidence for an ascending pinnal lamina in Vernicomacanthus uncinatus, while Dobunnacanthus waynensis gen. nov. lacks a ventral pinnal plate. A similar anterior lorical is also present in Parexus (Miles 65), while having at least one paired prepectoral spine is very common in a broad array of stem chondrichthyans (e.g. Promesacanthus, Climatius, Doliodus, Euthacanthus; Miles 65; Hanke 45; Burrow et al. 21; Maisey et al. 62). Because of this we consider there to be a lack of evidence that the genus is monophyletic and so we are erecting a new genus.

Material

NHMUK PV P 24938a,b [holotype]; NHMUK PV P 16614; NHMUK PV P 16615 II; NHMUK PV P 52441a,b; NHMUK PV P 52443.

Diagnosis

As for genus.

Remarks

Unlike Vernicomacanthus, Miles (65) described Dobunnacanthus gen. nov. in detail based on peels made from a series of moulds from Wayne Herbert Quarry. No new material has been described since then, but we have some observations to add as a result of the comparison of this material to Vernicomacanthus. Miles’ reconstruction is shown in Figure 7C.

Occurrence

All specimens are from Wayne Herbert Quarry, Herefordshire, UK (White 90; Allen & Tarlo 2).

Squamation

The tesserae of the head are similar to those in other climatiids: roughly hexagonal in shape and tuberculated (Fig. 13A). As Miles (65) observed, the flank scales of Dobunnacanthus gen. nov. are ornamented with anteroposteriorly aligned ridges (Fig. 13C, D). These appear to be very similar to the scales of Vernicomacanthus, with their laterally apposed odontodes. However, because the internal structure of the scales is not preserved, it is impossible to definitively diagnose this.

Shoulder girdle

Dobunnacanthus gen. nov. has an unusual morphology of the dermal shoulder girdle, noted by Miles (65). The description by Miles appears to be accurate; the two prepectoral spines in life would have been in the same anatomical position as those in other stem-group chondrichthyans, on the coracoid part of the shoulder girdle.

The moulds of the scapulocoracoid appear to lack a posterolateral angle, unlike Vernicomacanthus (Fig. 13E, F).

Spines

The pectoral fin spines of Dobunnacanthus gen. nov. are as described by Miles (65). Miles implies that the ornamentation of the pectoral fin spine converges obliquely on the leading edge of the spine and that they lack trailing-edge denticles; we confirm that this is the case (Fig. 13B, right pectoral spine). Miles also noted that the pectoral fin spines’ ‘beaded ridges’ dissolve into tubercles proximally. We note that this is also the case in Climatius (Burrow et al. 21, fig. 2c), but not in Vernicomacanthus (Fig. 1), Ankylacanthus (Burrow et al. 19) or Parexus (although clear views of this part of the ornament are rare) (Burrow et al. 20).