Angulithes mermeti ( Coquand, 1862 )

Wilmsen, Markus & Nagm, Emad, 2019, Palaeobiology and evolutionary context of Angulithes mermeti, a streamlined early Late Cretaceous shallow-water nautiloid, Acta Palaeontologica Polonica 64 (4), pp. 831-849 : 834-835

Angulithes mermeti ( Coquand, 1862)

Figs. 3–5 , 6A, B , 10A .

1862 Nautilus Mermeti H. Coq., Coquand 1862: 166 , pl. 2: 1, 2. 1886 Nautilus Munieri ; Choffat 1886: 1, pl. 1: 2, pl. 2: 1.

1907 Nautilus Mermeti Coquand ; Pervinquière 1907: 46.

1910 Nautilus Mermeti Coquand ; Eck 1910: 11.

1912 Nautilus munieri Choffat ; Schlagintweit 1912: 99, pl. 6: 9.

1914 Nautilus Mermeti Coquand ; Eck 1914: 183, pl. 9: 1.

non 1914 Nautilus Mermeti Coquand var. Munieri Choffat ; Eck 1914: 184, pl. 9: 2–4 (= Angulithes triangularis Montfort, 1808 ).

1956 Lissoniceras mermeti (Coquand) ; Benavides-Cáceres 1956: 435, pl. 40: 1–3.

1960 Angulithes (Angulithes) triangularis mermeti (Coquand) ; Wiedmann 1960: 188, pl. 22: h; pl. 25: 8, 9; pl. 26: 4; pl. 27: 1, 2; text-figs. 16–20.

1989 Angulithes mermeti (Coquand) ; Luger and Gröschke 1989: 358.

1992 Deltoidonautilus mermeti (Coquand) ; Abdel-Gawad et al. 1992: 326, pl. 1: 1.

2000 Angulithes mermeti ( Coquand, 1862) ; Wilmsen 2000: pl. 5: 3; text-fig. 5.

2002 Angulithes sp. ; Meister and Rhalmi 2002: 768, pl. 5: 1, 3; text-fig. 13b, c.

2004 Angulithes mermeti ( Coquand, 1862) ; Abdel-Gawad et al. 2004: pl. 1: 1.

2006 Angulithes mermeti ( Coquand, 1862) ; El Qot 2006: 114, pl. 24: 1, 2.

2006 Angulithes mermeti (Coquand) ; Abdel-Gawad et al. 2006: pl. 3: 4, 7.

2009 Angulithes mermeti ( Coquand, 1862) ; Nagm 2009: 52, text-figs. 5.1A, B, 5.2A.

2010 Angulithes sp. ; Cavin et al. 2010: text-fig. 7X.

2011 Angulithes mermeti ( Coquand, 1862) ; Ayoub Hannaa 2011: 205, pl. 21: 1; text-fig. 3.36.

2012 Angulithes sp. ; Benyoucef et al. 2012: pl. 1: 1.

2012 Angulithes mermeti ( Coquand, 1862) ; Ayoub Hannaa and Fürsich 2012: 64, text-fig. 7.

2015 Angulithes mermeti (Coquand) ; Nagm 2015: text-fig. 7D.

2015 Angulithes mermeti ( Coquand, 1862) ; Meister and Piuz 2015: 19, pl. 1: 1–4.

2017 Angulithes mermeti ( Coquand, 1862) ; Meister et al. 2017: 5, pl. 1: 1a, b.

2019 Angulithes mermeti ( Coquand, 1862) ; Nagm 2019: text-fig. 6C.

Material.—Eight internal moulds (listed in Table 1) from the lower upper Cenomanian Neolobites vibrayeanus Zone of the Galala Formation in Wadi Araba, north Eastern Desert of Egypt (Wadi Ghonima section, Wadi Irkas section), and northern Wadi Qena (Wadi Hawashiya; see Fig. 1A for location), ranging from complete adult specimens to small septate fragments. AFK 225 ( Fig. 3 ) is an excellently preserved complete adult specimen from Wadi Ghonima, Egypt.

Measurements. —See Table 1.

