Maghroharpes oufatenensis, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 77-78

Maghroharpes oufatenensis n. sp.

Plates 25H , 28A–O

Diagnosis. Genicranium broad and strongly vaulted. Glabella crest carinate, anteriorly rounded and free of tubercles or granulation. Axial furrows converging strongly towards well-defined preglabellar furrow. Occipital node barely inflated; tubercles on genal area. Eye lobes small (exsag.), moderately strongly inflated and with two lenses each, anterior lens being largest. Shape of lenses rectangular with rounded corners to subtriangular. Eye ridge absent. Prominent small tubercles on occipital ring, posterior border and internal rims. No caeca on genal roll. Brim width ratio 0.80, and standardised brim perforations around 170µm.

Etymology. Named after the locality where it was first collected and where it is most abundant.

Material and occurrence. Holotype: NHMUK It 29320 (1), Pl. 28A–E , from Hamar Laghdad, upper Pragian ( Fig. 2B, Map 11, site 8), dorsal exoskeleton of cephalon only . Paratypes: NHMUK It 29316 , NHMUK It 29319 and NHMUK It 29318 (1–9) from coral horizon at top of Pragian, Ihandar Formation; NHMUK It 29316, Pl. 28F–I , from Bid er Ras in south of Oufatene ( Fig. 2B, Map 8, site 23) ; NHMUK It 29319 and NHMUK It 29318 (1–9), Pls 28J–O , 25H , respectively, from Oued el Atchane west Oufatene ( Fig. 2B, Map 8, site 24 and site 2, respectively). All paratypes dorsal exoskeletons of cephala only .

Description. Cephalon sub oval, widest at alae. Genicranium broad, widest at posterior border. Glabella not inset, broad (width (tr.) 75% of length (sag.)), crest slightly carinate and flanks convex. Fine pits but no other sculpture. S1 slanting posteriorly, becoming effaced about halfway up flank of glabella; no furrows at S2, S3 or S4. Axial furrows convex, converging strongly anteriorly (170); preglabellar furrow distinct, straight in anterior view. Occipital furrow broad, deep and medially straight. Occipital ring in dorsal view not broadened medially, but broader (sag.) than posterior border (exsag.). In lateral view, sloping posteriorly and at its highest point, same height as glabella anterior to S0. Occipital node small, barely inflated ( Pl. 28B ), and prominent tubercles on dorsal surface of occipital ring. L1 inflated. Alae laterally directed, slightly inflated and small (tr.) in relation to length of glabella (sag.). Axial furrow crossing at junction of L1 and ala. Posterior border moderately short. Narrow preglabellar field.

Genal area moderately broad, without caeca but with small, low tubercles and very fine pits only visible on paratypes. Eye lobes small (exsag.), oval in shape and located close to inner margin of fringe. Each lobe has two lenses of equal size and without tubercles on its dorsal surface. No genal or eye ridges. Course of inner margin across anterior of genal area convex. Inner margin of fringe marked by bigger perforations across anterior boss only. Anterior boss, barely inflated, not joined to glabella and reaches down to weak girder kink. Genal roll moderately steep anteriorly (sag.) (≈ 540) and steep laterally (≈ 720). In lateral view, inner fringe narrowing strongly posteriorly. Genal roll lacks caeca, and has smaller perforations than on brim. Single row of larger perforations above girder. Girder moderately wide.

Brim concave, barely sloping and moderately wide (sag.), being 32% of cephalic length (sag.). Brim width ratio 0.83, and standardised brim perforations moderately large at ≈167µm. Row of larger perforations at distal and proximal edges, and caeca just reaching onto brim. External rim stout and without sculpture on dorsal surface. Marginal band near vertical, concave with ridges around top and bottom, and with tubercles. Prolongations around 80% of cephalic length (sag.). In dorsal view, internal rim subparallel to slightly curved adaxially, with concave profile in lateral view. Genal spine short, not following curve of exterior rim. Extension of girder meeting internal rim halfway down prolongation and with tubercles on dorsal surface. Proximal edge of brim steepening on prolongations.

Remarks. Maghroharpes oufatenensis complies with all the diagnostic characters of the genus shown in Table 5b. It is similar to M. ihmadii but differs in having: a broader (tr.) glabella which is carinate; a furrow at S1 that does not curve over the top of the muscle insertion scar; axial furrows that converge more strongly anteriorly; a broader genal area with tubercles; eye lobes that are much more inflated, oval rather than reniform and have only two eye lenses each, compared to four lenses in M. ihmadii ; no genal or eye ridges; a less inflated anterior boss; a girder that is 70% wider (sag. and exsag.); a weak girder kink that is not Σ-shaped like that of M.ihmadii ; standardised perforations on the brim that are some 50% bigger than those of M. ihmadii ; a brim width ratio around 0.80, rather than 0.93; a stout rather than fine external rim; a marginal band with tubercles; and tubercles on occipital ring and on the dorsal surfaces of the posterior borders and internal rims.

NHMUK It 29318 is an assemblage of 9 dorsal exoskeletons of cephala of differing sizes, the smallest having a length (sag.) 37% of the largest. In the Devonian of the Anti-Atlas, it is very rare to find such a wide intraspecies size range in trilobite specimens at the same locality. For some yet to be explained reason, differing holaspid development stages are poorly represented. The Upper Ordovician, Silurian and Devonian assemblages in obrution deposits figured by Brett et al. 2012, also show limited size ranges. Of the 8 assemblages figured it would appear that in only one is the sagittal length of the smallest exoskeleton under 70% of the largest.

Figures

PLATE 25 A–G Maghroharpes cf. 2 laatchanensis, Merzâ Akhsai Formation?, Pragian, Foum Zguid. A–D dorsal exoskeleton of cephalon only, NHMUK It 29310 (i), from Foum Zguid (Fig. 2A, Map 1, site 4). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–G dorsal exoskeleton of cephalon and disarticulated thorax, NHMUK It 29310 (ii), on the same plate as NHMUK It 29310 (i). E, dorsal, F, anterior and G, lateral view. H Maghroharpes oufatenensis n. sp., from coral at top of Pragian, Ihandar Formation, Oued el Atchane, Jbel Oufatene (Fig. 2B, Map 8, site 2), 9 cephala only, paratypes, NHMUK It 29318 (1 to 9), dorsal view of cephala. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 28. A–O Maghroharpes oufatenensis n. sp., A–E dorsal exoskeleton of cephalon, holotype, NHMUK It 29320 (1), from lower Pragian horizon, Hamar Laghdad (Fig. 2B, Map 11, site 8). A, dorsal and B, lateral view. C, lateral view and D, (uncoated) dorsal-lateral view of eye lobe, respectively. E, dorsal view of brim perforations. F–I dorsal exoskeleton of partial cephalon, paratype, NHMUK It 29316, Ihandar Formation, Jbel Oufatene (Fig. 2B, Map 8, site 23). F, dorsal, G, lateral and H, anterior view. I, dorsal view of brim perforations. J–O dorsal exoskeleton of partial cephalon, paratype, NHMUK It 29319, Ihandar Formation, Jbel Oufatene (Fig. 2B, Map 8, site 24). J, dorsal, K, anterior and L, lateral view. M, N and O, eye lobe in lateral, anterior lateral and posterior lateral view, respectively. Scale bars shown represent 1 cm unless otherwise indicated.