Harpes sphenocephalus, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 51-52

Harpes sphenocephalus n. sp.

Plate 4E–K

Diagnosis. Cephalon widest across eyes.Glabella narrow anteriorly-rounded cone without tubercles on dorsal surface. Brim broad (sag.), profile straight (neither convex or concave) and moderately steeply-sloping. External border runs straight, slanting adaxially, from point where it passes eyes to two thirds of way down (exsag.) the prolongations. Eyes set close to midway between axial furrow and inner margin of fringe. Perforations on brim moderately large, becoming smaller distally until middle of rim. Perforations on genal roll much finer except proximal to girder, where there are two rows of larger perforations. Terminal spines long, slanting obliquely adaxially.

Etymology. Derived from the word “sphenoeides” ancient Greek for wedge. The cephalon, in lateral view is wedge-shaped.

Material and occurrence. Holotype: NHMUK It 29246, Pl. 4E–K , from the “Cheirurid Couche” horizon 1, Section 1 ( Fig. 6 ), Er Remlia Formation, Emsian, Jbel Ou-Driss ( Fig. 2B, Map 4, site 15), dorsal exoskeleton with cephalon articulated, thorax disarticulated and partially hidden.

Other material: NHMUK It 29247, Harpes cf. sphenocephalus, Pl. 4L–O, from “Cheirurid Couche”, Er Remlia Formation, Emsian, Jbel Issoumour ( Fig. 2B, Map 7, site 18), dorsal exoskeleton of partial cephalon.

Both H. sphenocephalus and H. cf. sphenocephalus are found with the same cheirurid species but come from two different localities, some 60 km apart.

Description. Cephalon widest at eye lobes and genicranium broad, length (sag.) 78% of width (tr.), widest at posterior border. Width (tr.) of glabella anterior to S0 62% of length (sag.) Glabella crest rounded but flanks tectiform. S1 slanting posteriorly and not turning anteriorly near crest. Shallow muscle attachment impressions not rising out of axial furrow at S2 and S3. Glabella tapered anteriorly, axial furrows converging anteriorly at ≈ 180 to sagittal line. Preglabellar furrow very shallow and straight (tr.) in anterior view. Occipital furrow deep and wide. Occipital ring wide, not medially broadened, lacking tubercles on dorsal surface and in lateral view, lower than glabella anterior to S0. Occipital node moderately large, poorly inflated. L1 inflated with axial furrow crossing at junction with ala. Alae small, width (tr.) ≈25% of length (sag.) of glabella anterior to S0 and reaching ≈50% of way across genal area. Interalar furrow, low interalar ridge and alar depression present. Posterior border short, ≈30% of width (tr.) of occipital ring. Preglabellar genal area narrow (sag.) ( Pl. 4E ).

Genal area narrow with faint caeca and coarse pitting. Eye lobes large (≈37% (exsag.) of width (tr.) of glabella at S1), oval and with no tubercles on dorsal surface. Two oval eye lenses of equal size ( Pl. 4K ). No eye or genal ridges present. Course of inner margin of fringe across anterior of genal areas. Anterior boss barely inflated. Genal roll sloping gently (≈ 470) anteriorly, steeply (≈ 670) laterally and narrowing strongly posterolaterally. Row of large perforations above girder and at inner margin of fringe anterior to preglabellar genal area. Perforations quickly become smaller than those on brim away from girder. Girder narrow (sag. and exsag.).

Brim moderately wide (sag.), 33% of cephalic length (sag.) and narrowing strongly posterolaterally (brim width ratio 0.51). Slope of brim moderate. Brim perforations becoming smaller outwards from girder and moderately small in central area of brim. Larger row of perforations at proximal and distal edges. External rim fine and lacking tubercles on dorsal surface. Marginal band near vertical, without ridges but with central row of coarse tubercles and row of very fine tubercles at bottom edge.

