Lentitornoceras materni, Korn & Bockwinkel, 2022

Korn, Dieter & Bockwinkel, Jürgen, 2022, The tornoceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 806, pp. 32-51 : 45-46

Lentitornoceras materni gen. et sp. nov.

urn:lsid:zoobank.org:act:267ABA4A-0287-4DEA-B888-4D391FB8D96D

Fig. 8 ; Table 4

Diagnosis

Lentitornoceras gen. nov. reaching about 45 mm conch diameter. Extremely discoidal and involute adult stage (ww/dm ~ 0.25; umbilicus nearly closed at 30 mm dm); whorl profile strongly compressed (ww/ wh ~ 0.40); whorl expansion rate moderate (WER ~ 1.80). Flanks weakly convex, umbilical margin continuously rounded, venter very narrowly rounded. Ornament with lamellar, wide-standing biconvex growth lines.

Type material

Holotype GERMANY • Rhenish Mountains , Oberscheld ; late Givetian (from a Red Ironstone block together with Pharciceras oberscheldense ); Lotz 1901–1902 Coll.; illustrated in Fig. 8 ; MB.C.30413 .

Etymology

After Hans Matern, to honour his studies on the ammonoids from the Dillenburg region.

Description

Only the holotype is available for description and illustration. It is a specimen of almost 30 mm diameter in iron-rich limestone, largely preserved with its shell ( Fig. 8A ). The shape is that of a flat lens; the ww/ dm ratio is less than 25%. The umbilicus is almost completely closed; it is bounded by a very shallow umbilical margin. The flanks are slightly convex and converge slightly to the very narrowly rounded venter. The shell bears widespread, lamellar-appearing growth lines, which are biconvex with distinct dorsolateral projection and higher ventrolateral projection across the flank; the ventral sinus is narrow and deep ( Fig. 8C ). The growth lines are coarser on the venter than on the flanks. The suture line is

typically tornoceratid with a wide, asymmetric adventive lobe, a narrow ventrolateral saddle and a small external lobe ( Fig. 8B ).

Remarks

Lentitornoceras materni gen. et sp. nov. can hardly be confused with another species from the red ironstone because of its peculiar conch morphology. Tornoceratids from other localities and stratigraphic horizons usually have a much more broadly arched venter. A comparable form is the late Givetian ‘ Lobotornoceras bensaidi ’ ( Bockwinkel et al. 2013a) ; however, this form has a suture line with a very shallow adventive lobe.

Figures

Fig. 8. Lentitornoceras materni gen. et sp. nov., holotype (MB.C.30413; Lotz 1901–1902 Coll.) from Oberscheld. A. Ventral view, lateral view and dorsal projection. B. Suture line; at dm = 26.0 mm; ww = 6.4 mm; wh = 15.2 mm. C. Growth line course; at dm = 26.0 mm; ww = 6.4 mm; wh = 15.2 mm. Scale bar units = 1 mm.

Tables

Table4.Conchdimensionsand ratios ofLentitornoceras materni gen.et sp. nov.,holotype(MB.C.30413).

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
MB.C.30413	29.4	6.9	16.8	0.6	7.4	0.23	0.41	0.02	1.79	0.57