Pinnuloharpes hamarlaghdadensis Cronier et al. 2018

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 87-88

Pinnuloharpes hamarlaghdadensis Cronier et al. 2018

Plate 44A–M

Discussion. The new material figured here is similar to P. hamarlaghdadensis ( Crônier et al., 2018) which was described from 18 more or less fragmented cephala, one nominated as holotype but only five as paratypes. That material was from the same locality as that figured here. The description of this material is as full and complete as the material allows, and the author would only comment that the length (exsag.) of the prolongation of the holotype is probably around 80% of the cephalic length (sag.), not 50% as stated by Crônier et al. (2018, p. 257).

New Material. NHMUK It 29337, Pl. 44A–F , from a horizon containing Morocops granulops? ( Chatterton et al., 2006) , at the base of the “Red Cliff” ( Klug et al., 2002 & 2009), upper Emsian, Hamar Laghdad, Errachidia southeastern Morocco ( Fig. 2B, Map 11, site 1), dorsal exoskeleton with pygidium enrolled. NHMUK It 29338, Pl. 44G–J , from type horizon and location ( Fig. 2B, Map 11, site 2), dorsal exoskeleton of cephalon and the first two thoracic segments. NHMUK it 29339, Pl. 44K–M , from type horizon and location ( Fig. 2B, Map 11, site 3), crushed dorsal exoskeleton of cephalon and disarticulated thorax. NHMUK 29336 from an Emsian horizon at Timerzite ( Fig. 2B Map 10, site 3), dorsal exoskeleton and partial thorax.

Description. Exoskeletons figured here are similar those of P. hamarlaghdadensis but differ in having: glabella that slopes less steeply anteriorly; shallower furrow at S1; less inflated basal lobe (L1); 20% wider (tr.) preglabellar field; less steeply-sloping genal roll, anteriorly and laterally; perforations on genal roll which become progressively smaller for short distance away from girder; and finer external rim, being just under 10% of brim width (sag.), as opposed to around 18% of brim width (sag.) in the case of holotype.

The new specimens are more complete than fragmentary cephala of holotype and paratypes of P. hamarlaghdadensis and cannot be described on a comparative basis alone. The author therefore expands the description of material figured herein, as set out below.

Cephalon ovoid, widest (tr.) at mid-point between eye lobes and alae. S1 very shallow, becoming effaced halfway up glabella. Occipital node weakly inflated, not prominent, appearing as circular swelling stretching from occipital furrow to close to posterior edge of occipital ring. It has a CMO with four tiny, symmetrically-placed perforations ( Pl. 44E ) similar to those noted in P. cf. haustrum below. Preglabellar furrow shallow but clear. Alae hardly conspicuous, anterolaterally directed to reach about 45% of way across genal area.

Genal areas broad (tr.) and slightly convex. Eye lobe reniform, large (exsag.), ≈ 38 % of width (tr.) of glabella at S1; barely inflated; narrow (width 2/3 of length (exsag.)), and located at a level just behind preglabellar furrow and halfway between inner margin of fringe and axial furrow at start of anterolateral slope. Eye lobes weakly-inflated with two eye lenses each; anterior lens largest in shape of elongated rectangle with rounded corners; posterior lens oval and much smaller ( Pl. 44F ). Preglabellar field broad (sag.), width (tr.) being over 40% of length (sag.). Anterior boss narrow, width (tr.) around 60% of length (exsag.), and gently convex, reaching from preglabellar furrow down to girder kink. Genal roll inclined moderately anteriorly (≈ 430), much more steeply laterally (≈ 700); narrow in anterior view; and reaching about two-thirds of way up from girder to eye lobe. Posterolaterally, genal roll steepens and narrows by about 40%. Row of large perforations above girder, above which size of perforation quickly decreases over bottom third of genal roll to become a little finer than those on brim. Short row of larger perforations at inner margin of fringe, where it crosses anterior boss. Girder has Σ-shaped kink. Brim straight in profile, gently sloping (≈ 100) downwards and outwards, and has width (sag.) equal to about 30% of cephalic length (sag.). Brim width ratio around 0.70. Perforations on standardised brim number 20 per mm 2 and are moderately fine (just over 100 μm). Marginal band near vertical, straight and without tubercles. Brim on prolongations quickly steepens posteriorly, until reaching near vertical two-thirds of way back. Girder extends on to prolongations, curving gently upwards to meet internal rim about one third of way down its length (exsag.). In dorsal view, external rims on prolongations are straight, slanting obliquely posteromedially. Internal rims subparallel (exsag.) and in lateral view, nearly straight, sloping posteriorly gently downwards, before flattening out to meet external rim at an angle of around 15 o, and running for a short distance to end of prolongation, separated by a row of large perforations. Genal spines are long, following curve of external rim.

