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
Vestinautilus bicristatus
sp. nov.
urn:lsid:zoobank.org:act:
69CABBA5-6CDA-4264-B156-0FB2321AEDD5
Figs 20–21
,
Table 11
Diagnosis
Species of
Vestinautilus
with strongly depressed, rounded-trapezoidal whorl profile (ww/wh ~ 2.10), venter up to
30 mm
conch diameter broadly arched with two shallow submarginal grooves, which disappear in the adult stage. Ventrolateral shoulder defined by a subangular margin; one sharp ridge is located on the umbilical wall near the ventrolateral shoulder. Whorls weakly embracing, coiling very high (WER ~2.55). Ornament with delicate growth lines.
Etymology
From the Latin ‘
crista
’, meaning ‘crest’ and referring to the two lateral longitudinal ridges.
Type material
Holotype
ALGERIA
•
Mouydir
,
south of Oued Temertasset (locality MOU-C1)
;
Argiles de Teguentour
(
Helicocyclus-Ouaoufilalites
Assemblage; early late Tournaisian
);
Wendt
et al
.
Coll.; illustrated in
Fig. 20
;
MB.C.30473
.
Paratypes
ALGERIA
•
3 specimens
;
Mouydir
,
south of Oued Temertasset (locality MOU-C1)
;
Argiles de Teguentour
(
Helicocyclus-Ouaoufilalites
Assemblage; early late Tournaisian
);
Korn
et al
.
2002 Coll.; illustrated in
Fig. 21
;
MB.C.30474.1
–
MB.C.30474.3
.
Table 11.
Conch dimensions (in mm) and ratios of
Vestinautilus bicristatus
sp. nov.
| Specimen |
dm |
ww |
wh |
uw |
ah |
ww/dm |
ww/wh |
uw/dm |
WER
|
IZW
|
|
MB
.C.30473
|
38.0 |
31.9 |
14.9 |
14.0 |
14.3 |
0.84 |
2.13 |
0.37 |
2.57 |
0.04 |
Description
Holotype
MB.C.30473 is a desert-polished specimen with a diameter of
38 mm
, showing the conch shape and small areas of ornament (
Fig. 20
). The conch is broadly cylindrical and subevolute (ww/dm = 0.84; uw/dm =0.37) with a very high coiling rate (WER =2.57). The whorl profile is strongly depressed (ww/wh =2.13) and shows a flattened venter, which possesses two submarginal external grooves at size stages between 17 and
35 mm
diameter. These weaken considerably thereafter and are only visible as shallow longitudinal depressions at the maximum diameter of the specimen. The ventrolateral shoulder is distinguished by three edges, of which the two inner ones are strengthened by longitudinal ridges. Only small areas of shell ornament are visible; these show very fine growth lines on the venter with a deep external sinus.
Three
paratypes
in fragmentary preservation are available. They are larger specimens with whorl widths between 49 and
80 mm
, thus belonged to conchs with
60 to 90 mm
diameter. Two of them (MB.C.30474.2 and MB.C.30474.3;
Fig. 21B–C
) show the imprint of the preceding whorl with sublateral longitudinal grooves in the dorsal region; in
paratype
MB.C.30474.3 the edges of the ventrolateral shoulder are also still visible. Both have a broadly rounded venter. The largest
paratype
MB.C.30474.1 shows a shallow, broad depression in the middle of the venter at its largest diameter (
Fig. 21A
).
Paratype
MB.C.30474.3 shows the suture line with a broad and shallow external lobe and a narrow and shallow lateral lobe, which has a position on the umbilical wall (
Fig. 21C
). The siphuncle has a slightly subcentral position towards the venter.
Remarks
Vestinautilus bicristatus
sp. nov.
belongs to the species of the genus that possess a very broad whorl profile (ww/wh> 2.00) and an ornament with only a few spiral ridges. In this respect,
V. cariniferus
,
V. paucicarinatus
,
V. pinguis
and
V. semiplicatus
are similar, but these four species have a concave venter at least at times in ontogeny (
Sowerby 1825
;
de Koninck 1844
;
Foord 1891
,
1900
). The most similar
V. bicristatus
sp. nov.
is the species
V. padus
, which shows the same conch dimensions, but differs in the lack of the submarginal ventral grooves (
Korn
et al.
2022
).