Stockumites (?) involutus ( Schindewolf, 1924 )

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Gattendorf (Devonian-Carboniferous boundary; Upper Franconia, Germany), European Journal of Taxonomy 883, pp. 1-61 : 39-41

Stockumites (?) involutus ( Schindewolf, 1924)

Fig. 22

Gattendorfia involuta Schindewolf, 1924: 105 .

Gattendorfia involuta – Becker in Becker et al. 2021: 409.

non Gattendorfia involuta – Becker in Becker et al. 2021: 410, text-fig. 15.

Material examined

Lectotype GERMANY • Upper Franconia , 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1934 Coll.; illustrated in Fig. 22A ; MB.C.31282.

Description

Lectotype MB.C.31282 is a poorly preserved, incomplete specimen with a conch diameter of only 12 mm ( Fig. 22A ). A species diagnosis can thus not be given. The conch dimensions cannot be accurately determined, but it is clear that the conch is thickly discoidal and subinvolute (ww/dm=0.50; uw/dm=0.22). No shell is preserved and the internal mould shows several very shallow constrictions spaced 90 degrees apart.

Remarks

“ Gattendorfia involuta ” is a very problematic species; the name was not used for nearly hundred years. The type material, consisting only of one poorly preserved specimen, has never been described properly.

Becker (in Becker et al. 2021) was not aware of the type material of Gattendorfia involuta , and proposed a neotype for reviving the species. This was a specimen already figured by Vöhringer (1960) under the name Gattendorfia tenuis ; it became the holotype of the species G. schmidti newly introduced by Korn & Weyer (2023). However, this neotype determination seriously complicated the problematic research history of this species. For this reason, it is necessary to review and discuss the research history of this species (from Korn & Weyer 2023):

Schindewolf (1926b: 92) explained that after writing his article on the ammonoid assemblages of Saalfeld ( Schindewolf 1924), he had the opportunity to also study the Devonian–Carboniferous boundary section near Wocklum in the Rhenish Mountains in greater detail. During this visit he realised that the Gattendorfia Stufe is not older but younger than the Wocklumeria Stufe.

Schindewolf (1952: 297) discussed again his previously newly established third species “ Gattendorfia involuta Schindewolf, 1924 ”. In this discussion, he stated that this species had no valid name and that he would refer to it as the new species Gattendorfia tenuis . In this article, he described and illustrated a specimen of 73 mm diameter from Saalfeld as the type for that species. He also wrote that he had previously owned excellently preserved specimens from Oberrödinghausen in the Rhenish Mountains and Ebersdorf (Dzikowiec) in Silesia. A rather well-preserved specimen from Ebersdorf, collected by Schindewolf in 1918 and described as Gattendorfia tenuis by Weyer (1965: 447), belongs to G. schmidti described by Korn & Weyer (2023). From what has already been said above, it is clear that these specimens he mentioned did not belong to the type series.

Vöhringer (1960: 153) used the species name G. tenuis for specimens from Oberrödinghausen, which however belong to three different species. He presented a specimen with a diameter of 57 mm as a photograph and also cross sections of two other, smaller specimens. The assignment of his large specimen to G. tenuis is almost certainly in error, because it deviates considerably from the holotype in the direction of the constrictions. Nevertheless, this concept was accepted by Korn (1994, 2006).

Becker (in Becker et al. 2021: 409) saw the need to revive the hitherto unused species name “ Gattendorfia involuta Schindewolf, 1924 ” and designated specimen GPIT-PV-63952, illustrated by Vöhringer (1960: pl. 5 fig. 6) as G. tenuis , as the neotype for “ G. involuta ”. However, this procedure is to be criticised for several reasons: 1. The neotype does not come from the type region. The claim by Becker that Schindewolf possessed syntypes from Oberrödinghausen (and that this is one of the two type localities) is not correct (see above), since Schindewolf only carried out extensive studies in the Rhenish Mountains Devonian– Carboniferous boundary sections after writing his 1924 article.

2. With the determination of a neotype from another region, the species “ G. involuta ” would become a widespread species by definition, but not by empirical data.

3. The same is true for the stratigraphic range of the species. All ammonoid specimens from Gattendorf come from the lowest part of the Gattendorfia Limestone ( Acutimitoceras acutum Zone ), while the “ neotype ” comes from the highest bed of the Gattendorfia Limestone ( Eocanites delicatus Zone ). With the neotype proposal, Gattendorfia involuta would become a long-ranging species by definition, not by empirical data.

4. The determination of a neotype is unnecessary, because a specimen of “ G. involuta ” personally labelled by Schindewolf is present in the collection of the Museum für Naturkunde, Berlin; this specimen was probably taken by him when he moved from Marburg to Berlin in 1927.

5. The illustration of another supposedly “typical” specimen by Becker (in Becker et al. 2021: text-fig. 15) adds to the confusion. The poorly preserved specimen is from the basal bed of the Hangenberg Limestone, while the proposed neotype is from the highest bed of the unit. The specimen cannot be considered typical because it does not seem to have constrictions like the proposed neotype. Surprisingly, such differences in G. subinvoluta were attributed by Becker to “biogeographic separation through a narrow oceanic system”.

Here, we describe the small lectotype to clarify the nomenclatural problems with this species. However, the lectotype is so poorly preserved that it is not diagnostic. It is not clear either to which genus the specimen belongs. The conch shape argues against an identification as Gattendorfia ; it is more reminiscent of some species of the genus Stockumites , which only close the umbilicus at a late ontogenetic stage. Therefore, it cannot be clarified which relationships this problematic species has to other species. Apart from the poorly preserved lectotype, no other specimens are currently known; therefore, it is also not possible to make statements about the adult morphology of the species. The species must therefore be regarded as a problematic for the time being.

Figures

Fig.22.Stockumites (?)involutus(Schindewolf,1924)fromGattendorf, bed21.A.SpecimenMB.C.31282 (Schindewolf Coll.). B. Original label of lectotype MB.C.31282 (handwriting by Schindewolf). Scale bar units=1 mm.