Ammonoids of the Middle Devonian family Maenioceratidae in the Anti-Atlas of Morocco
Author
Bockwinkel, Jürgen
F7FE7EEA-B678-4FEE-879C-8C429F66BF3A
Dechant-Fein-Strasse 22, 51375 Leverkusen, Germany.
j.bockwinkel@t-online.de
Author
Korn, Dieter
286CA4F3-7EBC-4AEF-A66A-B2508D001367
Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany.
dieter.korn@mfn.berlin
text
European Journal of Taxonomy
2024
2024-01-30
921
1
1
35
https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2413/10641
journal article
10.5852/ejt.2024.921.2413
2118-9773
10590243
80B3C408-DD2C-4373-96AE-15F067D723F8
Afromaenioceras crassum
(
Bensaïd, 1974
)
Fig. 12
;
Table 9
Maenioceras crassum
Bensaïd, 1974: 105
, text-fig. 12c
1
, c
2
, pl. 2 fig. 11, 11a.
Afromaenioceras crassum
–
Becker
et al
. 2004
: pl. 1 figs 5–6.
non
Bensaidites crassus
–
Korn & Klug 2002: 141
, text-fig. 133e, i.
Diagnosis
Species of
Afromaenioceras
with thickly pachyconic and subinvolute conch at
5 mm
dm (ww/dm~ 0.80; uw/dm ~ 0.35); conch thinly pachyconic and subinvolute at
16 mm
dm (ww/dm~ 0.65; uw/dm~0.25) with weakly depressed whorl profile (ww/wh~ 1.45) and low coiling rate (WER ~1.60). Whorl profile at
16 mm
conch diameter C-shaped with convex, weakly convergent flanks, broadly rounded ventrolateral shoulder and rounded venter. Ventrolateral shoulder with faint spiral groove. Growth lines coarse, strongly biconvex. Suture line with wide external lobe, small, subangular E
2
lobe, inverted U-shaped ventrolateral saddle and U-shaped lateral lobe.
Material examined
Holotype
MOROCCO
•
Anti-Atlas
,
Oued Mzerreb
; middle
Givetian
; IGPB-Bensaid-22 (illustrated by
Bensaïd
1974
: pl. 2 fig. 11).
Additional material
MOROCCO
•
25
specs;
Anti-Atlas
,
Oued Mzerreb-W
; beds 10/11 (middle
Givetian
);
Bockwinkel
and
Ebbighausen
2004 Coll.;
MB.C.31965.1 to MB.C.31965.25
•
46
specs;
Anti-Atlas
,
Jebel Ouaoufilal
; middle
Givetian
;
Bockwinkel
and
Ebbighausen
2004 Coll.;
MB.C.31966.1 to MB.C.31966.46
.
Description
Specimen MB.C.31965.1 is a limonitic internal mould with
15.5 mm
conch diameter, which is well preserved on the left side (
Fig. 12A
). The conch is thinly pachyconic and subinvolute (ww/dm = 0.64; uw/dm = 0.26); the umbilicus starts closing at
12 mm
conch diameter. The whorl profile is weakly depressed (ww/wh = 1.46) and the coiling rate is low (WER = 1.62). The flanks are broadly convex and the venter is slightly flattened. A faint spiral groove marks the ventrolateral shoulder. Traces of coarse growth lines on the internal mould show a strongly biconvex course. The suture line has a Y-shaped external lobe with stair-shaped flank, and inverted U-shaped ventrolateral saddle and a deep, U-shaped lateral lobe (
Fig. 12D
). Housean pits are present on the outer flank. The last phragmocone volution has only eleven chambers.
Specimen MB.C.31965.2 is a limonitic internal mould with
10 mm
conch diameter, which is well-preserved on the left side (
Fig. 12B
). It is a thinly pachyconic, subevolute conch (ww/dm = 0.67; uw/dm = 0.33) with a moderately depressed whorl profile (ww/wh 1.79) and a low coiling rate (WER = 1.65). The ventrolateral shoulder shows a poorly developed spiral groove. The suture line has an external lobe with strongly pouched, divergent flanks and a broad and deep lateral lobe (
Fig. 12E
). The last phragmocone volution has only ten chambers.
Specimen MB.C.31965.3 ss a well-preserved small limonitic internal mould with
5 mm
conch diameter (
Fig. 12C
). It is thickly pachyconic and subevolute (ww/dm = 0.81; uw/dm = 0.34) with a strongly depressed whorl profile (ww/wh = 2.11) and a moderately high coiling rate (WER = 1.78). The umbilical wall is steep, flanks and venter are broadly convex. The suture line of the juvenile specimen shows a V-shaped external lobe with gently convex flanks and a wide, broadly rounded lateral lobe (
Fig. 12F
).
Fig. 12.
Afromaenioceras crassum
(
Bensaïd, 1974
)
from Oued Mzerreb-W, bed 10/11.
A
. Specimen MB.C.31965.1.
B
. Specimen MB.C.31965.2.
C
. Specimen MB.C.31965.3.
D
. Specimen MB.C.31965.1; suture line at wh = 6.6 mm.
E
. Specimen MB.C.31965.2; suture line at wh = 4.5 mm.
F
. Specimen MB.C.31965.3; suture line at wh = 1.5 mm. Scale bar units = 1 mm.
Table 9.
Conch dimensions (in mm) and ratios of
Afromaenioceras crassum
(
Bensaïd, 1974
)
.
specimen
|
dm
|
ww
|
wh
|
uw
|
ah
|
ww/dm
|
ww/wh
|
uw/dm
|
WER
|
IZR
|
MB.C.31965.1 |
15.5 |
9.9 |
6.8 |
4.0 |
3.3 |
0.64 |
1.46 |
0.26 |
1.62 |
0.51 |
MB.C.31966.1 |
12.8 |
8.6 |
5.0 |
4.0 |
2.9 |
0.67 |
1.72 |
0.31 |
1.67 |
0.42 |
MB.C.31965.2 |
9.9 |
6.7 |
3.7 |
3.2 |
2.2 |
0.67 |
1.79 |
0.33 |
1.65 |
0.41 |
MB.C.31966.2 |
7.7 |
5.8 |
2.5 |
2.5 |
1.7 |
0.75 |
2.32 |
0.32 |
1.62 |
0.34 |
MB.C.31965.3 |
4.8 |
3.9 |
1.9 |
1.6 |
1.2 |
0.81 |
2.11 |
0.34 |
1.78 |
0.35 |
Remarks
Afromaenioceras crassum
has a stouter and wider umbilicate conch (ww/dm ~ 0.65; ww/wh ~ 1.50; uw/dm ~ 0.25) at
15 mm
dm than
A. brumale
sp. nov.
(ww/dm ~ 0.55; ww/wh ~ 1.15; uw/dm ~ 0.20).