Gondwanaspis mrirtensis, Feist, 2002

Feist, Raimund, 2002, Trilobites from the latest Frasnian Kellwasser Crisis in North Africa (Mrirt, central Moroccan Meseta), Acta Palaeontologica Polonica 47 (2), pp. 203-210 : 205

Gondwanaspis mrirtensis sp. nov.

Fig. 2A, B, E, G, H .

“ Dudleyaspis ” aff. harborti (Richter, 1909) ; Feist and Schindler 1994: 211, pl. 4: 1–2.

Derivation of name:AfterthetownMrirtinthevicinityofthetypelocality.

Holotype: Cephalon ( UM2 − RF 170), Fig. 2A, B, G .

Type locality: Section 2 at Bou Ounabdou (section IV in El Hassani and Tahiri 1999), north of track, Sof Al Gara hill (see location map Fig.1C ).

Type horizon: Compact grey limestone bed immediately below the dark grey Upper Kellwasser beds.

Age: According to the conodont association (identification of C. Girard): Late Palmatolepis rhenana Zone, MN Zone 13.

Diagnosis.—As for the genus.

Material.—Figured specimens: 3 cephala ( UM2 − RF 170– 172); additional material from type locality: 5 fragmentary cephala ( UM2 − RF 173–177), 1 fragmentary thoracic segment ( UM2 − RF 178).

Description.—Cephalon very large and short, nearly three times wider than long (without spines), of subrectangular outline, flattened centrally, gently down−vaulted abaxially. Large inflated anterior border depressed in front of glabella, sloping to border furrow. Central lobe of glabella parallel−sided, protruding anteriorly, truncated in front, steeply down−curved to broad prefrontal depression, gently vaulted transversely, horizontal on top (sag.). Two pairs of poorly defined, not swollen lateral lobes, third pair inconspicuous or marked as minute swellings. L1 weekly convex, trapezoidal; L2 circular in outline, well separated from central lobe by longitudinal grooves. S1 a broad, shallow depression. Dorsal furrow ill defined, very shallow, sigmoid. Occipital lobe gently convex, medially separated from the glabella by a broad shallow occipital furrow. Posterior margin of the occipital lobe smooth, straight transversely. Lateral occipital lobes depressed, protruding forward, delimited in front and against the medial occipital furrow by sharply incised semi−circular groove that merges abaxially behind L1. Posterior part of the lateral occipital lobes incompletely separated from the medial lobe. Eye ridges rather long and straight, diverging from one another at an angle of 125°, closely adjacent to L2 adaxially, slightly broadening distally, running distally into hook−like palpebral lobes. Inside the eye ridge the large triangular fixed cheek is swollen and of the same height as lateral glabellar lobes. Behind the eye, it slopes gently downward to the posterior furrow. Anterior branch of suture curves obliquely inward and crosses anterior margin opposite to dorsal furrow (exsag.). No sutural ridges are developed. Eye relatively high, situated at mid−point between anterior and posterior margins (exsag.). Posterior suture without sutural ridge, runs parallel to posterior margin. Posterior border furrow and border ridge straight, the latter abruptly enlarged at its distal end.

Anterior central margin carries six horizontally directed spines; the antero−lateral margins of the broad rolled lateral borders are provided each with 12 slender, long spines that are straight and not down−curved. Main librigenal spine is straight and outwardly directed in the prolongation of the posterior border furrow, making an angle of 110° with the lateral librigenal margin. It is longer than the length of the glabella.

Sculpture of exoskeleton consists of closely−spaced, medium−sized granulation with a few sparse larger nodules.

Remarks.—The incompletely preserved cephalons from Coumiac identified by Feist and Schindler (1994) as “ Dudleyaspis ” aff. harborti share with the new species all diagnostic features, in particular the shape and disposition of the eye ridges, the low, uninflated lateral glabellar lobes and the large rolled border provided with spines. The species is considered here as belonging to Gondwanaspis mrirtensis sp. nov. Small differences in the shape of the coarser granulation of the exoskeleton might be of subspecific significance.

Figures

Fig. 2. A, B, E, G, H. Gondwanaspis mrirtensis gen. et sp. nov. from section “2”, upper trilobite association. A, B, G. Holotype, cephalon with damaged right cheek, UM2−RF 170, partially external mould, in dorsal view (A), × 9.2; in frontal view (B) showing frontal and left antero−lateral borders and eye elevation, × 8.3; lateral view (G), × 9.5. E. Cephalon with incomplete left cheek, UM2−RF 171, dorsal view, latex cast of external mould, × 8.1. H. Cephalon with incomplete left cheek, UM2−RF 172, dorsal view, external mould, × 11.1. C, D, F, I, J. Palpebralia brecciae Richter and Richter, 1927. C, F. Cranidium from section “2”, upper trilobite association, UM2−RF 179, external mould, in dorsal view (C), × 10; in lateral view (F), × 9.6. D. Librigena +

Fig. 1. A. Devonian outcrops in Morocco with location of the Mrirt area in the central Meseta east of Rabat. B. Measured section “1” showing the Lower (LKW) and Upper (UKW) Kellwasser horizons and the intervening limestone beds. The levels of the lower and upper trilobite associations are marked with a star. C. Location of the studied sections “1” and “2” at Bou Ounabdou, 4 km to the SE of Mrirt township (after Becker and House 1999 and Walliser et al. 1999). Section “1” is the same as Bou Ounabdou, section II of Lasreq (1992).