Maghroharpes terridus, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 76-77

Maghroharpes terridus n. sp.

Plate 32A–D

Diagnosis. Genicranium narrow, glabella very broad without any muscle attachment furrows, and L1 not inflated. Alar furrows and occipital furrows very shallow. Preglabellar furrow barely distinct and anterior boss joined to glabella. Brim barely sloping and with concave profile. Marginal band with three ridges. Internal rims subparallel.

Etymology. Terridus Latin for scared, inspired by the name of type locality Maharch, which is known the “pass of the conflict” after a fight between two tribes that took place there. Maharch is a narrow pass between Jbel el Mrakib and the southern extension of Jbel Otfal, an ideal ambush site and strategically important.

Material and occurrence. Holotype: NHMUK It 29321, Pl. 32A–D , from the narrowly turriculate caenogastropod horizon, ( Johnson & Fortey 2012, fig. 2, section 2, horizon 2, 17.5 metres above bottom of section), Ihandar Formation, Pragian, Maharch, Southern flank of Jbel el Mrakib ( Fig. 2B, Map 9, site 18), dorsal exoskeleton with thorax disarticulated and pygidium missing.

Description. Cephalon widest at mid-point between eye lobes and alae. Genicranium narrow, length (sag.) 78% of width (tr.) and widest at posterior border. Glabella not inset; very broad (width (tr.) 76% of length (sag.)); flanks convex; crest rounded and with granulation but no pitting. S1 not evident and no furrows at S2, S3 or S4. L1 not inflated. Axial furrows convex and converging weakly anteriorly. In lateral view, preglabellar furrow barely distinct and straight. Occipital furrow broad, shallow and medially straight. Occipital ring broader (sag.) than posterior border (exsag.), but not medially broadened, and has fine granulation on dorsal surface. In lateral view, it slopes posteriorly and is higher than glabella anterior to S0. Occipital node small and poorly inflated, located on anterior slope of occipital ring. Alae small (tr. and exsag.). Alae anterolaterally directed and alar furrow shallow, distally effaced. Posterior border moderately short (tr.). Narrow (sag.) preglabellar field.

Genal area moderately broad without caeca or pits, but evidence of small tubercles or granulation. Eye lobes inflated, oval, set away from inner margin of fringe (eye location ratio 0.77) and lacking sculpture on dorsal surface. No genal ridge, and eye ridge ill-defined. Inner margin of fringe convex across anterior of genal areas, with row of bigger perforations where it crosses anterior boss. Boss barely inflated, joined to glabella and reaching down to girder. Girder kink very weak. Genal roll moderately steep anteriorly (≈ 570) and laterally (≈ 620). Fringe narrowing strongly in lateral view. Genal roll with caeca and perforations smaller than on brim; perforations all the same size, apart from row of larger perforations above girder.

Brim barely sloping, concave, moderately wide (32% of cephalic length (sag.)) and with brim ratio of 0.84. Brim perforations moderately fine (≈120μ) with larger perforations around proximal and distal edges. Light caeca across brim. External rim stout. No tubercles on dorsal surface of rim and marginal band vertical, concave, ridge top and bottom, and without tubercles. Length (exsag.) of prolongations nearly 80% of cephalic length (sag.). Internal rims subparallel in dorsal view and concave in lateral view. External rims curving adaxially. No genal spine. Girder extension meeting internal rim halfway down prolongations, tubercles on dorsal surface of internal rim and only proximal edge of brim steepening on prolongation. Thorax widening (tr.) to 5 th segment, and no pitting or tubercles on axial rings or pleurae. Pleural furrows broad, very shallow, almost effaced and V-shaped in cross section. Outer portion of pleurae set at an angle to inner portion, curved posteriorly and terminating in a point.

Remarks. One character does not comply with the selected diagnostics for the genus shown in Table 5b, the location ratio of eye lobes being further from the internal margin of fringe than is the case with other species of the genus. Also, it is not possible to determine the girder width from the material presented here.

Maghroharpes terridus is unusual amongst maghroharpids, in having a glabella without furrows and L1 that is not inflated. These characters are more typical of Pinnuloharpes species. The narrow genicranium, caeca on genal roll, the concave brim and the lack of the steepening of the brim on the prolongations are, however, more typical of Magroharpes species.

Maghroharpes terridus is similar to M. oufatenensis , but differs in having: an ovoid cephalon that is widest at the mid-point between the eye lobes and the alae, rather than being sub oval and widest at the alae; a genicranium that is around 10% narrower; a glabella that has granulation and pitting on its dorsal surface, and a crest which is rounded not carinate; no muscle insertion furrows at S1; an uninflated L1; shallow preglabellar and occipital; fine granulation rather than tubercles on the occipital ring; alar furrows that are very shallow and distally effaced; genal areas with pitting; eye lobes that are located further from the inner margin of the fringe; an eye ridge, albeit ill-defined, that is missing on the cephalon of M. oufatenensis ; the anterior boss joined to glabella; the genal roll sloping less steeply laterally; the brim with perforations that are 25% finer than those of M. oufatenensis ; light caeca on the genal roll and caeca covering the whole of the brim, while M. oufatenensis has caeca crossing onto the inner part of the brim only and none on the genal roll; the dorsal surface of the external rim overhanging the marginal band, which lacks tubercles or a ridge around its base; internal rims which, in dorsal view, are subparallel rather than curving adaxially; and no genal spines, unlike M. oufatenensis which has short spines.

The holotype of M. terridus displays an unusual combination of characters as outlined above. Also, it is well preserved complete cephalon and partial thorax of a size that would indicate that they belonged to a well-developed holaspid. The cephalon is symmetrical and without any apparent pathological defects and has significant differences with M. oufatenensis , the species it is most similar too. On this basis the species has been erected although without the support of paratypes.

Figures

PLATE 32. A–D Maghroharpes terridus n. sp., Ihandar Formation, Pragian, Maharch, dorsal exoskeleton, thorax and pygidium disarticulated, holotype, NHMUK It 29321 (Fig. 2B, Map 9, site 18). A, dorsal, B, lateral and C, posterior view. D, dorsal view of brim perforations. E–Q Lioharpes scopulum n. sp., Ihandar Formation, bou Lachrhal. E–L dorsal exoskeleton of cephalon only, holotype, NHMUK It 29279 (Fig. 2B, Map 9, site 14). E, Dorsal, F, lateral and G, anterior view. H, lateral view of glabella (uncoated), I, dorsal view of brim perforations. J, and K, dorsal and lateral view of eye lobe respectively. L, dorsal view of occipital node. M–Q dorsal exoskeletons of partial cephala only, from type locality and horizon, paratypes, NHMUK It 29280 (1 to 3) (Fig. 2B, Map 9, site 3). M–N NHMUK It 29280 (1). M, dorsal view and N, dorsal view of eye lobe. O–P NHMUK It 29280 (2). O, dorsal view and P, dorsal view of brim perforations. Q, NHMUK It 29280 (3), dorsal view. Scale bars shown represent 1 cm unless otherwise indicated.