Length (exsag.) of prolongations ≈84% of cephalic length (sag.). In dorsal view, external and internal rims curving adaxially; in lateral view, internal rim concave, external rim curving gently up to meet internal rim at end of prolongation. Tubercles on dorsal surface of internal rim and row of larger perforations below. Genal spine long and slanting slightly adaxially. Extension of girder meeting internal rim third of the way down towards distal end.

Hypostome, thorax and pygidium not known.

Remarks. Harpes sphenocephalus has a weak girder kink rather than no girder kink but otherwise complies with the Harpes diagnostics shown in Table 5a.

H. spheno ce phalus is very similar to H. escoti but differs by having a wider genicranium and glabella; a glabella that is more carinated with rounded flanks and a more inflated L1; axial furrows that converge more strongly; a preglabellar furrow that is straight and not bowed upwards as is in the case of H. escoti ; a wider occipital furrow and an occipital ring that is much less broadened medially; larger alae (tr.) each with an interala ridge; a brim that slopes more steeply (sag.), has a lower brim width ratio and perforations that become smaller outwards from girder. Also, H. sphenocephalus has longer prolongation (exsag.) than H. escoti . As regards H. escoti the figured material only allowed 65% of the cephalic characters used in the matrix to be determined and it is likely therefore that there are other differences between the two species which are not included here.

Amongst the new Moroccan species Harpes sphenocephalus is similar to H. boudibensis but differs by having a glabella that is nearly 15% narrower and with no tubercles straddling the crest. The genal area is 20% wider, pitted and the alae stretch less than 60% of the way across it, compared with over 70% in H. boudibensis . The brim is 22% broader (sag.) and more steeply-sloping and has brim perforations that are 15% smaller and 60% more densely packed. On prolongations, the brim of H. sphenocephalus is less steeply-sloping and, in dorsal view, the external rim is straight rather than curved as it crosses onto the prolongations. The internal rim, in lateral view, is straight for the first two thirds of the way back, then curves gently upwards over the distal third of its length. In the case of H. boudibensis , the internal rim has a wave-like profile and the terminal spines are shorter.

Harpes cf. sphenocephalus ( Pl. 4L–O ) differs from H. sphenocephalus most noticeably in having a broader (tr.) genicranium, fine tubercles on the glabella anterior to S0, wider (tr.) alae with alar furrows distally effaced, no caeca on genal areas, eye tubercle larger (tr.) and extending to axial furrow, internal margin of fringe across front of the genal area convex rather than straight, no anterior boss, a wider girder, brim slightly convex with a 30% higher brim width ratio and larger perforations, a much more robust external rim and with fine tubercles on the dorsal surface.

The holotype of H. sphenocephalis is well preserved complete cephalon of a size that would indicate that it belonged to a well-developed holaspid. The cephalon is symmetrical and without any apparent pathological defects and has significant differences with H. escoti , the species it is most similar too. On this basis the species has been erected although without the support of paratypes.

Figures

PLATE 4. A–D Harpes supercilium n. sp., partial dorsal exoskeleton, paratype, NHMUK It 29248, horizon 10, Section 1 (Fig. 6), El Otfal Formation, Eifelian, Jbel Ou-Driss (Fig. 2B, Map 4, site 14). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–K Harpes sphenocephalus n. sp., dorsal exoskeleton and partial thorax enrolled, holotype, NHMUK It 29246, horizon 1, Section 1 (Fig. 6), Er Remlia Formation, lower Emsian, Jbel Ou-Driss (Fig. 2B, Map 4, site 15). E, dorsal, F, anterior and G, lateral view. H, dorsal view of brim perforations, I, anterior view of genal roll, J, anterior-dorsal view of perforations across brim, exsag. K, lateral view of eye lenses. L–O Harpes cf. sphenocephalus, partial dorsal exoskeleton, NHMUK It 29247, “Cherurid Couche”, Er Remlia Formation, lower Emsian Jbel Issoumour (Fig. 2B, Map 7, site 18). L, dorsal, M, anterior and N, lateral view. O, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.

FIGURE 6. Section 1 Jbel Ou-Driss