Description.—Involute, almost oxycone and large-sized nautiloid with strongly compressed whorl cross-section (Wb/ Wh = 0.5–0.6). The small and shallow umbilicus (5–7% of Dmax) has a rounded wall with a gradual transition onto the lower flanks where the maximum whorl breadth occurs. From there, the flanks converge to a venter which is acute in juvenile and adolescent stages, becoming very narrowly rounded in the adult stage. Maximum diameter is around 200 mm as indicated by septal approximation, e.g., in AFK 225. Ribbing has not been observed on any part of the internal moulds. The external suture is rather sinuous with a faint umbilical saddle and a low lobe on the umbilical wall rising to a prominent, knee-like saddle on the lower flank. The mid- and outer flanks are characterized by a wide lateral lobe that rises to a narrowly pointed saddle at the venter. The septal spacing is rather low (8–10 mm at D = 120 mm, ~ 12 mm at D = 180 mm), resulting in a high number of septa per whorl (e.g., 14 septa/half a whorl in specimen EN-WI-1 at D ~ 130 mm). The siphuncle has a subdorsal position, at about 1/5 of the distance from the dorsum to the venter. The nearly complete and mature specimen AFK 225 suggests that the length of the adult body chamber was relatively short and did not exceed 150° of the last whorl.

Stratigraphic and geographic range.—All specimens described herein from Wadi Araba and Wadi Qena (Eastern Desert, Egypt) are from the lower upper Cenomanian Neolobites vibrayeanus Zone that is broadly contemporaneous to the Calycoceras (C.) naviculare– C. (Proeucalycoceras) guerangeri Biozone of the NW European standard biostratigraphy (see Nagm et al. 2010a, b and Nagm and Wilmsen 2012 for details). This stratigraphic range seems to correspond to the records from literature which almost all fall into the late Cenomanian. The palaeogeographic distribution is confined to occurrences south and north of the (western) Neotethys in northern Africa and southern Europe with additional records from Peru and Oman.

Figures

Fig. 3. Hercoglossid nautiloid Angulithes mermeti (Coquand, 1862), AFK 225 from the Cenomanian of Wadi Ghonima, Egypt, in apertural (A1) and lateral (A2) views.

Fig. 4. Hercoglossid nautiloid Angulithes mermeti (Coquand, 1862) from the Cenomanian of Wadi Ghonima, Egypt. A. AFK 202 in lateral (A1, A3) and ventral (A2) views. B. AFK 218 in lateral (B1) and apertural (B2) views; arrow shows the position of the siphuncle.

Fig. 5. Cross-sections and external sutures of the hercoglossid nautiloid Angulithes mermeti (Coquand, 1862) from the Cenomanian of Wadi Ghonima, Egypt. A. AFK 225, shell shape in apertural view (A1), external sutures (A2); grey shading indicates position of the umbilical saddle. B. AFK 202, shell shape in ventral view. C. AFK 218, whorl shape, showing the position of the siphuncle.

Fig. 6. Shell form (A1–C1), external sutures (A2–C2), and whorl cross-section (D) of selected hercoglossid nautiloids. A. Nautilus mermeti (Coquand, 1862) from the Cenomanian of Ténoukla near Tébassa, northeast Algeria (after Coquand 1862: pl. 2: 1, 2). B. Nautilus munieri Choffat, 1886 from the upper Cenomanian of Villa Nova d’Ourem, Portugal (after Choffat 1886: pl. 2: 1). C. Angulithes triangularis Montfort, 1808 (MB.C.2052) from the lower Sardinero Formation, lower Middle Cenomanian of Langre, Cantabria, northern Spain (after Wilmsen 2000: pl. 1: 2b, pl. 5: 15). D. Nautilus triangularis Montfort, 1808 from the Cenomanian of Île de Madame, Charente-Maritime, France (after d’Orbigny 1840: pl. 12: 2).

Fig. 10. Palaeoecology of the hercoglossid nautiloid Angulithes mermeti (Coquand, 1862). A. Reconstruction of A. mermeti (Coquand, 1862) in the lagoonal shallow-water environment of the Galala Formation (background after a subaqueous photograph in the property of MW from a lagoonal site in the present-day Red Sea near Hughhada taken in 1999, treated by greyscale-filtering in Photoshop CS2); rudist illustrations from Mitchell (2002). B. Bioclastic rudist (r) floatstone, the lagoonal host sediment in which A. mermeti has been found in the Wadi Ghonima section (thin-section photomicrograph of sample 080217-18). C. Close-up of Fig. 9B showing the bioclastic packstone matrix in detail, including numerous fragments of dasycladalean algae (gr).