Extropharciceras metallicum, Korn & Bockwinkel, 2021

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 39-42

Extropharciceras metallicum sp. nov.

urn:lsid:zoobank.org:act:9C27C6D3-6295-46F4-8397-D1FF2AB7C89A

Figs 30–31 ; Tables 17–18

Diagnosis

Extropharciceras with extremely discoidal, evolute conch at 60 mm dm (ww /dm ~ 0.25; uw /dm ~ 0.50). Whorl profile weakly depressed or weakly compressed with convergent flanks and broadly rounded venter, umbilical wall steep. Growth lines rather coarse, strongly biconvex; ventrolateral shoulder with two spiral grooves in the middle growth stage. Outer suture line with lanceolate prongs of the external lobe, a tongue-shaped lateral lobe with acute base and V-shaped U 2 and U 4 lobes and a very small, rounded U 6.

Etymology

Named after the Latin ‘ metallicum ’, because of the origin of the specimens from iron ore.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld ( Grube Prinzkessel , Liegendes Lager auf der 130 m Sohle); late Givetian (Red Ironstone); Stahl 1902 Coll.; MB.C.22151 . ( Fig. 30A )

Paratypes GERMANY • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel, Liegendes Lager); late Givetian (Red Ironstone); Becker 1902 Coll.; MB.C.3610 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel, 125 m Lager); late Givetian (Red Ironstone); Lotz Coll.; MB.C.30244 • 1 specimen; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); MB.C.30242 .

Additional material

GERMANY • 2 specimens; Rhenish Mountains , Oberscheld (Grube Prinzkessel, 60 m Sohle); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.3612 , MB.C.30242 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel, Hangendes Lager); late Givetian (Red Ironstone); Dresler 1906 Coll.; MB.C.3643 • 3 specimens; Rhenish Mountains , Oberscheld ( Staatliche Grube ); late Givetian (Red Ironstone); Hubach 1920 Coll.; MB.C.4299 , MB.C.4301 , MB.C.4302 • 2 specimens; Rhenish Mountains , Weilburg (Grube Georg-Joseph); late Givetian (Red Ironstone); Kegel Coll.; MB.C.30245 , MB.C.30246 .

Description

Four specimens are selected for description and illustration:

Holotype MB.C.22151: rather well-preserved specimen with 61 mm conch diameter embedded in a block of haematite ore ( Fig. 30A ).

Paratype MB.C.3610: incomplete specimen with 59 mm conch diameter in haematite ore ( Fig. 30B ).

Paratype MB.C.30244: incomplete specimen with about 46 mm conch diameter in haematitic limestone ( Fig. 30C ).

Paratype MB.C.30242: incomplete specimen with about 50 mm conch diameter in haematite ore ( Fig. 30D ).

Holotype MB.C.22151 has an extremely discoidal and evolute conch (uw / dm =0.49); the whorl profile is compressed with oblique umbilical wall, rounded umbilical margin and slowly converging flanks and narrowly rounded venter ( Fig 30A ). Venter and flanks separated by a shallow spiral groove that is accompanied by delicate ridges. Lamellar biconvex growth lines are well-preserved on the specimen; they extend strongly biconvex on the flank to form a narrow and high ventrolateral projection. The ventral sinus is narrow and deep.

None of the specimens shows a complete outer suture line; in specimen MB.C.30242, for instance, the median saddle cannot be studied. The lateral prongs of the external lobe appears to be rather narrow and lanceolate. The lateral lobe is tongue-shaped but acute at its base; the U 2 and U 4 lobes are narrow and V-shaped, the U 6 lobe is small and rounded ( Fig. 31A ).

Remarks

Extropharciceras metallicum sp. nov. differs from Evopharciceras formosum gen. et sp. nov. in the slightly narrower, more evolute conch. The suture line differs in the shape of the lateral and U 2 lobes, which are very narrow and lanceolate in Evopharciceras gen. nov., but wider and tongue- or V-shaped in Extropharciceras .

Figures

Fig. 30. Extropharciceras metallicum sp. nov. A. Holotype MB.C.22151 (Stahl 1902 Coll.) from Oberscheld (Prinzkessel Mine). B. Paratype MB.C.3610 (Becker 1902 Coll.) from Oberscheld (Prinzkessel Mine). C. Paratype MB.C.30244 (Lotz 1902 Coll.) from Oberscheld (Prinzkessel Mine). D. Paratype MB.C.30242 from Oberscheld. Scale bar units = 1 mm.

Fig. 31. Extropharciceras metallicum sp. nov. A. Suture line of paratype MB.C.30242 from Oberscheld, at dm = 34.5 mm, wh =8.5 mm. B–E. Ontogeneric trajectories of the cardinal conch parameters. Scale bar units = 1 mm.