Early Carboniferous nautiloids from the Central Sahara, southern Algeria
Author
Korn, Dieter
286CA4F3-7EBC-4AEF-A66A-B2508D001367
Museum für Naturkunde, Leibniz Institut for Research on Evolution and Biodiversity, Invalidenstrasse 43, 10115 Berlin, Germany.
dieter.korn@mfn.berlin
Author
Bockwinkel, Jürgen
F7FE7EEA-B678-4FEE-879C-8C429F66BF3A
Dechant-Fein-Strasse 22, 51375 Leverkusen, Germany.
jbockwinkel@t-online.de
text
European Journal of Taxonomy
2022
2022-07-20
831
67
108
http://dx.doi.org/10.5852/ejt.2022.831.1871
journal article
105313
10.5852/ejt.2022.831.1871
e697ba5c-5a96-4a28-985c-748890333d6c
2118-9773
6885198
EAA2EAE2-DA8B-4516-B332-CB8423B8EEAA
Maccoyoceras concavum
sp. nov.
urn:lsid:zoobank.org:act:
CC00C3E7-5DF4-4FA9-844C-AAA60F1F5016
Fig. 29
,
Table 17
Diagnosis
Species of
Maccoyoceras
reaching about
100 mm
conch diameter. Conch with weakly compressed whorl profile (ww/wh ~ 0.90); venter weakly concave, ventrolateral shoulder narrowly subangular. Whorls weakly embracing the preceding. Ornament in the juvenile stage with few coarse, granulated spiral lines on the flank, in the adult stage without spiral lines. Fine, sharp growth lines on the flank, with weakly biconvex course with a shallow lateral sinus and a moderately high ventrolateral projection. Venter with delicate growth lines with deep sinus.
Etymology
After Latin ‘
concavum
’, referring to the shape of the venter.
Table 17.
Conch dimensions (in mm) and ratios of
Maccoyoceras concavum
sp. nov.
| Specimen |
dm |
ww |
wh |
uw |
ah |
ww/dm |
ww/wh |
uw/dm |
WER |
IZW
|
| MB.C.30486 |
66.9 |
21.7 |
23.4 |
27.6 |
23.3 |
0.32 |
0.93 |
0.41 |
2.35 |
0.00 |
Type material
Holotype
ALGERIA
•
Ahnet
,
west-southwest of Gara Azzel Matti
; ‘
Dalle des Iridet’
(
Ammonellipsites-Merocanites
Assemblage; Tournaisian–Viséan boundary interval);
Wendt
and
Kaufmann
1995 Coll.; illustrated in
Fig. 29
;
MB.C.30486
.
Description
Holotype
MB.C.30486 is a rather well-preserved, almost completely chambered specimen with
76 mm
conch diameter, from which the last, poorly preserved segment was removed before photography (
Fig. 29
). The specimen allows the study from both sides. The conch is extremely discoidal (ww/ dm =0.32) and subevolute (uw/dm =0.41) with a very high coiling rate (WER =2.35). The whorl profile is compressed hexagonal (ww/wh =0.93) and widest at the rounded umbilical margin. The flanks stand almost parallel and converge barely towards the angular ventrolateral shoulder that separates the flanks from the weakly concave venter. The umbilical wall is convexly rounded.
Two ontogenetic stages of the ornament development can be separated: up to
17 mm
conch diameter, six coarse, crenulated spiral lines on the flank are the dominant elements in the juvenile stage. Thereafter, fine but sharp narrow-standing growth lines with weakly biconvex course form the ornament on the flanks, but the venter bears very delicate growth lines with a deep ventral sinus. The suture line shows a shallow ventral lobe and a shallow lateral lobe. The siphuncle is almost central.
Remarks
Maccoyoceras concavum
sp. nov.
has conch proportions very similar to those of
M. pentagonum
from the contemporaneous ‘Dalle à
Merocanites
’ of Timimoun. However, the new species differs from this and from the other species of the genus by the concave venter.