Thorax has 22 or more segments. Axis narrow and tapering posteriorly, so that width (tr.) of last axial ring just under 40% of that of first. At 7 th segment, where thorax is broadest, axis comprises 25% of thoracic width. Postannulus narrows (sag.) medially and pleurae are flat (tr.) and lengthen (tr.) slightly posteriorly until the ninth segment, where they start to shorten (tr.) posteriorly. Pleural furrows are broad (tr.), very shallow and extend onto outer portions of pleurae, which are short and have rounded distal ends ( Pl. 44M ).

The pygidium and hypostome are unknown.

Remarks. There is a significant size difference between the partial cephala described by Crônier et al. (2018) and those figured here. For instance, NHMUK It 29337 has a cephalic length (sag.) that is over 2.5 times that of the P. hamarlaghdadensis holotype. This suggests that it is likely the two sets of material came from different horizons. It is less likely that they came from the same horizon as the two groupings would have been in close proximity to each other, the base of the “Red Cliff” measures about 40metres. Nevertheless, morphological differences could be ontogenetic especially as the jackknife support at the node between the holotype and the new material is 69%. The author therefore considers that the erection of a new species is not justified.

There is little literature on the ontogeny of Devonian harpetids. McNamara et al. (2009, pp. 16–19) described the ontogeny of Eskoharpes palanasus and E. wandjina from the Frasnian of the Canning Basin, Western Australia. Eskoharpes palanasus showed much greater ontogenetic development than E. wandjina and “with increasing size in later meraspid s and early holaspids (the size at which transition occurs not being known) the following trends are continued: brim widens; external rim becomes relatively narrower; glabella becomes less vaulted and less steeply inclined anteriorly and wider; genal areas less swollen; genal roll becomes less steeply inclined; axial and posterior furrows become shallower; alar furrows become evident.” ( McNamara et al. 2009, p. 18, para 3). If Pinnuloharpes had a similar ontogeny to that of Eskoharpes , it could be expected that the material described by Crônier et al. (holaspid fragments) would reflect many, if not all, the meraspid growth changes observed by McNamara and colleagues. It may be, however, that the narrowing of the external rim and the change in the anterior slope of the glabella and genal roll continued during early holaspid development. This would explain many of the morphological differences between the two sets of material.

Pinnuloharpes hamarlaghdadensis complies with the diagnostics shown in Table 5c, except that it has a medially broadened occipital ring, L1 is a little inflated and the genal roll is without caeca. The diagnostic characters 9 and 10 in Table 5c, cannot be confirmed in respect of the holotype and paratypes but the new material would suggest that the species is compliant with these 2 characters.

NHMUK 29336 from an Emsian horizon at Timerzite which is a poorly preserved specimen is designated as Pinnuloharpes cf. hamarlaghdadensis .

Figures

PLATE 44. A–M Pinnuloharpes hamarlaghdadensis (Cronier et al. 2018), from Hamar Laghdad, upper Emsian. A–F dorsal exoskeleton with pygidium enrolled, NHMUK It 29337 (Fig. 2B, Map 11, site 1) A, dorsal, B, anterior and C, lateral view. D, dorsal view of brim perforations, E, dorsal view of occipital node and F, lateral view of eye lobe. G–J dorsal exoskeleton of cephalon and 2 pleural segments of thorax, NHMUK It 29338 (Fig. 2B, Map 11, site 2) G, dorsal, H, lateral and I, anterior view. J, dorsal view of brim perforations. K–M dorsal exoskeleton with thorax disarticulated and pygidium absent, NHMUK It 29339 (Fig. 2B, Map 11, site 3) K, dorsal and I, anterior view. L, dorsal view of brim perforations and M, lateral view of distal ends of pleurae. Scale bars shown represent 1 cm unless otherwise indicated.