Paragattendorfia humilis 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 : 11-12

Paragattendorfia humilis Schindewolf, 1924

Fig. 5 ; Table 2

Paragattendorfia humilis Schindewolf, 1924: 105 .

Diagnosis

Species of Paragattendorfia with conchs reaching 40 mm diameter. Conch at 25 mm dm thickly pachyconic and subinvolute (ww/dm ~ 0.75; uw/dm ~ 0.18). Whorl profile at 25 mm dm moderately depressed (ww/wh ~ 1.70); coiling rate low (WER ~ 1.65). Venter broadly rounded, umbilical margin rounded. Growth lines lamellar, wide-standing, with convex course. Without constrictions on the shell surface.

Material examined

Lectotype GERMANY • Upper Franconia , 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1916 Coll.; MB.C.4691.

Additional material GERMANY • 1 specimen; Upper Franconia , 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1934 Coll.; illustrated in Fig. 5A ; BGRB X13380 .

Description

Lectotype MB.C.4691 is not suitable for an illustration; it is a phragmocone fragment with about 8.5 mm whorl width. It allows almost only a view of a septal surface of a crescent-shaped whorl profile.

Specimen BGRB X13380 is a laterally distorted conch with 26 mm diameter ( Fig. 5A ), showing shell remains but no suture line. The conch is thickly pachyconic (ww/dm ~ 0.75 and subinvolute (uw/dm ~ 0.17) with low coiling rate (WER ~ 1.68). The umbilical margin is rounded and the umbilical wall stands almost vertical to the symmetry plane. The flanks and venter are evenly broadly rounded. The shell bears unevenly distributed, lamellar growth lines, which are already slightly directed backwards on the inner flank and extend in a convex arc across the flanks. They form a shallow sinus on the venter.

Remarks

Paragattendorfia humilis was very inadequately defined in the original description. Schindewolf (1924: 105) stated only that it “was recorded at Gattendorf as a rare companion of Gattendorfia ” and that it is characterised by “a moderately wide umbilicus, very low whorls and a semilunate cross-section with a broadly convex external side”. An illustration was not provided and he did not explain at what size stage this morphology should be present. The species definition is therefore almost useless because it can refer to a number of different earliest Tournaisian ammonoids.

Only two specimens are available. The lectotype proposed here is a fragment of a phragmocone, labelled by Schindewolf himself as “ Paragattendorfia humilis ” ( Fig. 5B ). It is rather clear that this specimen belonged to the type series. The second specimen is much better preserved, but it belongs to the collection assembled by Schindewolf as late as 1934.

Paragattendorfia humilis differs from the other species P. patens and P. sphaeroides from the Rhenish Mountains in the course of the growth lines, which is strongly convex in P. humilis but nearly linear in P. patens and P. sphaeroides . Both species have a wider umbilicus than P. humilis ; the uw/dm ratio is about 0.30 in P. patens and 0.20 in P. sphaeroides , while below 0.20 in P. humilis .

Figures

Fig. 5. Paragattendorfia humilis Schindewolf, 1924 from Gattendorf, bed 21. A. Specimen BGRB X13380 (Schindewolf 1934 Coll.). B. Original label of lectotype MB.C.4691 (handwriting of Schindewolf). Scale bar units =1 mm.