Stockumites marocensis, Korn & Weyer, 2023

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 84-85

Stockumites marocensis sp. nov.

urn:lsid:zoobank.org:act:A143D72A-BF03-46B2-B337-F2FD600C598F

Tables 46–47

Acutimitoceras intermedium – Belka et al. 1999: pl. 5 figs 7–8. — Korn 1999: 166, pl. 2 fig. 8. — Bockwinkel & Ebbighausen 2006: 97, text-figs 13–14. — Ebbighausen & Bockwinkel 2007: 131, text-figs 8f–g, 10, 12a–b. — Korn & Feist 2007: 106, text-fig. 6b–c, h.

Stockumites intermedius – Becker et al. 2002: pl. 2 figs 13–14.

Diagnosis

Species of Stockumites with a thickly pachyconic and subinvolute conch at 5 mm dm (ww/dm = 0.75– 0.85; uw/dm = 0.15–0.25) and a pachyconic and involute conch at 15 mm dm (ww/dm = 0.65–0.75; uw/ dm = 0.00–0.10). Whorl profile at 15 mm dm weakly depressed (ww/wh ~1.20); coiling rate moderate to high (WER = 1.90–2.15). Venter broadly rounded throughout ontogeny, umbilical margin broadly rounded. Prominent internal shell thickenings with weakly biconvex course in the preadult stage. Suture line with lanceolate external lobe and symmetric, V-shaped adventive lobe with gently curved flanks.

Etymology

Named after Morocco, where the material comes from.

Material examined

Holotype

MOROCCO • Anti-Atlas , Bou Tlidat near Fezzou , bed 2; Ebbighausen & Bockwinkel Coll.; illustrated by Ebbighausen & Bockwinkel (2007: text-fig. 8g); MB.C.10155.1.

Paratypes

MOROCCO • 263 specimens; Anti-Atlas , Bou Tlidat near Fezzou , bed 2; Ebbighausen & Bockwinkel Coll.; MB.C.10155.2–MB.C.10155.264 • 14 specimens; Anti-Atlas , Tazoult near Fezzou , bed 2 ; Ebbighausen & Bockwinkel Coll.; MB.C.10193.1–MB.C.10193.14 • 26 specimens; Anti-Atlas , Tazoult near Fezzou , float material; Ebbighausen & Bockwinkel Coll.; MB.C.10206.1.1–MB.C.10206- 26 • 4 specimens; Anti-Atlas , Rich el Mbidia near Fezzou , bed 2 ; Ebbighausen & Bockwinkel Coll.; MB.C.10171.1–MB.C.10171.4 • 4 specimens; Anti-Atlas , Tizi Ibaouâne near Fezzou , bed 2; Ebbighausen & Bockwinkel Coll.; MB.C.10216.1–MB.C.10216.4 • 4 specimens; Anti-Atlas , Tizi Malilane near Fezzou , bed 2; Ebbighausen & Bockwinkel Coll.; MB.C.10239.1–MB.C.10239.4 • 16 specimens; Anti-Atlas , Mfis near Taouz , bed 1c ; Bockwinkel & Ebbighausen Coll.; MB.C.3807.1–16 • 5 specimens; Anti-Atlas , Mfis near Taouz , bed 2 ; Bockwinkel & Ebbighausen Coll.; MB.C.3813.1–5.

Description

The species newly named here has been described in detail by Bockwinkel & Ebbighausen (2006) and Ebbighausen & Bockwinkel (2007), hence reference can be made here to those articles.

Remarks

The material described here as the new species Stockumites marocensis sp. nov. was originally attributed to Acutimitoceras intermedium by several authors. In fact, both species have a very similar stout conch shape and even resemble each other in the shape of the umbilicus with a broadly rounded umbilical margin. However, there are considerable differences in the ontogenetic development of the conch; the ontogeny of S. marocensis is accelerated. This means that the umbilicus closes earlier than in S. intermedius . For example, the uw/dm ratio falls below the value of 0.20 already between 4 and 6 mm conch diameter, whereas in S. intermedius from bed 5 of Oberrödinghausen this is the case only above 10 mm diameter. Specimens of S. intermedius from bed 6 are similar in closure of the umbilicus to specimens of S. marocensis , but the latter has an accelerated increase in coiling rate.